Electromagnetic coupler structure, RFID printer / encoder

Abstract

The present disclosure relates to a dual frequency responsive near-field electromagnetic coupler structure for RFID inlays, particularly for encoding RFID inlays with electromagnetic signals. The central element of this structural arrangement is a double-ended linear metallic structure having a helical or elongated helical planar shape and including multiple looped metallic trace sections. The structure is connected to a power supply terminal, and the individual sections are interconnected by inductive and capacitive elements to form an LC filter network. The network is arranged to allow the coupler structure to operate efficiently in two different frequency ranges, particularly HF and UHF. The present disclosure further relates to an RFID printer / encoder incorporating the dual frequency responsive near-field electromagnetic coupler structure.

Description

[Technical Field]

[0001] The present disclosure relates generally to electromagnetic coupling technology. More specifically, non-limiting embodiments relate to an electromagnetic coupler structure suitable for use in a printer, operable in at least two different frequency ranges, for near-field encoding applications, such as encoding RFID inlays. [Background technology]

[0002] Radio frequency identification (RFID) is a technology that uses radio waves to transfer data from electronic tags (known as RFID tags or RFID inlays). Information is stored electronically on the tags. To read the information, an RFID reader sends a coded radio signal to interrogate the tag. To do this, RFID tags have a planar metal trace, more specifically a current loop suitable for inductive coupling. The same planar metal trace (current loop) can also be used to encode RFID tags by electromagnetic coupling.

[0003] An RFID device including a planar metal trace is commonly referred to as an inlay. Technically, an RFID inlay is an RF-terminated planar metal trace. Specifically, an inlay is an RFID device with a planar metal trace film supported on a flexible substrate that connects to a transponder. The transponder, contained in a current loop, is an integrated circuit for decoding signals sent to the inlay and received by the planar metal trace. The transponder is also used to transmit signals to the planar metal trace, which are then transmitted by the planar metal trace (sometimes referred to as an "antenna"). The inlay antenna may be tuned (i.e., sized) to communicate at a certain target frequency with a transceiver that includes at least a coupling element for communicating with the RFID inlay and an interrogator. For better understanding, the term "antenna" in this disclosure will be interpreted to mean a radiating device. However, this disclosure relates to reactive near-field coupling as opposed to radiative far-field coupling. Therefore, the use of the term "antenna" is limited to RFID inlays and tags. The antenna's intended operation and design target may be in the near field and / or far field of propagation.

[0004] Recently, printing devices have become known that can place RFID inlays on media such as paper and simultaneously encode the RFID inlays with desired information during printing. The encoding is accomplished by electromagnetic coupling, preferably in a reactive near-field. To this end, RFID printer / encoders include an electromagnetic coupler structure that fits into a cavity in the printer so that, as media is guided along a media path into the printer / encoder, an electromagnetic force carrying the encoded information couples with an RFID inlay located on the media.

[0005] A coupler structure having not only one coupling element but also a plurality of coupling elements arranged in a one-dimensional or two-dimensional array can also be used.

[0006] In actual implementations, there will be different RFID labels (tags) with different operating frequencies. For example, the operating frequency for encoding an RFID tag to be interrogated may be in the HF (high frequency) or UHF (ultra high frequency) frequency range. In this disclosure, "HF" is used to designate any frequency range between approximately 3 and 30 MHz (megahertz). A common center frequency for HF communications is 13.56 MHz. "UHF" is used to designate even higher frequency ranges. Common UHF frequencies range anywhere from approximately 300 MHz to 3 GHz (gigahertz).

[0007] Some RFID labels contain multiple tags, which may include HF and / or UHF tags. There may be a single physical chip that operates at both HF and UHF frequencies, or there may be two separate, spatially distributed tags (chips) within the inlay that operate at HF ​​and UHF frequencies, respectively. In the former case, the HF and UHF "antennas" may be on a single chip. Notably, there is a single RFID chip with separate connections for the HF and UHF antennas. In one example, the HF antenna is a near-field multi-turn magnetic coil, and the UHF antenna is tuned to propagate in the far field.

[0008] However, in certain applications, such as printer applications, the limited space requirements make it undesirable to use radiative (far-field) coupling. Therefore, it is desirable to implement a loop-type reactive near-field solution for UHF inlays as well. Although tag / inlay antennas have nominal radiative characteristics, these same structures can also be used for reactive near-field coupling applications, especially when equipped with loop-type structures.

[0009] For example, but not limited to, in printer applications, it may be desirable to communicate with labels (tags) using different frequency ranges, particularly tags of HF and UHF technology, using a single coupling structure. In particular, the printer needs to be able to encode (program) both HF and UHF RFID labels (tags) within a single hardware (and preferably software) platform.

[0010] Another challenge in printer environments, especially small printers such as label or tag printers, is the limited space available for mounting each electromagnetic coupler structure. While it may be possible in principle to envision multiple independent coupler structures for different frequency ranges, each connected to a corresponding interrogator within a single printer, this has the drawback of requiring greater space compared to a single-frequency encoding coupler structure.

