WO2025136641A1 - Implantable sensor signal lock through single ping transmission - Google Patents

Abstract

Systems and methods for locking onto a signal returned from a wireless sensor positioned within a body include generating and transmitting, via an external base unit, a first energizing signal having a first emission level, and receiving, via the base unit, first returned signals including a first sensor signal. The wireless sensor includes a circuit having a resonant frequency configured to vary in response to changes in pressure in the body. A first frequency associated with the circuit is determined based on an amplitude within the first returned signals. A second energizing signal having a second emission level that is lower than the first emission level is generated and transmitted. Second returned signals including a second sensor signal are received, a second frequency associated with the circuit is determined based on the first frequency and the second returned signals, and pressure in the body is determined based on the first frequency or the second frequency.

Description

IMPLANTABLE SENSOR SIGNAL LOCK THROUGH SINGLE PING TRANSMISSION CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to United States Provisional Application No. 63/612,505, titled “Implantable Sensor Signal Lock Through Single Ping Transmission”, which was filed on December 20, 2023, and to United States Provisional Application No. 63/574,200, titled “Implantable Sensor Signal Lock Through Single Ping Transmission”, which was filed on April 3, 2024, the complete subject matter of which are expressly incorporated herein by reference in their entireties. BACKGROUND [0002] The measurement of blood pressure within the human heart and its vasculature provides critical information regarding the organ's function. Many methods and techniques have been developed to give physicians the ability to monitor heart function to properly diagnose and treat various diseases and medical conditions. For example, a sensor placed within the chambers of the heart can be used to record variations in blood pressure based on physical changes to a mechanical element within the sensor. This information is then transferred through a wire from the sensor to an extracorporeal device that is capable of translating the data from the sensor into a measurable value that can be displayed. The drawback of this type of sensor is that there must be a wired connection between the sensor and the extracorporeal device, thus limiting Its use to acute settings. [0003] Many types of wireless sensors have been proposed that would allow implantation of the device into the body. Then, through the appropriate coupling means, pressure reading can be made over longer periods of interest. [0004] To overcome the two problems of power and physical connection, the concept of an externally modulated LC circuit has been applied to development of implantable pressure sensors. Of a number of patents that describe a sensor design of this nature, U.S. Pat. No, 6,113,553 to Chubbuck, incorporated herein by reference in its entirety, is a representative example. The Chubbuck patent demonstrates how a combination of a pressure sensitive capacitor placed in series with an inductor coil 15618WOO1 (013-0605PCT1) 1 PATENT   provides the basis for a wireless, un-powered pressure sensor that is suitable for implantation into the human body. Construction of an LC circuit in which variations of resonant frequency correlate to changes in measured pressure and in which these variations can be detected remotely through the use of electromagnetic coupling are further described in U.S. Pat. Nos.6,111,520 and 6,278,379, both to Allen et al., which are incorporated herein by reference in their entireties. [0005] Typically, the sensors utilize an inductive-capacitive ("LC") resonant circuit with a variable capacitor. The capacitance of the circuit varies with the pressure of the environment in which the sensor is located and thus, the resonant frequency of the circuit varies as the pressure varies. Thus, the resonant frequency of the circuit can be used to calculate pressure. [0006] Ideally, the resonant frequency is determined using a non-invasive procedure. Several examples of procedures for determining the resonant frequency of an implanted sensor are discussed in U.S. Pat. No. 6,111,520, which is herein incorporated by reference in its entirety. Some of the procedures described in the patent require the transmission of a signal having multiple frequencies. A drawback of using a transmission signal having multiple frequencies is that the energy in the frequency bands outside the resonant frequency is wasted. This excess energy requires more power which results in an increase in cost, size, and thermal requirements, as well as an increase in electromagnetic interference with other signals. Thus, there is a need for an optimized method that is more energy efficient and requires less power. [0007] There are unique requirements for communicating with an implanted sensor. For example, the system must operate in a low power environment and must be capable of handling a signal from the sensor with certain characteristics. For example, the signal from the sensor is relatively weak and must be detected quickly because the signal dissipates quickly. These requirements also impact the way that common problems are handled by the system. For example, the problems of switching transients and false locking need to be handled in a manner that accommodates the sensor signal characteristics. Thus, there is a need for a method for communicating with a wireless sensor that operates in a low power environment and that efficiently determines the resonant frequency of the sensor. 15618WOO1 (013-0605PCT1) 2 PATENT   [0008] Further “false lock” can occur when the phase lock portion of the reader (e.g., the external system) locks onto a signal other than the signal that is being returned from the implanted sensor. This situation can be common when there are metal or magnetic objects in the vicinity of the reader and/or sensor. For example, the signals transmitted by the system can cause undesirable objects to also return signals which may superimpose over or merge with the sensor signal, causing confusion. [0009] The resonant frequency of the sensor is a measured parameter that is correlated with the physical parameter of interest, such as blood pressure. Thus, there is a need for a system and method for communicating with a wireless sensor that can accurately identify the sensor signal and prevent false lock. SUMMARY [0010] In accordance with embodiments herein, a method for locking onto a signal returned from a wireless sensor positioned within a body comprises generating, via a base unit, a first energizing signal, wherein the base unit is external with respect to the body. The method transmits, via the base unit, the first energizing signal having a first emission level and receives, via the base unit, first returned signals including a first sensor signal in response to the first energizing signal. The wireless sensor comprises an inductive-capacitive (LC) circuit having a resonant frequency configured to vary in response to changes in pressure in the body. The method determines a first frequency associated with the LC circuit based on an amplitude within the first returned signals in response to the first energizing signal, generates, via the base unit, a second energizing signal, transmits, via the base unit, the second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level, and receives, via the base unit, second returned signals including a second sensor signal in response to the second energizing signal. The method determines a second frequency associated with the LC circuit based on the first frequency and the second returned signals, and determines the pressure in the body based on the first frequency or the second frequency. 15618WOO1 (013-0605PCT1) 3 PATENT   [0011] Optionally, the method further comprises transmitting, over a predetermined time period, a plurality of consecutive energizing signals having the second emission level. [0012] Optionally, wherein in response to the predetermined time period expiring, the method further comprises transmitting another energizing signal having the first emission level. [0013] Optionally, a time-averaged emission level over a time period is below a maximum average signal strength limit, the time-averaged emission level determined based on the first and second energizing signals transmitted over the time period. [0014] Optionally, the first emission level is greater than a maximum average signal strength limit associated with a time period, and the second emission level is less than the maximum average signal strength limit associated with the time period. [0015] Optionally, the method further comprises generating and transmitting, via the base unit, a third energizing signal having the second emission level, receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal, and determining a third frequency associated with the LC circuit based on the second frequency and the third returned signals. [0016] Optionally, the method further comprises generating and transmitting, via the base unit, a third energizing signal having the second emission level, receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor, determining third and fourth frequencies associated with the first and second peaks, and wherein, in response to the third and fourth frequencies being within a predetermined frequency range of each other, transmitting a fourth energizing signal having the first emission level. [0017] Optionally, the method further comprises receiving, via the base unit, fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level, and determining the frequency associated with the LC circuit based on a maximum amplitude within the fourth returned signals. [0018] Optionally, the method further comprises generating and transmitting, via the base unit, a third energizing signal having the second emission level, receiving, via 15618WOO1 (013-0605PCT1) 4 PATENT   the base unit, third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor, determining third and fourth frequencies associated with the first and second peaks, and wherein, in response to a difference between the third and fourth frequencies being greater than a predetermined frequency range, transmitting another energizing signal having the second emission level. [0019] Optionally, wherein determining the first frequency associated with the LC circuit is based on a maximum amplitude within the first returned signals. [0020] In accordance with embodiments herein, a system for communicating with a wireless sensor positioned within a lumen of a body comprises a base unit positioned external with respect to the body. The base unit comprises transmission circuitry configured to generate and transmit energizing signals, receiving circuitry configured to receive returned signals including a sensor signal associated with the wireless sensor in response to the energizing signals, the wireless sensor comprising a circuit having a resonant frequency configured to vary in response to changes in pressure in the lumen, memory configured to store program instructions, and one or more processors. The one or more processors, when executing the program instructions, are configured to generate and transmit a first energizing signal having a first emission level; receive first returned signals including a first sensor signal in response to the first energizing signal; determine a first frequency associated with the circuit within the wireless sensor based on the first returned signals; generate and transmit a second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level; receive second returned signals including a second sensor signal in response to the second energizing signal; and determine a second frequency associated with the circuit within the wireless sensor based on the first frequency and the second returned signals. [0021] Optionally, wherein the first frequency associated with the circuit is determined based on a maximum amplitude within the first returned signals. 15618WOO1 (013-0605PCT1) 5 PATENT   [0022] Optionally, wherein the one or more processors are further configured to determine the pressure in the lumen based on the first frequency or the second frequency. [0023] Optionally, wherein the pressure further comprises pulmonary arterial pressure. [0024] Optionally, the one or more processors are further configured to transmit, over a predetermined time period, a plurality of consecutive energizing signals having the second emission level, and in response to the predetermined time period expiring, transmit another energizing signal having the first emission level. [0025] Optionally, wherein a time-averaged emission level over a time period is below a maximum average signal strength limit, the time-averaged emission level determined based on the first and second energizing signals transmitted over the time period. [0026] Optionally, wherein the first emission level is greater than a maximum average signal strength limit, and the second emission level is less than the maximum average signal strength limit. [0027] Optionally, the one or more processors are further configured to generate and transmit a third energizing signal having the second emission level; receive third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determine third and fourth frequencies associated with the first and second peaks; and wherein, in response to a difference between the third and fourth frequencies being greater than a predetermined frequency range, transmit another energizing signal having the second emission level. [0028] Optionally, the one or more processors are further configured to generate and transmit a third energizing signal having the second emission level; receive third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determine third and fourth frequencies associated with the first and second peaks; and wherein, in response to the third and 15618WOO1 (013-0605PCT1) 6 PATENT   fourth frequencies being within a predetermined frequency range of each other, transmit a fourth energizing signal having the first emission level. [0029] Optionally, the one or more processors are further configured to receive fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level; and determine the frequency associated with the circuit based on a maximum amplitude within the fourth returned signals. [0030] These and other aspects, features and advantages may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS [0031] FIG. 1A is a perspective view of a first embodiment of an implantable wireless sensor, with the sensor body shown as transparent to reveal interior detail. [0032] FIG.1B illustrates a system that includes an IMD, an implantable sensor, and an external device implemented in accordance with embodiments herein. [0033] FIG.2 illustrates an exemplary system for communicating with the wireless sensor implanted within the body in accordance with embodiments herein. [0034] FIG.3A illustrates a graph of an example of pulmonary arterial pressure that can be measured using the sensor implanted within the pulmonary artery in accordance with embodiments here. [0035] FIG.3B is a graph illustrating the transmission levels of energizing signals when the energizing signals are transmitted at different levels to ensure true signal lock between a base unit and an implantable sensor in accordance with embodiments herein. [0036] FIG.3C is a graph illustrating the transmission levels of energizing signals in accordance with embodiments herein. [0037] FIG. 3D illustrates a graph showing frequencies of returned signals including a sensor signal returned in response to being energized by the relatively lower energizing signal, as discussed in FIG.3C, in accordance with embodiments herein. [0038] FIG.3E illustrates a graph showing frequencies of returned signals received immediately after the transmission of the relatively higher energizing signal as discussed in FIG.3C in accordance with embodiments herein. 15618WOO1 (013-0605PCT1) 7 PATENT   [0039] FIG.3F illustrates a graph showing frequencies of returned signals that are received after a delay period has passed, the delay period immediately following a relatively higher power energizing signal in accordance with embodiments herein. [0040] FIG.3G illustrates a graph showing frequencies of returned signals that are returned in response to an energizing signal transmitted at the relatively lower emission level in accordance with embodiments herein. [0041] FIG.3H illustrates a graph showing that the frequency of the sensor signal is tracked to a new frequency due to changes in the patient’s blood pressure in accordance with embodiments herein. [0042] FIG.3I illustrates a graph showing frequencies of returned signals wherein the frequency of the sensor signal has merged with, crossed over, or otherwise is indistinguishable from a peak associated with noise or an environmental object in accordance with embodiments herein. [0043] FIG.4 illustrates a computer-implemented method for achieving true sensor lock and determining pressure detected by an implantable pressure sensor in accordance with embodiments herein. [0044] FIG.5 is a block diagram of an exemplary system for communicating with a wireless sensor in accordance with embodiments herein. [0045] FIG.6A is a graph illustrating an exemplary energizing signal in accordance with embodiments herein. [0046] FIGS.6B, 6C and 6D are graphs illustrating exemplary coupled signals in accordance with embodiments herein. [0047] FIG. 7 is a block diagram of an exemplary base unit in accordance with embodiments herein. [0048] FIGS.8A and 8B are graphs illustrating exemplary phase difference signals in accordance with embodiments herein. [0049] FIG. 9 illustrates frequency dithering in accordance with embodiments herein. [0050] FIG.10 illustrates phase dithering in accordance with embodiments herein. [0051] FIG.11 illustrates a coupling loop in accordance with embodiments herein. 15618WOO1 (013-0605PCT1) 8 PATENT   [0052] FIG. 12 is a graph illustrating an exemplary charging response of an LC circuit in accordance with embodiments herein. [0053] FIG.13 illustrates a table reproduced from Comité International Spécial des Perturbations Radioélectriques (CISPR) 11, from 60601-1-2, that shows electromagnetic radiation disturbance limits for class B group 2 equipment measured on a test site. [0054] FIG.14 illustrates a computer-implemented method for communicating with a wireless sensor positioned within a lumen of a body in accordance with embodiments herein. DETAILED DESCRIPTION [0055] It will be readily understood that the components of the embodiments as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments. [0056] Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment. [0057] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obfuscation. The following description is intended only by way of example, and simply illustrates certain example embodiments. 