Electromagnetic coupler device

Abstract

The present disclosure relates broadly to a wireless electromagnetic coupler device for reactive near-field coupling comprising a sequential array of coupling elements arranged geometrically in one or two dimensions. In an initial sensing state, an automatic selection of a single coupling element or multiple coupling elements establishing a particularly strong and effective interaction with the inlay is performed by feeding an unmodulated electromagnetic energy wave into each of the coupling elements and the respective associated harvester elements. A switchable resistance array is used to activate the selected coupling elements for coupling information to / from the loop and to deactivate the remaining coupling elements by means of a respective feedback loop. The adaptive array of coupling elements can be flexibly applied to coupling to planar metal traces of arbitrary geometry (in particular: RFID inlays) without the need for a specific calibration or positioning procedure. There is no need to scan the inlay geometry ("inlay profile") nor an external control.

Description

Technical Field

[0001] This disclosure broadly relates to electromagnetic coupling technology. More specifically, non-limiting embodiments relate to electromagnetic coupler devices suitable for use in printers or other near-field coding applications for encoding RFID inlays. Background Technology

[0002] Radio Frequency Identification (RFID) is a technology that uses radio waves to transmit data from electronic tags (called RFID tags or RFID inlays). Information is stored electronically in the tag. To read the information, an RFID reader emits encoded radio signals to query the tag. RFID tags therefore include planar metallic traces, and more specifically, current loops suitable for inductive coupling. The same planar metallic traces (current loops) can also be used to encode RFID tags via electromagnetic coupling.

[0003] RFID devices including planar metallic traces are generally referred to as inlays. Specifically, an inlay is an RFID device comprising a planar metallic trace film supported on a flexible substrate and connected to a transponder. The transponder included in the current loop is an integrated circuit used to decode signals transmitted to the inlay and received by the planar metallic trace, and also used to transmit signals to the planar metallic trace, which are then transmitted by the planar metallic trace (sometimes also called an "antenna"). The inlay antenna can be tuned (i.e., sized) to communicate with a transceiver at a specific target frequency, the transceiver including at least a coupling element and an interrogator for communicating with the RFID inlay. Regarding the term "antenna," for better understanding, it should be noted that within this disclosure, the term "antenna" is interpreted as meaning a radiating device. However, this disclosure relates to coupling in the reactive near field, which is opposite to the far field of radiation. Therefore, the term "antenna" is avoided in this disclosure.

[0004] In recent years, printing devices have become known that can displace RFID inlays on a medium such as paper and simultaneously encode the RFID inlays with desired information during the printing process. Encoding is preferably performed via electromagnetic coupling in a reactive near-field. For this purpose, the RFID printer / encoder is equipped with an electromagnetic coupler device mounted in the printer cavity to couple electromagnetic power carrying the encoded information to the RFID inlay located on the medium as the medium is guided along the medium path through the printer / encoder.

[0005] Coupler devices with only a single coupling element can be used, as well as coupler devices with multiple coupling elements forming a one-dimensional or two-dimensional array.

[0006] The problem arises because it requires effectively encoding different inlays with various geometries (shape factors) without substantially altering the coupler device.

[0007] Whether in a single configuration constituting the entire coupler or in an array configuration, coupling elements are often suboptimally designed due to the wide variety of inlay geometries. In many cases, transmission line (TRL) techniques are used for coupling leakage fields from different TRL geometries. In others, radiating structures more like antennas are used at the expense of extensive shielding for radio frequency (RF) isolation. Regardless of the configuration used, suboptimal coupling is achieved. One solution for geometry adaptation could be an array configuration where individual elements are controlled to generate an optimized RF coupling field, thus overcoming the limitations of individual elements.

[0008] However, this has the following drawbacks: before actual encoding can be performed, calibration is required to adapt the coupling device to the specific inlay to be encoded. Either the location of the inlay used for optimal coupling must be known, or the inlay profile must be obtained and stored.

[0009] In the former (“static”) case, each inlay type has its own unique required positioning, which cannot be changed for a fixed coupler. In the latter (“externally controlled adaptive”) case, a scanning function is required to understand the inlay profile.

[0010] In the specific case of an array of electromagnetic coupling elements, an initial calibration step is required for each inlay geometry to determine (select) one or a limited number of elements in the array to be used (activated) for coupling power to that particular inlay type. Additionally or simultaneously, the (relative) position between the inlay to be communicated with (especially: the coded inlay) and the coupler device needs to be determined. It should be noted that, in most cases, it is also desirable to limit the effective coupling space (spatial selectivity) because the inlays are space-limited. This should preferably be achieved without requiring large shielding structures that would occupy space, and is therefore generally unsuitable for printer environments with limited space. Summary of the Invention

[0011] According to a first aspect, a wireless electromagnetic coupler device is provided for providing spatial selectivity in the interaction of electromagnetic energy with an RF-terminated planar metallic trace of arbitrary geometry. The electromagnetic coupler device includes a sequential array of coupling elements shunted onto a phase-compensated differential transmission line for coupling electromagnetic energy to the RF-terminated planar metallic trace via reactive near-field coupling. The electromagnetic coupler device also includes a plurality of switchable resistor elements included in a path between the differential transmission line and corresponding coupling elements in the array, to alternately switch the resistance of the electrical connection between the differential transmission line and the corresponding coupling element to a first value or a second value, wherein the second value is less than the first value, by controlling a corresponding switch. Each coupling element is associated with: a corresponding collector element for collecting energy fed from the differential transmission line; and a corresponding feedback loop for providing feedback from the collector element to a corresponding switch for switching the resistor element included in the corresponding path based on a DC voltage established at the collector element.

[0012] A specific method of a non-limiting implementation is to provide a radio electromagnetic coupler device in the form of an adaptive array of coupling elements. This device is capable of selectively switching the resistance of the feed path of each coupling element in the array between high and low values ​​based on the sensed interaction strength between each coupling element and an inlay present in the vicinity of the coupler device. Thus, by switching the corresponding resistance to a low value, only those coupling elements capable of efficient coupling with a particular inlay are automatically activated among the multiple coupling elements. Other coupling elements are deactivated so that the fed coupling energy is concentrated on those coupling elements capable of achieving the most efficient coupling. This is achieved by a collector element connected to the feed path of each individual coupling element in the array. The collector element provides feedback for switching the corresponding resistance based on the coupling strength between the coupling element and the inlay determined during the initial sensing phase of operation. Thus, spatial selectivity is automatically achieved among the coupling elements of the array interacting with a particular tag. This is achieved by automatically isolating (at least to some extent) those coupling elements that do not provide effective interaction during the sensing state under the current condition (i.e., the geometric alignment or shape of the tag).

