WO2022034262A1

WO2022034262A1 - A cover structure and a module for a miniaturized wearable rf-device and a wearable rf-device

Info

Publication number: WO2022034262A1
Application number: PCT/FI2021/050515
Authority: WO
Inventors: Kaarle Jaakkola; Colm MCCAFFREY; Tomi Mattila
Original assignee: VTT Technical Research Centre of Finland Ltd
Current assignee: VTT Technical Research Centre of Finland Ltd
Priority date: 2020-08-14
Filing date: 2021-07-02
Publication date: 2022-02-17
Anticipated expiration: 2023-02-14
Also published as: FI20205799A1

Abstract

The present invention relates to a cover structure made of a substrate material with low RF-losses and configured to cover at least a portion of a circuit board that comprises a plurality of electronic components. The cover structure comprises a radiating element of an open-ended microstrip antenna or a top part of a vertical loop antenna, wherein the antenna is configured, when in use, to emit electromagnetic radiation for wirelessly communicating data carrying signals over a radio frequency (RF) interface, and a plurality of support members protruding from the bottom face of the cover structure towards the underlying circuit board, the support members defining spaces for electronic components disposed between the circuit board and the cover structure. The invention also relates to a module comprising a cover structure and a wearable RF- device.

Description

A cover structure and a module for a miniaturized wearable RF-device and a wearable RF-device

Field

The present invention relates to an apparatus related to miniaturized wearable devices. More particularly, the present invention relates to a cover structure, a module and a miniaturized wearable radio frequency (R.F) device.

Background

At present, wrist- and chest-worn devices form the mainstream in wearable devices. Typical examples include smart watches, smart wristbands and chest strap-based heart rate monitors. Even finger-worn smart ring -type devices have recently emerged into the market.

In parallel, there is increasing trend in skin patch type wearable devices that are directly attached to skin. Common examples of such devices are the ECG patches used for Holter-monitoring. Emerging applications utilize various types of skin attachable monitoring devices that include one or more sensors and wired or wireless communication capabilities for communicating measurement results for processing and analysis.

There is a strong need in wearable device miniaturization, driven especially by wear performance. In particular, the patch-type devices are desired to be compact, both in vertical (device height) and lateral (device area) directions.

However, it is problematic to reach the desired wireless and mechanical properties in case of a miniaturized device.

Wireless performance of conventional antennas for those in the industrial, scientific and medical (ISM) radio bands such as 433.92 MHz, 315 MHz, 868 MHz, 915 MHz, and 2400 MHz, for example at 2.45 GHz frequency commonly employed for Bluetooth and similar wireless standards, is drastically worsened when the device is placed on skin. This is due to the radio frequency properties of human tissues that are essentially a cellular structure with high salt-water content. For example, conventional compact antenna solutions such as half wave electric dipoles as well as surface mounted device (SMD) chip antennas are ill-suited for skin-proximity placement due to strong reduction in radiation performance and undesirable radiation absorption into human tissue. The thinner the device, the more challenging it becomes to arrange a well-performing antenna.

From another viewpoint, miniaturization induces challenges for device packaging. The devices should be mechanically robust to achieve the required reliability and safety. As the device dimensions get smaller, in particular the height of the device, there are increasing challenges in reaching the required mechanical performance. A battery-operated information technology device may be subject to a standardized steel ball drop impact test, in which a standard weight steel ball (i.e. 0.5 kg) is dropped from a standardized height on the device, which device must not cause any risk or harm to a person wearing the device after such impact.

Thus, there is a clear need for a well-performing antenna for highly miniaturized wearable devices, in particular for devices that are attachable, skin patch type that enables creating a mechanically robust device within the maximally compact dimensions.

Description of the related art

Patent application WO 2016/189199 Al discloses an RF-module that has a sandwich structure with an antenna element, a ground plane below the antenna and a component board below the ground plane, in which integrated passive devices (IPD) -technology is utilized for matching and filtering components needed for the antenna element.

Patent application US 2017/0237149 Al discloses an electronic device with a conductive coil for generating magnetic flux for NFC-type communication or to be used for wireless charging. Patent application WO 2011/033172 Al discloses a vertical loop antenna that contains a ground layer.

