RFID tags with b-field focusing

Abstract

A radio frequency identification (RFID) tag includes circuit elements that result in a resonant frequency that is different from an excitation frequency of an RFID reader. When stacked with other similar RFID tags, the RFID tag directs a magnetic flux density field (B field) through the stack to power each of the tags in the stack. Thus, the B-field is collimated in a manner that increases the sensitivity (read range) in one dimension (along the chip stack) while limiting the sensitivity in two lateral dimensions, thereby providing a precise spatial resolution of each tag with respect to its position on the game table.

Description

[0001] Cross-reference of related applications

[0002] This application claims priority to U.S. Application No. 18 / 817,799, entitled "RFID Tags with B-Field Focusing," filed August 28, 2024, which claims the benefit of U.S. Provisional Application No. 63 / 579,645, entitled "RFID Tags with B-Field Focusing," filed August 30, 2023, which is incorporated herein by reference. Background Technology

[0003] This invention relates to games, and more particularly, to radio frequency identification (RFID) tags that, when placed (e.g., stacked) on a game table, focus a transmission field via a tag antenna to power a response from each of the tags on the table.

[0004] Unless otherwise indicated herein, the methods described in this section are not prior art to the claims of this application and are not considered prior art by virtue of their inclusion in this section.

[0005] A game generally refers to a competitive match between two or more entities (e.g., people) using game pieces or coins. Using electronic devices to determine or track the position or type of game pieces is generally more efficient than determining or tracking them manually. Game types include non-coin games and coin games.

[0006] Regarding token-based games, real-time tracking of token positions on gaming tables has the potential to revolutionize the industry by providing value management and enhanced security. Linking this data to specific players allows casinos to create accurate player profiles, while alleviating the routine tasks that game administrators would otherwise require years of experience to master.

[0007] Traditional RFID systems have attempted to address the challenges of the gaming market, but with limited success. In a typical RFID system, the excitation antenna defines a "working volume" within which the energy projected by the antenna is sufficient to power the RFID tag. This "working volume" is generally omnidirectional, with poorly defined boundaries when radio frequency (RF) power is the only option for adjusting the read range. However, this extends the read range in all directions, introducing crosstalk errors when multiple antennas are close together. Typical RFID products on the market suffer from several drawbacks, including being limited to discrete points (referred to as "coin placement points" in the context of coin games), having a limited coin stacking height, difficulty in distinguishing neighboring points, and higher than acceptable read errors.

[0008] These limitations restrict the available technology to games where the points are sufficiently separated or to identifying counterfeit game coins only before they are used on the game table.

[0009] Several patents by the inventors of this invention address these shortcomings, as demonstrated in U.S. Patents Nos. 8,395,525, 8,395,507, 8,432,283, 9,984,528, 11,346,914, and 11,630,964. These patents work together to track individual game tokens on a game table. To distill the essence of these patents for the design of RFID tags, three fundamental concepts work together. The first concept is the existence of a coupling capacitor that extracts sufficient energy from the excitation field to power the RFID tag. The second concept is tuning the resonance of each tag to a frequency higher than the excitation frequency such that any coupling between tags will shift the resonance toward the excitation frequency. The third concept is shaping the B-field generated by the excitation antenna.

[0010] The embodiments described in these earlier patents primarily address the third concept (shaping the B-field) by using a ferrite core or other high-permeability material in each label. This ferrite core collimates the B-field using material properties to increase flux density in a specific manner.

[0011] Overview of Ferrite Cores

[0012] The construction of ferrite core game tokens is based on non-resonant coupling induction similar to that of a typical transformer. This allows RFID technology to utilize near-field coupling and additional benefits, including high-performance data transfer between the reader and the tag, dynamic beamforming of the H-field as the tag is added to or removed from the excitation field, and the ability to resolve the tag's spatial coordinates within the excitation field.

[0013] The quality factor (also known as the "Q factor" or "Q") is a dimensionless parameter that compares the time constant of the decay of the amplitude of an oscillating physical system with its oscillation period. Equivalently, it compares the frequency of the system's oscillation with the rate at which the system dissipates its energy. A higher Q indicates a lower rate of energy dissipation relative to the oscillation frequency, and therefore the oscillations disappear more slowly.

[0014] In RFID circuitry, Q is a measure of the desired “quality” in a well-tuned circuit or other resonator. More specifically, when an RFID tag is driven by a sinusoidal excitation signal, its resonant behavior is strongly dependent on Q. A resonant system responds much more strongly to frequencies close to its natural frequency than to other frequencies. RFID tags with a high Q resonate with a larger amplitude (at the resonant frequency) than RFID tags with a low Q factor. The amplitude of the resonant response affects the read range. To improve sensitivity and read range, most existing RFID tags have relatively high Q. As a concrete example, many existing RFID tags have a Q between 10 and 20.

[0015] However, when multiple tags are close together, they interact. This interaction alters their resonant operating frequency. This interaction results in multiple resonances at the undesired frequency instead of a single resonance at the desired frequency. Therefore, when tags are close together, the tags are not powered and / or data is not successfully exchanged. Various methods can be used to mitigate this interaction, but these strategies typically reduce read range. Compensating for this reduction in read range by increasing the reader's power output is feasible, but not always effective.

[0016] Ferrite core tags are designed to meet this requirement for reading closely approaching RFID tags within an acceptable reading range.

[0017] In this ferrite core-based invention, the resonance of each individual tag is set to approximately 50 MHz (compared to 13.56 MHz), with the inductive coupling of multiple tags altering this resonance. The reader is designed to read individual tags even when their resonance is much higher than 13.56 MHz, due to their proximity to the excitation antenna. As more tokens are added, the overall resonance of the multiple tokens decreases due to the tight magnetic coupling of the ferrite core, thus shifting closer to 13.56 MHz. Therefore, as the number of tags increases, the read range expands, and the lower Q of the excitation antenna is offset by the inherent efficiency of the ferrite core. Consequently, despite tag-to-tag coupling, the system operates at low power over a significant read range.

[0018] Equally important is the ability of ferrite to guide the H-field away from adjacent tags, as this provides spatial resolution and allows specific tags to be assigned to specific excitation antennas.

[0019] In the case of coin-based games, an extreme scenario can be observed: if a player wins and is considered "hot" by other players, then after one person places coins, others quickly follow suit with the same or similar coin placements. This results in high coin stacks being surrounded by other high coin stacks. Certain challenges involve legal coin placement points being very close together, and the number of coins at any given point can be very large, with stacks often exceeding 30 coins.

[0020] Another important feature of almost all RFID tags is the presence of a protective Zener diode, which protects the rest of the circuit from overvoltage. This protective diode is designed to burn off excess energy as heat, which is a good idea in most applications, but has limitations when tags are stacked. The ferrite core system adds passive components to achieve two purposes. The first is achieved by using an inductor to tune the tag's built-in capacitance. (Many tags have built-in capacitance to resonate with the antenna coil; tags with different capacitance values ​​or no capacitance at all can be purchased.) The second is achieved by using a capacitor to lightly couple only the energy needed to power the tag to the antenna, thereby greatly reducing the effect of the Zener clamping diode and allowing excess energy to power other tags instead of being dissipated as heat. Summary of the Invention

[0021] Embodiments of this disclosure pertain to RFID tags that use resonant coupling to focus the B-field through tag stacking to improve detection.