[0013] The method outlined herein can be implemented using a wireless electromagnetic coupler device according to the first aspect described above. According to a non-limiting embodiment, the wireless electromagnetic coupler device comprises a sequential array of coupling elements, and for each coupling element, it includes a corresponding plurality of switchable resistor elements, a corresponding collector element, and a corresponding feedback loop.

[0014] According to a non-limiting embodiment, the collector element and the corresponding coupling element are connected together to the feed line (differential transmission line), so that the resistance of the connection is switched together for the collector element and the coupling element.

[0015] According to an alternative, non-limiting embodiment, the collector element is connected such that it is permanently coupled to the differential transmission line via an electrical connection having a first (larger) resistance value. As will be described in detail below, in this case, a lower resistance value, which is smaller than the large resistance value, is possible compared to the previous embodiment.

[0016] According to a preferred, non-limiting embodiment, the electromagnetic coupler device further includes an interrogator for feeding electromagnetic energy to be coupled to the planar metallic trace. More preferably, the electromagnetic coupler device further includes a balun electrically coupled between the interrogator and the differential transmission line. The balun forms the differential transmission line input by splitting the output of the interrogator into two parts with equal amplitude and a 180° phase shift.

[0017] Preferably, the interrogator is configured to feed unmodulated electromagnetic energy to the coupling element in the sensing state. The unmodulated electromagnetic energy is an RF carrier guided by a differential transmission line, wherein the resistance is initially switched to a first value for all coupling elements in the array. Thus, in the sensing state, the unmodulated electromagnetic energy is used to establish a certain DC voltage at the collector element, where this DC voltage depends on the strength of the interaction between the respective coupling element and the planar metal trace (inlay) present near the coupling element.

[0018] More preferably, the interrogator is configured to subsequently modulate the RF carrier into a communication signal for the coupling element. Accordingly, once a stable switching state has been established for each coupling element based on the sensing results of the sensing step, the modulated communication signal can be transmitted to encode the inlay.

[0019] More preferably, the interrogator is thus configured to feed a communication signal after a stable switching state of each switch in the switches has been established, taking into account the interaction between the unmodulated RF carrier and the RF termination planar metal trace.

[0020] According to a preferred, non-limiting embodiment, the differential transmission lines are terminated. However, termination of the differential transmission lines is not a mandatory feature. An alternative configuration can be implemented using appropriate phase compensation, in which the termination of the differential transmission lines can be omitted.

[0021] According to a preferred, non-limiting embodiment, each coupling element includes a transmission line loop for interacting with an RF termination planar metal trace via inductive coupling. The transmission line loop is a continuous transmission line of finite length formed such that its two terminals are close to each other and differentially fed via a differential transmission line. Such a configuration may also be referred to as a "differential transmission line loop" (DTLL).

[0022] More preferably, the transmission line loop has a hyperelliptical geometry represented by the following parameters (in Cartesian coordinates x and y):

[0023]

[0024] Here, parameters a (length) and b (height) determine the dimensions of the loop. Parameters m and n determine the curvature.

[0025] According to an alternative preferred non-limiting embodiment, each coupling element comprises an elongated helical planar transmission line pattern for interacting with an RF termination plane metal trace via inductive coupling. The elongated helical transmission line pattern is a continuous transmission line of finite length with terminals at both ends, wherein the terminals are positioned such that at least one turn of transmission line exists between the terminals. More preferably, the continuous transmission line of finite length is wound around a fixed center point, such that each turn includes straight sections arranged parallel to each other. Such coupling elements provide enhanced flexibility in achieving efficient coupling with inlays of various shapes. Because the arrangement of the coupling elements causes current to flow in the same direction in each of the parallel conductor sheets distributed on the coupler surface, a strong magnetic field is generated to be distributed across the entire surface of the coupler rather than just near a single loop conductor. Simultaneously, the magnetic field is kept confined to a region of the coupler surface, thus not affecting selectivity.

[0026] According to a preferred, non-limiting embodiment, the sequential array of coupling elements has a one-dimensional geometric arrangement.

[0027] According to an alternative preferred non-limiting embodiment, the sequential array of coupling elements has a two-dimensional geometric arrangement.

[0028] According to a preferred, non-limiting embodiment, the RF-terminated planar metal trace is an RFID inlay. More preferably, the electromagnetic coupler device is adapted to encode the RFID inlay by coupling electromagnetic power to it.

[0029] According to a preferred, non-limiting embodiment, the resistor is switched to a first value when the DC voltage at the collector exceeds a predetermined first threshold. As will be described in detail below, a high level of DC voltage at the collector indicates a lack of efficient interaction between the coupling element and the inlay. As indicated above, in this case, the coupling element should not be used for coupling (encoding). This is achieved by switching the resistor to a first (higher) value, thereby deactivating the corresponding coupling element used to encode the corresponding inlay.

[0030] Furthermore, according to a non-limiting preferred embodiment, when the DC voltage drops below a predetermined second threshold, the resistor is switched from a first value to a second value, wherein the second threshold is lower than the first threshold. This means that when starting from an initially high DC voltage value, as the inlay that causes the DC voltage value to decrease approaches the coupling element with which it has efficient coupling, the corresponding coupling element is activated for coupling (encoding) by switching the resistor to a lower value.

[0031] Furthermore, according to a non-limiting preferred embodiment, each feedback loop in the feedback loop includes an inverting operational amplifier. By employing an inverting operational amplifier, a high DC voltage is converted into a state where the switch is "off," while a low DC voltage is converted into a state where the switch is "on." Therefore, it is possible to achieve a situation where the switching state under high DC voltage conditions is the same as the initial switching state before any power is fed to the system. This contributes to operational stability.

[0032] Also preferably, a coupler device is used in the printer, wherein the RFID inlay to be encoded is arranged on the medium guided along the medium path in the printer.

[0033] According to a non-limiting embodiment, an RFID printer / encoder is provided, which includes a multilayer electromagnetic coupler device according to any one of the first aspects or any non-limiting embodiments thereof. Since the electromagnetic coupling for transmitting encoded information to the RFID inlay occurs in the reactive near field, the multilayer electromagnetic coupler device can be easily mounted in the printer cavity, close to the media path.