15618WOO1 (013-0605PCT1) 9 PATENT   [0058] The methods described herein may employ structures or aspects of various embodiments (e.g., systems and/or methods) discussed herein. In various embodiments, certain operations may be omitted or added, certain operations may be combined, certain operations may be performed simultaneously, certain operations may be performed concurrently, certain operations may be split into multiple operations, certain operations may be performed in a different order, or certain operations or series of operations may be re-performed in an iterative fashion. It should be noted that other methods may be used in accordance with an embodiment herein. Further, wherein indicated, the methods may be fully or partially implemented by one or more processors of one or more devices or systems. While the operations of some methods may be described as performed by the processor(s) of one device, additionally, some or all of such operations may be performed by the processor(s) of another device described herein. Terms [0059] The terms “energizing signal” and “energizing pulse” shall mean a radio frequency (RF) signal transmitted by an external base unit to energize an implantable medical device such as an implantable pressure sensor. The energizing signal shall have pulses having a relatively higher amplitude and pulses having a relatively lower amplitude. [0060] The term emission level shall mean an amplitude or power level of the energizing signal or energizing pulse. The emission level may also be referred to herein as power level, and the emission level shall be referred to in relative terms, such as relatively higher level, relatively lower level, relatively higher power, relatively lower power, relatively higher emission level, relatively lower emission level, etc. [0061] The term “returned signals” shall mean signals along a frequency spectrum that are received by the external base unit in response to an energizing signal or energizing pulse. The returned signals have amplitude peaks along the frequency spectrum, wherein one of the amplitude peaks corresponds to a sensor signal returned from an implantable sensor, and at least one other peak corresponds to noise or a signal returned from an environmental object. 15618WOO1 (013-0605PCT1) 10 PATENT   [0062] The term “false lock” shall mean that the external base unit locks on a frequency that does not correspond to the resonant frequency of the sensor and thus is tracking an incorrect peak within the signal frequencies returned in response to an energizing signal or energizing pulse. In false lock, the frequency is associated with a peak within the returned signals that is associated with noise or an environmental object. [0063] The terms “true signal lock” and “true sensor lock” shall mean that an external base unit has correctly locked onto and is tracking the sensor signal returned by an implantable sensor in response to an energizing signal. [0064] The term “maximum average signal strength limit” shall mean a predetermined electromagnetic radiation standard that is an average, “quasi-peak”, etc., of radiation limits determined over a predetermined time period (e.g., measured in seconds or minutes) by one or more regulatory body. [0065] The term “time-averaged emission level” shall mean an average emission level (e.g., amplitude) of energizing signals over a period of time or time period. The time-averaged emission level is less than or does not exceed the maximum average signal strength limit. [0066] The term “PAP” shall mean pulmonary arterial pressure. [0067] The term “real-time” shall mean, when used in connection with collecting and/or processing data utilizing an implantable medical device or an implantable pressure sensor, the transmission of energizing signals, receipt of returned signals, and processing operations performed substantially contemporaneous with a physiologic event of interest such as one or more heartbeats experienced by a patient. By way of example, in accordance with embodiments herein, pressure signals can be analyzed in real-time (e.g., during a physiologic event of interest or within a few minutes after the event of interest). As one example, a base unit or other external device collects and automatically determines and tracks frequencies of returned signals in real-time. As another example, the base unit or other external device automatically determines pressure measurements based on the frequencies. In other cases, the pressure measurements can be determined in real-time or after the data is collected, such as off- line, at a remote server or other computing location, and the like. 15618WOO1 (013-0605PCT1) 11 PATENT   [0068] The terms “processor,” “a processor”, “one or more processors” and “the processor” shall mean one or more processors. The one or more processors may be implemented by one, or by a combination of more than one implantable medical device, a wearable device, a local device, a remote device, a server computing device, a network of server computing devices and the like. The one or more processors may be implemented at a common location or at distributed locations. The one or more processors may implement the various operations described herein in a serial or parallel manner, in a shared-resource configuration and the like. [0069] The term “IMD” shall mean an implantable medical device. Embodiments may be implemented in connection with one or more implantable medical devices (IMDs). Non-limiting examples of IMDs include one or more of neurostimulator devices, implantable leadless monitoring and/or therapy devices, and/or alternative implantable medical devices. For example, the IMD may represent a subcutaneous cardioverter defibrillator, cardiac monitoring device, pacemaker, cardioverter, cardiac rhythm management device, defibrillator, neurostimulator, leadless monitoring device, leadless pacemaker, left atrial or pulmonary artery pressure sensor, blood glucose monitoring device, and the like. The IMD may measure electrical, mechanical, optical, impedance, blood oxygen, blood glucose, or pressure information. For example, the IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Patent Number 9,333,351, entitled “Neurostimulation Method And System To Treat Apnea” issued May 10, 2016 and U.S. Patent Number 9,044,610, entitled “System And Methods For Providing A Distributed Virtual Stimulation Cathode For Use With An Implantable Neurostimulation System” issued June 02, 2015, and U.S. patent application 17/820,654, entitled “System and Method for Intra-Body Communication of Sensed Physiologic Data”, filed August 18, 2022, which are hereby incorporated by reference. The IMD may monitor transthoracic impedance, such as implemented by the CorVue algorithm offered by St. Jude Medical. Additionally or alternatively, the IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Patent Number 9,216,285, entitled “Leadless Implantable Medical Device Having Removable And Fixed Components” issued December 22, 2015 and U.S. Patent Number 8,831,747, entitled “Leadless Neurostimulation Device And Method Including The Same” issued 15618WOO1 (013-0605PCT1) 12 PATENT   September 09, 2014, which are hereby incorporated in full by reference herein. Additionally or alternatively, the IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Patent Number 8,391,980, entitled “Method And System For Identifying A Potential Lead Failure In An Implantable Medical Device” issued March 05, 2013 and U.S. Patent Number 9,232,485, entitled “System And Method For Selectively Communicating With An Implantable Medical Device” issued January 05, 2016, which are hereby incorporated in full by reference herein. Additionally or alternatively, the IMD may be a subcutaneous IMD that includes one or more structural and/or functional aspects of the device(s) described in U.S. Patent Number 10,765,860, entitled “Subcutaneous Implantation Medical Device With Multiple Parasternal-Anterior Electrodes” issued September 08, 2020; U.S. Patent Number 10,722,704, entitled “Implantable Medical Systems And Methods Including Pulse Generators And Leads” issued July 28, 2020; U.S. Patent Number 11,045,643, entitled “Single Site Implantation Methods For Medical Devices Having Multiple Leads”, issued June 29, 2021; and U.S. published application US20210330239A1, entitled “Method and system for adaptive- sensing of electrical cardiac signals” filed March 4, 2021, which are hereby incorporated by reference in their entireties. Further, one or more combinations of IMDs may be utilized from the above incorporated patents and applications in accordance with embodiments herein. Embodiments may be implemented in connection with one or more subcutaneous implantable medical devices (S-IMDs). For example, the S-IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Patent Number 10,722,704, entitled “IMPLANTABLE MEDICAL SYSTEMS AND METHODS INCLUDING PULSE GENERATORS AND LEADS”, issued July 28, 2020 and U.S. Patent Number 10,765,860, entitled “SUBCUTANEOUS IMPLANTATION MEDICAL DEVICE WITH MULTIPLE PARASTERNAL-ANTERIOR ELECTRODES”, issued September 08, 2020, which are hereby incorporated by reference in their entireties. The IMD may represent a passive device that utilizes an external power source, an entirely mechanical plan will device, and/or an active device that includes an internal power source. The IMD may deliver some type of therapy/treatment, provide mechanical circulatory support, and/or merely monitor one or more physiologic characteristics of interest (e.g., PAP, CA signals, impedance, heart sounds. 15618WOO1 (013-0605PCT1) 13 PATENT   [0070] The term “treatment notification” shall mean a communication and/or device command to be conveyed to one or more individuals and/or one or more other electronic devices, including but not limited to, network servers, workstations, laptop computers, tablet devices, smart phones, IMDs, external diagnostic test (EDT) equipment and the like. When a treatment notification is provided as a communication, the treatment notification may present in an audio, video, vibratory or other user perceivable medium. The communication may be presented in various formats, such as to display patient information, messages, user directions and the like. The communication is presented on one or more of the various types of electronic devices described herein and may be directed to a patient, a physician, various medical personnel, various patient record management personnel and the like. The communication may represent an identification of a patient diagnosis and various treatment recommendations. The diagnosis and treatment recommendation may be provided directly to the patient. For example, in some circumstances, a diagnosis and treatment recommendation may be to modify a dosage level, in which case, the notification may be provided to the physician or medical practitioner. As another example, the diagnosis and treatment recommendation may be to begin, change or end certain physical activities, in which case, the notification may be provided to the patient, in addition to the physician or medical practitioner. As another example, the treatment notification may present an indication that a patient may or may not be a good candidate suited for implant of a ventricular assist device (e.g., LV assist device), a transplant, a valve repair procedure (e.g., a MitraClip^TM valve repair to correct mitral regurgitation) and the like. Other nonlimiting examples of a communication type notification include, in part or in whole, a recommendation to schedule an appointment with a physician, schedule an appointment for additional blood work, perform an additional at home POC blood analysis (e.g., utilizing at home EDT equipment), recommend that the patient collect additional EDT and/or IMD data. When a notification includes an action that may be performed by a patient alone, the notification may be communicated directly to the patient. Other nonlimiting examples of a communication type notification include communications sent to a patient (e.g., via a PDE device or other electronic device), where the communication informs the patient of how a patient’s lifestyle choices are directly affecting the patient’s health. For example, when a patient 15618WOO1 (013-0605PCT1) 14 PATENT   consumes too much sugar, a notification may be sent to the patient to inform them that the excessive sugar has caused a spike in the patient’s glucose level. As another example, when a patient avoids exercise for a period of time, the notification may inform a patient that the patient’s lack of exercise has raised a PAP trend and/or introduced an undue burden on a patient’s kidneys. [0071] When a treatment notification is provided as a device command, the treatment notification may represent an electronic command directing a computing device (e.g., IMD, EDT equipment, local external device such as a base unit, server) to perform an action. For example, the action may include directing the following: 1. IMD, EDT equipment, or external device to provide additional IMD data, EDT data, and/or sensor data already available; 2. IMD, EDT equipment, or external device to collect additional data and/or another type of data; 3. IMD to deliver a therapy and/or modify a prior therapy (e.g., a pacing therapy, neural stimulation therapy, appetite suppression therapy, drug delivery rate); 4. Local external device to provide additional information regarding past and present behavior of the patient, past and present blood pressure information of the patient, blood pressure trends, etc.; and 5. Server to analyze further information in the patient medical record and/or from another medical record. [0072] The term “treatment recommendation” shall mean a recommendation for the patient, medical personnel and/or a device (e.g., an IMD, local external device, remote server, or body generated analyte (BGA) device) to take an action and/or maintain a current course of action. Non-limiting examples of treatment recommendations include dispatching an ambulance to the patient’s location, instructing the patient immediately go to a hospital, instructing the patient schedule an appointment, instructing the patient change a prescription, instructing the patient undergo additional examinations (e.g., diagnostic imaging examinations, exploratory surgery and the like), instructing the patient undergo a POC test to collect new BGA data, instructing the patient take a nutritional supplement (e.g., an ONS), instructing the patient to add, 15618WOO1 (013-0605PCT1) 15 PATENT   increase, decrease, or cease taking a medication, instructing the patient start, stop or change a physical activity, instructing the patient to take another pressure measurement, or instructing the patient make no changes. The treatment recommendation may include an instruction to change, maintain, add or stop a therapy delivered by an active IMD, such as a pacing therapy, an ATP pacing therapy, a neural stimulation therapy, mechanical circulatory support, and the like. [0073] The term “external device” shall mean a commercial wireless device (e.g., a tablet computer, a smartphone, a laptop computer) and/or a specialized wireless device such as a programmer or bedside monitor or base unit. A patient, using an application, button, selection, etc., on the external device, may trigger the external device to transmit signals from the external device to the IMD and/or implantable sensor. The transmitted signals include a connection request that the IMD establish a communications link with the external device. The application may be written to be compatible with numerous operating systems. When the connection request is detected by the IMD, the IMD enters a communication initialization mode and implements a pairing and/or bonding procedure. The pairing and/or bonding procedure may be performed based on various wireless protocols (e.g., Bluetooth Low Energy (BLE), Bluetooth, ZigBee). The pairing and/or bonding procedure may include various levels of complexity and security. For example, the procedure may include added security such as exchanging information to generate passkeys in both the IMD and the external device to establish a secure bi-directional communication link. System Overview [0074] The signal strength (e.g., emission level) of the transmitted energizing signals that energize the implantable wireless sensor is limited by adherence to various standards. For example, there are standards required by the Federal Communications Commission (FCC) (i.e., FCC Part 18: 53dBuV/m https://www.ecfr.gov/current/title- 47/chapter-I/subchapter-A/part-18), Comité International Spécial des Perturbations Radioélectriques (CISPR), and other regulatory bodies meant to protect other electronic equipment, including consumer and aviation electronics, from disruption due to excessive electromagnetic radiation. By way of example only, CISPR is an international 15618WOO1 (013-0605PCT1) 16 PATENT   standard for electromagnetic emissions from industrial, scientific, and medical (ISR) equipment. For example, FIG.13 illustrates a table from CISPR 11, from 60601-1-2, that shows electromagnetic radiation disturbance limits for class B group 2 equipment measured on a test site. For reference, OATS indicates Open-Area Test Site, SAC indicates Semi-Anechoic Chamber, and FAR indicates Fully-Anechoic Room. The limits in the table are limits on electric and magnetic field strengths. While electric fields are measured in volts per meter (V/m, µV/m) and magnetic fields strengths in amperes per meter (A/m, µA/m), the limits can also be represented in dB, and although not shown, watts may be used. For example, the limits in the table associated with 30-80,872 MHz correspond to a maximum average signal strength limit 330 in Fig.3B. Other regulatory bodies (e.g., Food and Drug Administration (FDA) in the United States) require adherence to standards that protect medical equipment from disruption and that limit the amount of electromagnetic radiation absorbed by human tissue (e.g., Specific Absorption Rate (SAR)). The specific numerical limits within the standards are not included herein as they may vary by jurisdiction. For further reference, the FDA website at fda.gov/radiation-emitting-products/mri-magnetic-resonance-imaging/mri-information- industry suggests relevant information in at least: IEC 60601-2-33, NEMA NS 8, NEMA NS 10; a letter addressing the frequency range below 300 kHz from the FDA to the FCC on Radiofrequency Exposure referencing ICNIRP 1998 and IEEE C95.1-2005 can be found at www.fda.gov/media/135022/download; and the FCC regulations for SAR are 2.1091, 2.1093 and also discussed in OET