[0022] Compared to embodiments using ferrite cores, the embodiments described herein collimate the B-field in a novel and unexpected manner without requiring high-permeability materials. Specifically, the embodiments described herein use capacitors across the antenna windings to carefully tune each tag to produce a resonant coupling effect. This resonant coupling effect results in resonance that, upon approaching other similarly tuned tags, produces a “lens effect” that collimates the B-field in a manner similar to an optical lens focusing energy in one (desired) dimension while minimizing the effects in other directions.

[0023] This resonant coupling is a novel and unexpected result of multiple carefully tuned RFID tags interacting in a constructive manner.

[0024] Furthermore, this resonant coupling differs from the non-resonant coupling induction of existing ferrite core technology.

[0025] The potential benefits of the embodiments described herein include reduced commodity costs when manufacturing labels due to the elimination of ferrite materials, simplified manufacturing processes, improved performance due to stricter manufacturing tolerances for key components, and enhanced aesthetics (omitting exposed ferrite allows for a variety of decal types and designs).

[0026] According to an embodiment, a radio frequency identification (RFID) tag includes: RFID tag electronics; an antenna coupled to the RFID electronics; and a circuit element connected in parallel with the antenna, wherein the circuit element includes a capacitor. The RFID tag has a resonant frequency caused by the antenna and the circuit element, wherein the resonant frequency of the RFID tag is higher than the excitation frequency of a transmission generated by an RFID reader. The RFID tag is one of several RFID tags grouped together, wherein the group of RFID tags shapes the magnetic flux density field of the transmission generated by the RFID reader through the group of RFID tags. The group of RFID tags has a resonant frequency that is considered individually attributable to the resonant coupling and is lower than the resonant frequency of each of the RFID tags. The transmission generated by the RFID reader powers the RFID tag electronics via the resonant coupling.

[0027] The following detailed description and accompanying drawings provide a further understanding of the nature and advantages of embodiments of the present invention. Attached Figure Description

[0028] Figure 1 It is a perspective view illustrating an example of collimated B-fields under resonant coupling effect.

[0029] Figure 2 This is a block diagram of RFID tag 200.

[0030] Figure 3 This is a block diagram of RFID tag 300.

[0031] Figure 4 This is a block diagram of RFID system 400.

[0032] Figure 5 It is a graph 500 showing the transmission loss of the resonant coupled game coin stack.

[0033] Figure 6 It is a graph 600 showing the transmission loss of the resonant coupled game coin stack.

[0034] Figure 7 It is a graph 700 showing the transmission loss of the resonant coupled game coin stack.

[0035] Figure 8 It is a graph 800 showing the transmission loss of different types of game currency.

[0036] Figure 9 It is a graph 900 showing the transmission loss of a resonantly coupled stack of game coins, where the coupling capacitor is replaced by a resistor.

[0037] Figure 10It is a graph 1000 showing the transmission loss of a resonant coupled game coin stack, where the coupling capacitor is replaced by an inductor. Detailed Implementation

[0038] This document describes techniques for constructing RFID tags using resonant inductive coupling. In the following description, numerous examples and specific details are set forth for purposes of explanation in order to provide a thorough understanding of the invention. However, those skilled in the art will understand that the invention as defined by the claims may comprise only some or all of the features of these examples, or a combination of some or all of the features of these examples with other features described below, and may further include modifications and equivalents of the features and concepts described herein.

[0039] The following description details various methods, processes, and procedures. Although specific steps may be described in a certain order, this order is primarily for convenience and clarity. A specific step may be repeated more than once, may occur before or after other steps (even if those steps are described in a different order or in a different manner), and may occur concurrently with other steps. A second step should only be performed after the first step if it must be completed before starting the second step. This should be explicitly stated when the context is unclear.

[0040] In this document, the terms “and,” “or,” and “and / or” are used. These terms should be interpreted as inclusive. For example, “A and B” could mean at least: “both A and B,” or “at least both A and B.” As another example, “A or B” could mean at least: “at least A,” “at least B,” “both A and B,” or “at least both A and B.” As yet another example, “A and / or B” could mean at least: “A and B,” or “A or B.” When an exclusive OR is desired, this should be explicitly stated (e.g., “A or B,” or “at most one of A and B”).

[0041] In this document, the terms “RFID tag,” “RFID game tag,” “RFID game coin,” and “game coin” are used. These terms should be interpreted as broadly synonymous. (More precisely, “RFID game coin” can refer to the integrated circuit component of an “RFID tag,” which also includes additional components such as antennas, rigid housings, etc. However, this document primarily pertains to the broad use of these terms.) RFID tags generally respond to radio frequency signals from an RFID reader using their serial number or other identifier, allowing the RFID reader to access an inventory of nearby RFID tags. In a game context, RFID game tags may be placed on the game table, removed from the game table, or moved around the game table, depending on various game rules. RFID game tags may also be used in the context of game coins, where the tag can be marked with a value identifier.

[0042] To provide comparative examples, this patent disclosure includes a summary description of existing RFID tags based on using a ferrite core as a baseline to shape the B-field to illustrate the remarkable performance of the new resonant coupling embodiment. Detailed implementations of the resonant coupling embodiment have multiple degrees of design freedom, including (but not limited to) the geometry of the antenna (size, shape, number of turns), capacitor values, and the spacing between tags (e.g., the thickness of each coin). While the embodiments described in this document focus on their application to the design of RFID-enabled 39 mm coins, resonant coupling is a physical phenomenon (never documented to date) and is not limited to a single geometry. An embodiment of a 43 mm coin would differ from the design of a 39 mm coin. Similarly, this concept can be applied to "plaque coins" of different sizes and thicknesses.

[0043] Overview of resonant coupling

[0044] Unlike flux density concentration enhanced by the presence of ferrite materials, this disclosure is based on the physics of resonant inductive coupling (also known as magnetic phase synchronization coupling or resonant coupling). This phenomenon utilizes the inductive coupling between the source and the secondary load. Resonant inductive coupling is the near-field wireless transfer of electrical energy between magnetically coupled coils, which is part of a resonant circuit tuned to resonate at the same frequency as the drive frequency on the tag. Specifically, when the secondary load is tuned to resonate at the excitation frequency, the energy transfer efficiency between the drive coil and the receiving coil is significantly improved. To maximize this energy transfer efficiency, the resonant circuit has a very high Q. This improved energy transfer efficiency shapes the B-field, the net effect of which is to guide the B-field in a controlled manner.

[0045] Resonant inductive coupling (RIC) was first demonstrated by Nikola Tesla in 1894 and has been successfully used by others in a range of applications, including Marin Soljačić of MIT’s famous demonstration of wireless power transmission in 2007.

[0046] Regarding wireless power transfer, traditional wireless charging technology uses a pair of coils (one on a charging pad or base and one in the device to be charged) with a small air gap between them. Work by Soljačić and researchers from Aalto University in Finland (published in Physical Review, July 20, 2023) shows that careful tuning of the antenna loop can achieve 80% power transfer efficiency while minimizing radiation losses from the several-inch air gap. Further work is underway to apply this idea to charging vehicles in motion. In all cases, the target application is long-distance trickle charging.

[0047] Regarding RFID, resonant inductive coupling has also been (in very limited and specific use cases) applied to data transmission from individual active circuits (e.g., implantable medical devices) and passive circuits (e.g., passports and contactless smart cards). However, all these applications use established technologies outlined in numerous manufacturers' applications (e.g., "RFID Coil Design," Microchip application 00678b.pdf). Specifically, the secondary circuit is tuned to an excitation frequency with a very high Q (e.g., 13.56 MHz) to maximize read range sensitivity. All known current applications (as described) are limited by the same problem that plagues all RFID applications attempting to read multiple closely spaced tags in an excitation field: the tags will couple and detune to a point where the tag's resonant frequency falls outside the RFID reader's frequency band and is therefore not read.

