WO2024160365A1

WO2024160365A1 - Wristband for identifying a user

Info

Publication number: WO2024160365A1
Application number: PCT/EP2023/052364
Authority: WO
Inventors: Sergio LOPEZ SORIANO
Original assignee: FUNDACIO PER A LA UNIVERSITAT OBERTA DE CATALUNYA
Current assignee: FUNDACIO PER A LA UNIVERSITAT OBERTA DE CATALUNYA
Priority date: 2023-01-31
Filing date: 2023-01-31
Publication date: 2024-08-08
Anticipated expiration: 2025-07-31
Also published as: ES3035791R1; ES3035791A2

Abstract

A wristband for identifying a user is presented, the wristband comprising a band of dielectric material, an integrated circuit and two metallic strips on a side and a ground plane formed on another side of the band, the two metallic strips and the ground plane forming an antenna, whereby the antenna forms a transmission line along the length of the band.

Description

Wristband for identifying a user

BACKGROUND

Ultra-high frequency (UHF) radiofrequency identification (RFID) is widely used in systems for the identification and tracking of humans inside factories, hospitals and other facilities. However, such techniques present several challenges, one of the main ones being its low system reliability. In these types of systems, communications using UHF-RFID may suffer from multi-path propagation, and wave absorption (from materials with high losses, such as liquids, other humans, etc.). More specifically, when using wristbands to embed UHF-RFID transponders (using, for example, dipole-type antennas), an antenna is located close to a high loss substrate (the human body), and its radiation efficiency decreases dramatically.

Current commercial solutions, such as ultra-thin wristbands with dipole-type antennas present a poor performance when attached directly over the human skin. Some of these solutions have the antenna in a tag attached to the wristband but hanging out thereof (i.e. , not forming part of the wristband ring surrounding the wrist). These designs achieve high distance communications, but they are more susceptible to physical stress (rips, torns, wrinkles, bendings, etc...), thus being easily damaged. For example, they can be easily bent in normal use by patients’ beds or trousers pockets, which reduces the life cycle of the device.

Furthermore, in many situations, there is no direct line of sight (DLOS) between the tag and the reader. Thus, the communication is hindered by the own human body/arm and/or other objects. In such scenarios, the tags can’t be detected by a reader, leading to detection failures.

Therefore, reliable systems to identify users using an RFID identification wristband are needed.

SUMMARY

In a first aspect, a wristband for identifying a user is provided, the wristband comprising:

- A band of dielectric material with a length dimension, a width dimension and a thickness dimension; On a first side of the band, the band comprises an integrated circuit and two metallic strips;

On a second side of the band opposed to the first side, the band comprises a ground plane formed by a conducting surface;

Wherein,

The integrated circuit is connected to the two metallic strips and is configured to feed the strips in a balanced mode;

The two metallic strips and the ground plane are insulated from each other by the dielectric material of the band;

The two metallic strips are arranged parallel to each other along the length of the band, and separate from each other across the width of the band; and The integrated circuit, the two metallic strips and the ground plane form a first elongated antenna, wherein the two metallic strips are the poles of the antenna, whereby the antenna forms a transmission line along the length of the band, between the poles of the antenna and the ground plane.

According to the present disclosure, a band or a strip may be defined as having the length dimension greater than the width dimension, and the width dimension greater than the thickness dimension.

Furthermore, the length of the band of dielectric material described herein may be between 115 and 260 mm; the width may be less than 15% of the length dimension; and the thickness dimension may be less than 15% of the width dimension.

Two metallic strips may be arranged on a first side of the dielectric material band, wherein each metallic strip functions as a pole of an elongated antenna formed in the wristband. Furthermore, the metallic strips may have a dimension along the length dimension of the antenna greater than the width of the corresponding metallic strip.

Also, the ground plane may be a conducting surface comprising, for example, a coat of a conducting metallic material (such as, for example, copper), the ground plane being arranged on the side of the dielectric material band opposite to the first side, and wherein the ground plane may partially or totally cover the side where it is arranged.

Also, the two sides of the dielectric material band may be insulated from each other. For example, the thickness dimension of the dielectric material may be free of any connection between the two opposite sides of the band, thus insulating each side, and simplifying the manufacturing of the wristband.

The integrated circuit may feed the two metallic strips in a balanced mode, i.e. , the two poles of the antenna being fed carrying equal but opposite voltages. Therefore, by feeding the two metallic strips in such a way, an elongated antenna is formed between the two metallic strips (which function as poles of the antenna) and the ground plane, the antenna functioning as a transmission line, wherein, when in use, the transmission line is able to send a wave signal along the poles of the antenna, between the poles and the ground plane.