Summary

An object is to provide a method and apparatus so as to solve the problem of providing a mechanically robust miniaturized wearable RF-device with improved wireless performance. The objects of the present invention are achieved with a cover structure according to the characterizing portion of claim 1 and with a module according to the characterizing portion of claim 7 and a wearable RF- device according to claim 11.

The preferred embodiments of the invention are disclosed in the dependent claims.

According to a first aspect, a cover structure made of a substrate material with low RF-losses is provided. The cover structure is configured to cover at least a portion of a circuit board that comprises a plurality of electronic components. The cover structure comprises an open-ended microstrip antenna or a top part of a vertical loop antenna, wherein the antenna is configured, when in use, to emit electromagnetic radiation for wirelessly communicating data carrying signals over a radio frequency (RF) interface, and a plurality of support members extending from the bottom face of the cover structure towards the underlying circuit board, the support members defining spaces for electronic components disposed between the circuit board and the cover structure.

According to a second aspect, the open-ended microstrip antenna or the top part of the vertical loop antenna is disposed on a top face or on a bottom face of the cover structure or embedded within the cover structure.

According to a third aspect, the cover structure comprises at least one via extending at least partially through the cover structure for coupling said data carrying signals towards the open-ended microstrip antenna or the top part of the vertical loop antenna. According to a fourth aspect, the at least one via extends through one of the plurality of support members.

According to a fifth aspect, the cover structure is further configured to cover an area of the underlying circuit board intended to be occupied by a battery, and wherein at least part of the plurality of support members are further configured to define a space for the battery.

According to a sixth aspect, the bottom surface of the cover structure further comprises an electrode configured to provide an electrical contact to a terminal of the battery.

According to a seventh aspect, the cover structure is a 3D substrate structure with substrate removal for creating said spaces for the electronic components.

According to an eighth aspect, a module is provided that comprises a circuit board, a plurality of electronic components disposed on the circuit board, wherein the electronic components comprise an RF-circuitry configured to produce said data carrying signals to be communicated wirelessly over the radio interface, a space and two electrodes for two terminals of a battery and the cover structure according to any of the above mentioned aspects.

According to a ninth aspect, a ground plane for the open-ended microstrip antenna or a ground layer of the vertical loop antenna is formed by the circuit board and metallic parts in the electronic components disposed on the circuit board.

According to a tenth aspect, the cover structure further comprises a via configured to couple said electrode of the battery with said circuit board. According to an eleventh aspect, said plurality of electronic components further comprises at least one sensor generating said data to be carried over the R.F- interface.

According to a twelfth aspect, a wearable RF-device is provided, that comprising a module according any of the eight to eleventh aspects, and further comprising a battery.

According to a thirteenth aspect, the wearable RF-device is configured to be removably attached to skin of a subject with skin-compatible adhesive.

According to a fourteenth aspect, at least the module of the wearable RF-device is enclosed in one or more protective material layers for protecting the module from touch, moisture and/or dust.

The present invention is based on the idea of integrating an open-ended microstrip antenna or a top part of a vertical loop antenna in a cover structure that provides mechanical protection for the electronic components and optionally for a battery of the device. The term vertical loop antenna refers to the specific design of a vertical loop antenna that contains a ground layer as disclosed in WO 2011/033172 Al.

The present invention has the advantage that performance of the antenna is improved, which increases operation range of RF-communication and/or reduces required transmit power, which also facilitates increasing battery life. Utilizing the ground layer of the electronics as ground plane of the antenna improves immunity of the antenna to any electrically lossy tissue underneath. Also, reliability of the device is improved both by improved RF-performance and by improved mechanical robustness. The cover structure acts as a cap or lid that protects the mechanically sensitive parts below. The invention also enables minimizing amount of material needed, since the cover structure with antenna removes need for separate antenna device. Disposing the antenna or the top part of the vertical loop antenna in the cover structure provides maximum available area for the microstrip antenna or the top part of the vertical loop antenna in a highly miniaturized device. The solution is also well-suited for mass production. The cover structure with the antenna can easily be mass produced.