[0048] Previous inventions (centered on a ferrite core) overcame this fundamental limitation by improving the energy transfer efficiency between the excitation antenna and the RFID tag. This allows for individual tag resonant detuning, thereby making it insensitive to resonant shifts caused by coupling.

[0049] Resonant Coupling Example

[0050] The embodiments described in this disclosure utilize tight coupling between a source (in this case, an excitation antenna) and a receiver (in this case, one or more RFID tags) (similar to a coreless transformer). However, there are several important differences from typical RICs used for long-range charging or reading of smart cards. The first difference is that the embodiments use the efficiency of the excitation channel to transmit information back and forth between multiple RFID tags rather than a single charging coil / tag. The second difference is that the embodiments operate with a well-defined distance between the excitation coil and the tag. The third difference is that the tags are uniformly spaced in the embodiments. The fourth difference is that the embodiments have a passive tag antenna design fundamentally different from conventional RFID tags. The fifth difference is that the embodiments utilize coupling between tags to focus the B-field to further improve energy and data transmission efficiency. (It should be noted that a given embodiment may have one or more of the above differences from a typical RIC.)

[0051] As previously mentioned, the embodiments described herein incorporate several features from earlier patent applications filed by the inventors of this invention. One similar feature is that the tag design is tuned to a (higher) suboptimal frequency so that the reader can read a single tag or multiple tags, even though the resonance of multiple tags has been shifted due to coupling between the tags. Another similar feature is the use of a series capacitor to slightly couple the tag antenna to the RFID tag to limit the effects of overvoltage protection.

[0052] When compared to earlier work based on ferrite cores, the embodiments described in this disclosure have a key difference: tight coupling between the excitation antenna and multiple tags is achieved without the need for ferrite (or other flux-concentrating materials). This tight coupling is achieved by tuning the tag antenna across the antenna loop using an additional capacitor. This disclosure describes an embodiment that tunes this LC (inductor-capacitor) circuit in a manner that shapes the B-field. Furthermore, multiple tags can still be read even when this tuning is to a frequency higher than the reader's peak sensitivity (e.g., 24 MHz) (where the reader is still able to read a single tag, largely due to its proximity to the excitation antenna), because the coupling between the tags has shifted (e.g., reduced) the resonant frequency of interest to near the primary excitation frequency (e.g., 13.56 MHz).

[0053] Due to resonant coupling, when multiple tags are similarly tuned (e.g., to 24 MHz), the B-field is shaped (much like an optical lens) to achieve highly collimated flux. Therefore, even though this coupling between multiple tags has shifted the tag's resonant frequency, the embodiment can greatly improve the efficiency of energy coupling and robust energy (and data) transmission, thereby collimating the B-field in a way that allows for precise determination of the spatial coordinates of each tag.

[0054] Figure 1 It is a perspective view illustrating an example of collimated B-fields under resonant coupling effect. Figure 1 The system includes an antenna 102 and several RFID tags 104 (individually 104a to 104f). The antenna 102 can be implemented in a game table (not shown), with the RFID tags 104 on the table for gaming purposes. For a primary excitation frequency of 13.56 MHz, the RFID tags 104 can be sub-tuned to, for example, 24 MHz. The RFID tags 104 are shown without their housings to demonstrate how the thickness of each tag provides a consistent (e.g., uniform) spacing between the tags and how the antenna and other components generate resonant coupling to collimate the B-field 106 (shown as a wavy vertical line). Surprisingly, this resonant coupling collimates the B-field in a manner similar to that provided by ferrite core RFID tags, but without the need for a ferrite core. The resulting increased efficiency and proximity of the tags to the excitation field allow for sub-optimal tag tuning, thereby eliminating sensitivity to coupling between multiple tags.

[0055] Clearly, a uniform tag geometry increases performance predictability, but other embodiments can be used in other applications. The characteristics of the components used can be tailored to the needs of each additional application.

[0056] Figure 2This is a block diagram of RFID tag 200. RFID tag 200 includes tag electronics 202, series circuit elements 204, parallel circuit elements 206, and an antenna 208. RFID tag 200 may also include a housing (not shown) to give RFID tag 200 various sizes of game tokens, such as circular, rectangular, etc. As a specific example, the housing may provide an RFID tag 200 with a circular external size of 39 mm in diameter.

[0057] Tag electronics 202 generally implements the RFID functionality of RFID tag 200. Tag electronics 202 can be provided by existing commercially available RFID tag electronic integrated circuits. As a specific example, tag electronics 202 may correspond to the ICODE ILT-M RFID integrated circuit from NXP Semiconductors that implements the ISO 18000-3 Mode 3 RFID standard.

[0058] The series circuit element 204 generally provides the tag electronics 202 with the power received at antenna 208 from the RFID reader (not shown) to generate the excitation signal. The tag electronics 202 includes overvoltage protection circuitry (not shown; e.g., a Zener diode) to protect other circuitry of the tag electronics 202 from overvoltage conditions. In typical RFID use cases, the RFID reader intends to read only a single RFID tag, therefore the RFID tag electronics 202 includes protection circuitry to dissipate excess energy received from the reader as an excitation signal as heat. However, in use cases such as those where the RFID reader can read multiple RFID tags, the series circuit element 204 is used to lightly couple the tag electronics 202 to the energy received by antenna 208. Therefore, the tag electronics 202 receives only a portion of the total energy from the RFID reader, and the remaining energy can be received by other nearby RFID tags. In embodiments, the series circuit element may include a capacitor called a series capacitor. As an example, the series capacitor may be 3.9 pF. The series circuit element 204 may also include other circuitry, as discussed below.

[0059] Parallel circuit element 206 typically includes a capacitor operating as a tuning capacitor, which, in conjunction with antenna 208, results in the resonant frequency of RFID tag 200. For example, for a given antenna 208, the 22 pF capacitance of parallel circuit element 206 results in a 24 MHz resonant frequency for RFID tag 200. In this case, parallel circuit element 206 can be referred to as a parallel capacitor.

[0060] Antenna 208 typically receives read signals and other communications from an RFID reader. Antenna 208 is shown as a circular loop antenna with 5 turns, an outer diameter of 30.5 mm, and an inner diameter of 25.4 mm, making it suitable for use with RFID tags having a circular external dimension of 39 mm in diameter.

[0061] As further detailed below, the RFID tag 200 has a resonant frequency caused by the antenna 208 and the parallel capacitor 206, wherein the resonant frequency of the RFID tag is higher than the excitation frequency of the transmission generated by the RFID reader. Generally, the resonant frequency of the RFID tag 200 is between 1.5 and 2.2 times the excitation frequency of the transmission generated by the RFID reader. For example, the resonant frequency of the RFID tag 200 may be 24 MHz, and the transmission generated by the RFID reader may be 13.56 MHz. For a single RFID tag, this difference is considered inefficient; however, in a gaming environment, the proximity of the RFID tag 200 to the RFID reader means that the inefficiency in receiving signal power is still sufficient for the operation of the RFID tag 200.

[0062] However, when RFID tag 200 is one of several similar RFID tags that are grouped together, the group shaping is generated by the transmission of the magnetic flux density field of the group by the RFID reader. Due to resonant coupling, the group has a resonant frequency that is lower than the resonant frequency considered by RFID tag 200 itself.