[0011] It is therefore desirable to provide a universal electromagnetic coupler structure suitable for encoding RFID inlays that can operate over different frequency ranges and that is suitable for installation in devices with limited installation space, such as label and tag printers. Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems and provide a dual frequency electromagnetic coupler structure that uses a common hardware configuration for communication in both the first and second frequency ranges. [Means for solving the problem]

[0013] This is achieved by the features of claim 1. Further features and advantages of the embodiments of the invention are the subject of the dependent claims.

[0014] According to a first aspect, a dual frequency reactive near-field electromagnetic coupler structure for interconnecting with an RFID inlay via electromagnetic energy is provided. The electromagnetic coupler structure includes a ground plane and a double-ended linear metal structure having a spiral or elongated spiral planar shape and including multiple looped metal trace sections. Each section is connected to the next section by an inductive element. A first terminal of the first looped metal trace section and an end terminal of the last looped metal trace section are connected to first and second feed terminals, respectively, through the inductive elements. The inductive elements are positioned such that each inductive element is adjacent to the previous and next inductive elements along the current path of the linear metal structure. Each capacitive element is positioned to connect between each terminal of an inductive element and each terminal of an adjacent inductive element.

[0015] A specific approach of a non-limiting embodiment provides a reactive near-field electromagnetic coupler structure for encoding RFID inlays that can operate in at least two frequency ranges, such as HF and UHF. Specifically, the coupler structure comprises a double-ended linear metal structure having multiple loop-shaped metal trace sections connected to a feed terminal and connected to each other in a specific manner by respective inductive and capacitive elements forming a ladder-like LC filter network. This allows different operating methods to be achieved depending on the frequency range of the input signal supplied to the coupler structure. In lower frequency ranges (e.g., HF), the signal passes through each loop section in sequence, forming a spiral or elongated spiral loop as the effective loop. In higher frequency ranges (e.g., UHF), the individual loop sections are short-circuited to form a single loop with a thicker metal trace. While such a coupler topology is sufficient for the UHF frequency band, it should be considered that using the same physical length for HF as for UHF makes matching of the coupler system difficult due to the extremely short electrical length and very low loss at HF. Thus, the present invention increases the physical length and self-inductance by a factor corresponding to the number of individual loops in the ladder-type LC filter network structure. This electromagnetic coupler structure is particularly suitable for deployment in printers with RFID encoding capabilities, such as small label and tag printers.

[0016] This outlined approach can be realized by a wireless electromagnetic coupler structure according to the first aspect described above.

[0017] According to a non-limiting embodiment, the electromagnetic coupler structure has a multi-layer structure. In this structure, a double-ended linear metal structure is disposed in a top layer that forms the top surface of the electromagnetic coupler structure, which is disposed closest to the RFID inlay to which electromagnetic force is coupled. A (first) metal ground plane layer with a ground plane is disposed below the top layer. Capacitive and inductive elements are disposed in a component layer disposed on the opposite side of the top layer from the (first) ground plane layer. The ground plane layer is separated from the top layer by a substrate layer (first dielectric substrate layer) with vias therein for providing electrical connection between each component and the looped metal trace section. Similarly, another substrate layer (second substrate layer) with vias for electrical connection is disposed between the metal ground plane layer and the component layer. In this embodiment, the components are disposed on a layer separate from the top layer because, for most efficient near-field coupling, the actual metal coupling structure should be completely flat (planar), and the inductive and capacitive elements need to be disposed on a separate plane (layer). Preferably, the component layer further includes a feed network for feeding the first feed terminal and the second feed terminal, and may be referred to as a component and feed layer. In particular, the feed network may include a balun (balanced-to-unbalanced transformer) capable of realizing differential feeding of each feed terminal at least in a specific frequency range.

[0018] According to a preferred, non-limiting embodiment, the multilayer structure further includes an intermediate signal layer disposed on the opposite side of the (first) metal ground plane layer from the top layer. In this case, a (second) metal ground plane layer is further disposed between the intermediate signal layer and the component / component and feed layer. Third and fourth dielectric substrate layers are disposed between the first metal ground plane layer and the intermediate signal layer, and between the intermediate signal layer and the second metal ground plane layer, respectively. Vias are provided in the third and fourth dielectric substrate layers to electrically connect the component (component and feed) layer to the top layer and / or the intermediate signal layer. In the case of complex signal structures, such as those involving signal crossings in space, intermediate signal layers may be required to properly distribute signals input from the component and feed layers to the coupler structures on the top layer. Those skilled in the art will recognize that this type of multilayer structure is known in the art as a microstripline / stripline structure.

[0019] Preferably, the double-ended linear metallic structure has an elongated spiral planar shape, wound around a fixed center point so that each winding has a straight portion arranged parallel to each other. The first terminal of the first looped metal trace section and the end terminal of the last looped metal trace section are arranged so that at least one winding of the linear metallic structure exists between them. More preferably, the first terminal and the end terminal are arranged adjacent to a line extending perpendicular to the direction in which the linear metallic structure moves away from each terminal. Roughly speaking, the connecting line between the first terminal and the end terminal of the linear metallic structure is approximately perpendicular to the direction of the metallic trace near the terminal. The advantage of the elongated spiral shape described above compared to a strictly geometrical spiral shape is realized by the presence of parallel straight portions in each winding. In the case of differential feeding, i.e., in the high frequency range, current flows in the same direction along the entire transmission line loop as long as the electrical length is equal to or less than half the guided wavelength, thereby generating a uniform magnetic field along the line and distributing it throughout the entire loop length of the coupler. This allows for greater flexibility in achieving efficient coupling with inlays of various shapes, while at the same time confining the magnetic field to the area of ​​the coupler surface only, without affecting selectivity.