[0034] The disclosed non-limiting embodiments are broadly intended to provide improved electromagnetic coupler devices suitable for efficiently coupling electromagnetic power into inlays of arbitrary shapes without the need for calibration or external control.

[0035] These and other aspects and features of the non-limiting embodiments will now become apparent to those skilled in the art after viewing the following description of specific non-limiting embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0036] Additional features and advantages of the non-limiting embodiments will become apparent from the following description illustrated in the accompanying drawings, in which:

[0037] Figure 1 This is a block diagram of an electromagnetic coupler device according to a non-limiting embodiment;

[0038] Figure 2 This is a simplified diagram of the arrangement of switchable resistor elements used in a non-limiting embodiment;

[0039] Figure 3 This is a simplified diagram of the arrangement of switchable resistor elements used in another non-limiting embodiment;

[0040] Figure 4 This is a simplified functional diagram of a differential transmission line loop used as a coupling element in a non-limiting embodiment;

[0041] Figure 5 Several exemplary loop geometries based on the hyperelliptic equation are shown; and

[0042] Figure 6 An exemplary geometry of a coupling element with an elongated spiral planar shape is shown. Detailed Implementation

[0043] Throughout this specification, the word “comprising” or variations such as “including” or “containing” shall be understood to imply inclusion of the stated elements, integers or steps or groups of elements, integers or steps, but not to exclude any other elements, integers or steps or groups of elements, integers or steps.

[0044] This disclosure relates to an electromagnetic coupler device comprising an adaptive array of coupling elements for selectively and efficiently coupling electromagnetic energy to planar metallic traces of arbitrary shape, particularly for encoding RFID inlays. The disclosed non-limiting embodiments are particularly suitable for encoding inlays disposed on a medium such as an RFID printer / encoder.

[0045] In a non-limiting embodiment of the electromagnetic coupler device, an interrogator (sometimes also called an "RFID reader") is connected to the transmission line via a balun, thereby converting the transmission line into a differential transmission line with two sections fed with the output of the interrogator having equal amplitude and a phase offset of 180°. A sequential array of coupling elements is connected in parallel to the differential transmission line. Phase compensation is provided between the connections of the individual elements of the array to the transmission line to obtain a phase-compensated differential transmission line.

[0046] Between the phase-compensated differential transmission line and each coupling element, multiple switchable resistor elements are designed to alternately switch the resistance of the electrical connection between the differential transmission line and the corresponding coupling element by operating a corresponding controllable switch between a first (higher) value and a second (lower) value. Furthermore, the output terminals of the multiple switchable resistor elements are connected to a collector element, which can also be connected to the corresponding coupling element. Therefore, the collector element collects the energy fed from the phase-compensated differential transmission line to the corresponding coupling element.

[0047] The collector element harvests energy when the device is powered on, thereby converting the RF power fed into the system into DC voltage. The collector element is coupled via a feedback loop to a corresponding controllable switch of a plurality of switchable resistor elements.

[0048] The collector element (“power collector”) and its operation are well known in the art. Therefore, a detailed description thereof is omitted herein. For further explanation, see, for example, Pavel Nikitin’s paper “Self-Reconfigurable RFID Reader Antenna”, IEEE RFID Conference, May 9–11, 2017 (see also patent publication US 10,096,898B2).

[0049] The goal of using the structure described above is to selectively activate communication only between a portion of the multiple couplers forming the array and the inlays (responders) present in the vicinity of the array. More specifically, only one (or several) of the coupling elements will be activated to enable efficient communication with specific inlays (responders) having a specific geometry.

[0050] To this end, the device is initially set to a sensing state to determine which coupler in the array provides the most efficient coupling and is therefore to be activated. Based on the sensing result, the desired coupler is automatically activated (by switching a controllable switch to set the resistance between the phase-compensated differential transmission line and the coupling element to a reduced (second) value). The resistance values ​​of the remaining couplers are still switched to a high (first) value, allowing only minimal interaction with the transponder.

[0051] According to a non-limiting implementation, the sensing state is established as follows. Initially, when the interrogator is turned on, all resistors in the array are switched to a first (high) value. The interrogator then powers the system by feeding (unmodulated electromagnetic) waves toward the differential transmission line. As the feed proceeds along the path with the first resistance value, the DC voltage established at each of the acquisition elements gradually increases. However, the switch is not triggered by the increased DC voltage. This can be achieved, for example, by including an inverting operational amplifier in the feedback loop such that the switching state during voltage increase remains the same as the switching state in the initial unpowered state (i.e., switched to the first value).

[0052] Once the transponder (inlay) is present near the coupling element, the interaction between the coupling element and the transponder begins and causes a mismatch, resulting in impedance changes in the corresponding element of the array. This affects the DC voltage at the acquisition element. Specifically, the higher the amount (efficiency) of the interaction between a particular coupling element and the transponder, the lower the DC voltage at the acquisition element becomes. Specifically, under a certain intensity of interaction, the DC voltage drops below a predetermined threshold (“second threshold”). This means that the corresponding switch is powered through the feedback loop, and the resistance value of the corresponding element in the array is switched to a second (lower) value, resulting in an increase in the amount of energy supplied to the corresponding coupler element of the array. That is, due to the efficient interaction between the transponder and the coupling element, the corresponding coupling element is activated, which causes the DC voltage at the acquisition element to drop below the second threshold.

[0053] An important feature of the apparatus according to this disclosure is that, in the sensing state described above, the individual coupling elements are well isolated. This isolation in the sensing state avoids destructive interference that would occur when all coupling elements are active.

[0054] Further details of operation will now be described based on various embodiments of the switchable resistor arrangement. Specifically, in the active state, by switching the resistor to a first value, the DC voltage can be raised again to exceed a higher first threshold, resulting in the corresponding feed path being deactivated again. Preferably, the arrangement is configured such that for each coupling element, in the presence of a specific inlay, a specific switching state is achieved to maintain stability.

[0055] However, generally speaking, it can be said that only one or a few coupler elements in the array (coupler elements with sufficient interaction to reduce the voltage below a second threshold) are automatically switched into an active state via low-value resistors, while other coupler elements are set to an inactive state by de-energizing their respective switches. In this state, actual communication with the inlay is performed via a modulated signal feed system for writing (or reading). Other couplers with their respective feed paths' resistors set to a first value will not be able to perform communication efficiently enough, causing communication to concentrate on those "active" coupler elements.

[0056] By providing an adaptive array of coupling elements, efficient communication with transponders (tags, inlays) of various shapes and geometries is flexibly achieved without needing to know or determine the exact location of individual transponders.