[0063] In the context of gaming, "close" generally means that the RFID tag is located within a single defined game point. Typically, each game point is associated with an antenna connected to an RFID reader, and the RFID reader reads all RFID tags near that antenna (e.g., all RFID tags located within the corresponding game point). In a coin-based game example, the game table may have game points available for placing each coin (e.g., more than 100 game points).

[0064] In a game context, grouping generally means that RFID tags are grouped together within a bounded area and treated equally within a specific game environment. Generally, the bounded area corresponds to a game point, and grouping can be stacked (see...). Figure 1 Tags can be grouped into stacks or piles. Generally, tags in a stack completely overlap, but they can also partially overlap. As discussed above, grouping collectively leads to resonant coupling between RFID tags. Coupling is most efficient for stacks, but it is also true for piles, where efficiency increases with the amount of overlap.

[0065] Due to resonant coupling, the power transmitted by the RFID reader supplies power to the tag electronics 202 to perform RFID operations.

[0066] The size and configuration of the antenna 208 and the capacitance of the parallel capacitor 206 can be adjusted as desired to achieve different resonant frequencies of the RFID tag 200. Further example configurations of the antenna 208 and the parallel capacitor 206 are discussed below. Additionally, other components can be added to the RFID tag 200 as desired to change its resonant frequency.

[0067] Figure 3 This is a block diagram of RFID tag 300. RFID tag 300 includes tag electronics 302, a parallel capacitor 306, and an antenna 308. RFID tag 300 and RFID tag 200 (see...) Figure 2 Similarly, except that tag electronics 302 is customized according to the resonant coupling embodiment, while tag electronics 202 uses an existing commercially available RFID integrated circuit system.

[0068] More specifically, tag electronics 302 omits the overprotection circuitry (e.g., Zener diode) present in tag electronics 202. Therefore, series circuit element 204 is unnecessary in RFID tag 300. Furthermore, parallel capacitor 306 is incorporated as a component of tag electronics 302, rather than being a separate element like parallel capacitor 206. For example, capacitance could be provided by a metal layer deposited on a non-conductive film (also known as an RFID inlay). Antenna 308 is largely similar to antenna 208.

[0069] Similar to RFID tag 200, the parameters of the components of RFID tag 300, including parallel capacitor 306 and antenna 308, can be adjusted as desired to adjust the resonant coupling effect, including adjusting the resonant frequency of RFID tag 300. As further detailed below, the number of turns of antenna 308 and the capacitance of parallel capacitor 306 are inversely proportional; therefore, for a large number of turns, the capacitance of parallel capacitor 306 (or 206) can be attributed to the increase in inductance of antenna 308, which leads to a decrease.

[0070] Both RFID tags 200 and 300 utilize prior experience (e.g., U.S. Patent No. 11,346,914), where the improved efficiency of the modified B-field (whether generated by ferrite material or resonant inductive coupling) allows the RFID reader to operate regardless of the resonance variations caused by the coupling between tags. Although the degree of coupling between ferrite core (FC) tags and resonant inductively coupled (RIC) tags differs significantly, the result can still be used to achieve the desired goal of gaming applications, specifically, to correctly assign multiple tags to their respective antennas with sufficient spatial resolution to track individual coins on a gaming table. As a concrete example of coin-based gaming, a gaming table using RFID tags 200 or 300 can track individual coin placements at each of 100 or more coin placement points.

[0071] Figure 4 This is a block diagram of RFID system 400. RFID system 400 typically uses resonant coupling to game tokens (e.g., RFID tag 200) as described in this document (see...). Figure 2 ), RFID tag 300 (see) Figure 3 (etc.) operations. The RFID system 400 can be implemented in a game table. As a specific example of a game with game coins, the RFID system 400 can be implemented in a game table. The RFID system 400 includes several RFID antennas 402, several RFID tags 404, one or more RFID readers 406, and a control system 408. The RFID system 400 may also include (for brevity) other components not described in detail.

[0072] RFID antennas 402 (eight shown, 402a to 402h) are arranged at various locations on the game table. Generally, each of the RFID antennas 402 is associated with one of the game points on the game table. However, more than one RFID antenna may be associated with a single game point; for example, a large game point may have multiple smaller antennas instead of a single large antenna.

[0073] Each of the RFID tags 404 generally corresponds to the resonant coupled game tokens described herein, such as RFID tag 200, RFID tag 300, etc. The RFID tags 404 can be placed around the game table at various game points corresponding to the RFID antenna 402. Two groups of RFID tags, 404a and 404b, are shown.

[0074] One or more RFID readers 406 are connected to RFID antenna 402. (To reduce clutter in the figures, complete wiring to each of the antennas 402 is not shown.) Each of the one or more RFID readers 406 may be connected to more than one of the RFID antennas 402, for example, via a multiplexer or a switching network (not shown). In some embodiments, such as when the number of RFID antennas 402 is small or a single RFID reader operates fast enough in a given game environment, one or more RFID readers 406 may be a single RFID reader.

[0075] Generally, one or more RFID readers 406 (referred to as RFID reader 406 for simplicity) generate their excitation signals transmitted via RFID antenna 402; any of the RFID tags 404 receiving the excitation signals then communicates with the RFID reader according to its RFID protocol. As discussed above, each RFID tag 404 is tuned to a resonant frequency higher than the resonant frequency of the excitation signal generated by the RFID reader 406, but due to resonant coupling effects, the group of RFID tags 404 has a lower resonant frequency and is therefore more closely matched to the resonant frequency of the RFID reader 406. The excitation signal used for RFID transmission is typically 13.56 MHz, but similar results can be obtained using frequencies close to the excitation frequency (e.g., between 13 MHz and 14 MHz). As a specific example, the RFID reader 406 can generate a signal at 13.56 MHz and the RFID tags 404 can be tuned to 25 MHz; however, the group of RFID tags 404 will have a resonant frequency lower than 25 MHz, where the exact resonant frequency depends on the number of tags in the group, the arrangement of the tags in the group, etc. Furthermore, as Figures 5 to 10 As shown, the resonant frequency can include multiple resonant frequencies, with the embodiment using the strongest resonant frequency, which can also be the lowest resonant frequency. Depending on the sensitivity of the RFID reader, other embodiments may use other resonant frequencies as desired.

[0076] The control system 408 generally controls the operation of the RFID system 400. For example, the control system 408 may control the RFID reader 406 to send a read signal via the selected player in the RFID antenna 402. A subset of RFID tags 404 in the game point associated with the selected RFID antenna responds with their tag identifiers, and the control system 408 associates those tag identifiers with the game point associated with the selected RFID antenna. In this way, the RFID system 400 tracks the position of the RFID tags 404 on the game table. As another example, the control system 408 may control the operation of a multiplexer or switching network (not shown) to connect the RFID reader 406 to the selected player in the RFID antenna 402. A processor and memory implemented, for example, in a computer, may perform the functions of the control system 408.

[0077] The RFID system 400 can operate using other features described by the inventors of this invention in other patent applications. For example, the RFID system 400 can operate using the network analyzer system described in U.S. Patent No. 10,430,621. As another example, the RFID system 400 can operate using the antenna array system described in U.S. Patent No. 10,088,547. As another example, the RFID system 400 can operate using the network analyzer and controllable reactance network system described in U.S. Patent No. 11,630,964. As another example, the RFID system 400 can operate using the SPEEDscan system described in U.S. Patent Application No. 18 / 665,943, filed May 16, 2024, entitled "Determining the Locations of RFID Tags".