[0020] According to a preferred, non-limiting embodiment, the electromagnetic coupler structure further includes a balun as a feed network. The balun has a first balun terminal connected to the first feed terminal and a second balun terminal connected to the second feed terminal. The balun is configured to provide equal-amplitude, 180° out-of-phase electromagnetic signals to the linear metal structure when operating in a first frequency range (a higher frequency range), and to provide signals to the first feed terminal only while the second feed terminal is grounded when operating in a second frequency range (lower than the first frequency range). More preferably, the balun has a third balun terminal serving as a coupler input connected to an interrogation device for providing electromagnetic energy coupled to the RFID inlay. A first current path between the third balun terminal and the first balun terminal includes at least one inductive element. The first current path is connected to ground via at least one capacitive element. A second current path between the third balun terminal and the second balun terminal includes at least one capacitive element and is connected to ground via at least one inductive element. The balun's structure, as described above, allows the balun itself to implement an LC filter structure, enabling different behavior depending on the power supply frequency. In particular, as mentioned above, in the high frequency range (e.g., UHF), the balun is a double-ended structure that allows for differential power supply. In lower frequency ranges (e.g., HF), the balun operates as a single-ended structure with one terminal grounded. The specific implementation of the balun in the form of an LC filter network is described in more detail below.

[0021] According to a preferred, non-limiting embodiment, the electromagnetic coupler structure further comprises an interrogation device for providing a signal (an interrogation signal or a coded signal to be coupled to the RFID inlay) and / or for processing a response signal received from the RFID inlay via the electromagnetic coupler structure, the interrogation device being coupled to the third balun terminal for providing electromagnetic energy to be coupled to the RFID inlay.

[0022] According to an alternative preferred, non-limiting embodiment, the interrogation device may be provided separately from the actual construction of the electromagnetic coupler structure.

[0023] According to a preferred, non-limiting embodiment, the first (high) frequency range is a UHF frequency range and the second (low) frequency range is a HF frequency range. More preferably, the electrical length of one looped metal trace section does not exceed half a guided wavelength in the first frequency range. Otherwise, zero crossings of the current along the loop may occur at UHF, which may degrade coupling to the inlay.

[0024] According to a preferred, non-limiting embodiment, the electromagnetic coupler structure is configured to encode the RFID inlay by coupling electromagnetic forces.

[0025] Also preferably, the coupler structure is suitable for use in a printer, and the encoded RFID inlay is disposed on media guided through the printer along a media path.

[0026] According to a further non-limiting particular aspect, there is provided an RFID printer / encoder comprising an electromagnetic coupler structure according to the first aspect or any of its non-limiting embodiments. Because the electromagnetic coupling for transferring encoded information to the RFID inlay occurs in a reactive near-field, the multi-layer electromagnetic coupler structure can be easily fitted within a cavity of the printer in proximity to the media path.

[0027] According to a preferred, non-limiting embodiment, the RFID printer / encoder further comprises an interrogator that provides electromagnetic energy that is coupled to the RFID inlay, and more preferably, the interrogator comprises an HF interrogator and a UHF interrogator integrated into a single unit and embedded on the motherboard.

[0028] The disclosed non-limiting embodiments broadly aim to provide an improved electromagnetic coupler structure applicable for efficiently coupling electromagnetic power into inlays of any shape in at least two frequency ranges.

[0029] These and other aspects and features of the non-limiting embodiments will become apparent to those skilled in the art from the following description of specific non-limiting embodiments taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0030] Additional features and advantages of the non-limiting embodiments will become apparent from the following description taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of a printer with RFID encoding capabilities according to an embodiment of the present disclosure. [Figure 2] 1A-1C illustrate the geometry of an electromagnetic coupler structure having an elongated, spiral, double-ended linear metallic structure according to an embodiment of the present disclosure. [Figure 3] 3 is a schematic electrical circuit diagram of the embodiment of the electromagnetic coupler structure shown in FIG. 2. [Figure 4] FIG. 1 is a schematic diagram of a feeding network including a balun suitable for feeding an electromagnetic coupler structure, according to an embodiment of the present disclosure. [Figure 5] FIG. 1 is a schematic electrical circuit diagram of an example implementation of a balun suitable as a power feed network, according to an embodiment of the present disclosure. [Figure 6] 1 is a schematic diagram of an electromagnetic coupler structure having a multi-layer structure, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0031] Throughout this specification, the word "comprises" or variations thereof (such as including) means the inclusion of a stated element, integer, or step, or collection of elements, integers, or steps, but does not exclude any other element, integer, or step, or collection of elements, integers, or steps.

[0032] The present disclosure relates to an electromagnetic coupler structure operating in at least two different frequency ranges (such as HF and UHF) for intercoupling with, and particularly encoding, RFID inlays.