Brief description of the drawings

In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawings, in which

Figures la and lb show perspective views of a cover structure of a first embodiment.

Figure 2a and 2b show perspective views of the cover structure of a first embodiment installed on a circuit board.

Figures 3a and 3b show perspective views of a module with a cover structure according to a second embodiment.

Figure 4a and 4b show perspective views of a module with a cover structure according to a third embodiment.

Figure 5a and 5b show perspective views of a module with a cover structure according to a fourth embodiment.

Figures 6a, 6b and 6c illustrate cross-sections of various embodiments of the invention.

Figures 7a, 7b and 7c illustrate cross-sections of further embodiments of the invention.

Detailed description

Figures la and lb show perspective views of a cover structure (10) of a first embodiment as a wireframe (la) and with grayscale (lb). Figures 2a and 2b show perspective views of a module comprising the cover structure of figures la and lb as a wireframe (2a) and with grayscale (2b). The cover structure (10) is preferably made of a substrate material with low R.F- losses. Any suitable substrate material may be used. For example, common plastics such as polyethylene (PE), polypropylene (PP), polycarbonate (PC) or acrylonitrile butadiene styrene (ABS) are well-suited, along with PTFE- of ceramic-based PCB laminates designed for radio frequency applications. Such include e.g. RT/Duroid® and R04300®. The cover structure (10) preferably comprises an essentially flat portion (11) that forms a roof of the protective cover over its underlying electrical components and a plurality of support members (12) extending downwards from the bottom face of the flat portion of the cover structure.

An antenna (20) is preferably disposed on bottom or top face of the flat portion (11) or embedded within the flat portion (11). Bottom face of the cover structure refers to the face that is intended to be disposed towards an underlying circuit board and electronic components and also towards a subject wearing a wearable device when the cover structure is comprised in a module, in particular in a wearable RF-device. Top face of the cover refers to the surface opposite the bottom face that is towards ambience of the cover, away from the circuit board and the intended subject.

The cover structure (10) according to the first embodiment is configured to cover and mechanically protect from above a portion of a circuit board (40) on which a plurality of electronic components (50) may be attached. Preferably, sensitive electronic components for example one or more sensor components and one or more data processing components, such as a microcontroller, are attached on top face of the circuit board (40) so that they reside between the circuit board (40) and the cover structure (10).

Support members (12) of the cover structure (10) define spaces for the electronic components (50) disposed between the cover structure (10) and the circuit board (40). Thus, when the cover structure (10) is integrated in a module with a circuit board, the electronic components become mechanically protected from top side by the cover structure and from bottom side by the circuit board.

The cover structure (10) comprises an open-ended microstrip antenna (20) configured to emit electromagnetic radiation for wirelessly communicating data signals over a radio frequency (R.F) interface. The RF-interface may be for instance a radio interface using at least one industrial, scientific and medical (ISM) band frequency, such as 2.4 GHz or 2.45 GHz band commonly used by WiFi and Bluetooth communication devices, or 863 to 870 MHz used for so called short range radio devices. For example, the microstrip antenna may be designed as a quarter wave antenna with length corresponding to approximately X/4, in other words approximately a quarter of the wavelength of the electromagnetic radiation at the frequency used for communication.

When a module is assembled, the antenna (20) is provided with a galvanic contact with circuitry on the circuit board (40). The cover structure (10) may comprise a via (25) enabling coupling of the antenna (20) with the circuitry on the circuit board. In this example, the antenna (20), which is made of a metallic microstrip, is coupled at its one end to a connecting pin or pole (70) coupling the antenna (20) with the circuitry of the circuit board (40). It is also possible to print or otherwise dispose the antenna conductor as a conformal structure on the outer or inner surface of the cover structure (10) so that a separate via is not needed. The antenna conductor (20) may also be formed on a flexible PCB that is an extension of the main circuit board (40), which is then folded on the cover structure (10). If the antenna (20) is embedded within the cover structure or is disposed on the top face of the cover structure, a metallized via (25, 70) is preferably provided in the cover structure at one end of the antenna (20) to enable galvanic connection of the antenna (20) with the coupling pin or pole. Alternatively, the cover structure (10) may comprise a metallized via that extends through the cover structure (10) from the antenna (20) to a bottom surface of a support member (12) so that the via enables electrically attaching the antenna (20) with circuitry on the circuit board (40). The circuit board (40) may comprise a contact pad (71) for facilitating the connection.