As a result, the antenna provides a wide angular operational range, which overcomes the efficiency decrease of widely used dipole and patch antennas, when the wristband is close to a high loss substrate, such as the human body, i.e., when the user is wearing the wristband, liquids, etc. The radiation pattern of the presently disclosed antenna may be modified, for example may be widened or narrowed in the direction of the axis of the wristband, thus improving or worsening its radiation lobes in such direction or in other directions. For example, a design may comprise the two poles with the same widths and lengths, thus maximizing its radiation lobes in directions parallel to the direction of the axis of the wristband. The radiation pattern may be modified by designing or determining the relative widths and lengths of the two poles.

In use, the band forming the wristband is wound in a ring and placed around the wrist of a user. In the present specification, the expression “axis of the wristband” is defined as the axial direction of the ring formed by the band. This direction coincides, in use, with the longitudinal direction of the arm of the user.

Furthermore, in use, this results in the lobes radiating outwards of the wrist of the user, thus minimizing the radiation of the antenna in the direction towards the wrist of the user and making the most of the generated signal (i.e., avoiding parts of the signal being absorbed by the user’s body).

The enhancement of the angular operational range of the antenna increases the probability of detection across RFID portals and identification spots by enabling a higher range of communication between the wristband and reader antennas placed on the ground or on a ceiling, where no other obstacles can block the communication between the reader and the wristband, thus substantially increasing the system uptime.

Furthermore, compared to other wristbands using dipole type antennas attached to a hanging ultra-thin band (wherein the wristband itself is usually made of thin and elastic plastic bands), the wristband disclosed herein may be much more resistant to mechanical stress and may have a much longer expected life cycle, at the expense of comfort. That is, the dielectric material used in the present disclosure may be more rigid than the other wristbands described above.

According to an example, the wristband may further comprise a second elongated antenna on the first side of the band, wherein the first elongated antenna is arranged along a first part of the length of the band, and the second elongated antenna is arranged along a second part of the length of the band.

The two different parts of the length of the band may be arranged along the band such that the gap between the two corresponding antennas is of between 0.5 and 15 mm.

Furthermore, the two antennas may be arranged such that the respective poles are arranged along in opposite directions along the length of the band.

The poles of each antenna are connected to the corresponding IC at their end that is adjacent the gap between the two antennas. That is, the two antennas are arranged in such a way that the transmission line formed by each antenna radiates away from the gap.

By arranging the two antennas in two different parts of the band, the respective radiation lobes may not interfere with each other, and the overall angular coverage of the wristband (i.e., the sum of the coverage of both antennas) may be increased. Therefore, the system becomes redundant in a way that, when one antenna is blocked by, for example, a body part of the user, the other one may still radiate outwards from the body of the user, thus enabling a continuous communication of the wristband with a reader over time.

According to another example, the integrated circuit may be configured to feed both the first and the second antenna, by using, for example, a microchip with dual- differential antenna ports.

More precisely, the first antenna may be fed by a single integrated circuit, connecting the integrated circuit terminals to each pole of the first antenna. In a similar manner, the second antenna may also be fed by a single integrated circuit, through two terminals of the circuit each connected to a pole of the second antenna.

Alternatively, a dual-differential port integrated circuit may be used to feed both the first and the second antenna, the dual port integrated circuit comprising four terminals, each connected to the first and second antenna respectively. In an example, either a single integrated circuit per antenna or a dual port integrated circuit for the two antennas may also be arranged in an area of the band between the two antennas. This way, the surface of the band may be maximized to be covered by each antenna, and the connectors connecting each pole to the respective port of the integrated circuit may be minimized, avoiding interference with the radiation lobes of the antennas.

In another example, the integrated circuit or circuits may feed each antenna in a balanced mode, i.e., the two poles of each antenna being fed carrying equal but opposite voltages.

According to another example, the two poles of each antenna may have the same length, and the poles of the second antenna may have the same length as the poles of the first antenna.

In this example, the radiation maxima of the radiation lobes of the antennas may be in directions nearly parallel to the axis of the wristband. More specifically, in use, the wristband may be arranged as a ring, and thus it can be modelled as a hollow cylinder: therefore, in use, in this case, the axis of the wristband would correspond to the width dimension of the wristband.

For example, in the case of a user wearing the wristband and standing upright with his/her arms straight, hands pointing towards the ground, most of the radiation of the antennas would occur towards the ceiling and towards the ground.

Above all, the efficiency of the system may improve because the wristband has a much larger angular range and a higher persistence, i.e. the time in which the wristband may not be detected by the system (by, for example, a reader device) may decrease due to the use of two antennas.

This way, each antenna functions as two transmission lines formed between each of its two poles and the ground plane. These transmission lines consist of two stubs (the two poles of the antenna) disposed in parallel between each other and connected throughout the integrated circuit. Therefore, each antenna can be modelled as the series connection of the two stubs, its input impedance being:

Z_a = ZTL1 + ZTL2

Wherein Z_a is the antenna input impedance, ZTLI is the input impedance of a first stub and ZTL2 is the input impedance of a second stub.