[0057] Further details of non-limiting embodiments will be described below with reference to the accompanying drawings.

[0058] Figure 1 This is a block diagram providing a system overview of an electromagnetic coupler device 1 according to a non-limiting embodiment.

[0059] The electromagnetic coupler device includes an interrogator 10, a balun B, and multiple sequentially coupled elements (element 1, ..., element n, ..., element N) of a phase-compensated differential transmission line PC TRL. "Sequential coupling" refers to the sequential electrical coupling of each element to the differential transmission line, which must be distinguished from the geometry, which may represent, for example, a one-dimensional or two-dimensional array. For simplicity, the elements arranged between those explicitly shown in the figures and other elements arranged between the wavy lines are omitted. Furthermore, the figures are disconnected between the balun B and element 1. The coupling element TLL and the corresponding collector element H are coupled to each of the elements via a switchable resistor ISO. A switch for switching the resistance value is included in block ISO. Reference will be made below. Figure 2 and Figure 3 A non-limiting embodiment of the device is described in more detail. The feedback loop 3 from each collector element in the collector elements to the corresponding switch is indicated by dashed lines.

[0060] More specifically, the interrogator 10 is adapted to supply electromagnetic energy (in the form of an unmodulated wave or a modulated wave representing a signal) to power the system, represented by a single line extending from the interrogator 10 to the balun B. The balun splits the electromagnetic wave (signal) into two waves (signals) of equal amplitude and phase offset by 180°. Therefore, the balun B converts the transmission line extending from the interrogator into a differential transmission line. This is represented by two parallel lines forming the differential transmission line, with the coupling element TLL and the collector H connected in parallel to the differential transmission line via a switchable resistor ISO. Between each of the two elements of the differential transmission line, phase compensation for the corresponding electrical length is provided, which converts the differential transmission line into a phase-compensated differential transmission line PC TRL. This is represented by the box labeled "PC TRL" in the figures. It should also be noted that in the preferred copper transmission line, high-frequency (RF or UHF) losses are relatively small.

[0061] According to a non-limiting implementation, the operating frequency range is approximately 860 MHz to 960 MHz.

[0062] exist Figure 1 In the attached diagram, the phase-compensated differential transmission line is terminated by impedance Z. term The differential transmission line is terminated after element N (on the right-hand side of the figure). The termination impedance is used to compensate for mismatch along the differential transmission line. However, the presence of termination is optional and, depending on system parameters, the unterminated differential transmission line is within the scope of this disclosure. For example, in the exemplary case of 32 switching elements sequentially coupled to a single balun B, good matching can be achieved without providing termination impedance.

[0063] Generally, the switchable resistor ISO forces the coupling element to be alternately connected more strongly or weakly to the RF path of the PC TRL. When the inlay interacts electromagnetically with the coupling element, the inlay transponder impedance acts as a load. In the absence of interacting inlays, the resistance of the coupling element is high. During the presence of an inlay interacting with the coupling element (not shown in the figures), the coupling element is in a loaded state when strongly connected and in an isolated state when weakly connected. The isolated state is the default state. The transition from the isolated state to the loaded state is triggered by the electromagnetic interaction between the inlay (when present) and the corresponding coupling element. If the coupling element is close enough to the inlay, a strong electromagnetic interaction will exist, and the coupling element will be triggered. As long as the inlay remains present, the trigger will lock the corresponding coupling element into the loaded state. The internal control feedback loop 3 of the data acquisition unit is not subject to external interference, and whether the coupling element is triggered is not monitored externally to the coupling element.

[0064] Regarding geometry, it should be noted that the size of a single tag is typically smaller than the geometry of the adaptive array of coupling elements. That is, for short-pitch applications, processing is anticipated to activate only a single coupling element or a subset of coupling elements (subarray activation) within the array.

[0065] The size of the array (the number of coupling elements in the coupler device) is generally not limited. Typical values ​​can be 8, 16, or 32, but are not limited to these. Within the array of coupling elements, for a given inlay shape and arrangement (position and orientation), one or several (e.g., two or three) coupling elements can be activated during adaptive sensing. However, the number of activated coupling elements is not limited to the non-limiting examples described above, and furthermore, in certain cases, it can even be unpredictable, as it depends on the interaction parameters between each particular inlay and each coupling element, which are not externally controlled or transmitted to the outside.

[0066] In the following text, we will refer to Figure 1 The operation of the coupler device is explained in more detail by a non-limiting exemplary arrangement of the circuit system in the box marked ISO. Figure 2 and Figure 3 As shown in the image.

[0067] Figure 2 An exemplary arrangement of a circuit system in block "ISO" according to a non-limiting implementation is shown.

[0068] Accordingly, the electrical input path is divided into two parallel paths characterized by having different resistances, shown as resistors R1 and R2. Following the convention used in this specification, the resistance value of the first resistor R1 is greater than the resistance value of the second resistor R2. A switch 2, arranged on the output side of the block, allows switching between the two parallel paths. The common output is divided into two terminals for connecting the collector on one side and the coupling element on the other. The operation of the switch is controlled by a signal provided from the collector element H via feedback loop 3. This is indicated by the dashed lines in the accompanying drawings.

[0069] As those skilled in the art will recognize, obvious modifications to the illustrated configuration are permissible and do not affect operation. According to the obvious modification, switch 2 is not arranged on the output side of the parallel circuit with two resistors R1 and R2, but rather on the input side. It should also be noted that, in order to connect the acquisition unit and coupling elements to the differential transmission line, connections are made in each section (element) of the phase-compensated differential transmission line as follows... Figure 1 As shown and in Figure 2 The two identical devices shown in detail are ISO.

[0070] The following describes the operation used to automatically achieve a stable activation state of a single coupled element in the presence of a specific inlay.

[0071] Initially, before energy is fed from interrogator 10, the system is in a default state where the resistance in all electrical paths is switched to a (larger) first value R1. Preferably, this arrangement corresponds to the unpowered state of switch 2. Subsequently, the feeding of unmodulated electromagnetic waves begins (sensing state). In this state, and as long as there is no inlay near the coupling element TLL, the coupling element TLL itself has a fairly high resistance, and therefore, despite the switchable resistance being a large value R1, the collector element H collects energy to establish a high-level DC voltage. This does not trigger any change in the switching state. In a preferred embodiment where feedback loop 3 includes an inverting operational amplifier, the high DC voltage is converted into a low-level feedback signal, causing switch 2 to remain unpowered.

