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 and 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). The tags store information electronically. To read the information, an RFID reader sends a coded radio signal to interrogate the tag. To do so, an RFID tag comprises 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 an RFID tag by electromagnetic coupling.

[0003] RFID devices that include planar metal traces are usually referred to as inlays. Technically speaking, an RFID inlay is an RF terminated planar metal trace. In particular, an inlay is an RFID device with a planar metal trace film supported on a flexible substrate that connects to a transponder. The transponder, included 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 send signals to the planar metal trace, which are further transmitted by the planar metal trace (sometimes also 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" is taken to mean a radiating device in this disclosure. However, this disclosure is related to reactive near-field coupling as opposed to radiative far-field coupling. Thus, the use of the term "antenna" is limited to RFID inlays and tags. The intended operation or design target of the antenna may be in the near field and / or far field of propagation.

[0004] Recently, printing devices have become known that allow the placement of an RFID inlay on a medium such as paper and at the same time allow the RFID inlay to be encoded with desired information during printing. The encoding is performed by electromagnetic coupling, preferably in a reactive near field. To this end, an RFID printer / encoder includes an electromagnetic coupler structure that fits into a cavity in the printer such that as the medium is guided along the medium path into the printer / encoder, an electromagnetic force carrying the encoded information couples with an RFID inlay located on the medium.

[0005] It is also possible to use a coupler structure having not only one coupling element but also a one-dimensional or two-dimensional array of multiple coupling elements.

[0006] In practical implementations, there will be different RFID labels (tags) each with a different operating frequency. 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 from approximately 3 to 30 MHz (megahertz). A common center frequency for HF communications is 13.56 MHz. "UHF" is used to designate an even higher frequency range. Common UHF frequencies range anywhere from approximately 300 MHz to 3 GHz (gigahertz).

[0007] There are also RFID labels that contain multiple tags, which may include either 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) in the inlay that operate at HF ​​and UHF frequencies, respectively. In the former case, there may be an HF and a UHF "antenna" 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. It is therefore desirable to implement looped reactive near-field solutions for UHF inlays as well. Although the tag / inlay antennas have nominal radiative characteristics, these same structures can also be used for reactive near-field coupling applications, especially when equipped with looped 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 with printer environments, especially small printers such as label or tag printers, is the limited space available in which to mount each electromagnetic coupler structure. In principle, it may be possible to foresee multiple independent coupler structures for different frequency ranges, each connected to a corresponding interrogator in a single printer, but this would have the disadvantage of requiring larger space requirements 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 is further suitable for installation in devices with limited mounting space, such as label and tag printers. Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE PRESENT EMBODIMENT 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 a first frequency range and a second frequency range. [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 by electromagnetic energy is provided. The electromagnetic coupler structure comprises a ground plane and a double-ended linear metal structure having a helical or elongated helical planar shape and including a number of 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 power supply terminals, respectively, via respective inductive elements. The inductive elements are arranged such that each inductive element is adjacent to its previous inductive element and to its next inductive element along the current path of the linear metal structure. Each capacitive element is arranged to connect between each terminal of the inductive element and each terminal of the adjacent inductive element.

[0015] It is a specific approach of a non-limiting embodiment to provide 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 with multiple loop-like metal trace sections connected to a feed terminal, connected to each other in a specific way by respective inductive and capacitive elements forming a ladder-like LC filter network. This allows different operation methods depending on the frequency range of the input signal fed to the coupler structure. In the lower frequency range (such as HF), the signal passes through each loop section in turn, forming a spiral or elongated spiral loop as the effective loop. In the higher frequency range (such as UHF), the individual loop sections are shorted to form a single loop with a thicker metal trace. Although such a coupler topology is sufficient for the UHF frequency band, it should be considered that if the same physical length is used for HF as for UHF, the electrical length at HF ​​becomes extremely short and the losses are very low, making it difficult to match the coupler system. Thus, the present invention increases the physical length and self-inductance by a factor corresponding to the number of individual loops in the ladder LC filter network structure. In particular, the electromagnetic coupler structure is suitable for placement in printers with RFID encoding capabilities, such as small label and tag printers.

