WO2025221742A1 - Rfid antenna for rejecting unwanted rf signals - Google Patents

Abstract

A RFID label is shown and described herein. The RFID label includes a RFID antenna configured to provide attenuation of unwanted signals at relatively high frequencies, e.g., above 2 GHz and in the range of about 2 to about 5 GHz. The RFID label comprises a dipole antenna having a plurality of resonant circuits that attenuate or reject signals at high frequencies such as, for example, those frequencies at which microwave ovens operate.

Description

RFID ANTENNA FOR REJECTING UNWANTED RF SIGNALS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No. 63/634,709, filed on April 16, 2024, titled “RFID ANTENNA FOR REJECTING UNWANTED RF SIGNALS,'’ the entirety of which is incorporated herein by reference.

BACKGROUND

[0001] Radio frequency identification (RFID) labels are used to label a wide array of consumer products to provide a way of tracking items. The food industry and food products are sectors where the use of RFID labels is growing and for which demand will continue to increase. RFID technology can be used to label and track products with expiration dates such as, but not limited to, meats, dairy products, fruits, vegetables, and other such produce. Because of the nature of RFID technology, food prices can be updated and adjusted without manually relabeling the items or the display. For example, RFID technology can be employed in a system for identifying items that are close to their expiration date. Stores can use that information and, if desired, reduce the price of items to entice customers to buy the products before the expiration date. Products whose expiration date has expired can be quickly located and removed from the sales floor.

[0002] In the case of some food products, e.g., frozen or some refrigerated products, the product may be provided such that it is to be heated in a microwave prior to consumption. In many instances the RFID technology⁷ is embedded or applied to the packaging in a manner that it is not or may not be removed prior to being exposed to the microwave operating conditions. In these circumstances, the RFID technology could be damaged and/or the food product package can be damaged from the microwaves interacting with the RFID label.

[0003] The present disclosure relates to an RFID antenna suitable for use in applications where the label will be exposed to power outputs that exceed the maximum input power of a conventional RFID label. The RFID antenna is configured to reject out-of-band signals to protect the RFID label from out-of-band waves. The present invention also relates to the labels and packaging comprising such an RFID antenna and use of the same.

SUMMARY

[0004] The following presents a summary of this disclosure to provide a basic understanding of some aspects. This summary is intended to neither identify key or critical elements nor define any limitations of embodiments or claims. Furthermore, this summary may provide a simplified overview of some aspects that may be described in greater detail in other portions of this disclosure.

[0005] In one aspect, provided is a RFID label comprising a RFID antenna that attenuates incoming power signals at frequencies above 2.4 GHz. In one embodiment, the RFID label includes a RFID antenna comprising a dipole antenna and a loop segment, where the loop segment comprises a plurality of resonant circuits configured to provide attenuation of incoming signals at frequencies above 2.4 GHz.

[0006] In some embodiments, the desired level of attenuation of signal is at least 27 dB. In other embodiments, the desired level of attenuation of signal is at least 35 dB. In further embodiments, the antenna provides attenuation at a predetermined frequency band that is greater than 2 GHz, and in some embodiments the predetermined frequency band is from about 2 GHz to about 14.5 GHz, and in other embodiments the predetermined frequency band is between about 2.4 GHz to about 4.0 GHz. In further embodiments, the resonant circuits provide from 0 dB to about 40 dB, aboaut 5 dB to about 40 dB, about 5 dB to about 35 dB. about 10 dB to about 30 dB, or about 15 dB to about 25 dB of attenuation for a predetermined frequency band of between about 2.4 GHz to about 4.0 GHz. In additional embodiments, the resonant circuits provide from about 35 dB to about 40 dB of desired attenuation for the predetermined frequency band of between about 2.4 to about 4.0 GHz.

[0007] In further embodiments, the dipole antenna further includes a circuit chip in electrical connection with the loop segment, wherein the resonant circuits disposed on the loop segment attenuate signals at a frequency of at least about 2.4 GHz so as to effectively shield the circuit chip from receiving signals that may damage the chip.