About the Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields." [0075] New and unique aspects herein take advantage of requirements of the various standards being imposed on a time-averaged emission level (average, quasi- peak, etc.), rather than an instantaneous level. It makes sense for most standards, e.g., SAR-related standards, to be tied to average levels. Sensitive electronics are often less sensitive to ultra-brief emissions bursts, and even should there be a momentary disruption, critical systems have check sums and means to repeat a signal if needed. [0076] In accordance with new and unique aspects herein, methods and devices are described wherein the transmitter in an external base unit, positioned outside of the 15618WOO1 (013-0605PCT1) 17 PATENT   skin of the patient, occasionally operates at a very high signal level (e.g., relatively higher emission level) to guarantee true sensor lock to the correct portion of the signal phase. The relatively higher emission level may exceed a maximum average signal strength limit set by regulatory bodies. The sensor is an implantable sensor positioned within a patient, such as to detect a level of pressure within a vessel, lumen, or organ. The terms vessel, lumen, and organ are used interchangeably herein, and the embodiments are not restricted to one location or type of location within the body. The duration of this high signal level operation is extremely short, lasting only a few periods of the transmitter frequency, and perhaps as short as a single period. The frequency of the sensor can by determined by identifying the frequency associated with a peak within the returned signals that has the greatest amplitude. Once true sensor lock is assured, there is no need to continue operating at this relatively higher emission level again for a relatively long time, such as thousands of periods or even longer. During the time period following the relatively higher emission level, the transmitter operates at levels (e.g., relatively lower emission levels) well below the maximum average signal strength limit set by standards, such that the time-averaged emission level satisfies the applicable standards. Eventually, as set by a timer or by monitoring the quality of the phase-locked signal, the transmitter again sends out a single “ping” at the relatively higher emission level (or two or more “pings”) to confirm true sensor lock (e.g., true signal lock). [0077] Embodiments are directed toward a system and method for communicating with a wireless implantable sensor. Briefly described, according to new and unique aspects, the systems and methods determine the resonant frequency of the sensor by transmitting a first energizing signal at a relatively higher amplitude signal level (e.g., relatively higher emission level). The first energizing signal energizes the sensor and induces a current in the sensor that can be used to track the resonant frequency. The system receives returned signals, including the sensor signal of the sensor (e.g., ring down response of the sensor), in response to the first energizing signal and determines the resonant frequency of the sensor based on an amplitude of a peak within the returned signals. For example, the amplitude of the sensor signal will be relatively higher, and in some cases much greater, than the amplitudes of signals returned from environmental objects. The resonant frequency can be used to calculate the measured physical 15618WOO1 (013-0605PCT1) 18 PATENT   parameter (e.g., pressure). The system thus achieves true sensor lock by identifying the greatest signal level within the returned signals. The system then transmits a series of consecutive energizing signals at a relatively lower amplitude (e.g., relatively lower emission level) and identifies (e.g., tracks) the frequency of the sensor signal based on the previously identified frequency. The system tracks the frequency of the sensor signal from amongst a plurality of signals that are returned to the system from the sensor and other objects in the environment. When a time expires or a peak that is not associated with the sensor is too close in frequency to the peak associated with the sensor, the system and method transmit another energizing signal at the relatively higher amplitude signal level (e.g., relatively higher emission level). [0078] According to new and unique aspects, the pressure data can be used by another implantable device within the patient to adjust sensing parameters and/or treatment parameters, deliver and/or adjust pacing pulses, and the like. Additionally, the system can generate suggestions and/or a clinician can use the pressure data to prescribe/change the patient’s therapy (e.g., prescribe new medication, change medication, change diet, recommend physical therapy, recommend to implant IMD, change programmed parameters of IMD already implanted). Suggestions and/or changes to the patient’s therapy and/or actions can be conveyed to the patient via the internet, a patient application, a device external to the patient body, and the like. Exemplary Implantable Sensor [0079] Referring now to the drawings, FIG. 1A illustrates a sensor 10 for the measurement of physical parameters. The sensor can be fabricated using micro- machining techniques and is small, accurate, precise, durable, robust, biocompatible, and insensitive to changes in body chemistry, or biology. Additionally, the sensor can incorporate radiopaque features to enable fluoroscopic visualization during placement within the body. Furthermore, this sensor is encased in a hermetic, unitary package of electrically insulating material where the package is thinned in one region so as to deform under a physiologically relevant range of pressure. The LC circuit contained in the packaging is configured so that one electrode of the capacitor is formed on the thinned region. This sensor does not require the use of external connections to relay pressure 15618WOO1 (013-0605PCT1) 19 PATENT   information externally and does not need an internal power supply to perform its function. The pressure sensor of the current invention can be attached to the end of a catheter to be introduced into a human body and delivered to an organ or vessel using catheter- based endovascular techniques. [0080] The sensor 10 includes a body 12. The body 12 is formed from electrically insulating materials, such as biocompatible ceramics. In some embodiments, the body is comprised of fused silica. The sensor 10 comprises a deflectable region 14 at the lower end of the body 12. The body 12 further comprises a lower chamber 19 and an upper chamber 21. [0081] An LC resonator is hermetically housed within the body 12 and comprises a capacitor 16 and an inductor 20. As used herein, the term "hermetic" will be understood to mean "completely sealed, especially against the escape or entry of air and bodily fluids." The capacitor 15 is located within the lower cylindrical chamber 19 and comprises at least two plates 16, 18 disposed in parallel, spaced apart relation. The inductor 20 comprises a coil disposed within the upper chamber 21 and which is in conductive electrical contact with the capacitor 15. [0082] The lower capacitor plate 18 is positioned on the inner surface of the deflectable region 14 of the sensor body 12. The upper capacitor plate 16 is positioned on a fixed region of the sensor body 12. A change in ambient pressure at the deflectable region 14 of the sensor 10 causes the deflectable region 14 to bend, thereby displacing the lower plate 16 with respect to the upper plate 18 and changing the capacitance of the LC circuit. Because the change in capacitance of the LC circuit changes its resonant frequency, the resonant frequency of the sensor 10 is pressure-dependent. [0083] It should be understood that the implantable sensor shown and discussed in FIG.1A is an example and represents only one implantable sensor that may be used together with the new and unique aspects discussed herein. Additionally or alternatively, other implantable sensors having a pressure-dependent circuit can be used. [0084] The disclosed sensor features a completely passive inductive-capacitive (LC) resonant circuit with a pressure varying capacitor. Because the sensor is fabricated using completely passive electrical components and has no active circuitry, it does not require on-board power sources such as batteries, nor does it require leads to connect 15618WOO1 (013-0605PCT1) 20 PATENT   to external circuitry or power sources. These features create a sensor which is self- contained within the packaging material and lacks physical interconnections traversing the hermetic packaging, such interconnects frequently being cited for failure of hermeticity. Furthermore, other sensing capabilities, such as temperature sensing, can be added using the same manufacturing techniques. For example, temperature sensing capability can be accomplished by the addition of a resistor with known temperature characteristics to the basic LC circuit. In some embodiments, the sensor can include a battery to power some functionality. [0085] The capacitor in the pressure sensor consists of at least two conductive elements separated by a gap. If a force is exerted on the sensor, a portion of the sensor deflects, changing the relative position between the at least two conductive elements. This movement will have the effect of reducing the gap between the conductive elements, which will consequently change the capacitance of the LC circuit. An LC circuit is a closed loop system whose resonance is proportional to the inverse square root of the product of the inductance and capacitance. Thus, changes in pressure alter the capacitance and, ultimately, cause a shift in the resonant frequency of the sensor. The pressure of the environment external to the sensor is then determined by referencing the value obtained for the resonant frequency to a previously generated curve relating resonant frequency to pressure. [0086] Because of the presence of the inductor, it is possible to couple to the sensor electromagnetically and to induce a current in the LC circuit via a magnetic loop. This characteristic allows for wireless exchange of electromagnetic energy with the sensor and the ability to operate it without the need for an on-board energy source such as a battery. Thus it is possible to determine the pressure surrounding the sensor by a simple, non-invasive procedure by remotely interrogating the sensor, recording the resonant frequency, and converting this value to a pressure measurement. [0087] One method of sensor interrogation is explained in U.S.7,245,117 entitled “Communicating with Implanted Wireless Sensor” and filed April 13, 2005, which is incorporated herein by reference in its entirety. According to this invention, the interrogating system energizes the sensor with a low duty cycle, gated burst of RF energy having a predetermined frequency or set of frequencies and a predetermined amplitude. 15618WOO1 (013-0605PCT1) 21 PATENT   The energizing signal is coupled to the sensor via a magnetic loop. The energizing signal induces a current in the sensor that is maximized when the frequency of the energizing signal is substantially the same as the resonant frequency of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor, which is then used to determine the measured physical parameter. The resonant frequency of the sensor is determined by adjusting the frequency of the energizing signal until the phase of the ring down signal and the phase of a reference signal are equal or at a constant offset. In this manner, the energizing signal frequency is locked to the sensor’s resonant frequency and the resonant frequency of the sensor is known. The pressure of the localized environment can then be ascertained. [0088] Q factor (Q) is the ratio of energy stored versus energy dissipated. The reason Q is important is that the ring down rate of the sensor is directly related to the Q. If the Q is too small, the ring down rate occurs over a substantially shorter time interval. This necessitates faster sampling intervals, making sensor detection more difficult. Also, as the Q of the sensor increases, so does the amount of energy returned to external electronics. Thus, it is important to design sensors with values of Q sufficiently high enough to avoid unnecessary increases in complexity in communicating with the sensor via external electronics. [0089] The Q of the sensor is dependent on multiple factors such as the shape, size, diameter, number of turns, spacing between the turns and cross-sectional area of the inductor component. In addition, Q will be affected by the materials used to construct the sensors. Specifically, materials with low loss tangents will provide a sensor with higher Q factors. [0090] The body of the implantable sensor is preferably constructed of ceramics such as, but not limited to, fused silica, quartz, pyrex and sintered zirconia, that provide the required biocompatibility, hermeticity and processing capabilities. These materials are considered dielectrics, that is, they are poor conductors of electricity but are efficient supporters of electrostatic or electroquasistatic fields. An important property of dielectric materials is their ability to support such fields while dissipating minimal energy. The lower 15618WOO1 (013-0605PCT1) 22 PATENT   the dielectric loss, the lower the proportion of energy lost, and the more effective the dielectric material is in maintaining high Q. [0091] With regard to operation within the human body, there is a second important issue related to Q, namely that blood and body fluids are conductive mediums and are thus particularly lossy. As a consequence, when a sensor is immersed in a conductive fluid, energy from the sensor will dissipate, substantially lowering the Q and reducing the sensor-to-electronics distance. It has been found that such loss can be minimized by further separation of the sensor from the conductive liquid. This can be accomplished, for example, by coating the sensor in a suitable low-loss-tangent dielectric material. The potential coating material must also meet stringent biocompatibility requirements and be sufficiently compliant to allow transmission of fluid pressure to the pressure-sensitive deflective region. One preferred material for this application is silicone rubber. It should be appreciated that use of a coating is an optional feature and is not required per se but such coatings will preserve the Q of the sensor which can prove advantageous depending on the intracorporeal location of the sensor. [0092] The sensors described above can be adapted for use within an organ or a lumen, depending upon what type of attachment or stabilizing means is employed. For example, some sensors are suitable for use within an organ such as the heart. The sensor has a generally cylindrical body that hermetically houses the capacitor and inductor elements previously described. The sensor further has a pressure sensitive surface on one end of the cylindrical body and a screw-type anchoring device extending upward from the opposite end of the body for anchoring within a chamber of the heart. [0093] By changing the anchoring means, in other embodiments the same sensor can be adapted for use within a lumen such as an artery or arteriole in the pulmonary artery vasculature. The sensor has a wire loop or other fastening mechanism extending outward from the sensor body. The wire loop causes the sensor to lodge within a lumen. In some cases, the sensor is located centrally within the lumen, allowing blood flow all around the sensor. In other cases, the sensor can be located close to or against a wall of the lumen. [0094] FIG.1B illustrates a system 101 that includes an IMD 100, an implantable sensor 102, and an external device 104 implemented in accordance with embodiments 15618WOO1 (013-0605PCT1) 23 PATENT   herein. The IMD 100 and the implantable sensor 102 are implanted within the body of a patient. The external device 104 is outside of the patient body. The external device 104 may be a base unit, a programmer, an external defibrillator, a workstation, a portable computer (e.g., laptop or tablet computer), a personal digital assistant, a cell phone (e.g., smartphone), a bedside monitor, and the like. The IMD 100 may represent a cardiac monitoring device, a pacemaker, a cardioverter, a cardiac rhythm management device, a defibrillator, a neurostimulator, a leadless monitoring device, a leadless pacemaker, and the like, implemented in accordance with one embodiment of the present invention. The IMD 100 may be a dual-chamber stimulation device capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, anti-tachycardia pacing and pacing stimulation, as well as capable of detecting heart failure, evaluating its severity, tracking the progression thereof, and controlling the delivery of therapy and warnings in response thereto. [0095] The IMD 100 includes a housing 106 that is joined to a header assembly 108 that holds receptacle connectors connected to a right ventricular lead 130 and an atrial lead 120, respectively. The atrial lead 120 includes a tip electrode 122 and a ring electrode 123. The right ventricular lead 130 includes an RV tip electrode 132, an RV ring electrode 134, an RV coil electrode 136, and an SVC coil electrode 138. The leads 120 and 130 detect intracardiac electrogram (IEGM) signals that are processed and analyzed as described herein, and also deliver therapies as described herein. [0096] The IMD 100 may be implemented as a full-function biventricular pacemaker, equipped with both atrial and ventricular sensing and pacing circuitry for four chamber sensing and stimulation therapy (including both pacing and shock treatment). Optionally, the IMD 100 may further include a coronary sinus lead with left ventricular electrodes. The IMD 100 may provide full-function cardiac resynchronization therapy. Alternatively, the IMD 100 may be implemented with a reduced set of functions and components. For instance, the IMD 100 may be implemented without ventricular sensing and pacing. [0097] The implantable sensor 102 is configured to be implanted at a location remote from the electrodes of the leads 120 and 130. The implantable sensor 102 may be implanted in a blood vessel, such as an artery or vein. In an embodiment, the sensor 15618WOO1 (013-0605PCT1) 24 PATENT   102 is implanted within the pulmonary artery (PA) to measure pulmonary arterial pressure (PAP). The sensor 102 may be anchored to the vessel wall of a blood vessel using one or more expandable loop wires. The diameter of each loop should be larger than the diameter of target blood vessel in order to provide adequate anchoring force. Optionally, instead of the loop wire, the sensor 102 may be attached to the end of a self- expandable stent and deployed into the blood vessel through a minimally invasive method. [0098] Alternatively, the implantable sensor 102 may be secured to tissue outside of blood vessels. The sensor 102 may be secured in place by using a fixation screw (e.g., helix) attached to the housing. The screw may anchor the sensor 102 to patient heart tissue, such as cardiac tissue of the left or right ventricle. The sensor 102 is configured to sense a physiologic parameter of interest (PPOI) and to generate signals indicative of the PPOI. In a non-limiting example, when the sensor 102 is disposed within the PA, the sensor 102 may sense, as the PPOI, blood pressure. Interrogation System and Method [0099] FIG. 2 illustrates an exemplary system 200 for communicating with a wireless sensor 202 implanted within a body 203 in accordance with embodiments herein. In some environments the sensor 202 can be the sensor 10 discussed with respect to FIG.1A and/or the sensor 102 of FIG.1B. The system 200 of FIG.2 can be included within the system discussed further below in FIG. 5 and/or in the base unit discussed in FIG.7. [0100] FIG.2 illustrates an external base unit 204 that is positioned outside of the body 203. In some embodiments, the base unit 204 may have components configured to interface with and/or contact skin and/or clothing of the patient, such as a pillow, garment, and the like. The base unit 204 is capable of communicating (e.g., communications circuit 224) with external device(s) 226 such as smart phones, cellular phones, watches, computers, laptops, tablets, programmers, etc., as well as communicating wirelessly and over wired communication technologies to convey information between remote servers, computers, etc., and the base unit 204. 