[0078] Performance characteristics

[0079] As discussed above, RFID tags 200 and 300 can be implemented as circular game tokens with a diameter of 39 mm. Furthermore, the external dimensions are not limited, and the shape and size can be adjusted as desired for other game environments. For example, the size of the token can be increased (e.g., to 43 mm) or decreased (e.g., to 35 mm). The shape of the token can be changed to, for example, a square or a rectangle. The thickness of the token can be changed, for example, increased (e.g., a decorative token, dominoes, or a tile) or decreased.

[0080] For a given gaming application, the size and shape of the tokens can be defined, but other variables can be adjusted to provide the desired resonant frequency for the resonant coupling effect. These design variables include antenna geometry (size, shape, number of turns, etc.), tuning that results in a given resonant frequency (e.g., the capacitance of the parallel capacitor and the inductance, capacitance, and resistance of other components), and the spacing between tags (e.g., the thickness of each token). The table and figures below explore these options.

[0081] Comparison between game currency types

[0082] The following paragraphs describe the performance differences between various game coin types. The experimental setup defines 0 dB loss as follows. The output port of the network analyzer is connected to a single-turn magnetic sensing loop with a diameter of 22 mm. The receive port of the network analyzer is connected to another single-turn magnetic sensing loop with a diameter of 22 mm. These loops are placed one above the other with a spacing of 0.7 mm between them.

[0083] As a baseline, we consider the transmission loss from bottom to top for various stack heights of game tokens without RFID circuitry. Between 10 MHz and 30 MHz, these tokens exhibit a generally constant transmission loss as the stack height increases. For example, a stack of 1 token has a transmission loss of approximately -6 dB at the top, a stack of 5 tokens has approximately -21 dB, a stack of 10 tokens has approximately -36 dB, a stack of 15 tokens has approximately -44 dB, and a stack of 20 tokens has approximately -50 dB.

[0084] As expected, for the ferrite core case, the transmission loss is lower than the baseline case. Between 10 MHz and 30 MHz, ferrite core coins exhibit a generally constant transmission loss with increasing stack height. For example, a stack with 1 coin has a transmission loss of approximately -4 dB at the top of the stack, a stack with 5 coins has approximately -14 dB, a stack with 10 coins has approximately -19 dB, a stack with 15 coins has approximately -22 dB, and a stack with 20 coins has approximately -26 dB.

[0085] Figures 5 to 6 This displays the transmission loss of a resonantly coupled coin used for comparison with baseline and ferrite core cases. It should be noted that this data was generated using a coin with only an antenna and parallel capacitor, without RFID electronics or series capacitors.

[0086] Figure 5 This is graph 500, showing the transmission loss of resonant coupled game coin stacks (1, 5, and 10 stacks). The x-axis is frequency in MHz, and the y-axis is transmission loss in dB. Line 502 shows the transmission loss of 1 game coin, line 504 shows the transmission loss of 5 game coins, and line 506 shows the transmission loss of 10 game coins.

[0087] Figure 6 This is graph 500 showing the transmission loss of resonant coupled game coin stacks (10, 20, and 30 stacks). The x-axis is frequency in MHz, and the y-axis is transmission loss in dB. Line 602 shows the transmission loss for 10 game coins, line 604 shows the transmission loss for 20 game coins, and line 606 shows the transmission loss for 30 game coins.

[0088] Line 502 (1 coin) exhibits a single peak at approximately 25 MHz, indicating that this frequency is the coin's resonant frequency. The number of peaks increases as more coins are added to the stack. For example, line 504 (5 coins) exhibits 2 peaks, with the lowest peak at approximately 17 MHz. Line 506 (10 coins) exhibits 5 peaks, with the lowest peak at approximately 15 MHz. Line 604 (20 coins) exhibits 8 peaks, with the lowest peak at approximately 14 MHz. Line 606 (30 coins) exhibits 13 peaks, with the lowest peak at approximately 13.5 MHz. (Note that there may be additional peaks above 30 MHz that are not shown.) Additionally, the lowest resonant frequency decreases as more coins are added to the stack. For example, note the listed reductions in peak frequency, from 25 MHz (1 token) to 17 MHz (5 tokens) to 15 MHz (10 tokens) to 14 MHz (20 tokens) to 13.5 MHz (30 tokens). Finally, it should be noted that as more tokens are added to the stack, the peak with the lowest frequency approaches the transmission frequency of the RFID reader (i.e., 13.56 MHz), where the lowest resonant frequency of the tag group is generally within 10% of 13.56 MHz. In these embodiments, the lowest resonance is used to optimize tuning, but other resonances can also be used for optimization.

[0089] The transmission loss of the resonant coupled coins is generally improved compared to the baseline and ferrite core cases. At 13.56 MHz, line 502 (1 coin) has a transmission loss of approximately -5 dB, which is roughly the same as the baseline and ferrite core cases with 1 coin. Line 504 (5 coins) has a transmission loss of approximately -10 dB, which is an improvement of approximately 11 dB compared to the baseline and approximately 4 dB compared to the ferrite core case. Line 506 (10 coins) has a transmission loss of approximately -10 dB, which is an improvement of approximately 26 dB compared to the baseline and approximately 9 dB compared to the ferrite core case. Line 604 (20 coins) has a transmission loss of approximately -15 dB, which is an improvement of approximately 35 dB compared to the baseline and approximately 9 dB compared to the ferrite core case.

[0090] Figure 7 This is a graph (700) showing the transmission loss of resonantly coupled game coin stacks (10, 20, and 30 stacks). The x-axis is frequency in MHz, and the y-axis is transmission loss in dB. Figures 5 to 6 Compare, Figure 7The data is generated using game coins that have antennas, parallel capacitors, and series capacitors, but no RFID electronics. Line 702 shows the transmission loss for 10 game coins, line 704 shows the transmission loss for 20 game coins, and line 706 shows the transmission loss for 30 game coins. Figure 7 The data display in the middle, and Figures 5 to 6 The data comparison shows that the presence of a series capacitor has a minimal impact on the resonant coupling performance.

[0091] Figure 8 This is a graph 800 showing the transmission loss of different types of game tokens, each containing 20 tokens in a stack. The x-axis is frequency in MHz, and the y-axis is transmission loss in dB. Line 802 shows the transmission loss of plastic game tokens without RFID circuitry, antennas, and capacitors. Line 804 shows the transmission loss of ferrite core game tokens. Line 806 shows the transmission loss of game tokens with only antennas and parallel capacitors, without RFID electronics or series capacitors (e.g., with...). Figures 5 to 6 The transmission loss of game coins (similar to the setup) is discussed. Line 808 demonstrates an antenna, parallel capacitors, and series capacitors without RFID electronics (e.g., similar to...). Figure 7 The transmission loss of the resonant coupling game coin (similar to the setting) is reduced.

[0092] Over most of the frequency range from 12 MHz to 30 MHz, the resonant coupled coin (line 808) exhibits a significantly improved sensitivity compared to the ferrite core coin (line 804). The addition of the series capacitor (line 808) shifts the frequency response (as seen in the x-direction) compared to the coin without a series capacitor (line 806), but the magnitude of the sensitivity (as seen in the y-direction) remains approximately the same.

[0093] Relationship between antenna and parallel capacitor

[0094] For antenna coils (e.g.) Figure 3 The number of turns on the antenna (308) and the value of the tuning capacitor (e.g., parallel capacitor 306) need to be varied to make the selected resonant frequency (e.g., the lowest resonant frequency) of the desired stack height close to the operating frequency of the RFID reader. For example, a stack height of 30 game coins and an operating frequency of 13.56 MHz are common design goals. Table 1 shows the number of turns of the antenna and the capacitor values ​​used to achieve a resonance close to 13.56 MHz.