[0008] In yet another aspect of the invention, a radio frequency identification (RFID) label is provided comprising a dipole antenna in accordance with the present technology disposed on a substrate. The substrate may have an adhesive for attaching the label to a surface.

[0009] In yet another aspect of the invention an article is provided. The article includes a RFID label attached to the article.

[0010] In one aspect, provided is an RFID antenna comprising: an antenna segment coupled to a loop segment; and the loop segment comprising a plurality of resonant circuits and a circuit chip; wherein the antenna is configured to have an output frequency between 775 MHz and 1,050 MHz and attenuate a received signal above 2.4 GHz. [0011] In one embodiment, the antenna segment is a folded dipole antenna comprising a first dipole element and a second dipole element disposed on opposite sides of an intermediate segment.

[0012] In one embodiment, the first dipole element is configured to terminate at a first pad and the second dipole element is configured to terminate at a second pad.

[0013] In one embodiment, the first dipole element has a electrical length and a first physical length, the first physical length being measured from a center of the intermediate segment to an end of the first pad, and the second dipole element has a second electrical length and a second physical length, the second physical length being measured from a center of the intermediate segment to an end of the second pad.

[0014] In one embodiment, the first physical length of the first dipole element is shorter than the electrical length of the first dipole element, and the second physical length of the second dipole element is shorter than the second electrical length of the second dipole element.

[0015] In one embodiment, the first physical length of the first dipole element is equal to the electrical length of the first dipole element, and the second physical length of the second dipole element is equal to the second electrical length of the second dipole element.

[0016] In one embodiment, the first physical length of the first dipole element is greater than the electrical length of the first dipole element, and the second physical length of the second dipole element is greater than the second electrical length of the second dipole element.

[0017] In one embodiment in accordance with any previous embodiment, the first dipole element and the second dipole element are configured in an undulating pattern.

[0018] In one embodiment in accordance with any previous embodiment, the circuit chip comprises a memory unit configured to store identification information.

[0019] In one embodiment in accordance with any previous embodiment, the RFID antenna comprises a sensor for measuring an environmental feature, where the sensor is internally connected with the circuit chip or external to the circuit chip.

[0020] In one embodiment, the sensor is for measuring temperature.

[0021] In one embodiment in accordance with any previous embodiment, the RFID antenna comprises a gap between the antenna segment and the loop segment, wherein the antenna segment is magnetically coupled to the loop segment.

[0022] In one embodiment in accordance with any previous embodiment, the loop segment comprises a first vertical segment, a second vertical segment opposite the first vertical segment, an upper horizontal segment disposed between the first and second vertical segments, and a lower horizontal segment disposed between the first and second vertical segments, the lower horizontal segment disposed adjacent to the antenna segment.

[0023] In one embodiment in accordance with any previous embodiment, the plurality of resonant circuits comprises, a resonant circuit disposed on the first vertical segment, a resonant circuit disposed on the second vertical segment, and a resonant circuit disposed on the lower horizontal segment.

[0024] In one embodiment in accordance with any previous embodiment, the circuit chip is disposed upper horizontal segment.

[0025] In one embodiment in accordance with any previous embodiment, each of the plurality of resonant circuits comprise an inductor and a capacitor.

[0026] In one embodiment, at least one of the capacitors comprises an interdigital capacitor.

[0027] In one embodiment, the inductor and the capacitor of at least one of the plurality of resonant circuits is connected in parallel.

[0028] In one embodiment in accordance with any previous embodiment, the impedance of the antenna is 377 ohms.

[0029] In one embodiment in accordance with any previous embodiment, the attenuation of the received signal is at least 27 dB. \

[0030] In one embodiment in accordance with any previous embodiment, the the plurality of resonant circuits provide from about 5 dB to about 40 dB of attenuation of the received signal at a frequency of from about 2.4 GHz to about 4.0 GHz.

[0031] In one embodiment in accordance with any previous embodiment, the the plurality of resonant circuits provide from about 35 dB to about 40 dB of attenuation of the received signal at a frequency of from about 2.4 GHz to about 4.0 GHz.