15618WOO1 (013-0605PCT1) 25 PATENT   [0101] The base unit 204 includes a programmable microcontroller 206 that controls various operations of the base unit 204, including cardiac monitoring such as monitoring blood pressure. The microcontroller 206 can include a microprocessor (or equivalent control circuitry, one or more processors, etc.), RAM and/or ROM memory, logic and timing circuitry, state machine circuitry, I/O circuitry, and the like. [0102] The base unit 204 also includes transmitter circuitry 230 capable of generating and transmitting energizing signals having emission levels that are relatively higher and lower with respect to each other. Receiver circuitry 232 receives returned signals that include sensor signals from the sensor 202 and other returned signals, such as from environmental object(s) 228. [0103] The base unit 204 can also include an emission level adjustment module 208 for selecting the emission level / amplitude of the energizing signal. For example, the emission level adjustment module 208 selects a relatively higher emission level when transmitting an energizing signal to ensure true sensor lock, and a relatively lower emission level when true sensor lock is achieved and the frequency of the sensor 202, and thus the associated pressure, can be tracked. [0104] As noted herein, the energizing signal with the relatively higher emission level (i.e., ping) can be initiated by i) a timer, ii) the merger or near merger of the true peak with a false peak (e.g., a false peak is within a frequency range of the true peak), and/or iii) the true peak splitting. Turning to a timer-based ping interval, in some embodiments a typical interval between timer-based relatively higher emission level energizing signals will be a fraction of the time that the pressure changes, i.e., a fraction of the heart’s natural pulse. For example, the timer can be set and/or adjusted based on a patient’s heart rate. If a maximum pulse of 200 beats per minute (bpm) is assumed, and the timer-based relatively higher emission level energizing signal is to be transmitted at least 20 times per heartbeat, that would set a shortest interval between the timer- based relatively higher emission level pings of 15 milliseconds. In the other extreme, in other embodiments wherein a patient has a pulse of 45 bpm and a timer-based relatively higher emission level energizing signal is transmitted only twice per heartbeat, that would set a longest interval between the timer-based relatively higher emission level energizing 15618WOO1 (013-0605PCT1) 26 PATENT   signals of 0.625 seconds. It should be understood that the microcontroller 206 can set the intervals anywhere within this range. [0105] In some embodiments, the amplitude of the relatively higher emission level energizing signal can be as high as: [(amplitude of regular lower emission level energizing signal) multiplied by (number of lower emission level transmissions per one relatively higher emission level energizing signal) divided by 2]. For example, if the base unit 204 transmits 1000 times per second at the lower emission level and transmits 10 times per second at the relatively higher emission level, the amplitude of the relatively higher emission level energizing signal could be 50 times stronger than the regular lower emission level. In some cases, this may be a maximum limit. In other cases, the relatively higher emission level energizing signal can have an amplitude of approximately twice or at least twice that of the relatively lower emission level energizing signal. [0106] In some embodiments, the lower emission level energizing signal can be below the average level (e.g., limit) allowed by the standards; for example, in the range 10–30 dB µV/m when measured at a distance of 3 m. The higher emission level energizing signal can be at least twice that, and in some embodiments, 50–100 times higher or more, depending on the ratio of number of higher emission level energizing signals to the number of lower emission energizing signals as discussed herein. In some cases, the lower and the higher emission level energizing signals can be below the limit. In other embodiments, the higher emission level energizing signals can be in the range 60–1500 dB µV/m. [0107] An amplitude determination module 210 determines amplitudes of peaks within the returned signals. For example, the returned signals will have multiple amplitude peaks across a frequency spectrum. The sensor signal will have an associated peak with an associated amplitude, and other peaks, not associated with the sensor 202, will also have associated amplitudes. If the amplitude determination module 210 is analyzing the returned signals that are received in response to an energizing signal having the relatively higher emission level, the peak that is identified as having the highest amplitude is identified as being associated with the sensor signal. [0108] A frequency determination and comparison module 212 determines the frequencies associated with at least one of the peak amplitudes. If a peak has been 15618WOO1 (013-0605PCT1) 27 PATENT   identified as being associated with the sensor signal, such as being identified in response to an energizing signal having the relatively higher emission level, the frequency of the peak and thus the frequency of the sensor signal is determined. [0109] As discussed herein, the frequency of the peak of the sensor signal will increase or decrease based on the change of pressure within the body 203. However, the reflected change along the frequency spectrum of returned signals is gradual and thus once true sensor lock is achieved, the base unit 204 can track the frequency of the sensor signal based on the currently returned signals and the previously determined sensor frequency. Additionally, the frequency determination and comparison module 212 can compare the previously determined frequency that is associated with the sensor 202 to one or more frequencies that are associated with peaks greater than and less than the sensor signal frequency to determine if the frequency of any peak not associated with the sensor 202 is within a frequency range of the sensor signal frequency. For example, if the frequency of the peak associated with the sensor 202 is moving toward another peak, when the two peaks are within a frequency range of each other, a trigger may be set to transmit another energizing signal at the relatively higher emission level. In some embodiments, the frequency range can be preset, such as within .5 MHz as shown in FIG.3H, or within less than .5 MHz. In other embodiments, the frequency range can be determined based on the Q of the sensor 10. In some cases, as a theoretical minimum an energizing signal at the relatively higher emission level can be triggered if the frequency separation of the two peaks is less than f/(2*Q), where f is the operating frequency. In other cases, the relatively higher emission level energizing signal can be triggered when the separation is greater, such as approximately two or three times the calculated minimum value. Further, it should be noted that the relatively higher emission level energizing signal can be triggered either when two frequency peaks (the true peak and a false peak) merge, and/or when the true peak splits (splitting into a true peak and a false peak). [0110] A pressure determination module 214 determines the pressure based on the returned characteristics of the sensor signal. In some embodiments, the pressure can be determined based on the frequency of the peak associated with the sensor signal. In some cases, the pressure can be determined as the frequency of each of the returned 15618WOO1 (013-0605PCT1) 28 PATENT   sensor signals is identified, while in other embodiments the pressure can be determined based on a pre-set time interval or after the data acquisition session is complete. [0111] A timing control module 216 can control the timing of the energizing signals. For example, after an energizing signal at the relatively higher emission level is transmitted, a timer can be set for a predetermined time during which the base unit 204 will transmit energizing signals at the relatively lower emission level. If the timer expires before the frequency determination and comparison module 212 sets the trigger, the timing control module 216 can direct the emission level adjustment module 208 to transmit the energizing signal at the relatively higher emission level. [0112] A memory 222 or other storage medium stores program instructions, settings, signal data such as phase, amplitude, and pressure, data received from the sensor 202 and/or object 228, etc. [0113] For example, the base unit 204 can perform a method for locking onto a signal returned from a wireless sensor 202 positioned with a body. The wireless sensor can have an LC circuit having a resonant frequency that varies in response to changes in pressure in the body. The base unit 204 can generate and transmit a first energizing signal having a first emission level. The first emission level can be set by the emission level adjustment module 208 and the energizing signal can be transmitted by the transmitter circuitry 230. First returned signals can be received, such as by the receiver circuitry 232, that include a first sensor signal in response to the first energizing signal. A first frequency associated with the LC circuit is determined or generated, such as by the amplitude determination module 210 and the frequency determination and comparison module 212, based on an amplitude within the first returned signals. The base unit 204 can then generate and transmit a second energizing signal having a second emission level that is lower than the first emission level. Second returned signals are received including a second sensor signal in response to the second energizing signal. A second frequency associated with the LC circuit is determined or generated based on the first frequency and the second returned signals, such as by the frequency determination and comparison module 212, and the pressure in the body is determined or generated based on the first frequency or the second frequency, such as by the pressure determination module 214. 15618WOO1 (013-0605PCT1) 29 PATENT   [0114] In some cases, determining the first frequency associated with the LC circuit is based on a maximum amplitude within the first returned signals. In other cases, the base unit 204 can transmit, over a predetermined time period, such as determined by the timing control module 216, a plurality of consecutive energizing signals having the second emission level; in response to the predetermined time period expiring, another energizing signal having the first emission level can be transmitted. In some embodiments, a time-averaged emission level over a time period is below a maximum average signal strength limit, and the time-averaged emission level can be determined based on the first and second energizing signals transmitted over the time period. In other embodiments, the first emission level is greater than a maximum average signal strength limit associated with a time period, and the second emission level is less than the maximum average signal strength limit associated with the time period. [0115] The base unit 204 can generate and transmit, such as by the emission level adjustment module 208 and the transmitter circuitry 230, a third energizing signal having the second emission level, receive, such as by the receiver circuitry 232, third returned signals including a third sensor signal in response to the third energizing signal, and determine or generate a third frequency associate with the LC circuit, such as by the frequency determination and comparison module 212, based on the second frequency and the third returned signals. In other embodiments, the base unit 204 can receive the third returned signals having a first peak associated with the sensor and a second peak not associated with the sensor, determine or generate third and fourth frequencies associated with the first and second peaks, such as with the frequency determination and comparison module 212, and, in response to the third and fourth frequencies being within a predetermined frequency range of each other, transmit a fourth energizing signal having the first emission level. In other cases, the base unit 204 can receive fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level, and determine or generate the frequency associated with the LC circuit based on a maximum amplitude within the fourth returned signals. [0116] In still further embodiments, the base unit 204 can generate and transmit a third energizing signal having the second emission level, receive third returned signals 15618WOO1 (013-0605PCT1) 30 PATENT   including a first peak associated with the sensor and a second peak not associated with the sensor, determine or generate third and fourth frequencies associated with the first and second peaks, and in response to a difference between the third and fourth frequencies being greater than a predetermined frequency range, transmit another energizing signal having the second emission level. [0117] FIG. 3A illustrates a graph 300 of an example trace 306 of pulmonary arterial pressure that can be measured using the sensor 202, implanted within the pulmonary artery of the patient, in accordance with embodiments here. Vertical axis 302 indicates the signal strength of the pressure in the pulmonary artery, while horizontal axis 304 indicates time. Energizing signals 308 that are transmitted from the base unit 204 toward the sensor 202 have a much higher frequency compared to a human pulse. It should be understood that the frequency of the energizing signals 308 as shown is for illustration purposes only, and in reality, the frequency may be much higher than shown. [0118] FIG. 3B is a graph 310 illustrating the transmission levels of energizing signals when the energizing signals are transmitted at different levels to ensure true signal lock between a base unit 204 and an implantable sensor 202 in accordance with embodiments herein. Transmission signal strength when the transmitter circuitry 230 is active is indicated on vertical axis 312 and time is indicated on horizontal axis 314, and may indicate a second or a fraction of a second. In some embodiments, as amplitude is directly related to the power of the RF signal, or the energizing signal transmitted by the base unit 204, signal strength may be measured in Watts (W) or decibels (dB) but is not so limited. In some embodiments, the transmission signal strength indicated on the vertical axis 312 can be represented in units such as: W, mW, µW, dB W, dB mW, dB µW, V/m, mV/m, µV/m, dB V/m, dB mV/m, dB µV/m, A/m, mA/m, µA/m, dB A/m, dB mA/m, and/or dB µA/m. [0119] Portions of transmission level trace 316 are shown having a greater or higher transmission signal strength at a first emission level 320 associated with higher power energizing signal(s) and other portions of the trace 316 are shown having a lower signal strength at a second emission level 326 associated with lower power energizing signals. 15618WOO1 (013-0605PCT1) 31 PATENT   [0120] The relatively higher power energizing signals having the first emission level 320 can be referred to as the “ping” that guarantees true sensor lock to the correct portion of the signal phase. In some embodiments, a single relatively higher power energizing signal, transmitted during time period 322, can be transmitted by the transmitter circuity 230 at the first emission level 320, while in other embodiments, a plurality of relatively higher power energizing signals can be transmitted during the time period 322 at the first emission level 320. The time period 322 can be predetermined by the system, and may be related to the sensor 202, the environment the base unit 204 is being used in, the number of energizing signals to be transmitted, and the like. The relatively larger first emission level 320 of the relatively higher power energizing signal(s) results in an increased amplitude of the returned sensor signal, ensuring that the sensor signal has a greater amplitude compared to ambient noise and/or signals returned from object(s) 228 in the environment. Additionally, the returned sensor signal may last for a longer period of time or time period compared to sensor signals that are returned from energizing signals having a relatively lower emission level or returned signals that are returned from other object(s) 228. The increased amplitude and/or the extended length of the returned sensor signal provide the advantage of distinguishing the sensor signal from the signals returned from other environmental objects 228. [0121] The time period 322 is followed by a much longer time period 324 (e.g.,  thousands of periods or more), during which the base unit 204 transmits a very high number of relatively lower power energizing signals at a second emission level 326. The time period 324 can be set, for example, by the timing control module 216. The individual energizing signals transmitted during the time period 324 may have the same characteristics as each other or can have varying phase and/or frequency, as further discussed below. [0122] The time period 324 can be followed by one or more relatively higher power energizing signals that have the relatively higher first emission level 320. In some embodiments, the emission levels of subsequent “pings” can have the same signal strength as each other. In other cases, the base unit 204 may adjust the higher emission levels 320 to be different for different energizing signals, while still being relatively higher than the relatively lower second emission level 326. 15618WOO1 (013-0605PCT1) 32 PATENT   [0123] Maximum average signal strength limit 330, as required by standards and/or regulations, is indicated. It should be understood that the maximum average signal strength limit 330 can change based on regulations and/or jurisdictions. The relatively higher emission level or higher power energizing signals have emission levels (e.g., first emission level 320) that are greater than or exceed the predetermined electromagnetic radiation standard shown by the maximum average signal strength limit 330 (although one, some, or all of the relatively higher level energizing signals can be lower than the limit 330), while the relatively lower emission level or lower power energizing signals transmitted during the time period 324 are less than the limit 330, having emission levels at the second emission level 326. By way of example, a time-averaged emission level 334 is shown at a slightly greater amplitude than the second emission level 326, while being far less than the first emission level 320. The maximum average signal strength limit 330 may be determined over a predetermined time period (e.g., measured in seconds or minutes). In some embodiments, the time-averaged emission level 334 can be determined over the same predetermined time period as the maximum average signal strength limit 330 to ensure compliance. The base unit 204 may set one or more of the time periods 322, 324, the amplitude levels of the energizing signals at the higher emission level 320, and the amplitude levels of the lower emission level energizing signals to ensure that the maximum average signal strength limit 330 is not exceeded, while still maintaining true sensor lock. In some embodiments, the first and second emission levels 320, 326 can be set by a healthcare provider, and may vary depending on jurisdiction, operating environment, and the like. [0124] As discussed further below, a relatively higher power energizing signal may be transmitted at a predetermined interval, such as after time period 332, 324 or earlier. For example, the time periods 322 and 324 may be predetermined, and the relatively higher and lower energizing signals transmitted accordingly. In other embodiments, if there are signals returned from environmental objects 228 that are received at frequencies near to the signal returned by the implantable sensor 202, the base unit 204 can transmit a relatively higher power energizing signal as needed to ensure true sensor lock. 15618WOO1 (013-0605PCT1) 33 PATENT   [0125] In some embodiments, if the base unit 204 transmits relatively higher power energizing signals 20 times per heartbeat and transmits 10 relatively lower power energizing signals per each higher power ping, each heartbeat/PAP pulse beat can be resolved with approximately 200 datapoints, which in many clinical applications is sufficient. In other embodiments, if the noise environment changes on a timescale faster than the human heartbeat, false peaks can be caused to move within the spectrum faster than the pressure-caused motion of the true peak. In such a case, the number of relatively higher power energizing signals per heartbeat can be increased, as long as the overall transmissions remain below the maximum average signal strength limit 330. [0126] FIG. 3C is a graph 340 illustrating the transmission levels of energizing signals in accordance with embodiments herein. The graph 340 represents a small segment of the energizing signals transmitted during a collection period. Transmission signal strength is indicated on vertical axis 344 and time is indicated on horizontal axis 346. [0127] Relatively higher power energizing signal 318 (i.e., a “ping”) is transmitted at the first emission level 320 by the base unit 204, followed by lower emission level energizing signals 348, 350, etc., that are transmitted by the base unit 204 at the second emission level 326, which is followed by relatively higher power energizing signal 328 (i.e., a “ping”). Not all of the lower emission level energizing signals are shown during the time period 324. It should be understood that the representations of the levels of the emission signal strengths are for illustration purposes only. By way of example, each of the relatively higher power energizing signals, which may be a few microseconds long, for example, may be transmitted a couple of times per second up to 100 or more times per second. The transmission interval (e.g., time period 324) may be determined based on a predetermined time or signal quality as discussed herein. [0128] As discussed herein, the relatively higher power energizing signals 318, 328 can refer to a single transmitted signal, more than one transmitted signal, and/or more than one consecutively transmitted signal that is transmitted within signal transmission time period 322. Similarly, the relatively lower power energizing signals 348, 350 can refer to a single transmitted signal, more than one transmitted signal, and/or more than one consecutively transmitted signal that is transmitted within signal transmission time 15618WOO1 (013-0605PCT1) 34 PATENT   period 352. Each of the energizing signals 318, 328, 348, 350 can be transmitted over an extremely short time period, lasting a single period or only a few periods of the transmitter frequency. Time periods 353, 354 between the energizing signals 318, 348, 350, 328, etc., represent time when the base unit 204 is not transmitting, and thus the transmission signal strength is zero. Instead, the base unit 204 is listening for received signals and/or waiting to listen for received signals. In other embodiments, separate transmitter / receiver systems in the base unit 204 may allow constant or near constant transmission while simultaneously detecting returned signals. [0129] Referring to the relatively higher power energizing signal 318, a listening time period 353 follows the signal transmission time period 322 wherein the base unit 204 is receiving and recording received signals from the sensor 202 and other objects 228. The listening time period 353 can include an optional delay period 355 and an active listening period 357. In some embodiments, during the delay period 355 the base unit 204 may not record or may discard returned signals while the noise in the returned signals (not shown) dies down. After the delay period 355, the base unit 204 records / analyzes / processes returned signals received during the active listening period 357. [0130] Similarly, the relatively lower power energizing signals 348 and 350 are followed by listening time periods 354. The listening time period 354 can include an optional delay period 356 and an active listening period 358. Again, in some embodiments, during the delay period 356 the base unit 204 may not record or may discard received signals while the noise in the returned signals dies down, while in the active listening period 358, the base unit 204 records / analyzes / processes returned signals. [0131] FIG. 3D illustrates a graph 360 showing frequencies of returned signals including a sensor signal returned in response to being energized by the relatively lower power energizing signal 348, 350, as discussed in FIG. 3C, in accordance with embodiments herein. Returned signal strength (e.g., amplitude) is indicated on vertical axis 362 and frequency in megahertz (MHz) is indicated on horizontal axis 363. As can be seen, there are multiple peaks 364a, 364b, 364c, 364d, 364e, 364f having similar amplitudes across the frequency spectrum. If the base unit 204 has not already identified and locked onto the sensor signal, it may be difficult to determine which peak 364 is 15618WOO1 (013-0605PCT1) 35 PATENT   associated with the sensor 202 and which of the peaks 364 are returned from environmental objects 228. In some cases, the base unit 204 may lock onto and begin tracking an incorrect peak, which can be referred to as “false lock”. [0132] FIG. 3E illustrates a graph 366 showing frequencies of returned signals received immediately after the transmission of the relatively higher power energizing signal 318, 328 as discussed in FIG.3C, in accordance with embodiments herein. For example, the graph 366 can indicate signals received during the delay period 355 at the beginning of the time period 353 immediately following the energizing signal 318. Returned signal strength (e.g., amplitude) is indicated on vertical axis 362 and frequency in MHz is indicated on horizontal axis 363. [0133] The returned signals include a sensor signal. In some cases, a noise source (e.g., environmental object 228) may also be amplified along with the signal returned from the sensor 202. By way of example, the graph 366 shows peak 368a and peak 370a having higher amplitudes than the other peaks. In an example, a sensor signal is associated with peak 368a, which is amplified in comparison with sensor signal associated with the peak 364d shown in FIG. 3D. The peak 370a, also amplified in comparison with the peak 364f shown in FIG.3D, is associated with a noise source. [0134] FIG. 3F illustrates a graph 372 showing frequencies of returned signals returned in response to a relatively higher power energizing signal 318, 328 in accordance with embodiments herein. FIG. 3F shows the returned signals that are received during the active listening period 357 that follows the delay period 355. Similar to FIGS.3D and 3E, returned signal strength (e.g., amplitude) is indicated on vertical axis 362 and frequency in MHz is indicated on horizontal axis 363. [0135] Compared to the signal response shown in FIG. 3E, the signal response from the noise source, peak 370b, has died down or diminished, while the amplitude of the signal returned from the sensor 202, peak 368b, has remained strong. The higher amplitude of the peak 368b clearly indicates which resonant frequency is associated with the sensor 202 (e.g., approximately 33.5 MHz), and true signal lock, such as by employing a phase lock loop (PLL) as discussed further below, is accomplished by the base unit 204. Therefore, an advantage is realized as the true signal of the sensor 202 can quickly be discerned by the base unit 204 based on the amplitude of the signal (e.g., 15618WOO1 (013-0605PCT1) 36 PATENT   peak 368b) relative to other signal amplitudes. In some cases, the amplitude of the sensor signal may be larger than the other ambient signals because the Q of the implantable sensor 202 is higher than the Q of any ambient noise source, resulting in the a_{mplitudes of the signals returned from noise sources quickly diminishing.  