[0072] When the inlay approaches, the electromagnetic interaction between the inlay and the coupling element TLL causes a decrease in the DC voltage at the collector element H, as generally explained above. The stronger (more effective) the electromagnetic interaction, the more significant the decrease in DC voltage (i.e., the smaller the resulting DC voltage). Accordingly, if there is an efficient interaction between a specific type of inlay and a specific coupling element in the array of coupling elements TLLs, the DC voltage decreases below a predetermined threshold (a second lower threshold), which triggers switch 2. In a particularly preferred embodiment with an inverting operational amplifier, the low-level DC voltage is converted into a high-level feedback signal, thereby powering switch 2. Thus, the corresponding electrical path is switched to a lower value resistor R2 via a switchable resistor element. This corresponds to the activation of the corresponding coupling element TLL and enables efficient interaction between that specific coupling element and the inlay. On the other hand, if the interaction between the inlay and another coupling element TLL is less efficient (e.g., due to different relative geometric configurations), the decrease in the collector DC voltage is less (i.e., the DC voltage level remains high), it does not fall below the predetermined (second) threshold, and switch 2 is not triggered. Therefore, in this case, the resistance of the electrical path between the differential transmission line PC TRL and the coupling element TLL remains large (R1), and the coupling element TLL is thus in a deactivated state, in which there can be no effective interaction between the coupling element TLL and the inlay.

[0073] When activated, as a further result of the small resistor R2, the DC voltage at the collector H rises again. When this exceeds a predetermined first (higher) threshold, it causes the trigger switch 2 to switch back to the higher resistor R1.

[0074] It must be remembered that a permanent switching between the two states of switch 2 within a short period of time, due to the behavior described above, should be avoided. That is, this would be an unstable situation, making effective encoding impossible. Instead, the "active" switching state should be maintained for at least a sufficiently long time to allow for the subsequent feeding and processing of the modulated signal used to encode the inlay. To achieve this, it is important that there is no significant difference between the two resistor values ​​R1 and R2. More specifically, the ratio of the resistance of the parallel combination of TLL and collector after switch 2 has been triggered (with the inlay present) to the sum of the resistance of R2 and the parallel combination of TLL and collector must be strictly less than the corresponding ratio of the resistance of the parallel combination of TLL and collector to the sum of the resistance of R1 and the parallel combination of TLL and collector before the inlay is present. On the other hand, this means that even in the inactive switching state (R1), there are still some possible interactions that allow communication to be facilitated even by the "inactive" coupling element TLL. In a practical implementation, possible orders of magnitude could be, for example, R1 = 1000 Ω and R2 = 600 Ω. Of course, these specific values ​​are purely exemplary and for illustrative purposes, and this disclosure is by no means limited to these values ​​or similar values.

[0075] Figure 3 An exemplary arrangement of a circuit system in block "ISO" according to another non-limiting embodiment is shown.

[0076] In this embodiment, with Figure 2 A similar approach is used in the implementation to separate the electrical paths between two parallel paths with resistance values ​​R1 and R2. However, the connection of the collector element H is different. More specifically, the collector element H remains permanently connected to the electrical path with the higher resistance R1. This is achieved by arranging switch 2 at a position after the terminal to which the collector element H is connected in the current from the phase-compensated differential transmission line PC TRL toward the coupling element TLL. Therefore, only the connection between the differential transmission line PC TRL and the coupling element TLL is switched, while the connection to the collector element H remains unaffected by the switch. The feedback loop 3 is again indicated by dashed lines. As can be seen from the figures, when switch 2 is on the side of resistor R1, there is a short-circuit connection between the collector element H and the coupling element TLL. However, when switch 2 is switched toward resistor R2, the current connection between the collector H and the coupling element TLL is interrupted.

[0077] The operation of this implementation is generally similar to Figure 2 The operation is as described above: in the initial (unpowered) state, the switching position is oriented towards the first (larger) resistance value R1. Therefore, in the sensing state, when unmodulated electrical energy is fed, it is in accordance with... Figure 2 In the same manner as in the implementation, a high-level DC voltage is established at the collector element H.

[0078] When the inlay appears near the array of coupling elements TLL, this again leads to a decrease in the DC voltage level, which depends on the strength (efficiency) of the interaction. In the case of efficient interaction, the DC voltage level decreases below a second (lower) threshold. Until this point, operation with... Figure 2 The implementation methods are the same because the electrical connections are identical.

[0079] More specifically, as long as switch 2 is in the switch position connected to the higher resistance value R1, a short-circuit connection exists between the coupling element TLL and the collector element H. As a result, in the absence of an inlay, a well-matched condition (resonance condition) can be established in the circuit section including the (primarily inductive) coupling element and the (primarily capacitive) collector element. When an inlay is present, the situation remains the same as... Figure 2 The implementation is the same. The electrical path between the differential transmission line PC TRL and the coupling element TRL is switched back to a lower value R2, i.e., the corresponding coupling element TLL is activated. However, after switch 2 is triggered, the situation is the same as... Figure 2 The implementation methods differ. Figure 3 In this implementation, the resonant condition is interrupted by switch 2. The collector element remains outside the resonant circuit. Therefore, the DC voltage at collector element H is not expected to rise rapidly, or the DC voltage may even drop further.

[0080] Therefore, even when the second resistance value R2 is very low (one or even several orders of magnitude smaller than R1) such that the electrical path between the differential transmission line PC TRL and the coupling element TLL can be considered almost a short circuit from a practical point of view, the active state remains stable.

[0081] When the interaction strength (efficiency) between the inlay and the coupling element TLL is insufficient, and the DC voltage level at the collector element H does not drop below a predetermined (second) threshold, switch 2 is not triggered and the situation remains the same. Figure 2 The implementation method is the same as in the previous one, that is, the corresponding coupling element TLL is not activated.

[0082] Therefore, through Figure 3 This implementation method, and by using different resistor values ​​(making R2 much smaller than R1), can achieve better selectivity and improved stability. On the other hand, the contribution of the unselected (inactive) coupling element TLL to the coupling is negligible in this case.

[0083] It is worth mentioning again that each section (element) of the phase-compensated differential transmission line PC TRL is arranged with Figure 3 The structure shown, or any functionally equivalent structure, is marked with two corresponding boxes in ISO to establish a feed connection for the corresponding coupling element TLL connected in parallel to the differential transmission line.