When designing a wristband, according to the present disclosure, with a specific thickness of the dielectric material band (i.e., the substrate of the antenna), the stubs length and width can be tuned to provide the required complex impedance for the conjugate, thus matching the impedance of the integrated circuit used to feed each antenna, thus maximizing the power transfer between the integrated circuit and the antenna connected therein. The matching may be such that it complies with the following, wherein Zic* is the complex conjugate of the impedance of the integrated circuit:

Z_a = Zic*

Furthermore, the stubs can be open-ended, short-ended (which adds a miniaturization factor of 2 to the required size of the stubs), or loaded with any other intermediate value load.

A list of exemplary commercially available integrated circuits used herein may be Alien Higgs-4, Alien Higgs-EC, Alien Higgs-9, Impinj Monza 4i, Impinj Monza R6, NXP UCODE 8, NXP UCODE 9.

In another example, the dielectric material may be a synthetic polymer material. More specifically, in order to reduce the manufacturing cost, synthetic polymers may be used, which, when the dielectric band is manufactured with a thickness ranging the previously described values, may also render the dielectric material band flexible, in order to be bent when the wristband is in use, arranged around the wrist of the user, forming a ring. More specifically, for example, when the user wears the wristband, the band may be wound forming a ring, wherein the first side of the band is the outer side of the ring.

When choosing the material of the substrate, there is always a trade off between cost, performance and antenna size. In this sense, artificial polymers are cost- effective. Requiring a minimum reading range for a specific application will also need a dielectric material with low losses. However, even though some polymers present low dielectric losses, which enhances the antenna radiation efficiency, they also have low permittivity, therefore, not helping in the antenna miniaturization. Thus, when imposing strict size constraints to the antenna design, like in the wristband according to the present disclosure, wherein two antennas may be enclosed in a thin band of fixed width and length, additional antenna miniaturization can be achieved. Therefore, the antenna design of the present disclosure allows reducing the antenna size to the half, and it enables embedding two antennas in a single wristband using a low-cost substrate.

A list of low-cost and low-loss polymers may be the following: Expanded Polyvinyl Chloride, Silicon, Polyethylene, Polystyrene, Polycarbonate, Tetrafluoroethylene.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of the present disclosure will be described in the following, with reference to the appended drawings, in which:

Figure 1 depicts an example of the wristband mounted to be used around the wrist of a user, according to the present disclosure.

Figure 2 depicts an example of the wristband extended flat, according to the present disclosure.

Figure 3A and 3B show radiation diagrams of an example of the wristband according to the present disclosure.

DETAILED DESCRIPTION OF EXAMPLES In figure 1 , an example of a specific embodiment of the presently disclosed wristband 1 is presented, arranged as a ring to be wrapped around the wrist of a user. The wristband 1 shown in figure 1 comprises a low-cost low-profile flexible tag antenna design to be used in UHF RFID human identification, arranged on a dielectric material band 20. The antenna design comprises two antennas 101 and 102 arranged on top of a first surface of the dielectric material band 20, wherein the antennas 101, 102 are each connected to an integrated circuit (IC) 21 , 22 respectively. The integrated circuits feed the antenna in order to emit a radiowave signal (in this example, a signal within the UHF band) to be read by an RFID UHF reader, the integrated circuits being, in this example, Alien Higgs-4 model integrated circuits. The Alien Higgs-4 ICs have been selected for this example because of their high sensitivity and availability. Furthermore, each antenna comprises two radiating poles 101A, 101 B, 102A, 102B formed by a copper strip each, arranged along the length dimension of a first surface of the dielectric band 20.

Also, as seen in figure 1 , the wristband 1 further comprises, on the band 20 surface opposite to the surface where the two antennas are arranged, an inner conductive sheet 30, in order to partially isolate the radiation of the radiating elements from the human arm. The conductive sheet 30 also works as a conductor of waves originated by the antennas, thus forming two transmission lines between the inner conductive sheet 30 and each pair of radiating poles 101A-102B, when connected to their respective ICs 21 , 22. In this example, the conductive sheet 30 is a copper sheet which covers all of the surface of its side of the dielectric band 20, thus maximizing the size of the antennas on the surface of the wristband.

By forming the two transmission lines with two antennas disposed symmetrically along the length dimension of the dielectric band 20 of the wristband, the visibility of each antenna is highly improved. More specifically, in use, when the link between a first antenna and a reader is hindered, the link between the second antenna and the reader may still be available.

In order to decrease the cost of manufacturing of any device comprising a substrate material, plastic materials are usually chosen for the substrate. In this example, the material of the dielectric band is TEFLON. More precisely, TEFLON has low losses, which improves the radiation efficiency of each antenna; flexibility, which allows the wristband to be easily folded around the human arm; and it has a low cost. The specific electrical properties of TEFLON are the following: electrical permittivity between 2.0-2.1 and loss tangent of 0.00028 measured at 3 GHz.