In some} embodiments, the effect of the relatively higher emission level energizing signal lasts for microseconds; the ringdown time in cycles is Q/4.53, i.e., after Q/4.53 cycles the amplitude is cut in half. For example, if Q is 30, the amplitude would be half after 6-7 cycles, where one cycle at 30 MHz is 0.03 microseconds. [0136] FIG.3G illustrates a graph 374 showing frequencies of returned signals that are returned in response to an energizing signal 348, 350 transmitted at the relatively lower emission level (e.g., second emission level 326) in accordance with embodiments herein. Similar to FIGS.3D–3F, received signal strength (e.g., amplitude) is indicated on vertical axis 362 and frequency in MHz is indicated on horizontal axis 363. [0137] At this point, the approximate current resonant frequency of the sensor 202 can be tracked based on the previous determination of approximately 33.5 MHz that was made in evaluation of the response to the signal transmitted at the relatively higher emission level 320. In some embodiments, the base unit 204 can search, such as within a frequency range of the previously identified resonant frequency, to identify a peak associated with the sensor 202. Therefore, even though there may be multiple amplitude peaks with relatively similar amplitudes at different frequencies, the base unit 204 knows which of the peaks is associated with the sensor 202 as the base unit 204 has locked onto the previously known frequency. In some cases, the base unit 204 has adjusted the frequency of the energizing signal, such as the energizing signal 348, 350 of FIG.3C, to better match the resonant frequency of the sensor 202. [0138] FIG. 3H illustrates another graph 376 showing that the frequency of the sensor signal is tracked to a new frequency due to changes in the patient’s blood pressure in accordance with embodiments herein. The returned signals shown in FIG. 3H are returned in response to an energizing signal transmitted at the relatively lower emission level (e.g., second emission level 326). For example, within a time scale of approximately tens of milliseconds or less, the blood pressure is changing due to the patient’s pulse, and thus the resonant frequency of the sensor 202 is shifting. Similar to 15618WOO1 (013-0605PCT1) 37 PATENT   FIGS.3D–3G, received signal strength (e.g., amplitude) is indicated on vertical axis 362 and frequency in MHz is indicated on horizontal axis 363. [0139] For example, the approximate frequency of the sensor signal indicated by peak 368c in FIG.3G is around 33.6 MHz, while the approximate frequency of the sensor signal indicated by peak 368d in FIG.3H is around 33.9 MHz. Because true sensor lock is achieved, the base unit 204 tracks the resonant frequency of the sensor signal and accurately determines the associated frequency of the sensor signal, and thus also the pressure within the body 203. As shown, the peak 368d is still distinct but has moved closer to peak 364e (previously indicated in FIG.3D). [0140] FIG. 3I illustrates a graph 378 showing frequencies of returned signals wherein the frequency of the sensor signal has merged with, crossed over, or otherwise is indistinguishable from a peak associated with noise or an environmental object 228 in accordance with embodiments herein. The returned signals shown in FIG. 3I are returned in response to an energizing signal transmitted at the relatively lower emission level (e.g., emission level 326). Similar to FIGS.3D–3H, received signal strength (e.g., amplitude) is indicated on vertical axis 362 and frequency in MHz is indicated on horizontal axis 363. [0141] In comparison with the sensor signal identified in FIG.3H (e.g., peak 368d), the frequency of the sensor signal in FIG.3I has increased to be between 34.2 MHz and 34.5 MHz, and is now indistinguishable as part of peak 380. Referring again to FIG.3H, the peak 368D of the sensor signal may have merged with peak 364e, and the resonant frequency may be larger, smaller, or approximately the same as the peak 364e. [0142] To prevent the loss of true signal lock due to the returned sensor signal being indistinguishable from another peak, the base unit 204 can transmit an energizing signal with a relatively higher emission level (e.g., the ping or energizing signal 318, 328 of FIG.3C) to energize the sensor 202 with a higher power transmission, resulting in a greater sensor response, thus distinguishing the sensor signal from other returned signals and ensuring that true signal lock is achieved. In some embodiments, the base unit 204 can monitor the frequency of the sensor signal as well as one or more peak frequencies to identify when the sensor signal may become indistinguishable from another peak, determine when the frequency separation is less than f/(2*Q), and/or 15618WOO1 (013-0605PCT1) 38 PATENT   determine when the peak associated with the sensor signal splits into two peaks. In yet further embodiments, the base unit 204 may wait until the sensor signal is indistinguishable from another peak, such as to minimize the amount of transmitted radiation. [0143] FIG.4 illustrates a computer-implemented method for achieving true sensor lock and determining pressure detected by an implantable pressure sensor in accordance with embodiments herein. All or a portion of the operations of FIG.4 may be implemented by one or more processors of the base unit 204 configured with executable instructions, and all or a portion of the operations of FIG.4 may be implemented by one or more processors of the system of FIG. 7 configured with executable instructions. Portions of the operations of FIG.4 may also be implemented by one or more processors of one or more of a local external device, a remote server, and/or the sensor 202. It should be recognized that while the operations of the method are described in a somewhat serial manner, one or more of the operations of the method may be continuous and/or performed in parallel with one another. For example, the various operations of the base unit 204 may be continuous and/or performed in parallel with one another and/or other functions of the base unit 204. The method may be performed alone or in combination with one or more other methods discussed and/or incorporated herein. Also, unless otherwise indicated, each operation of the method is performed under the control of one or more processors configured with program instructions. [0144] As discussed herein, the time-averaged emission level 334 of the energizing signals remains below the maximum average signal strength limit 330 (FIG. 3B). In some embodiments, one or more limit to the number of energizing signals at the relatively higher level within a predetermined time period may be predetermined and stored in a memory such as the memory 222 of the base unit 204. Thus, in the method below, one or more processors may track the number of relatively higher level energizing signals and prevent the system from transmitting at levels that would exceed regulatory limits. The regulatory limit may be set based on jurisdiction, and in some embodiments may be selectable via a graphical user interface, set remotely, factory set, etc. The limitations can be set using software and/or hardware. 15618WOO1 (013-0605PCT1) 39 PATENT   [0145] Referring again to FIG.3B, maximum average signal strength limit 330, as required by standards and/or regulations, is indicated. The energizing signals 318 and 328 are greater than the predetermined electromagnetic radiation standard shown by the maximum average signal strength limit 330, while the energizing signals transmitted during the time period 324 are less than the limit 330. By way of example, a time- averaged emission level 334 is shown at a slightly greater amplitude than the second emission level 326, while being far less than the first emission level 320. The maximum average signal strength limit 330 may be determined over a predetermined time period (e.g., measured in seconds or minutes). [0146] At 402 of FIG.4, one or more processors generate a relatively higher-level energizing signal. Parameters such as frequency may be predetermined. [0147] At 404, the one or more processors transmit the energizing signal at a relatively higher emission level, such as the energizing signals 318, 328 shown in FIG. 3C. By way of example, the transmitter circuitry 230 can transmit the energizing signal, or similarly, transmitter 718 and coupling loop 742 of FIG.7 can transmit the energizing signal. The energizing signal 318 can be an RF signal transmitted by the transmitter circuitry 230 of the base unit 204. The RF signal can be a burst or pulse having a predetermined amplitude, for example. The emission level of the higher-level energizing signal may be predetermined by the emission level adjustment module 208. [0148] At 406, the one or more processors receive one or more returned signals. In some embodiments, a coupling loop 740 and RF receiver 710 (shown and discussed in FIG.7) or the receiver circuitry 232 of the base unit 204 can receive the signals. The signals may include signals returned from the implantable sensor 202, as well as noise and signals returned from objects 228 in the environment. In some embodiments, the one or more processors wait for a delay period after the transmitter has transmitted the higher emission level energizing signal 318, 328. The delay period 355 allows the noise in the returned signals to die down or diminish. At the end of the delay period 355, the receiver receives the signals to be evaluated. The signals can collectively be referred to as the returned signals, and will include multiple peaks at different amplitudes and frequencies. 15618WOO1 (013-0605PCT1) 40 PATENT   [0149] At 408, the one or more processors evaluate the peaks within the returned signals to identify a sensor signal associated with the sensor 202 based on amplitude. For example, the amplitude determination module 210 may identify the peak having the greatest amplitude. Because the amplitude/power/emission level of the energizing signal 318 was high, the response from the sensor 202 is also high, allowing the one or more processors to identify the correct signal. In some embodiments, the one or more processors may only consider a signal having a minimum predetermined amplitude. [0150] At 410, the one or more processors determine a frequency associated with the sensor signal, such as with the frequency determination and comparison module 212. For example, the frequency associated with the peak 368b of FIG. 3F can be determined. [0151] At 412, the one or more processors employ PLL to lock the sensor signal as discussed further below, such as in FIGS.5 and 7. For example, the phase and/or frequency of the energizing signals may be adjusted to better match the sensor signal. In some embodiments, if true signal lock is not achieved, the method may return to 402 to generate and transmit another higher emission level energizing signal. In other embodiments, the method may automatically generate two or more consecutive higher emission level energizing signals. In some embodiments, the duty cycle for the transmission of the energizing signals at the relatively higher emission level can be the same as the duty cycle for the transmission of the energizing signals at the relatively lower emission level. In other embodiments, the duty cycle for the transmission of the energizing signals at the relatively higher emission level can be increased to allow for a longer delay between the signal transmission and the reading of the returned signals. [0152] At 414, the one or more processors determine pressure associated with the frequency of the sensor signal. For example, the pressure determination module 214 can determine the pressure, which can then be output to a display, saved in a file in the memory 222, saved temporarily, transmitted to another device/location via wired and/or wireless methods (e.g., communications circuit 224, external device 226). In some embodiments, the one or more processors can wait until a minimum number of pressure measurements have been obtained before outputting / transmitting the pressure 15618WOO1 (013-0605PCT1) 41 PATENT   information. In some embodiments, the pressure can be identified using a graph, curves, tables, calculations using the identified frequency, and the like. [0153] At 416, the one or more processors generate a second energizing signal (e.g., energizing signal 348, 350) that is at a relatively lower emission level. The emission level of the relatively lower power energizing signal 348 may be predetermined by the emission level adjustment module 208. [0154] At 418, the one or more processors transmit the energizing signal at the relatively lower emission level, such as by using the transmitter circuitry 230 or transmitter 718 and coupling loop 742. [0155] At 420, the one or more processors receive signals, such as with the receiver circuitry 232 or the coupling loop 740 and the RF receiver 710. Again, the signals may include signals returned from the implantable sensor 202, as well as noise and signals returned from objects 228 in the environment. Again, the one or more processors may wait the delay period 356 after the energizing signal 348 is transmitted to allow the ambient noise signals to decay. [0156] At 422, the one or more processors determine at least some of the peaks within the returned signals, such as with the amplitude determination module 210, and the frequencies of the peaks with the frequency determination and comparison module 212. For example, as true signal lock was achieved, the one or more processors may look at amplitudes within a predetermined range of the frequency of the sensor signal determined immediately prior to identify any peaks near the sensor peak, such as within a predetermined frequency range. In other embodiments, the one or more processors determine all of the peaks within the returned signals. [0157] At 424, the one or more processors determine the frequency associated with the sensor signal. For example, as true signal lock was achieved, the frequency of the most recently received sensor signal is likely to be very close to the frequency of the sensor signal received immediately prior. Phase-lock allows the base unit 204 to track the returned sensor signal as the frequency changes with the change in the pressure of the environment of the implantable sensor 202. Therefore, the frequencies of the returned signals can be compared to the previously determined frequency associated 15618WOO1 (013-0605PCT1) 42 PATENT   with the sensor 202, and the frequency of the sensor 202 at the corresponding peak can be identified. [0158] At 426, the one or more processors determine the pressure associated with the frequency of the sensor signal. For example, the pressure determination module 214 can determine the pressure and output and/or save the result as discussed above. [0159] At 428, the one or more processors determine whether the data collection is complete. For example, the pressure data may be acquired for a predetermined number of seconds or minutes, such as approximately 15 seconds, 18 seconds, 30 seconds, 45 seconds, one minute, two minutes or more, etc. In some embodiments, pressure data acquired later in a collection session, such as later within a two-minute collection session, may be used. In some cases, this can allow a patient’s heart rate to settle during the first portion of the collection session if they have been active. If the data collection is not complete, flow passes to 430. [0160] At 430, the one or more processors determine whether the time period, such as the time period 332 (FIG. 3B) or time period 324 shown in FIG. 3C, has expired, indicating that another higher-level energizing signal should be transmitted. The time period 332, 324 can be determined as discussed herein. In some embodiments, if a patient has an extremely low resting heartrate, the time period 332, 324 may be approximately 625 milliseconds. If yes, flow returns to 402 to generate the next higher- level energizing signal. In some embodiments, the base unit 204 can steer the frequency and/or phase of the next energizing signal. If the time period 324, 332 has not expired, flow passes to 432. In other embodiments, the one or more processors may determine if a minimum number of the relatively lower emission level energizing signals have been transmitted after the most recent relatively higher emission level energizing signal. A minimum number of relatively lower emission level energizing signals may be set to ensure that the maximum average signal strength limit 330 is not exceeded. In this example, if the minimum number is not satisfied, flow returns to 416. [0161] At 432, the one or more processors evaluate the quality of the phase-locked signal. For example, the frequency determination and comparison module 212 can determine whether another peak is within a predetermined frequency range of the sensor frequency determined at 424. In some embodiments this can indicate that the sensor 15618WOO1 (013-0605PCT1) 43 PATENT   frequency, such as indicated by the peak 368d shown in FIG. 3H, is nearing another peak 364. The frequency determination and comparison module 212 can also determine whether the peak associated with the sensor frequency has split into two peaks. [0162] If the sensor peak and another peak are within the predetermined frequency range of each other, or the sensor peak has split into two peaks, flow passes to 402 to generate the next higher-level energizing signal. In some embodiments, the predetermined frequency range can extend both above and below the sensor frequency, while in other embodiments, the predetermined frequency range extends in the direction the sensor frequency is moving, such as toward higher or lower frequencies. In some embodiments, the base unit 204 can steer the frequency and/or phase of the next energizing signal. This provides the advantage of renewing and/or ensuring that the base unit 204 remains locked onto the correct returned signal and avoiding a situation as shown in FIG.3I, wherein the peak 380 indicates uncertainty as the sensor peak has merged, crossed over, or otherwise overlaps another peak. [0163] If, at 432, the one or more processors determine that there are no other peaks within a predetermined frequency range of the sensor frequency determined at 424, the quality of the phase-locked signal is acceptable, and flow returns to 416 to generate and transmit the relatively lower power energizing signal 348. [0164] Returning to 428, if the one or more processors determine that the data collection is complete, flow passes to 434 and the base unit 204 stops transmitting and collecting information. In some embodiments, the base unit 204 can transmit information to another external device, determine and show data on a screen, such as by telling the patient that the data collection is successful and/or informing the patient of the pressure data, and/or providing a treatment recommendation, displaying and/or transmitting a treatment notification and/or treatment recommendation to the patient, an IMD, another external device, and the like. [0165] It should be understood that the one or more processors prevent the base unit 204 from transmitting too many energizing signals with the relatively higher emission level within a predetermined time period to prevent exceeding the maximum average signal strength limit 330. In some cases, such as at 432, the one or more processors can also monitor how many relatively higher emission level energizing signals have been 15618WOO1 (013-0605PCT1) 44 PATENT   transmitted within a predetermined time period to stay below the maximum average signal strength limit. In some embodiments, this may limit the renewal of the signal lock. In some cases, flow may return to 416 to continue to generate energizing signals at the relatively lower emission level to stay below the maximum average signal strength limit, while in other cases, the one or more processors may generate an error that can be stored by the base unit 204 and transmitted, such as with the acquired pressure data, to the clinician. [0166] FIG.14 illustrates a computer-implemented method for communicating with a wireless sensor positioned within a lumen of a body in accordance with embodiments herein. All or a portion of the operations of FIG.14 may be implemented by one or more processors of the base unit 204 configured with executable instructions, and all or a portion of the operations of FIG.14 may be implemented by one or more processors of the system of FIG.7 configured with executable instructions. Portions of the operations of FIG.14 may also be implemented by one or more processors of one or more of a local external device, a remote server, and/or the sensor 202. It should be recognized that while the operations of the method are described in a somewhat serial manner, one or more of the operations of the method may be continuous and/or performed in parallel with one another. For example, the various operations of the base unit 204 may be continuous and/or performed in parallel with one another and/or other functions of the base unit 204. The method may be performed alone or in combination with one or more other methods discussed and/or incorporated herein. Also, unless otherwise indicated, each operation of the method is performed under the control of one or more processors configured with program instructions. [0167] At 1402, one or more processors generate and transmit a first energizing signal having a first emission level. [0168] At 1404, the one or more processors receive first returned signals including a first sensor signal in response to the first energizing signal. [0169] At 1406, the one or more processors determine a first frequency associated with the circuit within the wireless sensor based on the first returned signals. 