[0033] In a non-limiting embodiment of the electromagnetic coupler structure, an interrogator (also called an "RFID reader") is connected to a helical or elongated helical coupling element via a balun.

[0034] The disclosed non-limiting embodiments are particularly suited for encoding inlays provided on media, such as RFID printer / encoders.

[0035] Thus, the present invention provides an RFID-enabled printer that has the ability to program both HF and UHF RFID labels (tags) within a single software and hardware platform. Thus, a combination of HF and UHF RFID functionality is included in a single printer product. Furthermore, multiple tags of either HF technology, UHF technology, or a combination thereof may comprise one and the same RFID label.

[0036] FIG. 1 is a general conceptual diagram of a dual frequency printer / encoder according to an embodiment of the present disclosure.

[0037] The figure shows a schematic representation of a printer (RFID printer / encoder) 100 having a platen roller 10 as an element for feeding print media 20. The printer further comprises an electromagnetic coupler 30 for encoding an RFID inlay provided (embedded) on the print media 20. The coupler 30 is coupled (via a respective cable) to an interrogator 40 embedded in the printer. The embedded interrogator 40 comprises, among other things, an HF interrogator 40a for providing the coupler 30 with signals in the HF frequency range and a UHF interrogator 40b for providing the coupler 30 with signals in the UHF frequency range.

[0038] Those skilled in the art will recognize that this type of printer / encoder includes several additional components, which are not shown here to reduce drawing complexity and focus on elements of printer 100 relevant to the key features of this disclosure. In particular, components related to the actual printing are omitted, as are components that provide control functions. These components may be implemented in any manner known in the art, and the particular implementation is irrelevant to, and therefore not required by, the present invention.

[0039] Although the HF and UHF interrogator components are shown as two separate components of an embedded interrogator in this diagram, the present disclosure is not limited to such an implementation. Depending on the level of integration, separate HF and UHF interrogators can be used when implementing the teachings of the present disclosure, or separate HF and UHF interrogator components can be used within a single interrogator. Specifically, two separate interrogator components (interrogation units) can be embedded on the printer's motherboard. An even higher level of integration can be achieved by embedding a single interrogator on the motherboard that can generate and process both HF and UHF signals. As described below, for integrated HF and UHF interrogators, an implementation that uses only a single power feed for both frequency ranges is particularly advantageous. For example, this can be achieved by a power feed network that includes a balun that can separate the two frequency ranges.

[0040] In other words, the interrogator 40 may be separated into two physical units (40a and 40b) for HF and UHF technology, respectively, depending on the available space. Furthermore, these units may be housed in different housings, although the term "embedded" is typically used for such configurations since the interrogator housing is located within the printer housing.

[0041] Another possibility is to integrate HF and UHF technologies in one unit and housing, which would reduce the size and therefore make it applicable to small printers. Yet another possibility is "on-chip" integration directly on the printer's motherboard. Again, the HF and UHF technologies may be more or less integrated, either in a multi-frequency chip solution or in separate frequency-dependent chips.

[0042] Each programmed RFID medium may be of a different type in the combined HF / UHF interrogator approach, and may be capable of different countermeasures in frequency and / or spatial sense. In the case of a single RFID inlay / tag, there may be a single physical chip that operates at both HF and UHF frequencies, or there may be two separate, spatially distributed inlays / tags that operate at HF ​​and UHF frequencies, respectively, among other possibilities.

[0043] The present invention provides a universal coupler that operates in two frequency bands (ranges), thereby achieving the technical advantage of providing a spatially compact coupler solution that easily fits within a single label / inlay pitch length. Regarding pitch length, note that in an RFID printer / encoder, individual RFID labels (tags) are embedded on a print medium, such as a roll of paper, with multiple labels attached, each label having an RFID tag. In this case, the "pitch length" corresponds to the distance between adjacent RFID tags on the print medium. Because it is desirable to encode each RFID tag individually (in principle, because each tag needs to encode different information), it is necessary to achieve targeted (selective) coupling with only a single RFID tag at a time. To this end, it is desirable for the coupler structure to be limited to a single label, specifically the pitch length.

[0044] FIG. 2 is a diagram illustrating a schematic structure of an electromagnetic coupler structure 300 according to an embodiment of the present disclosure.

[0045] Specifically, the structure shown is in the form of an elongated spiral path of copper traces on a protection circuit board (PCB, also known as a printed circuit board).

[0046] The electromagnetic coupler structure 300 comprises a double-ended linear metal structure 36 that includes a plurality of looped metal trace sections. In this example, three looped metal trace sections 36a, 36b, and 36c are shown. However, the number of looped metal trace sections is not limited to three, and any other number of looped metal trace sections (windings) is possible. Preferably, the metal structure is made of copper, but is not limited to this particular metal.

[0047] As can be further seen, two power supply terminals 31 and 32 are provided adjacent to each other. In the area of ​​the power supply terminals there is also provided a ladder structure 34, an enlarged view of which is shown in the center of the left side of the figure. Each loop of metal trace that emerges from the right side of ladder structure 34, makes a complete circuit and then returns to the left side of ladder structure 34 represents a looped metal trace section.