Figure 2 shows two views 1A, 1B of the same wristband 1 of the example of figure 1, when it is deployed on a flat surface, a first view 1A (top view) showing the length and width dimensions of the dielectric band, and a second view 1 B (side view) showing the length and thickness dimensions of the dielectric band, in a cross-section view of the band. As it can be seen, in this example, each element of the wristband 1 has the following dimensions: the thickness of the dielectric band 20 is H = 1 mm, the width of the dielectric band 20 is W = 30 mm, the space between the two metallic strips which form each radiating poles 101A-102B is W2 = 10 mm, the width of each radiating poles 101A-102B is wi = W3 =10 mm the length of the dielectric band 20 is L = 240 mm, the length of the copper strips forming the radiating poles of each antenna 101A to 102B is h = U = 110 mm, the space in between the two antennas is I2 = 3 mm , and the width of the ports connecting the antennas to the ports of each IC, which is the same width as the ICs themselves is I3 = 1 mm. As it may be understood, the dimensions of the width of each radiating poles 101A-102B, wi and W3 may be varied such that their relative dimensions provide different radiation patterns and different antenna input impedance. The length of the copper strips forming the radiating poles of each antenna 101 A to 102B, and may further be varied such that their relative dimensions provide different radiation patterns and different antenna input impedance.

These dimensions are specifically designed for the impedance matching of the two antennas when each pair of radiating poles 101 A to 102B are connected to two Alien Higgs-4 integrated circuits 21 , 22 as used in the present example. In the present example, the most determinant parameter when tuning the impedance of the antenna is the length of the radiating poles, otherwise known as stubs (i.e., , Y

The wristband of the present example is designed to meet the constraint of having a limited width W of 30 mm, in order to achieve a wide enough opening of the radiation lobes of each antenna when arranged around a user’s wrist, whilst being comfortable to wear for the user. The width (l/l/) and thickness (/-/) of the dielectric substrate both influence the antenna gain, in such a way that the higher the product Wx H, the larger the antenna gain will be. Furthermore, in this example, the dimensions wi and W2 are designed to maximize the antenna gain as well.

Figures 3A and 3B depict two cuts (in the direction of the W dimension of the dielectric band of the example of the previous figures) of the radiation pattern of the wristband of the examples of figures 1 and 2. More precisely, figure 3A corresponds to the plane that divides the wristband symmetrically (defined by >=0°), and figure 3B corresponds to the plane perpendicular to the plane of figure 3A (i.e., (p=90°). Both figures show that, in this example, the radiation of the wristband is maximized towards the direction of the width dimension of the band (seen in figure 3A), while power radiated in the direction of the length dimension of the band is drastically reduced. Therefore, this wristband redirects the field radiation towards the floor and ceiling, when the user is standing or walking with his/her arms parallel to the body.

Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and/or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

1. A wristband for identifying a user, the wristband comprising:

- A band of dielectric material with a length dimension, a width dimension and a thickness dimension;

On a first side of the band, the band comprises an integrated circuit and two metallic strips;

Wherein,

The integrated circuit is connected to the two metallic strips and is configured to feed the strips in an unbalanced mode;

2. A wristband according to claim 1 , further comprising a second elongated antenna on the first side of the dielectric material band, wherein the first elongated antenna is arranged along a first part of the length of the dielectric material band, and the second elongated antenna is arranged along a second part of the length of the dielectric material band.

3. A wristband according to claims 1 or 2, wherein the integrated circuit is configured to feed both the first and the second antenna, in a balanced mode.

4. A wristband according to any of claims 1 to 3, wherein the two poles of each antenna have the same length, and wherein the poles of the second antenna have the same length as the poles of the first antenna.

5. A wristband according to any of claims 1 to 4, wherein the dielectric material is a synthetic polymer.

6. A wristband according to any of claims 2 to 5, wherein the band is wound forming a ring, and the first side of the band is the outer side of the ring.

7. A wristband according to any of claims 3 to 6, wherein the integrated circuit is arranged in an area of the band between the two antennas.

8. A wristband according to any of claims 1 to 7, wherein the dielectric material band has a thickness dimension less than 15% of the width dimension.

9. A wristband according to any of claims 1 to 8, wherein the band comprises a gap between the two antennas, and the poles of each antenna are connected to the corresponding integrated circuit at the end of each antenna that is adjacent the gap between the two antennas.

10. A wristband according to claim 9, wherein the gap between the two antennas is between 0.5 and 15 mm.

11. A wristband according to any of claims 2 to 10, further comprising a second integrated circuit is connected to the second elongated antenna and configured to feed the second elongated antenna in an unbalanced mode.