15618WOO1 (013-0605PCT1) 45 PATENT   [0170] At 1408, the one or more processors generate and transmit a second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level. [0171] At 1410, the one or more processors receive second returned signals including a second sensor signal in response to the second energizing signal. [0172] At 1412, the one or more processors determine a second frequency associated with the circuit within the wireless sensor based on the first frequency and the second returned signals. [0173] In some embodiments, some or all of the operations of FIGS.4 and 14 can be accomplished in real-time, such as performed substantially contemporaneous with one or more heartbeats experienced by a patient. Further, the base unit or other external device can collect returned signals and automatically determine frequencies of returned signals. Additionally, the base unit or other external device automatically determines pressure measurements based on the frequencies. Exemplary System [0174] FIG.5 illustrates an exemplary system for communicating with a wireless sensor implanted within a body. The system includes a coupling loop 500, a base unit 502, a display device 504 and an input device 506, such as a keyboard. The base unit 502 can be connected to the internet, have the ability to communicate wirelessly, etc., to upload any acquired and entered information to a patient care network 510, such as the Merlin.net.TM. patient care network operated by Abbott Laboratories (headquartered in the Abbott Park Business Center in Lake Bluff, Ill.). The base unit 502 can similarly receive information, settings, programming updates, and the like from the patient care network 510. [0175] The coupling loop 500 is formed from a band of copper. In one embodiment, the loop 500 is eight inches in diameter. The coupling loop 500 includes switching and filtering circuitry that is enclosed within a shielded box 501. The loop 500 charges the sensor and then couples signals from the sensor into the receiver. The antenna can be shielded to attenuate in-band noise and electromagnetic emissions. 15618WOO1 (013-0605PCT1) 46 PATENT   [0176] Another possible embodiment for a coupling loop is shown in FIG.11, which shows separate loops for energizing 1102 and for receiving 1104, although a single loop can be used for both functions. PIN diode switching inside the loop assembly is used to provide isolation between the energizing phase and the receive phase by opening the RX path pin diodes during the energizing period, and opening the energizing path pin diodes during the coupling period. Multiple energizing loops can be staggered tuned to achieve a wider bandwidth of matching between the transmit coils and the transmit circuitry. [0177] Returning to FIG.5, the base unit 502 includes an RF amplifier, a receiver, and signal processing circuitry. Additional details of the circuitry are described below in connection with FIG.7. [0178] The display 504 and the input device 506 are used in connection with the user interface for the system. In the embodiment illustrated in FIG.5 the display device 504 and the input device 506 are connected to the base unit 502. In this embodiment, the base unit 502 also provides conventional computing functions. In other embodiments, the base unit 502 can be connected to a conventional computer, such as a laptop, via a communications link, such as an RS-232 link. If a separate computer is used, then the display device 504 and the input devices 506 associated with the computer can be used to provide the user interface. In one embodiment, LABVIEW software is used to provide the user interface, as well as to provide graphics, store and organize data and perform calculations for calibration and normalization. The user interface records and displays patient data and guides the user through surgical and follow-up procedures. [0179] An optional printer 508 is connected to the base unit 502 and can be used to print out patient data or other types of information. As will be apparent to those skilled in the art, other configurations of the system, as well as additional or fewer components, can be utilized. [0180] Patient and system information can be stored within a removable data storage unit, such as a portable USB storage device, floppy disk, smart card, or any other similar device. The patient information can be transferred to the physician's personal computer for analysis, review, or storage manually and/or via a network 15618WOO1 (013-0605PCT1) 47 PATENT   connection provided to automate storage or data transfer. Once the data is retrieved from the system, further data analysis can be accomplished. In some embodiments, the analysis can include reviewing trends, suggesting medication adjustments and/or new medications, suggesting additional procedures and/or monitoring, suggesting behavior change (e.g., activity level, food, hydration), and the like. [0181] FIG.5 illustrates the system communicating with a sensor 520 implanted in a patient. The system can be used in multiple environments: 1) the operating room during implant, 2) the doctor's office during follow-up examinations, 3) the patient’s home or other location on a regular or periodic basis and/or on-demand. During implantation the system is used to record at least two measurements. The first measurement is taken during introduction of the sensor for calibration and the second measurement is taken after placement for functional verification. The measurements can be taken by placing the coupling loop 500 either on or adjacent to the patient's back or the patient's stomach for a sensor 520 that measures properties associated with an abdominal aneurysm. For other types of measurements, the coupling loop 500 may be placed in other locations. For example, to measure properties associated with the heart, the coupling loop 500 can be placed on the patient's back or the patient's chest. [0182] The system communicates with the implanted sensor 520 to determine the resonant frequency of the sensor 520. As described in more detail in the patent documents referenced in the Background section as well as the description of the sensor 10 in FIG.1A, a sensor 520 typically includes an inductive-capacitive ("LC") resonant circuit having a variable capacitor. The distance between the plates of the variable capacitor varies as the surrounding pressure varies. Thus, the resonant frequency of the circuit can be used to determine the pressure. [0183] The system energizes the sensor 520, 202 with an RF burst (e.g., energizing signal or energizing pulse). The energizing signal is a low duty cycle, gated burst of RF energy of a predetermined frequency or set of frequencies and two or more predetermined amplitudes, as discussed herein with respect to the relatively higher emission level energizing signal 318 and the relatively lower emission level energizing signal 348. Typically, the duty cycle of the energizing signal ranges from 0.1% to 50%. In one embodiment, the system energizes the sensor with a 30- 37 MHz fundamental 15618WOO1 (013-0605PCT1) 48 PATENT   signal at a pulse repetition rate of 100 kHz with a duty cycle of 20%. The energizing signal is coupled to the sensor via a magnetic loop. This signal induces a current in the sensor which has maximum amplitude at the resonant frequency of the sensor. During this time, the sensor charges exponentially to a steady-state amplitude that is proportional to the coupling efficiency, distance between the sensor and loop, and the RF power. FIG.12 shows the charging response of a typical LC circuit to a burst of RF energy at its resonant frequency. The speed at which the sensor charges is directly related to the Q (quality factor) of the sensor. Therefore, the "on time" of the pulse repetition duty cycle is optimized for the Q of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor. FIG.6A illustrates a typical energizing signal and FIGS.6B, 6C and 6D illustrate typical coupled signals (e.g., returned signals) for various values of Q (quality factor) for the sensor. When the main unit is coupling energy at or near the resonant frequency of the sensor, the amplitude of the sensor return is maximized, and the phase of the sensor return will be close to zero degrees with respect to the energizing phase. The sensor return signal is processed via phase-locked-loops to steer the frequency and phase of the next energizing pulse. [0184] By way of example only, FIG.6A can illustrate a typical energizing signal (e.g., having the relatively lower transmission level that is below the regulatory limits) that is transmitted during the time period 324 (FIG 3C). It should be understood that an energizing signal having the relatively greater emission level, such as the first energizing signal 308, would be similar, but would have a much increased amplitude in comparison. Operation of the Base Unit [0185] In some embodiments, some or all of the operations of the exemplary base unit 204 discussed below can be used together with the new and unique features disclosed herein, namely transmitting the energizing signal at relatively different emission levels. [0186] FIG. 7 is a block diagram of the signal processing components within an exemplary base unit, such as the base unit 204 of FIG. 2, in accordance with embodiments herein. In some embodiments, the base unit determines the resonant 15618WOO1 (013-0605PCT1) 49 PATENT   frequency of the sensor by adjusting the energizing signal so that the frequency of the energizing signal matches the resonant frequency of the sensor. In the embodiment illustrated by FIG.7, two separate processors 702, 722 and two separate coupling loops 740, 742 are shown. In one embodiment, processor 702 is associated with the base unit and processor 722 is associated with a computer connected to the base unit. In other embodiments, a single processor is used that provides the same functions as the two separate processors. One or both of the processors 702, 722 can include the processing functionality described in connection with FIG.2. In other embodiments a single loop is used for both energizing and for coupling the sensor energy back to the receiver, as shown in FIG.5. As will be apparent to those skilled in the art, other configurations of the base unit are possible that use different components. [0187] The embodiment illustrated by FIG.7 includes a pair of phase lock loops ("PLL"). One of the PLLs is used to adjust the phase of the energizing signal and is referred to herein as the fast PLL. The other PLL is used to adjust the frequency of the energizing signal and is referred to herein as the slow PLL. The base unit provides two cycles: the calibration cycle and the measurement cycle. In one embodiment, the first cycle is a 10 microsecond energizing period for calibration of the system, which is referred to herein as the calibration cycle, and the second cycle is a 10 microsecond energizing/coupling period for energizing the sensor and coupling a return signal from the sensor, which is referred to herein as the measurement cycle. During the calibration cycle, the system generates a calibration signal for system and environmental phase calibration and during the measurement cycle the system both sends and listens for a return signal, i.e. the sensor ring down. Alternatively, as those skilled in the art will appreciate, the calibration cycle and the measurement cycle can be implemented in the same pulse repetition period. [0188] The phase of the energizing signal is adjusted during the calibration cycle by the fast PLL and the frequency of the energizing signal is adjusted during the measurement cycle by the slow PLL. The following description of the operation of the PLLs is presented sequentially for simplicity. However, as those skilled in the art will appreciate, the PLLs actually operate simultaneously. 15618WOO1 (013-0605PCT1) 50 PATENT   [0189] Initially the frequency of the energizing signal is set to a default value determined by the calibration parameters of the sensor. Each sensor is associated with a number of calibration parameters, such as frequency, offset, and slope. An operator of the system enters the sensor calibration parameters into the system via the user interface and the system determines an initial frequency for the energizing signal based on the particular sensor. Alternatively, the sensor calibration information could be stored on portable storage devices, bar codes, or incorporated within a signal returned from the sensor. The initial phase of the energizing signal is arbitrary. [0190] The initial frequency and the initial phase are communicated from the processor 702 to the DDSs (direct digital synthesizers) 704, 706. The output of DDS1 704 is set to the initial frequency and initial phase and the output of DDS2706 (also referred to as local oscillator 1) is set to the initial frequency plus the frequency of the local oscillator 2. The phase of DDS2 is a fixed constant. In one embodiment, the frequency of local oscillator 2 is 4.725 MHz. The output of DDS1 is gated by the field programmable gate array (FPGA) 708 to create a pulsed transmit signal transmit by transmitter 718 having a pulse repetition frequency ("PRF"). The FPGA provides precise gating so that the base unit can sample the receive signal during specific intervals relative to the beginning or end of the calibration cycle. [0191] As discussed above, the pulsed transmit signal has more than one amplitude or emission level. The system of FIG. 7 can have components, circuitry, programming, and the like to enable the generation and transmission of energizing signals having at least two energizing levels that are different from each other. The transmitter 718 and coupling loop 742 thus output signals, such as energizing signals 318, 328 that are at a relatively higher emission level, and energizing signals 348, 350 that are at a relatively lower emission level. [0192] During the calibration cycle, the calibration signal which enters the receiver 710 is processed through the receive section 711 and the IF section 712 and is sampled. In one embodiment, the calibration signal is the portion of the energizing signal that leaks into the receiver (referred to herein as the energizing leakage signal). The signal is sampled during the on time of the energizing signal by a sample and hold circuit 714 to determine the phase difference between the signal and local oscillator 2. In the 15618WOO1 (013-0605PCT1) 51 PATENT   embodiment where the calibration signal is the portion of the energizing signal that leaks into the receiver, the signal is sampled approximately 100 ns after the beginning of the energizing signal pulse. Since the energizing signal is several orders of magnitude greater than the coupled signal, it is assumed that the phase information associated with the leaked signal is due to the energizing signal and the phase delay is due to the circuit elements in the coupling loop, circuit elements in the receiver, and environmental conditions, such as proximity of reflecting objects. [0193] The phase difference is sent to a loop filter 716. The loop filter is set for the dynamic response of the fast PLL. In one embodiment, the PLL bandwidth is 1000 Hz and the damping ratio is 0.7. A DC offset is added to allow for positive and negative changes. The processor 702 reads its analog to digital converter (A/D) port to receive the phase difference information and adjusts the phase sent to direct digital synthesizer 1 (DDS1) to drive the phase difference to zero. This process is repeated alternatively until the phase difference is zero or another reference phase. [0194] The phase adjustment made during the energizing period acts to zero the phase of the energizing signal with respect to local oscillator 2. Changes in the environment of the antenna or the receive chain impedance, as well as the phase delay within the circuitry prior to sampling affect the phase difference reading and are accommodated by the phase adjustment. [0195] During the measurement cycle, the energizing signal may be blocked from the receiver during the on time of the energizing signal. During the off time of the energizing signal, the receiver is unblocked and the coupled signal from the sensor (referred to herein as the coupled signal or the sensor signal) is received. The coupled signal is amplified and filtered through the receive section 711. The signal is down converted and additional amplification and filtering takes place in the IF section 712. In one embodiment, the signal is down converted to 4.725 MHz. After being processed through the IF section, the signal is mixed with local oscillator 2 and sampled by sample and hold circuits 715 to determine the phase difference between the coupled signal and the energizing signal. In one embodiment, the sampling occurs approximately 30 ns after the energizing signal is turned off. 15618WOO1 (013-0605PCT1) 52 PATENT   [0196] In other embodiments, group delay or signal amplitude is used to determine the resonant frequency of the sensor. The phase curve of a second order system passes through zero at the resonant frequency. Since the group delay i.e. derivative of the phase curve reaches a maximum at the resonant frequency, the group delay can be used to determine the resonant frequency. Alternatively, the amplitude of the sensor signal can be used to determine the resonant frequency. The sensor acts like a bandpass filter so that the sensor signal reaches a maximum at the resonant frequency. [0197] The sampled signal is accumulated within a loop filter 720. The loop filter is set for the dynamic response of the slow PLL to aid in the acquisition of a lock by the slow PLL. The PLLs are implemented with op-amp low pass filters that feed A/D inputs on microcontrollers, 702 and 722, which in turn talk to the DDSs, 704 and 706, which provide the energizing signal and local oscillator 1. The microcontroller that controls the energizing DDS 704 also handles communication with the display. The response of the slow PLL depends upon whether the loop is locked or not. If the loop is unlocked, then the bandwidth is increased so that the loop will lock quickly. In one embodiment, the slow PLL has a damping ratio of 0.7 and a bandwidth of 120 Hz when locked (the Nyquist frequency of the blood pressure waveform), which is approximately ten times slower than the fast PLL. [0198] A DC offset is also added to the signal to allow both a positive and a negative swing. The output of the loop filter is input to an A/D input of processor 722. The processor determines a new frequency and sends the new frequency to the DSSs. The processor offsets the current frequency value of the energizing signal by an amount that is proportional to the amount needed to drive the output of the slow PLL loop filter to a preset value. In one embodiment the preset value is 2.5V and zero in phase. The proportional amount is determined by the PLL's overall transfer function. [0199] The frequency of the energizing signal is deemed to match the resonant frequency of the sensor when the slow PLL is locked. Once the resonant frequency is determined, the physical parameter, such as pressure, is calculated using the calibration parameters associated with the sensor, which results in a difference frequency that is proportional to the measured pressure. 15618WOO1 (013-0605PCT1) 53 PATENT   [0200] The operation of the slow PLL is qualified based on signal strength. The base unit includes signal strength detection circuitry. If the received signal does not meet a predetermined signal strength threshold, then the slow PLL is not allowed to lock and the bandwidth and search window for the PLL are expanded. Once the received signal meets the predetermined signal strength threshold, then the bandwidth and search window of the slow PLL is narrowed and the PLL can lock. In the preferred embodiment, phase detection and signal strength determination are provided via the "I" (in phase) and "Q" (quadrature) channels of a quadrature mixer circuit. The "I" channel is lowpass filtered and sampled to provide signal strength information to the processing circuitry. The "Q" channel is lowpass filtered and sampled to provide phase error information to the slow PLL. Avoiding False Locks [0201] The system provides unique solutions to the false lock problem. A false lock occurs if the system locks on a frequency that does not correspond to the resonant frequency of the sensor. There are several types of false locks. The first type of false lock arises due to the pulsed nature of the system. Since the energizing signal is a pulsed signal, it includes groups of frequencies. The frequency that corresponds to a false lock is influenced by the pulse repetition frequency, the Q of the sensor, and the duty cycle of the RF burst. For example, a constant pulse repetition frequency adds spectral components to the return signal at harmonic intervals around the resonant frequency of the sensor, which can cause a false lock. In one embodiment, false locks occur at approximately 600 kHz above and/or below the resonant frequency of the sensor. To determine a false lock, the characteristics of the signal are examined. For example, pulse repetition frequency dithering and/or observing the slope of the baseband signal are two possible ways of determining a false lock. In one embodiment where the system locks on a sideband frequency, the signal characteristics correspond to a heartbeat or a blood pressure waveform. [0202] The second type of false lock arises due to a reflection or resonance of another object in the vicinity of the system. This type of false lock can be difficult to discern because it generally does not correspond to a heartbeat or blood pressure 15618WOO1 (013-0605PCT1) 54 PATENT   waveform. The lack of frequency modulation can be used to discriminate against this type of false lock. Changing the orientation of the magnetic loop also affects this type of false lock because the reflected false lock is sensitive to the angle of incidence. The third type of false lock arises due to switching transients caused by switching the PIN diodes and analog switches in the RF path. These transients cause damped resonances in the filters in the receive chain, which can appear similar to the sensor signal. Typically, these types of false locks do not correspond to a heartbeat or blood pressure waveform because they are constant frequency. These types of false locks are also insensitive to orientation of the magnetic loop. [0203] To avoid the second type of false lock, the system can periodically transmit the relatively higher emission level signal, ensuring that the returned signal from the sensor has the greatest amplitude. Additionally or alternatively, the system can transmit the relatively higher emission level signal when peaks in frequency are detected that are near the resonant frequency of the sensor, such as within a predetermined range of the resonant frequency of the sensor. [0204] To avoid the first type of false lock, the embodiments herein determine the slope of the baseband signal (the phase difference signal at point 730). In one embodiment, if the slope is positive, then the lock is deemed a true lock. However, if the slope is negative, then the lock is deemed a false lock. In another embodiment, a negative slope is deemed a true lock and a positive slope is deemed a false lock. The slope is determined by looking at points before and after the phase difference signal goes to zero. The slope can be determined in a number of different ways, including but not limited to, using an analog differentiator or multiple sampling. FIGS. 8A and 8B illustrate a true lock and a false lock respectively, when a positive slope indicates a true lock. In one embodiment, if a false lock is detected, then the signal strength is suppressed so that the signal strength appears to the processor 722 to be below the threshold and the system continues to search for the center frequency. In other embodiments, any non-zero slope can be interpreted as a false lock resulting in zero signal strength. [0205] The system can also use frequency dithering to avoid the first type of false lock. Since the spectral components associated with a constant pulse repetition 15618WOO1 (013-0605PCT1) 55 PATENT   frequency can cause a false lock, dithering the pulse repetition frequency helps avoid a false lock. By dithering the pulse repetition frequency, the spectral energy at the potential false lock frequencies is reduced over the averaged sampling interval. As shown in FIG. 9, the energizing signal includes an on time t1 and an off time t2. The system can vary the on time or the off time to vary the PRF (PRF=1/(t1+t2)). FIG.9 illustrates different on times (t1, t1') and different off times (t2, t2'). By varying the PRF, the sidebands move back and forth and the average of the sidebands is reduced. Thus, the system locks on the center frequency rather than the sidebands. The PRF can be varied between predetermined sequences of PRFs or can be varied randomly. Reducing Switching Transients [0206] The coupling loop switches between an energizing mode and a coupling mode. This switching creates transient signals, which can cause the third type of false lock. Phase dithering is one method used to reduce the switching transients. As shown in FIG. 10, the system receives a switching transient 1003 between the end of the energizing signal 1002 and the beginning of the coupled signal 1004. To minimize the transient, the phase of the energizing signal may be randomly changed. However, changing the phase of the energizing signal requires that the system redefine zero phase for the system. To redefine zero phase for the system, the phase of DDS2 is changed to match the change in phase of the energizing signal. Thus, the phase of the energizing signal 1002' and the coupled signal 1004' are changed, but the phase of the transient signal 1003' is not. As the system changes phase, the average of the transient signal is reduced. [0207] Changing the resonant frequency of the antenna as it is switched from energizing mode to coupling mode also helps to eliminate the switching transients. Eliminating the switching transients is especially important because of the characteristics of the coupled signal. The coupled signal appears very quickly after the on period of the energizing signal and dissipates very quickly. In one embodiment, the methods and system operate in a low power environment with a passive sensor so that the magnitude of the coupled signal is small. However, the methods and systems are not limited to working with a passive sensor. 