[0048] In this ladder structure, each horizontally hatched element in the center (corresponding to a "step" on the ladder) represents an inductive element. Thus, in general, each inductive element connects the (e.g., left) terminal of one looped metal trace section to the (e.g., right) terminal of the next (i.e., subsequent) looped metal trace section along the current path. Thus, in the illustrated example, the terminal of trace section 36a (left of the second step of the ladder) is connected to the terminal of trace section 36b (right of the second step of the ladder), and the other terminal of trace section 36b (left of the third step of the ladder) is connected to the terminal of trace section 36c (right of the third step of the ladder). The only exceptions are the beginning and end of the linear metal structure. That is, the first terminal of the first trace section 36a (right of the first step of the ladder) is connected to the first power supply terminal 31 (left of the first step of the ladder) via an inductive element. Meanwhile, the end terminal of the last trace section 36c (left of the fourth rung of the ladder) is connected via an inductive element to the second feed terminal 32 (right of the fourth rung of the ladder). Note that, because the entire structure is perfectly symmetrical, it is not important to the present disclosure which of the illustrated feed terminals (31 and 32) are designated "first" and "second," and which of the trace sections are accordingly designated "first" and "last." By convention, the innermost elongated spiral trace section (36a) is designated "first," and the outermost trace section (36c) is designated "last," although those skilled in the art will recognize that these designations may be changed to other conventions within the framework of the present invention.

[0049] In ladder structure 34, vertically hatched elements (those on either side of the structure and located between the ladder "rungs," i.e., in the region of the ladder "bars") represent capacitive elements. Thus, capacitive coupling typically exists between each terminal of each trace section (the "first" and "second" along the current path) and each adjacent trace section. More specifically, the "first" terminal of second trace section 36b capacitively couples with the "first" terminals of both first trace section 36a and third ("last") trace section 36c (on the right side of the ladder structure). Similarly, for each "second" terminal (on the left side of the ladder structure).

[0050] The only exceptions are at the beginning and end of the entire structure: there is a capacitor coupling between the first feed terminal 31 and the second terminal of the first trace section 36a (top left corner of ladder structure 34), and between the second feed terminal 32 and the first terminal of the third ("last") trace section 36c (bottom right corner of ladder structure 34).

[0051] Furthermore, as can be seen from the figures, the coupler structure in the given example has an elongated spiral shape, as opposed to a spiral shape in the strict geometric sense, which differs from the illustrated shape in that it has no straight sections. The "elongated spiral shape" as understood in this disclosure as shown is a structure in which multiple windings (each corresponding to one of the metal trace sections) are wound around a central point (35 in the figures). However, there are linear (or nearly linear) sections (particularly across the width of the figures). As can be seen from the figures, the straight sections of each winding are arranged parallel to one another (connected by curved sections), and each feed terminal is positioned so that there is at least one winding of the metal structure between them. As will be explained in more detail below, it is these straight or nearly linear sections that particularly contribute to improving coupling efficiency.

[0052] To give some idea, but not by way of limitation, the width dimension of the structure shown in FIG. 2 may be on the order of 10 mm (millimeters).

[0053] FIG. 3 is an equivalent circuit diagram of the structure shown in FIG.

[0054] In the following, the functionality of the electromagnetic coupler structure 300 shown in FIG. 2 will be explained with reference to FIG.

[0055] On the right side of the figure, metal trace sections 36a, 36b, and 36c are shown as current loops. On the left side, power supply terminals 31 and 32 (labeled "Port 1" and "Port 2," respectively) are shown. The center of the drawing shows interconnections via capacitive (C) and inductive (L) elements arranged in a ladder structure 34 (schematically shown in a dashed box).

[0056] As can be seen in this diagram, the interconnections within the ladder structure 34 form an LC filter network. This filter network separates low and high frequencies. That is, at low frequencies (e.g., HF), inductors represent a low-resistance path for the signal, while capacitors are high-resistance. For higher frequencies (e.g., UHF), the opposite is true. When following a low-frequency path, such as HF, the signal passes through each loop sequentially, and therefore the effective loop is a spiral loop. When following a high-frequency path, such as UHF, each loop is shunted, forming a single loop with a thicker metal trace (e.g., copper trace).

[0057] As mentioned above, one requirement is that the loop must not exceed half the guided wavelength at UHF, which can be important to maintain high coupling efficiency. In this case, zero crossings of the current occur along the loop, meaning poor coupling to the inlay. At HF, the electrical length is much shorter, so the number of turns in the spiral loop is not important in this case. In both cases, the strength of the current along the loop is important to enable strong reactive near-field coupling to the inlay.

[0058] Of course, the electrical parameters (values) of the inductive and capacitive elements used in a particular implementation must be selected and adjusted according to the frequency values ​​to be isolated, i.e., the frequency range over which the coupler is desired to operate. For example, a value of 100 nH at the UHF frequency of 890 MHz represents a reactance of 560 Ω, which is considered high resistance. On the other hand, at the HF frequency of 13.56 MHz, the corresponding value is 8.5 Ω, which is considered low resistance. A 20 pF capacitor has values ​​of 8.9 Ω and 590 Ω, which are considered low and high resistances, respectively. However, these values ​​are merely examples and are not intended to limit the scope of the present invention.