For enabling a compact and mechanically robust design, lateral dimensions of the cover structure preferably at least partially match with lateral dimensions of the underlying circuit board.

Electronic components (50) disposed on the circuit board (40) comprise at least an RF-circuitry that, when in use, produces data carrying signals to be communicated wirelessly over a RF-interface using the antenna (20). Data to be carried may be provided for example by one or more sensor components disposed on the circuit board and coupled to the RF-circuitry either directly or via one or more intermediate electronic components. The RF-circuitry may comprise or may be connected to a microcontroller, which receives data from the one or more sensors and produces said data carrying signals.

Although not shown, the module shown in the first embodiment comprises a place for disposing a battery. If the battery is not covered by the cover structure, thickness of the cover structure material may be selected such that it matches, at least approximately, height of a battery intended to be placed on the circuit board so that the top face of the module becomes approximately flat when the battery is installed.

Figures 3a and 3b show perspective view of a module with a cover structure according to a second embodiment, as wireframe (3a) and with grayscale (3b). In the second embodiment, the antenna (20) and the portion of the cover structure covering the electronic components (40) may be like the first embodiment. The cover structure (10) is further extended to cover an area intended to be occupied by a battery (60), thus providing improved mechanical protection for the battery (60) from impacts coming from above. Total height of the substrate used for manufacturing the cover structure should in this case be higher than height of the intended battery so that a layer of substrate material remains on top of the battery when the battery is installed in the module. The battery provides operating energy to the electronic components and the antenna. The battery may be replaceable and/or removably attached to the module. Thus, the module itself does not necessarily include a battery. Connection for the upper electrode of the battery (60) (not shown) may be provided by any known means.

This structure facilitates improved impact safety of the module. The flat portion and one or more support members (12) of the cover structure preferably define a space for the battery (60) within the module.

Increased height of the cover structure in comparison to the first embodiment moves the antenna further away from the ground plane, which improves radiation characteristics of the antenna.

Figures 4a and 4b show perspective view of a module with a cover structure according to a third embodiment. In comparison to the second embodiment, the cover structure (10) is further provided with an electrode (65) configured to provide an electrical contact to a terminal of the battery (60). The electrode (65) is galvanically coupled to the circuitry on the circuit board (40). Like for the antenna (20), the connection for the electrode (65) may be provided for example with a connector pole or pin or a metallized via (30) extending through a support member (12) of the cover structure (10). Figures 4a and 4b illustrate two possible options for a galvanic connection between the cover structure (10) and the circuit board (40). The antenna (20) is coupled using a connector pin or pole (70) extending through free space between the cover structure (10) and circuitry on the circuit board (40) and the electrode (65) is coupled using a via (30) extending through material of a support member (12). However, either of the connection types may be used for any required connection. Selection between different connection types is a design option. Manufacturability, reliability and mechanical robustness of the structure of the module is one important factor in making decision between different connection types. As in the second embodiment, the battery is not an integral part of the module itself. The battery (60) may be replaceable and/or removably attached to the module.

Figures 5a and 5b show perspective views of a module with a cover structure (10) according to a fourth embodiment, as wireframe (5a) and with grayscale (5b). According to this embodiment, the antenna is a vertical loop antenna that contains a ground layer and a top part (20') in the cover structure (10) instead of the open-ended microstrip antenna (20). The top part (20') is coupled at its both ends to a ground plane formed by the circuit board (40) and metallic parts in the electronic components (50). The top part (20') may be coupled to the ground plane at its ends using pins or poles (70) or vias (30) to form a vertical loop antenna that contains a ground layer, as known for example from WO 2011/033172 Al. Although this embodiment is illustrated in connection with a module (10) with all parts but the antenna arrangement similar to the second embodiment, the vertical loop antenna that contains a ground layer may be applied to any of the above disclosed embodiments as an alternative.