[0084] The differential feed coupling element (TLL) can be one of various geometric arrangements, shapes, etc. The following will refer to... Figures 4 to 6 The accompanying drawings describe some exemplary and non-limiting embodiments in more detail.

[0085] According to a preferred, non-limiting embodiment, the structure described below for use as a coupling element TLL in an electromagnetic coupler device according to this disclosure is typically embedded in a multilayer structure (using one of the known microstrip or stripline technologies), which includes a feed layer, a metal ground plane layer, and a top surface layer arranged closest to the termination plane metal trace (the inlay to be encoded). The top surface layer includes the coupling element, examples of which will be explained in more detail below. Note that although the reference numeral "TLL" (used for "transmission line loop") is generally used for the coupling element throughout the disclosure, this does not imply any limitation on the structure of a suitable coupling element.

[0086] In a typical arrangement, there is only a small distance between the top surface layer (coupling element) and the planar metal trace to be coupled (insert), approximately 1 mm or on the order of 0.5 mm to 1.5 mm, but not limited to this range.

[0087] The typical size of the inlay can be about 4 inches, or about 100 mm, to fit the 4-inch wide media used in barcode printers. More compact inlay designs, about 30 mm to 50 mm, are also available, which are compatible with narrower media widths.

[0088] Figure 4 This is a simplified functional diagram of a first example of a coupling element, which will be referred to as a "differential transmission line loop" (DTLL). The coupling element is constructed from a continuous transmission line (e.g., which may be manufactured using microstrip technology) shaped to form a (nearly) closed loop 6. The open ends of loop 6 form terminals 21 and 22, which are fed with signals 7 and 8 (shown as dashed lines) having a phase difference of 180° relative to each other. (Refer to above...) Figure 1 As explained, signals 7 and 8 are output from a balun, resulting in the input signal being split into two signals of equal amplitude and opposite phase, as described above. Figures 1 to 3The feed is described in more detail via a phase-compensated differential transmission line PC TRL and the shunted connection.

[0089] As a result of differential feeding, the direction of the current flowing in loop 6, indicated by the arrow, can be the same throughout the loop (at a given moment).

[0090] The design of the coupling element in a continuous transmission line loop representing distributed field theory components can be performed without considering matching. Conversely, if discrete components are included at intermediate locations in the loop structure, unnecessary iterations between field theory coupling optimization and component value optimization will be required for input matching purposes. Therefore, a continuous transmission line loop offers considerable design advantages compared to mixing distributed and discrete components within a coupled structure. For proper functioning, the DTLL must be arranged opposite a ground plane (not shown). According to a non-limiting embodiment, all discrete components are arranged on the feed side of the device or the balun side, i.e., the side of the ground plane opposite the coupling element.

[0091] Therefore, the non-limiting implementation firstly (and independently) helps optimize the geometry of the transmission line loop, and secondly, helps perform impedance matching on the balun side by selecting appropriate electrical components after the geometry of the transmission line loop has been optimized. The balun has three functional characteristics. The first characteristic includes splitting the input signal into two parts of equal amplitude. The second characteristic includes shifting the two parts in phase by a 180° interval. The third characteristic includes impedance transformation from, for example, a non-differential impedance of a 50Ω external feed system interface to a differential impedance level as seen at the input of the loop. That is, a balun according to the non-limiting implementation can be considered to include a converter and can be designated as a "balanced-to-unbalance transformer" because it also implements the third function of impedance transformation. Impedance transformation is typically characterized by an impedance transfer ratio k. In the case associated with the non-limiting implementation, where the non-differential impedance is transformed into a differential impedance, k is equal to twice the ratio of the differential impedance value (at the input of the DTLL) to the non-differential impedance value (at the external feed system interface). In the case of a 50Ω external feed system, and assuming that the differential impedance level at the input of the loop is 500Ω, the impedance transfer ratio will be k = 5.

[0092] Typically, baluns "see" high reactive impedance (or high Q value) at their output due to the inductive characteristics of the transmission line loop and the presence of a ground plane. This impedance is matched to the impedance on the feed side by incorporating appropriate electrical components.

[0093] Since the Q factor typically represents the relationship between the resonant frequency and bandwidth (half-power bandwidth) of a circuit, a high Q value (a high Q factor or quality factor) corresponds to efficient but reduced bandwidth inductive coupling. This means that the frequency range in which power can be delivered efficiently is limited. Therefore, it is preferable to match the Q value in a way that reduces it to an acceptable level. For example, this can be achieved by including an internal resistor at the output of the balun. Given the potentially very high coupling factor achievable at a single frequency between the differential feed transmission line loop and the inductor loop of the inlay, it is possible to receive some reduction in the delivered power from the transponder chip while still exhibiting an overall high coupling factor over the desired bandwidth.

[0094] As a specific example of coupler loop geometry, in Figure 5 The diagram illustrates multiple coupler loops with different hyperelliptical shapes. The hyperelliptical shape, suitable for a non-limiting implementation, is parameterized in Cartesian coordinates x and y according to the following formula:

[0095]

[0096] In these formulas, parameters a (length) and b (height) have length dimensions and define the size of the hyperellipse in the x and y dimensions, respectively (and are thus generalizations of the semi-axis of a regular ellipse), while parameters n and m define the curvature, i.e., the deviation from the regular ellipse (n = m = 2) toward a rectangular shape (for n, m > 2). θ is a variable parameter representing the parametric representation of the curve.

[0097] exist Figure 5 In the examples, for 'a', parameter values ​​of a = 7.5 mm (above example) and a = 15.5 mm (below example) have been shown. In all examples, 'b' has been set to a fixed value of b = 4.6 mm. For 'n' and 'm', values ​​of n = m = 2 (left-hand example) and n = m = 20 (right-hand example) are used. Dashed lines indicate axes of symmetry. Double axes of symmetry are common for hyperelliptical shapes.

[0098] From an electrical perspective, due to the strongly constrained electromagnetic field, the coupler loop input at the terminals is well approximated by a function that depends only on the loop length and trace width, not on the shape. Therefore, many other asymmetric shapes exist that are not covered by this particular geometry and are potential candidates for effective reactive near-field coupling, and the loop is not limited to... Figure 5 The specific geometry shown.

[0099] As shown in the simulation, if the length dimension of the loop ( Figure 5If the x-axis becomes so large that the coupler's transmission line loop also covers the inlay antenna (radiator) of the RFID tag immediately adjacent to the coupler, then coupling with the inlay antenna becomes important in addition to coupling with the inlay's current loop. This can lead to destructive interference.