[0095]

[0096] Table 1

[0097] Table 1 shows that, to achieve the target resonant frequency, the value of the parallel capacitor decreases as the number of antenna turns increases. This results in a single coin resonance ranging from 23.3 MHz to 24.1 MHz and a minimum resonant frequency ranging from 13.4 MHz to 13.9 MHz for a stack of 30 coins, which is well-suited to the given RFID reader's excitation frequency of 13.56 MHz. Table 1 also shows the resulting S21, where S21 is the transmission (scattering parameter) from the bottom to the top of the stack as previously described. In this specific embodiment used to generate the data shown, the outer diameter of the antenna coil is 26 mm, and the inner diameter of the antenna decreases as the number of antenna turns increases. In these experiments, the series capacitor used to decouple the RFID protection circuit from the antenna (e.g., Figure 2 The 204 in the figure is 3.9 pF for all antenna turns, and the thickness of the game coin is 3.51 mm.

[0098] Relationship between thickness and parallel capacitors

[0099] It has an antenna with 7 turns and an outer diameter of 26 mm (e.g.) Figure 2 Antenna 208) and a series coupler of size 3.9 pF with protection circuitry for decoupling the RFID tag (e.g., antenna 208) and a series coupler of size 3.9 pF with protection circuitry for decoupling the RFID tag. Figure 2 The 204) game coins were well tuned across the coil with a 16 pF capacitor for a stack height of 30 game coins. If the game coins are thicker than 3.51 mm (i.e., the spacing between the antennas) and a parallel capacitor (e.g.) is used... Figure 2 If 206 in the stack remains unchanged, then the signal level from the bottom to the top of the stack (S21) is significantly reduced. This degradation can be significantly mitigated by changing the tuning capacitor (e.g., parallel capacitor 206) to make the selected resonant point (e.g., the lowest resonant point) close to 13.56 MHz, as shown in Table 2.

[0100]

[0101] Table 2

[0102] Table 2 shows that as the thickness of the spacing between tags (e.g., due to the thickness of the game coin) increases, the value of the parallel capacitor can be increased to achieve the target resonant frequency.

[0103] Relationship between antenna size and parallel capacitor

[0104] The above discussion has primarily focused on round tokens with circular antennas. However, tokens can have other dimensions, including square and rectangular shapes. In such cases, the antenna in the token can be either square or rectangular. This section provides data on rectangular tokens (also known as slab tokens) with a thickness of 6 mm and a stack height of 10 slab tokens. Table 3 shows the results of changing the values ​​of the parallel capacitor.

[0105]

[0106] Table 3

[0107] Table 3 shows that as the size of the antenna increases, the value of the parallel capacitor can be reduced to achieve the target resonant frequency.

[0108] Additional tests were conducted to demonstrate how the lensing effect caused by the resonant coupling of the collimated B-field can significantly improve the read range of a set of trinkets. Specifically, when the RFID reader was operating at 1 watt and using the same 60mm x 80mm trinkets as in Table 3, the results showed that a single trinket could be read at a distance of 56 mm above the excitation antenna, but a stack of 10 trinkets (almost twice the read range) could be read at 110 mm above the antenna, all attributable to the lensing effect.

[0109] Alternative embodiments of coupling circuits

[0110] As discussed above, RFID tag 200 (see...) Figure 2 The series circuit element 204 is included to lightly couple the tag electronics 202 to the antenna 208 sufficient to power the RFID integrated circuit and minimize the impact of the protection circuit so that as much residual excitation energy as possible can be used to power other tags. However, a capacitor, resistor, or inductor (or a combination of one or more of the three elements) may also be used for this purpose instead. In this case, the series circuit element 204 may include one or more of a capacitor, inductor, and resistor.

[0111] Figure 9 This is graph 900 showing the transmission loss of a resonantly coupled stack of game coins, where the coupling capacitor (e.g., series circuit element 204) is replaced by a 3.92 kΩ resistor. The x-axis is frequency in MHz, and the y-axis is transmission loss in dB. Line 902 shows the transmission loss for 1 game coin, line 904 for 5 game coins, line 906 for 10 game coins, line 908 for 15 game coins, and line 910 for 20 game coins. Figure 7 In comparison, the transmission loss is similar but slightly worse. Therefore, a resistor can replace a series capacitor as a series element.

[0112] Figure 10 This is graph 1000 showing the transmission loss of a resonantly coupled stack of game coins, where the coupling capacitor (e.g., series circuit element 204) is replaced by a 27 uH inductor. The x-axis is frequency in MHz, and the y-axis is transmission loss in dB. Line 1002 shows the transmission loss of 1 game coin, line 1004 shows the transmission loss of 5 game coins, line 1006 shows the transmission loss of 10 game coins, line 908 shows the transmission loss of 15 game coins, and line 1010 shows the transmission loss of 20 game coins. Figure 7 In comparison, the transmission loss is similar but slightly worse. Therefore, an inductor can replace a series capacitor as a series element.

[0113] Figure 7 and Figures 9 to 10 The results shown together demonstrate that a series-coupled element (e.g., series circuit element 204) may include one or more of capacitors, resistors, and inductors of appropriate size based on other components of the resonant coupling game coin.

[0114] Comparison between ferrite cores and resonant coupled game coins

[0115] The inventors of this invention conducted an experiment between a set of ferrite core tokens and a set of resonant coupled tokens. The experimental setup included a single antenna with clearly defined boundaries, a fixed power level for transmission from an RFID reader, a stack of 30 ferrite core tokens, and a stack of 30 resonant coupled tokens, both types of tokens being circular with a diameter of 39 mm.

[0116] Both types of tokens exhibited similar results in terms of signal strength. This is based on unexpected results from previous work on ferrite core tokens, as it was previously thought that the presence of a ferrite core was necessary to provide good signal strength. Therefore, the performance of the resonantly coupled tokens was an unexpected result.

[0117] For the two types of game tokens, the antenna boundary results in a high signal level within the boundary, a low signal level at the boundary, and a medium signal level outside the boundary, where the medium signal level decreases with increasing distance outside the boundary. These different signal levels can be detected by the system to correctly locate the game token positions for the two types of game tokens. For example, when two adjacent game points exist, the detectable difference in signal levels allows the system to correctly determine which of the adjacent game points contains a stack of game tokens.

[0118] The experiment further demonstrates that resonant-coupled tokens exhibit higher signal strength outside the boundary than ferrite-core tokens. Given existing experience with ferrite-core tokens, this is another unexpected result for these resonant-coupled tokens. The signal strength outside the boundary is still lower than inside, thus the different signal levels allow the system to correctly assign each token to its appropriate coordinates on the game table (and, within the context of the token game, correctly determine the value of each token at a specific placement point).

[0119] Additional Examples

[0120] While the embodiments described in this document focus on their application in the design of RFID-enabled 39 mm gaming coins, the resonant coupling phenomenon can be applied to non-gaming applications. One example of a non-gaming application is the packaging of pharmaceuticals.

[0121] One challenge for caregivers is adherence to medication prescription protocols. A common practice is to provide pillboxes with compartments for holding pills, each compartment corresponding to a specific time of day, with pills distributed to each compartment according to the schedule. For example, a pillbox might contain seven columns (corresponding to the seven days of the week) and four rows (corresponding to four times of day, such as breakfast, lunch, dinner, and bedtime).