Figures 6a to 6c illustrate cross-sections of various embodiments of the invention. Figures are not in scale, but dimensions have been exaggerated for visualization.

In the figure 6a, the antenna (20) is disposed on the bottom face of the flat portion (11) of the cover structure (10), and a via (30) provides a connection between the circuit board (40) and the antenna (20). In the figure 6b, the antenna (20) is embedded within the flat portion (11) of the cover structure (10) so that it is not exposed on either face of the cover structure (10). In the examples of figures 6a and 6b electrical connection for the battery (60) is provided by a pole or pin (70).

Placement of the antenna as shown in the figures 6a and 6b has a further benefit that the antenna is protected by the cover structure (10) from the outside for example from being touched or scratched. This reduces sensitivity of the antenna to proximity of external objects, for example a finger or hand of a user. In the figure 6c, the antenna (20) is disposed on the top face of the cover structure (10). This enables maximizing distance of the antenna (20) from the ground plane formed by the circuit board (40) and metallic parts in the electronic components (50), which improves radiation characteristics of the antenna and reduces absorption of undesirable radiation into human tissue when a RF-module with the cover structure (10) is placed on skin of a human subject. In this version, the electrical connections between the circuit board (40) and the electrode (65) and between the circuit board (40) and the antenna (20) are provided by vias (30).

Although all figures 6a to 6c include the battery (60) and an electrode (65) for the battery, disclosed alternatives for placement of the antenna (20) may be used in with any of the above described embodiments. Selection between different connection types, namely pins or poles (70) and/or vias (30), between the antenna (20) and the circuit board, and between the electrode (65) and the circuit board is a design option.

Figures 7a to 7c illustrate various embodiments of a module implemented using a vertical loop antenna that contains a ground layer. Connections towards the circuit board (40) and thus to the ground plane are provided by the pins or poles (70) or vias (30) are at both ends of the top part (20') arranged in the flat portion (11) of the cover structure (10). In the figure 7a, the top part (20') of the vertical loop antenna is disposed primarily on the bottom face of the flat portion (11) of the cover structure, and connected to the circuit board (40) at one end by a pin or pole (70) and at the other end by a via (30).

In the figure 7b, the top part (20') of the vertical loop antenna is embedded within the flat portion (11) of the cover structure (10), and coupled to the circuit board (40) with one via (30) and with one pin or pole (70). A further via (25) is provided in the cover structure (10) for enabling connection between the pin or pole (70) and the top part (20'). In the figure 7c, the top part (20') of the vertical loop antenna is placed at the top face of the cover structure (10), and coupled to the circuit board (40) by vias (30) at both ends of the top part (20')-

Also in the examples of figures 7a to 7c, selection between different connection types, namely pins or poles (70) and/or vias (30), between the top part (20') of the vertical antenna and the circuit board (40), and between the electrode (65) and the circuit board (40) is a design option.

As described above, the microstrip antenna (20) or the top part (20') of the vertical loop antenna is preferably disposed on a substrate material that has low R.F losses. The device electronics and the circuit board act as a ground plane for the antenna, thus reducing both problematic effects of tissue proximity towards the antenna performance and electric field exposure to the tissue. Distance of the microstrip or the top part of the loop antenna from this ground plane is determined by thickness of the substrate material and remains stable, which maintains the stable input impedance of the antenna that, in turn, ensures the optimal antenna operation and maximum operation range. The RF-chip providing RF-signal towards the antenna is disposed on the circuit board with other device electronics, thus mechanically protected by the cover structure.

The concept of the cover structure with an integrated microstrip antenna has been tested with a prototype having a three-axis acceleration sensor, a microcontroller with single-ended Bluetooth (BT) radio output. The cover was manufactured using a substrate with only 1.5 mm thickness before removing substrate material for creating spaces for the electronic components. Passive components in classic 'pi' topology were used for matching the antenna. In comparison to a corresponding device implemented using a traditional chip antenna, the invented cover structure integrated antenna provided 10 dB increase in signal level, when disposed on a human forearm. Instead of removing substrate material for creating spaces for the electronic components, the cover structure may be manufactured for example by using 3D printing or equivalent. The term "3D substrate with substrate removal" refers to any substrate structure with spaces within the volume or the substrate for the electronic components, wherein the spaces are defined by support structures made of the substrate material itself by removing substrate material for generating its 3D structure.