[0059] In Figure 3, the capacitor CPC (capacitive phase compensation) and resistor RQVR (Q-reducing resistor) are optional components. The reason for including these components is as follows: LC networks with specially tuned components can have a very high "quality factor" but at the same time have a very narrow bandwidth, which affects matching. Using the additional resistor RQVR reduces the Q factor, achieving a wider bandwidth and better matching. The value of capacitor CPC can be set to match the system impedance for a given input. In other words, CPC may compensate for the overall inductive characteristics of the vortex, resulting in a total net impedance. This net impedance (resistance) may be shunted by RQVR towards a lower value for an acceptable bandwidth / efficiency compromise.

[0060] 4 is a schematic diagram of a circuit including a balun suitable for use as a power feed network within the framework of the present disclosure. Generally speaking, a balun is a functional block that converts a balanced channel (which may carry differential signals) into an unbalanced or single-ended channel.

[0061] As can be seen from the figure, the balun 2 has an input terminal 1 and two output terminals 7 and 8.

[0062] An input signal of a predetermined frequency band, such as from a given 50 ohm coaxial cable system, is input to input terminal 1. Balun 2 splits the input signal into two signals, which are output to output terminals 7 and 8. Output terminals 7 and 8 are connected to first and second supply terminals 31 and 32 of the electromagnetic coupler structure, respectively, to provide the split signals. Specifically, balun 2 operates to split the input signal into two signals of equal amplitude but 180° out of phase with each other, at least for input signals in a certain (higher) frequency range, such as UHF. The combination of such signals output to output terminals 7 and 8 is considered a "differential signal."

[0063] Furthermore, differential feeding, i.e., feeding with differential signals at feed terminals 31 and 32, demonstrates why the elongated spiral shape of the coupler structure is preferable to a strict geometric spiral. As a result of differential feeding at terminals 31 and 32, the current flows in the same direction in the elongated parallel portion of metal structure 36 at each instant of time. This corresponds to a more uniformly distributed current density, generating a magnetic field along the coupler's transmission line loop path. This results in highly efficient coupling with RFID tags of various shapes. Meanwhile, because the electric field strength rapidly decreases outside the metal structure area, the magnetic field is limited to the coupler surface area, which does not affect the high spatial selectivity.

[0064] For the sake of completeness, it is noted that a simple spiral shape (in the strict mathematical sense, i.e., without any flattened strips) would be suitable as a coupler geometry according to the present disclosure, although the particular advantage of providing a uniform current distribution over the entire top surface for improved adaptability with respect to various RFID tag shapes would not be achieved in this case.

[0065] An exemplary embodiment of the balun 2 will now be described in more detail with reference to FIG.

[0066] FIG. 5 is an equivalent circuit diagram of a particular embodiment of a balun 2 suitable as a feeding network in a loop configuration, as described above with reference to FIGS. 2 and 3 and shown diagrammatically in FIG.

[0067] Such structures are typically used as balun transformers for differential feeding of coupled loops at UHF.

[0068] As can be seen from the figure, balun 2 generally has a three-port structure, with input terminal 1 labeled "Port 1" and two output terminals 7 and 8 labeled "Port 2" and "Port 3," respectively. For clarity in the following discussion, it will be assumed that output terminal 7 is coupled to input terminal 31 of structure 300 in FIG. 3, and output terminal 8 is coupled to input terminal 32 of structure 300 in FIG. 3.

[0069] As can be further seen from the figure, input port 1 is connected to output port 7 via first current path 51 and to output port 8 via second current path 52. Specifically, first current path 51 connects input terminal 1 and output terminal 7 via inductive elements (shown as LLP1 and LLP2). This current path is further connected to ground via capacitive elements (shown as CLP and CHP2). Second current path 52 connects input terminal 1 and output terminal 8 via a capacitive element (shown as CHP2). This current path is further connected to ground via an LC filter comprising two inductive elements (shown as LLP1 and LLP2) and a capacitive element CLP in a further branch, as shown. In this figure, "LP" stands for "low pass" and "HP" stands for "high pass." In particular, it can be seen that elements LLP1, LLP2, and CLP each form the structure of a low pass filter. However, for historical reasons of development, the label "CHP2" is used.

[0070] Based on the method of FIG. 5, a similar network analysis to that described above can be performed on the loop structure of FIG.

[0071] At low frequencies (e.g., HF), a capacitor is a high-resistance path and an inductor is a low-resistance path. This results in a low-resistance path from input terminal 1 to output terminal 7, and output terminal 8 has a low-resistance path to ground. Input terminal 1 (“Port 1”) here represents the coupler input connected to interrogator 40, and as shown above, output terminal 7 (“Port 2”) is connected to one of the loop terminals (i.e., feed terminal 31 for clarity, but this is not required for symmetry). Output terminal 8 (“Port 3”) is connected to the other loop terminal (i.e., feed terminal 32 for clarity), and is therefore grounded. Thus, at lower (HF) frequencies, the balun structure is actually a single-ended solution.

[0072] On the other hand, at higher frequencies (e.g., UHF), the situation becomes more complex. The balun components (LLP1, LLP2, CLP, CHP2) have specific values ​​that follow design equations for operation at the desired frequencies (especially UHF). This results in the balun structure at high frequencies (UHF) being a tuned device that allows differential feeding at feed terminals 31 and 32 of loop structure 36 (which, as mentioned above, operates as a single loop at these frequencies).