[0016] This approach as outlined can be realised 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 which the double-ended linear metallic structures are arranged in a top layer forming the top surface of the electromagnetic coupler structure that is located closest to the RFID inlay to which the electromagnetic power is to be coupled. A (first) metallic ground plane layer with a ground plane is arranged below the top layer. The capacitive and inductive elements are arranged in a component layer arranged on the opposite side of the (first) ground plane layer from the top 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 connections between the components and the looped metallic trace sections. Similarly, another substrate layer (second substrate layer) with vias for electrical connections is arranged between the metallic ground plane layer and the component layer. The reason for arranging the components in a layer separate from the top layer in this embodiment is that for the most efficient near-field coupling, the actual metallic coupling structure should be a completely flat (planar) structure, and the inductive and capacitive elements need to be arranged in 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 converter) 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 multi-layer structure further comprises 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 layer / component and feed layer. A third and a fourth dielectric substrate layer 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 the 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 a complex signal structure, such as one including signal crossings in space, an intermediate signal layer may be required to properly distribute the signal input from the component and feed layer to the coupler structure of the top layer. Those skilled in the art will recognize that this type of multi-layer 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, which is wound around a certain center point such that each winding has straight portions arranged parallel to each other. The first terminal of the first looped metallic trace section and the end terminal of the last looped metallic trace section are arranged such that there is at least one winding of the linear metallic structure between them. More preferably, the first terminal and the end terminal are arranged adjacent to a straight line extending perpendicular to the direction in which the linear metallic structure leaves each terminal. Roughly speaking, the connection line between the first terminal and the end terminal of the linear metallic structure is approximately perpendicular to the direction of the metallic traces in the vicinity of the terminal. The advantage of the elongated spiral shape mentioned 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, the current flows in the same direction along the entire transmission line loop as long as the electrical length is less than or equal to half the guided wavelength, so that a uniform magnetic field is generated along the line and distributed over the entire loop length of the coupler. This allows for greater flexibility in achieving highly 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 comprises a balun as a feeding network. The balun has a first balun terminal connected to the first feeding terminal and a second balun terminal connected to the second feeding terminal. The balun is configured to feed electromagnetic signals of equal amplitude and 180° out of phase to the linear metallic structure when operating in a first frequency range (which is a higher frequency range) and to feed signals to the first feeding terminal only while the second feeding terminal is grounded when operating in a second frequency range (which is 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 to couple to the RFID inlay. A first current path between the third balun terminal and the first balun terminal comprises 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 comprises at least one capacitive element and is connected to ground via at least one inductive element. The structure of the balun as described above allows the balun itself to implement an LC filter structure and to operate differently depending on the power supply frequency. In particular, as mentioned above, in the high frequency range (such as UHF), the balun is a double-ended structure that allows differential power supply. In the lower frequency range (such as HF), the balun operates as a single-ended structure with the terminals 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 a 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, degrading the 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 specific 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. Since the electromagnetic coupling for transferring the 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 close proximity to the media path.

[0027] According to a preferred non-limiting embodiment, the RFID printer / encoder further comprises an interrogation device providing electromagnetic energy that is coupled to the RFID inlay, more preferably the interrogation device comprises an HF interrogator and a UHF interrogator integrated as 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 in at least two frequency ranges to inlays of any shape.

[0029] These and other aspects and features of the non-limiting embodiments will become apparent to those of ordinary skill in the art from the following description of specific non-limiting embodiments taken in conjunction with the accompanying drawings. [Brief description 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 in accordance with an embodiment of the present disclosure. [Diagram 2] 1 illustrates a geometrical configuration of an electromagnetic coupler structure having an elongated, helical, double-ended linear metallic structure according to an embodiment of the present disclosure. [Diagram 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. [Diagram 5] FIG. 1 is a schematic electrical circuit diagram of an example implementation of a balun suitable as a power feed network in accordance with 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 PREFERRED EMBODIMENTS

[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 not the exclusion of any other element, integer, or step, or collection of elements, integers, or steps.

[0032] The present disclosure relates to electromagnetic coupler structures operating in at least two different frequency ranges (eg, HF and UHF) for intercoupling with, and in particular encoding, RFID inlays.

[0033] In a non-limiting embodiment of the electromagnetic coupler configuration, an interrogator (also referred to as 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 make up one and the same RFID label.

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

[0037] The figure shows diagrammatically a printer (RFID printer / encoder) 100 having a platen roller 10 as an element for feeding a print medium 20. The printer further comprises an electromagnetic coupler 30 for encoding an RFID inlay provided (embedded) on the print medium 20. The coupler 30 is coupled (via a respective cable) to an interrogator 40 embedded in the printer. The embedded interrogator 40 comprises in particular 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 in order to reduce drawing complexity and to focus on the elements of printer 100 that are 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 of the implementation methods known in the art, and the particular implementation method is not relevant to, and therefore not required by, the present invention.

[0039] Although the HF and UHF interrogator components are shown in the figure as two separate components of an embedded interrogator, the present disclosure is not limited to such implementation. Depending on the degree 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 may be used within one interrogator. In particular, two separate interrogator components (interrogation units) can be embedded in the motherboard of the printer. An even higher degree of integration can be achieved by embedding a single interrogator on the motherboard that can generate and process both HF and UHF signals. As will be explained below, for integrated HF and UHF interrogators, an implementation that uses only a single feed line for both frequency ranges is particularly advantageous. For example, this can be achieved by a 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, and these units may even be housed in different housings, although since the interrogator housing is located within the printer housing, it is common to use the term "embedded" in such a configuration.