For implementing a wearable RF-device, the module according to any of the above examples is provided with a battery, if not already included in the module. The battery provides operating energy for the electronic components and the antenna. Further, the module with the battery is preferably enclosed in one or more further protective material layers for protecting the module and/or the battery from touch, moisture and/or dust. For making the wearable RF-device comfortable for wearing, the protective material layers may be at least partially bendable or flexible. If the wearable RF-device is intended to be attached to skin of a subject, the wearable RF-device is preferably provided with means for attaching the device to the skin. For facilitating comfort and easy attachment, the one or more protective material layers preferably provide at least partially flexible or bendable contact surface towards skin. A skin-compatible adhesive may be applied for removably attaching the wearable RF-device to the skin.

It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims

1. A module comprising a cover structure made of a substrate material with low RF-losses, and a circuit board with a plurality of electronic components attached on a first face thereof, wherein the cover structure is disposed on the first face of the circuit board to cover at least a portion of the circuit board with the plurality of electronic components, so that the plurality of electronic components are disposed between the circuit board and the cover structure, the circuit board and the cover structure together forming mechanical protection against impacts for the plurality of electronic components, wherein the cover structure comprises:

- a radiating element of an open-ended microstrip antenna or a top part of a vertical loop antenna, wherein the antenna is configured, when in use, to emit electromagnetic radiation for wirelessly communicating data carrying signals over a radio frequency (RF) interface,

- a plurality of support members protruding from a bottom face of the cover structure that faces towards the first face of the circuit board, the support members defining spaces for the plurality of electronic components disposed between the circuit board and the cover structure.

2. The module according to claim 1, wherein the radiating element of the open-ended microstrip antenna or the top part of the vertical loop antenna is disposed on the bottom face of the cover structure that faces towards the first face of the circuit board or on a top face of the cover structure that is opposite to the bottom face or is embedded within the cover structure.

3. The module according to claim 1 or 2, wherein the cover structure comprises at least one via extending at least partially through the cover structure for coupling said data carrying signals towards the radiating part of the open-ended microstrip antenna or the top part of the vertical loop antenna.

4. The module according to claim 3, wherein the at least one via extends through one of the plurality of support members.

5. The module according to any of claims 1 to 4, wherein the cover structure is further configured to cover an area of the underlying circuit board intended to be occupied by a battery, and wherein at least part of the plurality of support members are further configured to define a space for the battery.

6. The module according to claim 5, wherein the bottom surface of the cover structure further comprises an electrode configured to provide an electrical contact to a terminal of the battery.

7. The module according to any of claims 1 to 6, wherein said cover structure is a 3D substrate structure manufactured using substrate removal for creating said spaces for the electronic components, or a 3D substrate structure manufactured by 3D printing.

8. The module according to any one of claims 1 to 7,

- wherein the plurality of electronic components disposed on the first face of the circuit board comprise an RF-circuitry configured to produce said data carrying signals to be communicated wirelessly over the radio interface, and the module further comprises

- a space and two electrodes for two terminals of a battery. The module according to claim 8, wherein a ground plane for the open- ended microstrip antenna or a ground layer of the vertical loop antenna is formed by the circuit board and metallic parts in the electronic components disposed on the circuit board. The module according to claim 8 or 9, wherein, when dependent on claim 6, the cover structure further comprises a via configured to couple said electrode with said circuit board. The module according to any of claims 8 to 10, wherein said plurality of electronic components further comprises at least one sensor generating said data to be carried over the RF-interface. A wearable RF-device comprising a module according to any of claims 8 to 11, further comprising a battery. The wearable RF-device according to claim 12, wherein the wearable RF-device is configured to be removably attached to skin of a subject with skin-compatible adhesive. The wearable RF-device according to any of claims 12 to 13, wherein at least the module of the wearable RF-device is enclosed in one or more protective material layers for protecting the module from touch, moisture and/or dust.