[0032] In one embodiment in accordance with any previous embodiment, the antenna is configured to receive signals between 860 MHz and 960 MHz and attenuate a received signal at a frequency between 2.4 GHz and 3 GHz at least by 40 dB.

[0033] In another aspect, provided is a radio frequency identification (RFID) device comprising the RFID antenna of any of the previous embodiments.

[0034] In still another aspect, provided is a label comprising the RFID antenna of any of the previous embodiments.

[0035] In yet another aspect, provided is article of manufacture comprising the label. [0036] The following description and the drawings disclose various illustrative aspects. Some improvements and novel aspects may be expressly identified, while others may be apparent from the description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings illustrate various systems, apparatuses, devices, and related methods, in which like reference characters refer to like parts throughout.

[0038] FIG. 1 is an example of a RFID label in accordance with at least one embodiment of the invention.

[0039] FIG. 2 is an example of a close up of a section of the RFID label of FIG. 1.

[0040] FIG. 3 is an example of an alternative embodiment of a capacitor employed in

FIG. 2.

[0041] FIG. 4 is a conjugate match factor display for the comparative antenna of FIG. 1.

[0042] FIG. 5 is a display showing sensitivity performance for the RFID label of FIG. 1.

[0043] FIG. 6 is a display showing sensitivity performance for the RFID label of FIG. 1 before and after exposure to microwave radiation.

[0044] FIG. 7 is a display showing sensitivity performance for the RFID label of FIG. 1 before and after TUV testing of the label.

DETAILED DESCRIPTION

[0045] Reference will now be made to exemplary⁷ embodiments, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized and structural and functional changes may be made. Moreover, features of the various embodiments may be combined or altered. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments. In this disclosure, numerous specific details provide a thorough understanding of the subject disclosure. It should be understood that aspects of this disclosure may be practiced with other embodiments not necessarily including all aspects described herein, etc.

[0046] As used herein, the words “example” and “exemplary ” means an instance, or illustration. The words “example” or “exemplary” do not indicate a key or preferred aspect or embodiment. The word “or” is intended to be inclusive rather than exclusive, unless context suggests otherwise. As an example, the phrase “A employs B or C,” includes any inclusive permutation (e.g., A employs B; A employs C; or A employs both B and C). As another matter, the articles '‘a” and “an” are generally intended to mean “one or more” unless context suggest otherwise.

[0047] Provided is a RFID label that is suitable for use in an environment such as a microwave oven. A RFID tag or label may be exposed to microwave radiation during their use. For example, RFID labels might be used on food packaging (frozen or non-frozen) for use with an inventory or product tracking system. Many such products may be microwaveable products in which the RFID label is not removed prior to exposure to the microwave radiation. RFID labels may also be used in medical or laboratory settings to identify medical specimens, manufacturing products, forensic samples, or other laboratory samples that are processed with the aid of microwave energy in laboratory or production equipment. Microwave energy is supplied as electromagnetic radiation at approximately 2.45 GHz frequency or at other frequencies in the range of about 2 to 14.5 GHz in commercial or experimental laboratory or production equipment. Commercial or home-use microwave ovens provide microwave energy as 2.45 GHz frequency electromagnetic radiation to heat foods and beverages. In either case, the RFID tag or label may be exposed to approximately 2.45 GHz frequency radiation at power levels ranging from 100 to 1200 watt, for times ranging from 1 second to many hours, with either continuous or pulsed microwave exposure.