[0073] Details regarding the design of each component, including their respective design equations, can be found in the article "Design Equations for Lumped Element Balun With Inherent Complex Impedance Transformation" by Markus Frank, Mattias Thorsell, and Peter Enoksson (IEEE Transactions on Microwave Theory and Techniques, Vol. 65, No. 12, December 12, 2017). As noted therein, the balun arrangement shown in FIG. 5 is merely an example, and balun structures applicable within the framework of this disclosure are not limited thereto. For example, arrangements including a high-pass filter in one of the current paths, or more complex structures, would also be possible to achieve the goal of achieving a device tuned for differential feeding at UHF and a single-ended structure at HF.

[0074] However, the implementation details of the exemplary balun are not essential for use within the framework of this disclosure - all that matters is that the structure and component values ​​be selected to allow for a differentially fed arrangement in the high frequency range (UHF) and a single-ended grounded arrangement in the low frequency range (HF).

[0075] As a result, Balun 2 can operate at both HF and UHF because the electrical lengths differ significantly between HF and UHF operation, making a single-ended ground connection not a disadvantage at HF.

[0076] A more distributed type of coupler is also possible, with multiple elements, each operating in a single or multiple frequency bands as explained above. This may be desirable if programming over a larger spatial region is required. In this case, a coupler element array can be applied.

[0077] FIG. 6 is a diagram illustrating an example of a multi-layer structure implementing an electromagnetic coupler structure according to a non-limiting embodiment of the present disclosure.

[0078] This exemplary multi-layer structure has five metal signal layers (s1, s2, s3, s4, s5). A plurality of four dielectric substrate layers (d1, d2, d3, d4) are positioned between, and "sandwiched" by, adjacent two metal layers, providing electrical isolation between the signal layers. However, electrical connections can be made through vias in the substrate layers if desired (not shown).

[0079] In the illustrated structure, layer s5 corresponds to the top layer including the double-ended linear metal structure 36. Figure 6 further shows an encoded RFID tag 60 that is positioned proximate to top layer s5. In other words, in the printer, top layer s5 is positioned near the printer's media path along which the encoded RFID tag is guided.

[0080] Furthermore, in the illustrated structure, layers s4, s3, s2, and s1 correspond to the aforementioned first ground plane layer, intermediate signal layer (optional), second ground plane layer (optional), and power / component layer, respectively. The intermediate signal layer is realized with stripline technology and is always sandwiched between two ground plane layers, while the top layer and the component and power layers are implemented with microstrip technology and combined into a single ground plane. As noted above, the intermediate signal layer s3 and second ground plane layer s2 are optional. Thus, the minimum stackup has three metal layers: s5, s4, and s1 (with two substrates d4 and d1 between them).

[0081] The structure according to the present disclosure provides several advantages over the prior art in the related art.

[0082] According to the present disclosure, a single RFID printer product can be used to program both HF and UHF inlays (tags), potentially reducing costs for customers who require both HF and UHF printer technology compared to purchasing HF and UHF printer products separately.

[0083] Currently, both HF and UHF RFID are viable and existing technologies, allowing printer manufacturers to streamline production.

[0084] The development towards multi-frequency concepts will encourage the development of smaller solutions and integration, which will allow implementation in a wider range of products.

[0085] A more streamlined product in terms of RFID frequency ranges could also mean reduced costs for agency approval.

[0086] The foregoing description outlines some of the more suitable non-limiting embodiments. Those skilled in the art will recognize that modifications to the disclosed non-limiting embodiments may be achieved without departing from the spirit and scope thereof. Accordingly, the described non-limiting embodiments should be considered merely illustrative of some of their more prominent features and applications. Other beneficial results may 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 following: Combinations and matching of features, elements, and / or functions among the various non-limiting embodiments are contemplated herein, and those skilled in the art will recognize that features, elements, and / or functions of one embodiment may be incorporated into other embodiments as appropriate, unless specifically noted above. While this description has been directed to particular structures and methods, the intent and concept thereof may be suitable and applicable to other structures and applications.

[0087] In summary, this disclosure relates to a dual-frequency-responsive near-field electromagnetic coupler structure for RFID inlays, particularly for encoding RFID inlays with electromagnetic signals. The central element of this structural arrangement is a double-ended linear metal structure having a helical or elongated helical planar shape and including multiple looped metal trace sections. The structure is connected to a feed terminal, and the individual sections are interconnected by inductive and capacitive elements to form an LC filter network. This network is arranged to allow the coupler structure to operate efficiently in two different frequency ranges, particularly HF and UHF. This disclosure also relates to an RFID printer / encoder incorporating the dual-frequency-responsive near-field electromagnetic coupler structure.