[0100] Figure 6 Alternative geometries for the coupling elements are shown. Figure 6 The shape of the coupling element shown differs from the previously described DTLL shape in that the actual coupling element not only comprises a single loop but also has a more complex shape, in which the transmission line 16 is wound around the fixed center 20 several times, such that there is at least one turn of transmission line between the two differential feed terminals. This shape can be described as an "elongated spiral shape".

[0101] More specifically, in Figure 6 In the example, the elongated spiral-shaped transmission line used as a coupling element is a continuous transmission line 16 of finite length with terminals 21 and 22 at both ends, which is wound around a fixed center 20 and formed into a planar shape. Each turn includes straight sections arranged parallel to each other, and the terminals are positioned such that there is at least one turn of transmission line between the terminals. Thus, the shape shown resembles a "spiral," but differs from the actual geometry of a spiral (characterized by a distance from the center point that continuously increases with the length of the curve) because it has (substantially) parallel "flat" sections, i.e., (substantially) straight sections. As will be explained in more detail below, it is these sections that particularly contribute to improving coupling efficiency. In the example shown, the substantially straight and substantially parallel sections are connected by curved sections. The two terminals 21 and 22 are arranged along lines perpendicular to the direction from which the transmission line 16 leaves the terminals 21 and 22.

[0102] The size of a transducer element (TLL) is highly dependent on the electrical length of the transmission line forming the TLL. The electrical length of the transmission line (TL) portion confined to the top surface of a multilayer arrangement can not exceed 180° (half a wavelength) to avoid zero-crossing of the current. For reference, a straight TL with a width of 1 mm on a 1 mm thick FR4 substrate has an electrical length of 180° corresponding to a physical length of approximately 92 mm. Therefore, any TLL has a surface size constraint corresponding to this TL length. It should be noted that for any TLL geometry, sub-sections of the loop that are very close to each other interact electromagnetically. Therefore, the actual size of the TLL can be affected by its shape. For example, a hyperelliptical shape can have a TL length quite close to that of a reference straight TL. Conversely, a spiral shape has several sub-sections that are close to each other. For any DTLL implementation, the differential input impedance corresponding to the 180° electrical length has a real value.

[0103] As a result of the differential feeding at terminals 21 and 22, the current direction in the extended parallel portion of the transmission line pattern 16 is the same at each moment. This corresponds to a more uniformly distributed current density and therefore to a magnetic field generated over the extended region of the top surface layer (in fact: the entire surface of the coupler) rather than just near a single ring conductor. This enables enhanced flexibility in achieving efficient coupling with RFID tags of various shapes. On the other hand, similar to the transmission line loop structure described previously, the field strength decreases considerably outside the transmission line region, ensuring that the magnetic field remains confined to the area of ​​the coupler surface and that high spatial selectivity remains unaffected.

[0104] For completeness, note that a simple spiral shape (in its strict mathematical sense, i.e., without flattened elongated portions) would be suitable as the geometry of the coupling element according to this disclosure. However, this would prevent the achievement of the specific advantage of enhanced flexibility with respect to various RFID tag shapes by ensuring a uniform current distribution on the top surface.

[0105] Furthermore, it should be emphasized that the exemplary geometric arrangements described above are merely examples for illustrative purposes, and this disclosure is by no means limited to these examples. Rather, any suitable differential feed coupling element structures known or to be known in the future by those skilled in the art are understood to be within the scope of this disclosure.

[0106] According to another non-limiting embodiment, a multilayer electromagnetic coupler device is provided for coupling electromagnetic power to the current loop of an RFID tag of arbitrary geometry via reactive near-field coupling. The electromagnetic coupler device includes a top surface layer forming the top surface of the device, the top surface layer being arranged closest to the RFID tag to which the electromagnetic power is to be coupled. The top surface layer also includes a helical or elongated helical transmission line (transmission line loop) for achieving electromagnetic coupling via inductive coupling with the current loop of the RFID tag. The helical or elongated helical transmission line loop is a continuous transmission line of finite length having a helical or elongated helical shape and terminals at both ends. The terminals are positioned such that at least one turn of transmission line exists between the terminals. The electromagnetic coupler device also includes a metallic ground plane layer and a feed layer for feeding to the two terminals.

[0107] According to another non-limiting preferred embodiment, the terminals are adapted to be differentially fed by signals of equal amplitude and phase offset by 180°.

[0108] Preferably, the transmission line is a continuous transmission line of finite length in an elongated helical shape, wound around a fixed center point such that each turn includes straight sections arranged parallel to each other. Also preferably, the two terminals are arranged on a straight line extending perpendicular to the direction of the transmission line away from the terminals. According to a preferred non-limiting embodiment, the elongated helical shape is planar.

[0109] Note that some relevant non-limiting embodiments have been outlined above. It will be apparent to those skilled in the art that modifications to the disclosed non-limiting embodiments can be made without departing from the spirit and scope of the disclosed non-limiting embodiments. Accordingly, the described non-limiting embodiments should be considered merely illustrative of some more prominent features and applications. Other beneficial results can be achieved by applying the non-limiting embodiments in different ways or modifying them in ways known to those skilled in the art. This includes the mixing and matching of features, elements, and / or functions among the various non-limiting embodiments expressly contemplated herein, such that those skilled in the art will understand from this disclosure that features, elements, and / or functions of one embodiment can be incorporated into another, as will be understood by those skilled in the art from this disclosure, unless otherwise stated above. While specific arrangements and methods have been described, their intent and conception may be adapted and applied to other arrangements and applications.

[0110] For example, in the non-limiting implementation of the operation described herein, it has been described in detail that the connections of all coupling elements are initially (i.e., when the feeding of the unmodulated electromagnetic wave to be applied in the sensing state begins) in an inactive state, i.e., the path from the phase-compensated differential transmission line to the coupling element is switched to a first (high) resistance value. However, the opposite is also possible within the framework of this disclosure. In this case, the DC voltage at the acquisition element rapidly reaches a high level (exceeding a first threshold), which can trigger a switch to switch the connection from a second (low) resistance value to a first (high) value, and then operation proceeds as described above.

[0111] For completeness, note that the previous alternative may not be related to... Figure 3 The structures shown operate together. In this case, the collector element may not trigger a switch quickly enough because it is always connected to the path with higher resistance.