[0048] Exposing RFID tags or labels to electromagnetic radiation generated by a microwave source, such as a microwave oven, may cause the RFID tag or label to become non-functional. Such RFID tags w ill often become non-functional if they are exposed to high microwave power levels, such as microwave power in the range of 100 to 1200 watts discussed above. For example, microwave ovens typically output 1000 watts of power (+60 dBm). This is 40 dB above the maximum input pow er of most ultra-high frequency (UHF) RFID devices, which is about +20 dBm. In such cases, the electromagnetic energy in a microwave oven may cause the RFID tag or antenna elements to become very hot, possibly hot enough to burst into flame, creating a safety hazard that may be an even worse problem than the problem of a non-functional label. The RFID label may also arc to the microwave oven power supply or other electrical grounds in the oven, creating sparks and possibly damaging the power supply. In these circumstances, it is also possible that the object to which the RFID label is affixed may also be damaged. In accordance with the present technology, provided is an RFID antenna and label comprising the same, where the label is configured to attenuate electromagnetic radiation signals having a frequency of about 2.4 GHz or greater.

[0049] Referring to FIGS. 1-3, an RFID label 10 comprises an RFID antenna 200 disposed on a substrate 100. The RFID antenna 200 can be provided in the form of transmission lines on a substrate material. The transmission lines are provided as conductive traces in a pattern typically formed from a conductive metal. The pattern is configured to transform the RFID integrated circuit to match that of free space (an impedance of 377 ohms). This is accomplished by the selection of the width and length of the antenna elements. RFID antennae are designed to operate between 860 MHz and 960 MHz. Conventional antennae may offer some rejection of RF signals at 2.45 GHz, but the attenuation provided, if at all. may not be sufficient to prevent the label from burning.

[0050] In accordance with the present disclosure, the RFID antenna can be provided with a dipole antenna segment and a loop segment, where the loop segment comprises a plurality⁷ of resonant circuits configured for blocking or attenuating the incoming signal at frequencies greater than 2.4 GHz. The resonant circuit elements are provided in a quantity with patterns to provide a desired level of attenuation to the unwanted signal.

[0051] FIGS. 1-3 illustrate an embodiment of an RFID antenna 200 in accordance with the present disclosure. The RFID label 10 includes a dipole antenna 200 comprising an antenna segment 210 and a loop segment 220 where the loop segment comprises a circuit chip 230 connected to the loop segment. The circuit chip can store identifying information along with any other information necessary⁷ for the operation of the RFID antenna. In some embodiments, the circuit chip 230 can include a plurality⁷ of memory units, where each memory⁷ unit contains information about a specific object (item, person, place, etc.) The circuit chip 230 can include unique tag identifiers which cannot be overwritten. In some embodiments, the circuit chip 230 can be writable by an RFID writer.

[0052] The antenna segment is configured as a folded dipole antenna comprising dipole elements (antenna segments) 212 and 214 disposed on opposite sides of a segment 216. Here, segment 216 is configured as a generally straight region. The first dipole element 212 and second dipole element 214 in the embodiment of FIG. 1 are provided as meandering dipole elements. The dipole elements 212 and 214 are provided as an undulating pattern with wave-like elements. In other embodiments, segments 212 and 214 can comprise of panel antennas, monopole antennas, loop antennas, composite antennas or other types of antennas.

[0053] In one embodiment, the dipole elements 212 and 214 have the same length and pattern design. As shown in FIG. 1, the pattern for antenna segments 212 and 214 are provided as a square wave. The number of cycles, the period of the waves, the width of the wave segments, etc. can be selected to tune the antenna to operate in a predetermined operating frequency range. In one embodiment, the predetermined operating frequency range can be between 860 and 960 MHz. In another embodiment, the dipole elements 212 and 214 can have the same length but have different patterns. In still another embodiment, the dipole elements can differ from one another in length and/or in the pattern of the dipole element.

[0054] As shown in FIG. 1, in one embodiment, the first dipole element 212 can terminate at the first pad 213. Further, the second dipole element 214 can terminate at the second pad 215. A physical length L of the first dipole element 212 measured from the center of segment 216 through the first pad 213 of the first dipole element 212 is shorter than an electrical length L2 of the first dipole element 212, and a physical length L3 of the second dipole element 214 measured from the center of segment 216 through the second pad 215 of the second dipole element 214 is shorter than an electrical length L4 of the second dipole element 214.