Claims

1. 1. A dual frequency responsive near-field electromagnetic coupler structure for interconnecting with an RFID inlay (60) by electromagnetic energy, comprising: A ground plane; a double-ended linear metallic structure (36) having a spiral or elongated spiral planar shape and comprising a plurality of looped metallic trace sections (36a, 36b, 36c), each section being connected to the next section by an inductive element (L); a first terminal of the first looped metal trace section (36a) and an end terminal of the last looped metal trace section (36c) are connected to first and second power supply terminals (31, 32), respectively, via respective inductive elements (L); The inductive elements (L) are arranged such that each inductive element (L) is adjacent to the previous inductive element (L) and the next inductive element (L) along the current path of the double-ended linear metallic structure (36); An electromagnetic coupler structure in which each capacitance element (C) is arranged so as to connect between each terminal of an inductive element (L) and each terminal of an adjacent inductive element (L).

2. 10. The electromagnetic coupler structure of claim 1, having a multi-layer structure, The multilayer structure includes a top surface layer (s5) that forms a top surface of an electromagnetic coupler structure that is located closest to an RFID inlay (60) that is to be coupled with electromagnetic force, and in which the double-ended linear metal structure (36) is located; a metal ground plane layer (s4) comprising the ground plane; a component and power supply layer (s1) in which the inductive element (L) and the capacitive element (C) are arranged, and further comprising a power supply network for supplying power to the first power supply terminal (31) and the second power supply terminal (32); an inductive element (L) and a capacitive element (C) electrically connected to the double-ended linear metallic structure (36) through vias in the first and second dielectric substrate layers (d4, d1); and a second dielectric substrate layer (d1) disposed between the metal ground plane layer (s4) and the component and power supply layer (s1).

3. 3. The electromagnetic coupler structure according to claim 2, an intermediate signal layer (s3) disposed on the opposite side of the metal ground plane layer (s4) from the top layer (s5); an additional metal ground plane layer (s2) disposed between the intermediate signal layer (s3) and the component and power layer (s1); and third (d3) and fourth (d2) dielectric substrate layers disposed between the metal ground plane layer (s4), the intermediate signal layer (s3) and the additional metal ground plane layer (s2), the dielectric substrate layers having vias for electrically connecting the component and power supply layer (s1) to the top layer (s5) and / or the intermediate signal layer (s3).

4. 4. An electromagnetic coupler structure according to claim 1, wherein the double-ended linear metallic structure (36) has an elongated spiral planar shape, the elongated spiral shape is planar, the double-ended linear metallic structure (36) is wound around a fixed center point (35), each winding comprises straight portions arranged parallel to each other, and the first terminal of the initial looped metal trace section (36 a) and the end terminal of the last looped metal trace section (36 c) are arranged such that at least one winding of the double-ended linear metallic structure (36) is therebetween.

5. 5. The electromagnetic coupler structure of claim 4, wherein the first terminal of the initial looped metal trace section and the end terminal of the final looped metal trace section are positioned adjacent to a line extending perpendicular to a direction in which the double-ended linear metal structure (36) moves away from each of the terminals.

6. 4. The electromagnetic coupler structure according to claim 1, further comprising a balanced-to-unbalanced transformer, a balun (2), as a feeding network, the balun having a first balun terminal (7) connected to the first feeding terminal (31) and a second balun terminal (8) coupled to the second feeding terminal (32), the balun (2) being configured to feed electromagnetic signals of equal amplitude and 180° out of phase to the double-ended linear metallic structure (36) when operating in a first frequency range, and to feed a signal to the first feeding terminal (31) only while the second feeding terminal (32) is grounded when operating in a second frequency range lower than the first frequency range.

7. 7. The electromagnetic coupler structure of claim 6, The balun (2) further comprises a third balun terminal (1) arranged to serve as a coupler input connected to an interrogation device (40) for providing electromagnetic energy to couple to the RFID inlay (60); a first current path (51) between the third balun terminal (1) and the first balun terminal (7) includes at least one inductive element (LLP1, LLP2), and the first current path (51) is connected to ground via at least one capacitive element (CLP, CHP2); an electromagnetic coupler structure, wherein a second current path (52) between the third balun terminal (1) and the second balun terminal (8) includes at least one capacitive element (CHP2), and the second current path (52) is connected to ground via at least one inductive element (LLP1, LLP2).

8. 8. The electromagnetic coupler structure of claim 7, further comprising an interrogation device (40) coupled to the third balun terminal (1) for providing electromagnetic energy coupled to the RFID inlay (60).

9. 4. The electromagnetic coupler structure of claim 1, wherein the electromagnetic coupler structure is operable in a first frequency range and a second frequency range lower than the first frequency range, the first frequency range being a UHF frequency range and the second frequency range being a HF frequency range.

10. 10. The electromagnetic coupler structure of claim 9, wherein the electrical length of one looped metal trace section (36a; 36b; 36c) does not exceed half a guided wavelength in the first frequency range.

11. 4. The electromagnetic coupler structure of any one of claims 1 to 3, configured to encode the RFID inlay (60) by coupling electromagnetic energy to the RFID inlay.

12. An RFID printer / encoder comprising an electromagnetic coupler structure (30, 300) according to any one of claims 1 to 3.

13. 13. The RFID printer / encoder of claim 12, further comprising an interrogation device (40) for providing electromagnetic energy coupled to said RFID inlay (60), said interrogation device (40) comprising an HF interrogator (40a) and a UHF interrogator (40b) integrated as a single unit and embedded on a motherboard.

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