[0122] Instead of manually dispensing pills into pillbox compartments, stacks of RFID-enabled packages containing pills can be filled and provided to patients. As patients remove each pill package for administration, the RFID detection system tracks pill inventory and usage.

[0123] Enumeration Instance Examples

[0124] Various aspects of the invention can be understood from the following enumerated examples and embodiments (EEE).

[0125] EEE1. A system for determining the position of an object in a game environment, the system comprising: a radio frequency identification (RFID) antenna disposed at a position on a game table; one or more RFID readers coupled to the RFID antenna; and RFID tags. A given RFID tag comprises: RFID tag electronics; an antenna coupled to the RFID electronics; and a circuit element connected in parallel with the antenna, wherein the circuit element includes a capacitor. The given RFID tag has a resonant frequency caused by the antenna and the circuit element, wherein the resonant frequency of the given RFID tag is higher than the excitation frequency of a transmission generated by the one or more RFID readers. The RFID tags are grouped together, wherein the group of RFID tags shapes the magnetic flux density field of the transmission generated by the one or more RFID readers through the group of RFID tags, wherein the group of RFID tags has a resonant frequency considered individually attributable to resonant coupling that is lower than the resonant frequency of each of the plurality of RFID tags, and wherein the transmission generated by the one or more RFID readers powers the RFID tag electronics via the resonant coupling.

[0126] EEE2. The system according to EEE1, wherein the group comprises at least one stack of RFID tags.

[0127] EEE3. The system according to EEE2, wherein the at least one stack contains at least two completely overlapping RFID tags.

[0128] EEE4. The system according to EEE2, wherein the at least one stack contains at least two partially overlapping RFID tags.

[0129] EEE5. A system according to any one of EEEs 1 to 4, wherein the group comprises a stack of RFID tags.

[0130] EEE6. The system according to EEE1, wherein the group comprises at least one stack of RFID tags and at least one pile of RFID tags.

[0131] EEE7. A system according to any of EEEs 1 to 6, wherein the number of turns of the antenna is selected based on the capacitance of the capacitor, wherein the selected number of turns increases as the capacitance decreases.

[0132] EEE8. A system according to any one of EEE1 to 7, wherein the RFID tag has a thickness between 3.51 mm and 5.49 mm, and wherein the capacitance of the capacitor is between 16 pF and 27 pF.

[0133] EEE9. A system according to any of EEE1 to 8, wherein the capacitance of the capacitor is selected based on the thickness of the RFID tag, wherein the selected capacitance decreases as the thickness decreases.

[0134] EEE10. A system according to any of EEE1 to 9, wherein the capacitance of the capacitor is selected based on the size of the antenna, wherein the selected capacitance decreases as the size increases.

[0135] EEE11. The system according to any one of EEE1 to 10 further includes a housing having a circular external dimension.

[0136] EEE12. A system according to any one of EEEs 1 to 11, wherein the antenna comprises a loop antenna having more than one loop.

[0137] EEE13. A system according to any one of EEEs 1 to 11, wherein the antenna comprises a loop antenna having five loops.

[0138] EEE14. The system according to any one of EEE1 to 10 and EEE12 to 13 further includes a housing having a rectangular external dimension.

[0139] EEE15. A system according to any one of EEEs 1 to 14, wherein the excitation frequency of the transmission generated by the RFID reader is between 13 MHz and 14 MHz.

[0140] EEE16. A system according to any of EEEs 1 to 15, wherein the excitation frequency of the transmission generated by the RFID reader is 13.56 MHz.

[0141] EEE17. A system according to any of EEEs 1 to 16, wherein the lowest resonant frequency of the RFID tag group approaches within 10% of the excitation frequency of the RFID reader as each RFID tag is added to the RFID tag group.

[0142] EEE18. A system according to any one of EEEs 1 to 17, wherein the circuit element is a component of the RFID tag electronics.

[0143] EEE19. A system according to any one of EEEs 1 to 17, wherein the circuit element is a component separate from the RFID tag electronics.

[0144] The foregoing description illustrates various embodiments of the invention and examples of how the invention can be implemented. These examples and embodiments should not be considered as the only possible embodiments, but are presented to illustrate the flexibility and advantages of the invention as defined by the appended claims. Based on the foregoing disclosure and the appended claims, those skilled in the art will understand and may employ other arrangements, embodiments, implementations, and equivalents without departing from the spirit and scope of the invention as defined by the claims. Claims (as amended under Article 19 of the Treaty) 1. A radio frequency identification (RFID) tag, comprising: RFID tag electronic devices; Antenna, which is coupled to the RFID electronics; and A circuit element, which is connected in parallel with the antenna, wherein the circuit element includes a capacitor. The RFID tag has a resonant frequency caused by the antenna and the circuit elements, wherein the resonant frequency of the RFID tag is higher than the excitation frequency of the transmission generated by the RFID reader. The RFID tag is one of a plurality of RFID tags grouped together, wherein the RFID tag group shapes the transmission generated by the RFID reader through the magnetic flux density field of the RFID tag group, wherein the RFID tag group has a resonant frequency that is considered individually attributable to resonant coupling and is lower than the resonant frequency of each of the plurality of RFID tags, and wherein the transmission generated by the RFID reader supplies power to the RFID tag electronics via the resonant coupling. 2. The RFID tag according to claim 1, wherein the circuit element is a first circuit element, and wherein the capacitor is a first capacitor, the RFID tag further comprising: A second circuit element is connected in series between the antenna and the RFID tag electronics, wherein the second circuit element includes at least one of a second capacitor, an inductor, and a resistor. The resonant frequency of the RFID tag is caused by the antenna, the first circuit element, and the second circuit element. 3. The RFID tag according to claim 1, wherein the resonant frequency is caused by the inductance of the RFID tag electronics, the antenna, and the capacitance of the circuit elements. 4. The RFID tag according to claim 3, wherein the inductance of the antenna is caused by one or more physical parameters of the antenna, wherein the one or more physical parameters include antenna shape, antenna size and number of loops. 5. The RFID tag of claim 3, wherein the inductance of the antenna and the capacitance of the circuit elements are selected to result in a given resonant frequency. 6. The RFID tag of claim 1, wherein the antenna comprises between 5 and 26 turns, and wherein the capacitance of the capacitor comprises between 1.2 pF and 30 pF. 7. The RFID tag of claim 1, wherein the capacitance of the capacitor is selected based on the number of turns of the antenna, wherein the selected capacitance decreases as the number of turns increases. 8. The RFID tag of claim 1, wherein the resonant frequency of the RFID tag group has a plurality of peaks, wherein the number of the plurality of peaks increases as the number of RFID tags in the RFID tag group increases. 9. The RFID tag of claim 1, wherein the capacitance of the capacitor is selected based on the thickness of the RFID tag, wherein the selected capacitance increases as the thickness increases. 10. The RFID tag of claim 1, wherein the antenna is a rectangular antenna having a first dimension between 50 mm and 62 mm and a second dimension between 75 mm and 97 mm, and wherein the capacitance of the capacitor is between 11 pF and 21.5 pF. 11. The RFID tag of claim 1, wherein the capacitance of the capacitor is selected based on the size of the antenna, wherein the selected capacitance increases as the size decreases. 12. The RFID tag of claim 1, wherein the resonant coupling is caused by a combination of two or more of the configuration of the antenna, the capacitance of the capacitor, and the thickness of the RFID tag. 13. The RFID tag of claim 1, wherein the antenna comprises a circular loop antenna. 14. The RFID tag of claim 1, wherein the antenna comprises a rectangular loop antenna. 15. The RFID tag of claim 1, wherein the resonant frequency of the RFID tag is between 1.5 and 2.2 times the excitation frequency of the transmission generated by the RFID reader. 16. The RFID tag of claim 1, wherein the lowest resonant frequency of the RFID tag group decreases as each RFID tag is added to the RFID tag group. 17. The RFID tag of claim 1, wherein the lowest resonant frequency of the RFID tag group approaches the excitation frequency of the RFID reader as each RFID tag is added to the RFID tag group. 18. The RFID tag of claim 1, wherein the RFID tag conveys an RFID tag identifier in response to the transmission generated by the RFID reader and the RFID electronics being powered. 19. A system for determining the position of an object in a game environment, the system comprising: Multiple radio frequency identification (RFID) antennas are arranged in multiple locations on the game table; One or more RFID readers coupled to the plurality of RFID antennas; and Multiple RFID tags, wherein a given RFID tag among the multiple RFID tags includes: RFID tag electronic devices; Antenna, which is coupled to the RFID electronics; and A circuit element, which is connected in parallel with the antenna, wherein the circuit element includes a capacitor. The given RFID tag has a resonant frequency caused by the antenna and the circuit elements, wherein the resonant frequency of the given RFID tag is higher than the transmission excitation frequency generated by the one or more RFID readers. The plurality of RFID tags are grouped together, wherein the RFID tag group shapes the transmission generated by the one or more RFID readers through the magnetic flux density field of the RFID tag group, wherein the RFID tag group has a resonant frequency that is considered individually attributable to resonant coupling and is lower than the resonant frequency of each of the plurality of RFID tags, and wherein the transmission generated by the one or more RFID readers supplies power to the RFID tag electronics via the resonant coupling. 20. The system of claim 19, further comprising: Control system In response to the transmission generated by the one or more RFID readers and the power supply to the RFID electronics, the given RFID tag conveys an RFID tag identifier, and In response to receiving the RFID tag identifier, the control system associates the given RFID tag with a position on the game table corresponding to one or more of the plurality of RFID antennas.