[0112] Alternatively, within the framework of this disclosure, the sensing state can be prepared when the inlay is already present and when the initial switching state is toward a higher resistance. In this case, the DC voltage at the collector element may drop after an initial rise due to strong interaction between one or more coupling elements and the inlay, which triggers the switch.

[0113] For structures such as Figure 2 The structure shown has been described as potentially problematic in terms of stability, as the coupling elements, once activated, will deactivate again after a short period, which is insufficient for a reliable encoding process. As a solution to avoid this, it is recommended to choose resistor values ​​R1 and R2 that are not too different from each other. As an alternative, a time delay element can be considered, which will switch back to a high-resistance state with a delay sufficient for the intended coupling (especially encoding) process.

[0114] In summary, this disclosure relates to a radio electromagnetic coupler device for reactive near-field coupling, comprising a sequential array of coupling elements arranged geometrically in one or two dimensions. In an initial sensing state, automatic selection of a single or multiple coupling elements to establish a particularly strong and effective interaction with the inlay is performed by feeding unmodulated electromagnetic energy waves to each coupling element and its corresponding associated collector element. A switchable array of resistors is used via a corresponding feedback loop to activate the selected coupling element to couple information to / from the loop and to deactivate the remaining coupling elements. The adaptive array of coupling elements according to this disclosure is flexibly adaptable to coupling to planar metallic traces (specifically, RFID inlays) of arbitrary geometries without requiring specific calibration or positioning processes. Scanning the inlay geometry (“inlay profile”) is not required, nor is external control necessary.

Claims

1. A radio electromagnetic coupler device for providing spatial selectivity in the interaction of electromagnetic energy with a planar metallic trace of an RF termination of arbitrary geometry, the electromagnetic coupler device comprising: A sequential array of coupling elements (TLLs) connected in parallel to a phase-compensated differential transmission line (PC TRL) is used to couple the electromagnetic energy to the RF-terminated planar metal trace via reactive near-field coupling. as well as Multiple switchable resistor elements (ISOs) are included in the path between the differential transmission line (PC TRL) and a corresponding coupling element in the array of coupling elements (TLLs) to alternately switch the resistance of the electrical connection between the differential transmission line (PC TRL) and the corresponding coupling element (TLL) to a first value or a second value (R1, R2) by controlling a corresponding switch (2), the second value (R2) being less than the first value (R1); Each of the coupling elements (TLL) is associated with the following: The corresponding collector element (H) is used to collect the energy fed from the differential transmission line (PC TRL); and The corresponding feedback loop (3) is used to provide feedback from the collector element (H) to the corresponding switch (2) to switch the resistor element (ISO) included in the corresponding path based on the DC voltage established at the collector element (H).

2. The electromagnetic coupler device according to claim 1, wherein, The electrical connection between each collector element (H) and the differential transmission line (PC TRL) and the electrical connection between the differential transmission line (PC TRL) and the corresponding coupling element (TLL) can be alternately switched between an electrical connection having a first resistance value (R1) and an electrical connection having a second resistance value (R2).

3. The electromagnetic coupler device according to claim 1, wherein, Each of the collector elements (H) is permanently coupled to the differential transmission line (PC TRL) via an electrical connection having a first resistance value (R1).

4. The electromagnetic coupler device according to any one of claims 1 to 3, further comprising: Interrogator (10) is used to feed electromagnetic energy to be coupled to the planar metal trace.

5. The electromagnetic coupler device according to claim 4, further comprising: A balun (B) is electrically coupled between the interrogator (10) and the differential transmission line (PC TRL), the balun (B) forming the differential transmission line input by splitting the output of the interrogator (10) into two parts with equal amplitude and 180° phase offset.

6. The electromagnetic coupler device according to claim 4, wherein, The interrogator is configured to feed unmodulated electromagnetic energy to the coupling element in a sensing state. The unmodulated electromagnetic energy is an RF carrier guided by the differential transmission line (PCTRL), wherein the resistance is initially switched to the first value (R1) for all coupling elements of the array.

7. The electromagnetic coupler device according to claim 6, wherein, The interrogator (10) is configured to subsequently modulate the RF carrier into a communication signal to the coupling element.

8. The electromagnetic coupler device according to claim 7, wherein, The interrogator (10) is configured to feed the communication signal after a stable switching state of each of the switches (2) has been established, taking into account the interaction between the RF carrier feeding the unmodulated electromagnetic energy and the RF termination planar metal trace.

9. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, The differential transmission line (PCTRL) is terminated.

10. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, Each of the coupling elements (TLL) includes a transmission line loop (6) for interacting with the RF termination planar metal trace via inductive coupling. The transmission line loop (6) is a continuous transmission line of finite length, which is formed as a loop such that the two terminals (21, 22) of the continuous transmission line are close to each other and differentially fed through the differential transmission line (PC TRL).

11. The electromagnetic coupler device according to claim 10, wherein, The transmission line loop (6) has a superelliptical geometry as indicated by the following parameters: ， Where x and y are Cartesian coordinates.

12. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, Each of the coupling elements (TLL) includes an elongated helical planar transmission line pattern (16) for interacting with the RF termination planar metal trace via inductive coupling, wherein the elongated helical transmission line pattern (16) is a continuous transmission line of finite length with an elongated helical shape having terminals (21, 22) at both ends, wherein the terminals are positioned such that there is at least one turn of transmission line between the terminals.

13. The electromagnetic coupler device according to claim 12, wherein, The finite-length continuous transmission line is wound around a fixed center point (20), such that each turn includes straight sections arranged parallel to each other.

14. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, The sequential array of the coupling elements has a one-dimensional geometric arrangement.

15. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, The sequential array of the coupling elements has a two-dimensional geometric arrangement.

16. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, The RF termination planar metal trace is an RFID inlay.

17. The electromagnetic coupler device of claim 16, adapted to encode the RFID inlay by coupling electromagnetic power to the RFID inlay.

18. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, When the DC voltage exceeds a predetermined first threshold, the resistor is switched to the first value.

19. The electromagnetic coupler device according to claim 18, wherein, When the DC voltage drops below a predetermined second threshold, the resistor is switched from the first value to the second value, where the second threshold is lower than the first threshold.

20. The electromagnetic coupler device according to any one of claims 1 to 3, wherein, Each feedback loop in the feedback loop (3) includes an inverting operational amplifier.

21. An RFID printer comprising an electromagnetic coupler device (1) according to any one of claims 1 to 20.

22. An RFID encoder comprising an electromagnetic coupler device (1) according to any one of claims 1 to 20.

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