[0055] In other embodiments, the physical length L of the first dipole element 212 measured from the center of segment 216 through the first pad 213 of the first dipole element 212 is equal to the electrical length L2 of the first dipole element 212, and a physical length L3 of the second dipole element 214 measured from the center of segment 216 through the second pad 215 of the second dipole element 214 is equal to the electrical length L4 of the second dipole element 214.

[0056] In an different embodiment, the physical length L of the first dipole element 212 measured from the center of segment 216 through the first pad 213 of the first dipole element 212 is longer than the electrical length L2 of the first dipole element 212, and a physical length L3 of the second dipole element 214 measured from the center of segment 216 through the second pad 215 of the second dipole element 214 is longer than to the electrical length L4 of the second dipole element 214. In some embodiments, the physical lengths of the elements 212, 214, 216 can differ and be a combination of lengths as described above.

[0057] In the RFID antenna 200, the dipole segment 210 and the loop segment 220 are magnetically coupled across a gap 205 between the loop segment 220 and segment 216 of the dipole segment 210. In some embodiments, the loop may be conductively coupled to the dipole segment.

[0058] In one embodiment, the RFID antenna 200 is configured such that the loop segment 220 and the dipole segment 210 are magnetically coupled. Configuring the antenna such that the loop segment 220 and the dipole segment 210 are separated can help reduce the heat in the antenna and further help protect the circuit chip from being damaged. The size of the gap between the loop segment and the dipole segment can be selected as desired. The gap can be selected to provide a desired level of RFID performance. In one embodiment, the gap between the loop segment and the dipole segment is from about 0. 1 mm to about 1 mm, from about 0.2 mm to about 0.8 mm, from about 0.3 mm to about 0.7 mm, or from about 0.4 mm to about 0.6 mm.

[0059] The circuit chip 230 can be in electrical connection with the loop segment 220 using a first connection 201 of the loop region 220 and a second connection 203 of the loop region 220.

[0060] The loop segment further comprises a plurality of resonant circuits defined in the loop region comprising a capacitor in parallel with a conductor, where the circuits are configured (tuned) to provide attenuation of unwanted signals. The resonant circuits disposed on the loop segment may also be referred to herein as “rejection circuits” or “traps.” In embodiments, the resonant circuits provide attenuation of frequencies of from about 2.4 to about 4.0 GHz. In embodiments, the rejection circuits can provide at least 35 dB of attenuation to unwanted signals at frequencies of from about 2.4 to 4.0 GHz. In embodiments, the resonant circuits can provide from about 0 dB to about 40 dB, about 5 dB to about 35 dB, about 10 dB to about 30 db, or about 15 dB to about 25 dB of attenuation for frequencies of from about 2.4 to about 4.0 GHz. In one embodiment, the resonant circuits provide from about 35 dB to about 40 dB of attenuation for frequencies of from about 2.4 to about 4.0 GHz.

[0061] For example, RFID antenna 200 includes the loop segment 220 with resonant circuits 240a, 240b, and 240c. Resonant circuits 240a and 240c are disposed on opposing vertically oriented ends of the loop segment, and circuit 240b is disposed on a horizontally oriented portion of the loop segment opposite the circuit chip 230 and nearer to the dipole 210. The resonant circuits 240a, 240b, and 240c can comprise an inductor (inductors 250a, 250b, and 250c, respectively) and a capacitor (260a, 260b, and 260c, respectively) electrically connected in parallel with the inductor.

[0062] The capacitors 260a, 260b, and 260c can be provided as interdigital capacitors comprising a plurality of “fingers.” For example, FIG. 2 illustrates a close up of the circuit 240a and shows the capacitor 260a comprising a metal layer having a set of fingers 262a and 264b with a gap 263 between the fingers 262a and 264b. The fingers 262a and 264b are each defined by traces with vertical portions and a horizontal portion connecting the vertical portions with a gap between the vertical segments of the fingers. It will be appreciated that other interdigital capacitor configurations can be employed as may be suitable to provide a desired level of attenuation for frequencies of about 2.4 MHz or greater. While the fingers shown in FIGS. 1 and 2 are formed by a continuous undulating pattern, the fingers could be defined by, for example, single traces extending form a common line or trace.