Claims

1. A radio frequency identification (RFID) tag, comprising: RFID tag electronic devices; An antenna coupled to the RFID electronics; and A circuit element, which is connected in parallel with the antenna, wherein the circuit element includes a capacitor. The RFID tag has a resonant frequency caused by the antenna and the circuit elements, wherein the resonant frequency of the RFID tag is higher than the excitation frequency of the transmission generated by the RFID reader. The RFID tag is one of a plurality of RFID tags grouped together, wherein the RFID tag group shapes the transmission generated by the RFID reader through the magnetic flux density field of the RFID tag group, wherein the RFID tag group has a resonant frequency that is considered individually attributable to resonant coupling and is lower than the resonant frequency of each of the plurality of RFID tags, and wherein the transmission generated by the RFID reader supplies power to the RFID tag electronics via the resonant coupling.

2. The RFID tag according to claim 1, wherein the circuit element is a first circuit element, and wherein the capacitor is a first capacitor, the RFID tag further comprising: A second circuit element is connected in series between the antenna and the RFID tag electronics, wherein the second circuit element includes at least one of a second capacitor, an inductor, and a resistor. The resonant frequency of the RFID tag is caused by the antenna, the first circuit element, and the second circuit element.

3. The RFID tag according to any one of claims 1 to 2, wherein the resonant frequency is caused by the inductance of the RFID tag electronics, the antenna, and the capacitance of the circuit elements.

4. The RFID tag according to claim 3, wherein the inductance of the antenna is caused by one or more physical parameters of the antenna, wherein the one or more physical parameters include antenna shape, antenna size and number of loops.

5. The RFID tag of claim 3, wherein the inductance of the antenna and the capacitance of the circuit elements are selected to result in a given resonant frequency.

6. The RFID tag according to any one of claims 1 to 5, wherein the antenna comprises between 5 and 26 turns, and wherein the capacitance of the capacitor comprises between 1.2 pF and 30 pF.

7. The RFID tag according to any one of claims 1 to 6, wherein the capacitance of the capacitor is selected based on the number of turns of the antenna, wherein the selected capacitance decreases as the number of turns increases.

8. The RFID tag according to any one of claims 1 to 7, wherein the resonant frequency of the RFID tag group has a plurality of peaks, wherein the number of the plurality of peaks increases as the number of RFID tags in the RFID tag group increases.

9. The RFID tag according to any one of claims 1 to 8, wherein the capacitance of the capacitor is selected based on the thickness of the RFID tag, wherein the selected capacitance increases as the thickness increases.

10. The RFID tag according to any one of claims 1 to 9, wherein the antenna is a rectangular antenna having a first dimension between 50 mm and 62 mm and a second dimension between 75 mm and 97 mm, and wherein the capacitance of the capacitor is between 11 pF and 21.5 pF.

11. The RFID tag according to any one of claims 1 to 10, wherein the capacitance of the capacitor is selected based on the size of the antenna, wherein the selected capacitance increases as the size decreases.

12. The RFID tag according to any one of claims 1 to 11, wherein the resonant coupling is caused by a combination of two or more of the configuration of the antenna, the capacitance of the capacitor, and the thickness of the RFID tag.

13. The RFID tag according to any one of claims 1 to 9 and 11 to 12, wherein the antenna comprises a circular loop antenna.

14. The RFID tag according to any one of claims 1 to 12, wherein the antenna comprises a rectangular loop antenna.

15. The RFID tag according to any one of claims 1 to 14, wherein the resonant frequency of the RFID tag is between 1.5 times and 2.2 times the excitation frequency of the transmission generated by the RFID reader.

16. The RFID tag according to any one of claims 1 to 15, wherein the lowest resonant frequency of the RFID tag group decreases as each RFID tag is added to the RFID tag group.

17. The RFID tag according to any one of claims 1 to 16, wherein the lowest resonant frequency of the RFID tag group approaches the excitation frequency of the RFID reader as each RFID tag is added to the RFID tag group.

18. The RFID tag according to any one of claims 1 to 17, wherein the RFID tag conveys an RFID tag identifier in response to the transmission generated by the RFID reader and the RFID electronics being powered.

19. A system for determining the position of an object in a game environment, the system comprising: Multiple radio frequency identification (RFID) antennas are arranged in multiple locations on the game table; One or more RFID readers coupled to the plurality of RFID antennas; and Multiple RFID tags, wherein a given RFID tag among the multiple RFID tags includes: RFID tag electronic devices; Antenna, which is coupled to the RFID electronics; and A circuit element, which is connected in parallel with the antenna, wherein the circuit element includes a capacitor. The given RFID tag has a resonant frequency caused by the antenna and the circuit elements, wherein the resonant frequency of the given RFID tag is higher than the transmission excitation frequency generated by the one or more RFID readers. The plurality of RFID tags are grouped together, wherein the RFID tag group shapes the transmission generated by the one or more RFID readers through the magnetic flux density field of the RFID tag group, wherein the RFID tag group has a resonant frequency that is considered individually attributable to resonant coupling and is lower than the resonant frequency of each of the plurality of RFID tags, and wherein the transmission generated by the one or more RFID readers supplies power to the RFID tag electronics via the resonant coupling.

20. The system of claim 19, further comprising: Control system In response to the transmission generated by the one or more RFID readers and the power supply to the RFID electronics, the given RFID tag conveys an RFID tag identifier, and In response to receiving the RFID tag identifier, the control system associates the given RFID tag with a position on the game table corresponding to one or more of the plurality of RFID antennas.

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