15618WOO1 (013-0605PCT1) 56 PATENT   [0208] The coupling loop is tuned to a resonant frequency that is based upon the sensor parameters. Changing the capacitors or capacitor network that is connected to the coupling loop changes the resonant frequency of the antenna. The resonant frequency typically is changed from approximately 1/10% to 2% between energizing mode and coupled mode. In some embodiments, the coupling loop is untuned. [0209] Additional alternative embodiments will be apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. For example, the system can operate with different types of sensors, such as non-linear sensors that transmit information at frequencies other than the transmit frequency or sensors that use backscatter modulations. Accordingly, the scope of the present invention is described by the appended claims and is supported by the foregoing description. [0210] Additionally or alternatively, the processes, systems, components, etc., described herein may be implemented utilizing all or portions of the structural and/or functional aspects of the methods and systems described in US published application number 2014/0330143, filed May 2, 2014, titled “Method and system for treating cardiovascular disease”; US published application number 2014/0288459, filed March 25, 2013, titled “Ventricular shunt system and method”; US published application number 2014/0288085, filed March 17, 2014, titled “Methods for the Treatment of Cardiovascular Conditions“; US published application number 2014/0275861, filed March 17, 2014, titled “Ambulatory sensing system and associated methods”; US published application number 2014/0155769, filed November 21, 2013, titled “Devices, Systems, and Methods for Pulmonary Arterial Hypertension (PAH) Assessment and Treatment”; US published application number 2014/0084943, filed September 21, 2012, titled “Strain monitoring system and apparatus; US published application number 2014/0088994, filed September 23, 2013, titled “Method and system for trend-based patient management”; US published application number 2013/0245469, filed March 15, 2013, titled “Pulmonary Arterial Hemodynamic Monitoring for Chronic Obstructive Pulmonary Disease Assessment and Treatment”; US published application number 2015/0133796, filed November 6, 2014, titled “Systems and methods for using physiological information”; US patent 8,669,770, filed November 15, 2010, titled “Selectively actuating wireless, passive 15618WOO1 (013-0605PCT1) 57 PATENT   implantable sensor”; US published application number 2013/0296721, January 29, 2013, titled “Hypertension System And Method”; US patent 8,264,240, July 20, 2009, titled “Physical property sensor with active electronic circuit and wireless power and data transmission”; US patent 8,159,348, filed February 26, 2009, titled “Communication system with antenna box amplifier”; US patent 7,667,547, filed August 22, 2007, titled “Loosely-coupled oscillator”; US patent 7,966,886, filed October 9, 2009, titled “Method and apparatus for measuring pressure inside a fluid system”; US patent 8,665,086, January 4, 2012, titled “Physiological data acquisition and management system for use with an implanted wireless sensor”; US patent 7,908,018, September 6, 2006, titled “Flexible electrode”; US patent 7,909,770, July 3, 2007, titled “Method for using a wireless pressure sensor to monitor pressure inside the human heart”; US patent 7,812,416, filed May 15, 2007, titled “Methods and apparatus having an integrated circuit attached to fused silica”; US patent 7,829,363, May 10, 2007, titled “Method and apparatus for microjoining dissimilar materials”; US published application number 2007/0199385, filed November 17, 2006, titled “Capacitor electrode formed on surface of integrated circuit chip”; US patent 7,748,277, filed October 18, 2006, titled “Hermetic chamber with electrical feedthroughs”; US published application number 2007/0158769, filed October 12, 2006, titled “Integrated CMOS-MEMS technology for wired implantable sensors”; US patent 7,710,103, filed January 7, 2009, titled “Preventing false locks in a system that communicates with an implanted wireless sensor”; US patent 8,896,324, filed September 26, 2011, titled “System, apparatus, and method for in-vivo assessment of relative position of an implant”; US published application number 2012/0016207, filed September 26, 2011, titled “Electromagnetically coupled hermetic chamber”; US patent 8,355,777, filed September 19, 2011, titled “Apparatus and method for sensor deployment and fixation”; US patent 7,854,172, filed February 17, 2009, titled “Hermetic chamber with electrical feedthroughs”; US patent 7,147,604, filed August 7, 2002, titled “High Q factor sensor”; US patent 7,618,363, filed August 6, 2003, titled “Hydraulically actuated artificial muscle for ventricular assist”; US patent 7,699,059, filed January 22, 2002, titled “Implantable wireless sensor”; US patent 7,481,771, filed July 7, 2007, titled “Implantable wireless sensor for pressure measurement within the heart”; US published application number 2022/0079456, filed October 21, 2021, titled “System and method for 15618WOO1 (013-0605PCT1) 58 PATENT   calculating a lumen pressure utilizing sensor calibration parameters”; PCT application number PCT/US24/52734, filed October 24, 2024, claiming priority to US serial number 63/596,402, filed November 6, 2023, titled “System and Method for Diastolic-Enhanced Systolic Peak Detection”; US patent 7,439,723, filed March 14, 2007, titled “Communicating with an implanted wireless sensor”; US patent 7,498,799, filed March 6, 2006, titled “Communicating with an implanted wireless sensor”; US patent 11,832,920, filed June 5, 2020, titled “Devices, Systems, and Methods for Pulmonary Arterial Hypertension (PAH) Assessment and Treatment”, and U.S. patent application Ser. No.63/574,335, filed April 4, 2024, titled “Method and Device for Cardiac Pressure Sensing Using an Active Implantable Device and Near Field Communication”, which are hereby expressly incorporated by reference in their entireties. [0211] All references, including publications, patent applications and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. [0212] Example 1. A method for locking onto a signal returned from a wireless sensor positioned within a body. The method comprises generating, via a base unit, a first energizing signal, wherein the base unit is external with respect to the body; transmitting, via the base unit, the first energizing signal having a first emission level; receiving, via the base unit, first returned signals including a first sensor signal in response to the first energizing signal, the wireless sensor comprising an inductive- capacitive (LC) circuit having a resonant frequency configured to vary in response to changes in pressure in the body; determining a first frequency associated with the LC circuit based on an amplitude within the first returned signals in response to the first energizing signal; generating, via the base unit, a second energizing signal; transmitting, via the base unit, the second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level; receiving, via the base unit, second returned signals including a second sensor signal in response to the second energizing signal; and determining a second frequency associated with the LC circuit based on the first frequency and the second returned signals. Optionally, Example 1 can 15618WOO1 (013-0605PCT1) 59 PATENT   include determining the pressure in the body based on the first frequency or the second frequency. [0213] Example 2. The method of example 1, further comprising transmitting, over a predetermined time period, a plurality of consecutive energizing signals having the second emission level. [0214] Example 3. The method of example 2, wherein in response to the predetermined time period expiring, the method further comprises transmitting another energizing signal having the first emission level. [0215] Example 4. The method of any one of examples 1 to 3, wherein a time- averaged emission level over a time period is below a maximum average signal strength limit, the time-averaged emission level determined based on the first and second energizing signals transmitted over the time period. [0216] Example 5. The method of any one of examples 1 to 4, wherein the first emission level is greater than a maximum average signal strength limit associated with a time period, and the second emission level is less than the maximum average signal strength limit associated with the time period. [0217] Example 6. The method of any one of examples 1 to 5, further comprising generating and transmitting, via the base unit, a third energizing signal having the second emission level; receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal; and determining a third frequency associated with the LC circuit based on the second frequency and the third returned signals. [0218] Example 7. The method of any one of examples 1 to 6, further comprising generating and transmitting, via the base unit, a third energizing signal having the second emission level; receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determining third and fourth frequencies associated with the first and second peaks; and wherein, in response to the third and fourth frequencies being within a predetermined frequency range of each other, transmitting a fourth energizing signal having the first emission level. 15618WOO1 (013-0605PCT1) 60 PATENT   [0219] Example 8. The method of example 7, further comprising receiving, via the base unit, fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level; and determining the frequency associated with the LC circuit based on a maximum amplitude within the fourth returned signals. [0220] Example 9. The method of any one of examples 1 to 8, further comprising generating and transmitting, via the base unit, a third energizing signal having the second emission level; receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determining third and fourth frequencies associated with the first and second peaks; and wherein, in response to a difference between the third and fourth frequencies being greater than a predetermined frequency range, transmitting another energizing signal having the second emission level. [0221] Example 10. The method of any one of examples 1 to 9, wherein the determining the first frequency associated with the LC circuit is based on a maximum amplitude within the first returned signals. [0222] Example 11. A system for communicating with a wireless sensor positioned within a lumen of a body comprises: a base unit positioned external with respect to the body, the base unit comprising: transmission circuitry configured to generate and transmit energizing signals; receiving circuitry configured to receive returned signals including a sensor signal associated with the wireless sensor in response to the energizing signals, the wireless sensor comprising a circuit having a resonant frequency configured to vary in response to changes in pressure in the lumen; memory configured to store program instructions; and one or more processors that, when executing the program instructions, are configured to: generate and transmit a first energizing signal having a first emission level; receive first returned signals including a first sensor signal in response to the first energizing signal; determine a first frequency associated with the circuit within the wireless sensor based on the first returned signals; generate and transmit a second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level; receive second returned signals 15618WOO1 (013-0605PCT1) 61 PATENT   including a second sensor signal in response to the second energizing signal; and determine a second frequency associated with the circuit within the wireless sensor based on the first frequency and the second returned signals. [0223] Example 12. The system of example 11, wherein the first frequency associated with the circuit is determined based on a maximum amplitude within the first returned signals. [0224] Example 13. The system of examples 11 or 12, wherein the one or more processors are further configured to determine the pressure in the lumen based on the first frequency or the second frequency. [0225] Example 14. The system of example 13, wherein the pressure further comprises pulmonary arterial pressure. [0226] Example 15. The system of any one of examples 11 to 14, wherein the one or more processors are further configured to: transmit, over a predetermined time period, a plurality of consecutive energizing signals having the second emission level; and in response to the predetermined time period expiring, transmit another energizing signal having the first emission level. [0227] Example 16. The system of any one of examples 11 to 15, wherein a time- averaged emission level over a time period is below a maximum average signal strength limit, the time-averaged emission level determined based on the first and second energizing signals transmitted over the time period. [0228] Example 17. The system of any one of examples 11 to 16, wherein the first emission level is greater than a maximum average signal strength limit, and the second emission level is less than the maximum average signal strength limit. [0229] Example 18. The system of any one of examples 11 to 17, wherein the one or more processors are further configured to: generate and transmit a third energizing signal having the second emission level; receive third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determine third and fourth frequencies associated with the first and second peaks; and wherein, in response to a difference between the third and fourth frequencies 15618WOO1 (013-0605PCT1) 62 PATENT   being greater than a predetermined frequency range, transmit another energizing signal having the second emission level. [0230] Example 19. The system of any one of examples 11 to 18, wherein the one or more processors are further configured to: generate and transmit a third energizing signal having the second emission level; receive third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determine third and fourth frequencies associated with the first and second peaks; and wherein, in response to the third and fourth frequencies being within a predetermined frequency range of each other, transmit a fourth energizing signal having the first emission level. [0231] Example 20. The system of example 19, wherein the one or more processors are further configured to: receive fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level; and determine the frequency associated with the circuit based on a maximum amplitude within the fourth returned signals. Closing [0232] It should be clearly understood that the various arrangements and processes broadly described and illustrated with respect to the Figures, and/or one or more individual components or elements of such arrangements and/or one or more process operations associated of such processes, can be employed independently from or together with one or more other components, elements and/or process operations described and illustrated herein. Accordingly, while various arrangements and processes are broadly contemplated, described and illustrated herein, it should be understood that they are provided merely in illustrative and non-restrictive fashion, and furthermore can be regarded as but mere examples of possible working environments in which one or more arrangements or processes may function or operate. [0233] Some or all of the Figures herein illustrate various methods and processes implemented in accordance with embodiments herein. The operations herein may be implemented by hardware, firmware, circuitry and/or one or more processors housed 15618WOO1 (013-0605PCT1) 63 PATENT   partially an/or entirely within an IMD, a local external device, remote server or more generally within a healthcare system. Optionally, the operations herein may be partially implemented by an IMD and partially implemented by a local external device, remote server or more generally within a healthcare system. For example, the IMD includes IMD memory and one or more IMD processors, while each of the external devices/systems (ED) (e.g., local, remote or anywhere within the healthcare system) include ED memory and one or more ED processors. [0234] As will be appreciated by one skilled in the art, various aspects may be embodied as a system, method or computer (device) program product. Accordingly, aspects may take the form of an entirely hardware embodiment or an embodiment including hardware and software that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects may take the form of a computer (device) program product embodied in one or more computer (device) readable storage medium(s) having computer (device) readable program code embodied thereon. [0235] Any combination of one or more non-signal computer (device) readable medium(s) may be utilized. The non-signal medium may be a storage medium. A storage medium may be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a storage medium would include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a dynamic random access memory (DRAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. [0236] Program code for carrying out operations may be written in any combination of one or more programming languages. The program code may execute entirely on a single device, partly on a single device, as a stand-alone software package, partly on single device and partly on another device, or entirely on the other device. In some cases, the devices may be connected through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made through other devices (for example, through the Internet using an Internet Service Provider) or 15618WOO1 (013-0605PCT1) 64 PATENT   through a hard wire connection, such as over a USB connection. For example, a server having a first processor, a network interface, and a storage device for storing code may store the program code for carrying out the operations and provide this code through its network interface via a network to a second device having a second processor for execution of the code on the second device. [0237] Aspects are described herein with reference to the figures, which illustrate example methods, devices and program products according to various example embodiments. The program instructions may be provided to a processor of a general- purpose computer, special purpose computer, or other programmable data processing device or information handling device to produce a machine, such that the instructions, which execute via a processor of the device implement the functions/acts specified. The program instructions may also be stored in a device readable medium that can direct a device to function in a particular manner, such that the instructions stored in the device readable medium produce an article of manufacture including instructions which implement the function/act specified. The program instructions may also be loaded onto a device to cause a series of operational steps to be performed on the device to produce a device implemented process such that the instructions which execute on the device provide processes for implementing the functions/acts specified. [0238] The units/modules/applications herein may include any processor-based or microprocessor-based system including but not limited to systems using microcontrollers, microcomputers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), a programmable logic controller (PLC), field- programmable gate arrays (FPGAs) and other programmable circuits, logic circuits, and any other circuit or processor capable of executing the functions described herein. Additionally, or alternatively, the modules/controllers herein may represent circuit modules that may be implemented as hardware with associated instructions (for example, software stored on a tangible and non-transitory computer readable storage medium, such as a computer hard drive, ROM, RAM, or the like) that perform the operations described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “controller.” The units/modules/applications herein may execute a set of instructions that are stored in 15618WOO1 (013-0605PCT1) 65 PATENT   one or more storage elements, in order to process data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within the modules/controllers herein. The set of instructions may include various commands that instruct the modules/applications herein to perform specific operations such as the methods and processes of the various embodiments of the subject matter described herein. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to user commands, or in response to results of previous processing, or in response to a request made by another processing machine. [0239] It is to be understood that the subject matter described herein is not limited in its application to the details of construction and the arrangement of components set forth in the description herein or illustrated in the drawings hereof. The subject matter described herein is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. [0240] It should be recognized that, to the extent embodiments herein are described to apply certain mathematical combinations of select variables, the same variables may be combined in other mathematical combinations that are also indicative of the same result. For example, when a single data point is utilized for a particular variable, additionally or alternatively, a mean, average, sum, or other mathematical combination of multiple data points may be utilized for the same variable. [0241] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects 15618WOO1 (013-0605PCT1) 66 PATENT   thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings herein without departing from its scope. While the dimensions, types of materials and coatings described herein are intended to define various parameters, they are by no means limiting and are illustrative in nature. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects or order of execution on their acts. 15618WOO1 (013-0605PCT1) 67 PATENT  