[0063] Referring to FIG. 3, an interdigital capacitor 360 may be defined by fingers 362a. 362b, and 362c extending from a terminal end 364. and have a gap 363 between the fingers 362a and 362b, and a gap 365 between fingers 362b and 362c.

[0064] The size of the inductors and capacitors of the RFID antenna 200 can be selected as desired. Generally, the inductor can be smaller as the capacitor becomes larger, and the inductor can be larger as the capacitor becomes smaller. Further, for the capacitor, the gap between the fingers may be made longer where the gap between is wide, and the fingers may be shorter where narrow er gaps are provided. The number of fingers in the capacitor segment can be selected to provide the desired level of attenuation for the circuit.

[0065] In one embodiment, resonant circuits 240a, 240b, and 240c can be provided to provide the desired level of attenuation of signal within the frequency band of 2.4 to 4.0 GHz. In other embodiments, the shape and location of the resonant circuits can be provided to provide the desired level of attenuation of signal above 2.4 GHz. For instance, the resonant circuits can be placed in different locations of the loop 220.

[0066] The location, shape, and/or size of the resonant circuits can be evaluated using electromagnetic simulation software. For instance, constructing and testing of RFID antenna 200 can be performed to confirm that the antenna shape with resonant circuits 240a, 240b, and 240c on the loop segment 220 provides the desired level of signal attenuation in the predetermined frequency range, such as the microwave range.

[0067] It will be appreciated that the antenna shown in FIGS. 1-4 are merely illustrative embodiments of possible RFID antennae. The shape and structure of the antenna, e.g., the configuration of the dipole elements with respect to the pattern, number of undulations, thickness of the regions, periodicity of the undulations, etc. can be selected as desired to provide a desired output within the region of 860 and 960 MHz, while also achieving the desired level of attenuation of signal above 2.4 GHz or in the frequency band of 2.4 to 4.0 GHz.

[0068] Materials chosen for RFID labels 10 of the present invention may be selected from a range of materials, with the choice being dependent on manufacturing cost, manufacturing yield, tag performance in its intended use, environmental factors (in addition to microwave radiation exposure), and similar considerations.

[0069] The integrated circuit may compnse a sensor configured to detect an environmental feature such as, for example, temperature. The sensor may be internal, i.e., built-in the integrated circuit. Alternatively, the sensor may be external to and independent from the integrated. The incorporation of a temperature sensor may allow, for example, monitoring and/or verification that a particular temperature was reached, which may be particularly beneficial for temperature sensitive foods that should be heated at or above a particular temperature.

[0070] An RFID label 10 includes an RFID antenna 200 in accordance with the present disclosure formed on a substrate 100. The substrate 100 can be selected as desired for any particular purpose or intended application. Examples of suitable substrates include, but are not limited to, paper, cardboard, or polymer substrates such as, for example, polyester terephthalate (PET), polyimide, polyethylene, epoxy or reinforced epoxy, or similar materials.

[0071] The RFID antenna 200 may be formed from an electrically conductive material formed on the substrate 100 in a pattern. The conductive pattern can be formed from any suitable material. Examples of suitable material includes, but is not limited to, copper, aluminum, silver, gold, other metals, or carbon. The RFID antennas may also be printed in conductive inks comprising dispersions of silver, gold, or other metals, or particles coated with silver, gold or other metallic conductors, or nonmetallic conductors such as carbon or polyaniline. The RFID antennas can be manufactured using commercially available flexible circuits that are produced using processes and designs of proven high yield. In general, the higher the conductivity of the antenna, the greater the current that will be produced in a coil of a particular size during microwave exposure. In general, the higher the conductivity of the antenna, the greater the read range of the RFID label 10 for a coil of a particular size.

[0072] Embodiments described herein are applicable to all forms of labels. Label 10 may also be referred to herein as tags. A "tag inlay'’ or “inlay’’ is defined as an assembled RFID device that generally includes an integrated circuit chip (and/or other electronic circuit) and antenna formed on a substrate, and is configured to respond to interrogations. A “tag label” or “label” is generally defined as an inlay that has been attached to a pressure sensitive adhesive (PSA) construction, or has been laminated, and cut and stacked for application. In one embodiment, an inlay is attached to another surface of an article, or between surfaces of an article, such as paper, cardboard, plastic, etc., for attachment to an article to be tracked, such as an article of clothing, food product, package of meat, etc.

[0073] The RFID tags of the present invention may optionally be molded into or incorporated in various objects, containers, or housings, or the like.

[0074] What has been described above includes examples of the present specification. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present specification, but one of ordinary skill in the art may recognize that many further combinations and permutations of the present specification are possible. Accordingly, the present specification is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term "includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.

[0075] Examples

[0076] A RFID label 10 is provided with the RFID antenna 200 as shown in FIG. 1 on a substrate 100. The substrate is a polyethyelene terephthalate material.

[0077] FIG. 4 shows a conjugate match factor display for the antenna of FIG. 1. The antenna shows match points in the range desired for RFID operation indicating that the antenna is well tuned between 775 MHz and 1.050 MHz. FIG. 4 also shows the antenna exhibits around 40 dB of rejection of an incoming signal at a frequency of 2.4 GHz to 3 GHz. [0078] The sensitivity of the RFID antenna 200 of FIG. 1 was also evaluated. The sensitivity' was evaluated from 800 MHz to 1000 MHz with the label associated with different package loadings including (i) no loading (air) 501, (ii) light loading 503, (iii) heavy loading 505, and (iv) on a tray with meat 507. The sensitivity performance is shown in FIG. 5. The more negative values reflect the higher sensitivity. The packages still exhibited a read range of greater than 5 meters in the ETSI (866 to 870 MHz) and FCC (902 to 928 MHz) frequency bands.

[0079] Microwave Survivability Testing

[0080] The RFID labels 10 were then applied to the exterior of a paper cup, half filled with tap water. A cup was placed in the center and on the edge of the rotating tray so that the labels faced directly towards the energy source of the microwave oven. Trials were run with exposure of the label to high power (1000 watts) for 90 seconds and 3 minutes. The 90 second trial and one of the 3-minute tnals was conducted with the container/label positioned in the center of the micro wave. One 3 -minute trial was run with the container/label positioned away from the center to simulate placement of a label/RFID on an edge of a container. There were no visible burns or browning of the facestock for 90 second, or 3-minute exposures at high power (1000 watts). After exposure, the RFID sensitivity was re-measured and compared to the pre-exposure result as shown in FIG. 6. There was no significant change noted. In another set of 90 second exposure tests, several labels survived (50) exposures without a significant change in sensitivity. Pre-exposure measurements were made with the label lying flat on the test platform. Post-exposure measurements were conducted with the label applied to the paper cup. The curvature of the cup caused a slight downw ard frequency shift, with the minimum levels matching the pre-exposure values.

[0081] Tests were then conducted according to the TUV “Microwave Safe’^? test standard. Inlays survived all tests without displaying any arcs or sparks or browning/buming of the label facestock. FIG. 7 illustrates the post exposure RFID sensitivity from one of the four TUV tests. As shown in FIG. 7, the RFID labels exhibited good performance and functionality after exposure to microwave radiation.

[0082] The foregoing description identifies various, non-limiting embodiments of a RFID label. Modifications may occur to those skilled in the art and to those who may make and use the invention. The disclosed embodiments are merely for illustrative purposes and not intended to limit the scope of the invention or the subject matter set forth in the claims.

Claims

CLAIMS What is claimed is:

1. An RFID antenna comprising: an antenna segment coupled to a loop segment; and the loop segment comprising a plurality of resonant circuits and a circuit chip; wherein the antenna is configured to have an output frequency between 775 MHz and 1,050 MHz and attenuate a received signal above 2.4 GHz.