Claims

WHAT IS CLAIMED IS: 1. A method for locking onto a signal returned from a wireless sensor positioned within a body, comprising: generating, via a base unit, a first energizing signal, wherein the base unit is external with respect to the body; transmitting, via the base unit, the first energizing signal having a first emission level; receiving, via the base unit, first returned signals including a first sensor signal in response to the first energizing signal, the wireless sensor comprising an inductive-capacitive (LC) circuit having a resonant frequency configured to vary in response to changes in pressure in the body; determining a first frequency associated with the LC circuit based on an amplitude within the first returned signals in response to the first energizing signal; generating, via the base unit, a second energizing signal; transmitting, via the base unit, the second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level; receiving, via the base unit, second returned signals including a second sensor signal in response to the second energizing signal; determining a second frequency associated with the LC circuit based on the first frequency and the second returned signals; and determining the pressure in the body based on the first frequency or the second frequency.

2. The method of claim 1, further comprising transmitting, over a predetermined time period, a plurality of consecutive energizing signals having the second emission level. 15618WOO1 (013-0605PCT1) 68 PATENT  

3. The method of claim 2, wherein in response to the predetermined time period expiring, the method further comprises transmitting another energizing signal having the first emission level.

4. The method of claim 1, wherein a time-averaged emission level over a time period is below a maximum average signal strength limit, the time-averaged emission level determined based on the first and second energizing signals transmitted over the time period.

5. The method of claim 1, wherein the first emission level is greater than a maximum average signal strength limit associated with a time period, and the second emission level is less than the maximum average signal strength limit associated with the time period.

6. The method of claim 1, further comprising: generating and transmitting, via the base unit, a third energizing signal having the second emission level; receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal; and determining a third frequency associated with the LC circuit based on the second frequency and the third returned signals.

7. The method of claim 1, further comprising: generating and transmitting, via the base unit, a third energizing signal having the second emission level; receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; 15618WOO1 (013-0605PCT1) 69 PATENT   determining third and fourth frequencies associated with the first and second peaks; and wherein, in response to the third and fourth frequencies being within a predetermined frequency range of each other, transmitting a fourth energizing signal having the first emission level.

8. The method of claim 7, further comprising: receiving, via the base unit, fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level; and determining the frequency associated with the LC circuit based on a maximum amplitude within the fourth returned signals.

9. The method of claim 1, further comprising: generating and transmitting, via the base unit, a third energizing signal having the second emission level; receiving, via the base unit, third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determining third and fourth frequencies associated with the first and second peaks; and wherein, in response to a difference between the third and fourth frequencies being greater than a predetermined frequency range, transmitting another energizing signal having the second emission level.

10. The method of claim 1, wherein the determining the first frequency associated with the LC circuit is based on a maximum amplitude within the first returned signals. 15618WOO1 (013-0605PCT1) 70 PATENT  

11. A system for communicating with a wireless sensor positioned within a lumen of a body, comprising: a base unit positioned external with respect to the body, the base unit comprising: transmission circuitry configured to generate and transmit energizing signals; receiving circuitry configured to receive returned signals including a sensor signal associated with the wireless sensor in response to the energizing signals, the wireless sensor comprising a circuit having a resonant frequency configured to vary in response to changes in pressure in the lumen; memory configured to store program instructions; and one or more processors that, when executing the program instructions, are configured to: generate and transmit a first energizing signal having a first emission level; receive first returned signals including a first sensor signal in response to the first energizing signal; determine a first frequency associated with the circuit within the wireless sensor based on the first returned signals; generate and transmit a second energizing signal having a second emission level, wherein the second emission level is lower than the first emission level; receive second returned signals including a second sensor signal in response to the second energizing signal; and determine a second frequency associated with the circuit within the wireless sensor based on the first frequency and the second returned signals.

12. The system of claim 11, wherein the first frequency associated with the circuit is determined based on a maximum amplitude within the first returned signals. 15618WOO1 (013-0605PCT1) 71 PATENT  

13. The system of claim 11, wherein the one or more processors are further configured to determine the pressure in the lumen based on the first frequency or the second frequency.

14. The system of claim 13, wherein the pressure further comprises pulmonary arterial pressure.

15. The system of claim 11, wherein the one or more processors are further configured to: transmit, over a predetermined time period, a plurality of consecutive energizing signals having the second emission level; and in response to the predetermined time period expiring, transmit another energizing signal having the first emission level.

16. The system of claim 11, wherein a time-averaged emission level over a time period is below a maximum average signal strength limit, the time-averaged emission level determined based on the first and second energizing signals transmitted over the time period.

17. The system of claim 11, wherein the first emission level is greater than a maximum average signal strength limit, and the second emission level is less than the maximum average signal strength limit.  

18. The system of claim 11, wherein the one or more processors are further configured to: generate and transmit a third energizing signal having the second emission level; receive third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; 15618WOO1 (013-0605PCT1) 72 PATENT   determine third and fourth frequencies associated with the first and second peaks; and wherein, in response to a difference between the third and fourth frequencies being greater than a predetermined frequency range, transmit another energizing signal having the second emission level.

19. The system of claim 11, wherein the one or more processors are further configured to: generate and transmit a third energizing signal having the second emission level; receive third returned signals including a third sensor signal in response to the third energizing signal, wherein the third returned signals include a first peak associated with the sensor and a second peak not associated with the sensor; determine third and fourth frequencies associated with the first and second peaks; and wherein, in response to the third and fourth frequencies being within a predetermined frequency range of each other, transmit a fourth energizing signal having the first emission level.

20. The system of claim 19, wherein the one or more processors are further configured to: receive fourth returned signals including a fourth sensor signal in response to the fourth energizing signal having the first emission level; and determine the frequency associated with the circuit based on a maximum amplitude within the fourth returned signals. 15618WOO1 (013-0605PCT1) 73 PATENT