2. The RFID antenna of claim 1, wherein the antenna segment is a folded dipole antenna comprising a first dipole element and a second dipole element disposed on opposite sides of an intermediate segment.

3. The RFID antenna of claim 2. wherein the first dipole element is configured to terminate at a first pad and the second dipole element is configured to terminate at a second pad.

4. The RFID antenna of claim 3, wherein the first dipole element has a electrical length and a first physical length, the first physical length being measured from a center of the intermediate segment to an end of the first pad, and the second dipole element has a second electrical length and a second physical length, the second physical length being measured from a center of the intermediate segment to an end of the second pad.

5. The RFID antenna of claim 4, wherein the first physical length of the first dipole element is shorter than the electrical length of the first dipole element, and the second physical length of the second dipole element is shorter than the second electrical length of the second dipole element.

6. The RFID antenna of claim 4, wherein the first physical length of the first dipole element is equal to the electrical length of the first dipole element, and the second physical length of the second dipole element is equal to the second electrical length of the second dipole element.

7. The RFID antenna of claim 4, wherein the first physical length of the first dipole element is greater than the electrical length of the first dipole element, and the second physical length of the second dipole element is greater than the second electrical length of the second dipole element.

8. The RFID antenna of any of claims 2-7, wherein the first dipole element and the second dipole element are configured in an undulating pattern.

9. The RFID antenna of any of claims 1-8, wherein the circuit chip comprises a memory unit configured to store identification information.

10. The RFID antenna of any of claims 1-9 comprising a sensor for measuring an environmental feature, where the sensor is internally connected with the circuit chip or external to the circuit chip.

11. The RFID antenna of claim 10, wherein the sensor is for measuring temperature.

12. The RFID antenna of any of claims 1-11 comprising a gap between the antenna segment and the loop segment, wherein the antenna segment is magnetically coupled to the loop segment.

13. The RFID antenna of any of claims 1-12, wherein the loop segment comprises a first vertical segment, a second vertical segment opposite the first vertical segment, an upper horizontal segment disposed between the first and second vertical segments, and a lower horizontal segment disposed between the first and second vertical segments, the lower horizontal segment disposed adjacent to the antenna segment.

14. The RFID antenna of claim 13, wherein the plurality of resonant circuits comprises, a resonant circuit disposed on the first vertical segment, a resonant circuit disposed on the second vertical segment, and a resonant circuit disposed on the lower horizontal segment.

15. The RFID antenna of claim 13 or 14. wherein the circuit chip is disposed upper horizontal segment.

16. The RFID antenna of any of claims 1-15, wherein each of the plurality’ of resonant circuits comprise an inductor and a capacitor.

17. The RFID antenna of claim 16, wherein at least one of the capacitors comprises an interdigital capacitor.

18. The RFID antenna of claim 16, wherein the inductor and the capacitor of at least one of the plurality of resonant circuits is connected in parallel.

19. The RFID antenna of any of claims 1-18, wherein the impedance of the antenna is 377 ohms.

20. The RFID antenna of any of claims 1-19, wherein the attenuation of the received signal is at least 27 dB.

21. The RFID antenna of any of claims 1-19, wherein the the plurality of resonant circuits provide from about 5 dB to about 40 dB of attenuation of the received signal at a frequency of from about 2.4 GHz to about 4.0 GHz.

22. The RFID antenna of any of claims 1-19, wherein the the plurality of resonant circuits provide from about 35 dB to about 40 dB of attenuation of the received signal at a frequency of from about 2.4 GHz to about 4.0 GHz.

23. The RFID antenna of any of claims 1-19, wherein the antenna is configured to receive signals between 860 MHz and 960 MHz and attenuate a received signal at a frequency between 2.4 GHz and 3 GHz at least by 40 dB.

24. A radio frequency identification (RFID) device comprising the RFID antenna of any of claims 1-23.

25. A label comprising the RFID antenna of any of claims 1-23.

26. An article of manufacture comprising the label of claim 25.

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