[0041] Another possibility is to integrate HF and UHF technologies in one unit and housing, which would reduce the size and therefore be applicable in small printers. Yet another possibility is an "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 different type in the combined HF / UHF interrogator approach. Different countermeasures may be possible 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, with various possibilities.

[0043] According to the present invention, by providing a universal type coupler that operates in two frequency bands (ranges), the technical advantage is realized of providing a spatially compact coupler solution that easily fits within a single label / inlay pitch length. With respect to pitch length, it is noted that in an RFID printer / encoder, individual RFID labels (tags) are provided (embedded) on a print medium, such as a paper roll with multiple labels attached, each label having an RFID tag. In that case, the "pitch length" corresponds to the distance between individual adjacent RFID tags on the print medium. Since it is desirable to encode each RFID tag individually (in principle, different (individual) information should be encoded on each tag), it is necessary to achieve targeted (selective) coupling with only a single RFID tag at a time. For this purpose, it is desirable for the coupler structure to be limited to within a single label, in particular the pitch length.

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

[0045] Specifically, the structure shown has 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 number 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 further be seen, two power supply terminals 31 and 32 are provided close to each other. In the region of the power supply terminals there is further provided a ladder structure 34, an enlarged view of which is shown in the center on the left side of the figure. Each loop of metal trace that leaves on the right side of the ladder structure 34 and returns to the left side of the ladder structure 34 after completing a circuit represents a looped metal trace section.

[0048] In this ladder structure, each central horizontally hatched element (corresponding to a "step" of 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 along the current path) looped metal trace section. 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 at the beginning and end of the linear metal structure: 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). It should be noted that, since 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 as "first" and "second" and which of the trace sections are accordingly designated as "first" and "last". According to the convention used in this detailed description, the innermost elongated spiral trace section (36a) is designated as "first" and the outermost trace section (36c) is designated as "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, the vertically hatched elements (those on either side of the structure and located between the ladder "rungs" or in the regions of the ladder "bars") represent capacitive elements. Thus, there is typically capacitive coupling 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), as well as with 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, i.e., the 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) is via a capacitor.

[0051] Moreover, as can be seen from the figures, in the given example the coupler structure 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 at all. The illustrated "elongated spiral shape" as understood in this disclosure is wound with a number of windings (each winding corresponding to one of the metal trace sections) around a central point (35 in the figures), although there are linear (or nearly linear) extending parts (in particular across the width of the figures). As can be seen from the figures, the straight parts of each winding are arranged parallel to one another (connected by curved sections) and each power supply terminal is arranged such that there is at least one winding of the metal structure between them. It is this straight or nearly straight part that particularly contributes to improving the coupling efficiency, as will be explained in more detail below.

[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, respectively. On the left side, power supply terminals 31 and 32 (labeled "Port1" and "Port2", respectively) are shown. In the center of the drawing, interconnections are shown via capacitive (C) and inductive (L) elements arranged in a ladder structure 34 (schematically shown in a dashed box).

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

[0057] As mentioned above, one of the requirements is that the loop should 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. The number of turns in the spiral loop is not important in this case, since the electrical length is much shorter at HF. In both cases, it is the strength of the current along the loop that is important to allow 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 a UHF frequency of 890 MHz represents a reactance of 560 Ω, which is considered a high resistance. On the other hand, at a HF frequency of 13.56 MHz, the corresponding value is 8.5 Ω, which is considered a low resistance. A 20 pF capacitor has values ​​of 8.9 Ω and 590 Ω, which are considered low and high resistances, respectively. However, the values ​​given are merely examples and the invention is not limited to them.

[0059] In FIG. 3, the capacitor CPC (capacitive phase compensation) and resistor RQVR (resistor for reducing Q) are optional components. The reason for including these components is as follows: LC networks with specially tuned components can have a very high “Q (quality) factor”, but at the same time the bandwidth is very narrow, affecting the matching. By using the additional resistor RQVR, the Q factor can be reduced to achieve a wider bandwidth and better matching. The value of the capacitor CPC can be set to match the system impedance for a given input. In other words, CPC may compensate for the overall inductive properties of the volute, 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 in 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, 8.

[0062] An input signal of a given frequency band, such as from a given 50 (Ω) 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 and 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] Moreover, the differential feeding, i.e. feeding with differential signals at the feeding terminals 31 and 32, shows why the elongated spiral shape of the coupler structure is preferable to a strictly geometrical spiral shape. That is, the differential feeding at the terminals 31 and 32 results in the same current direction in the elongated parallel part of the metal structure 36 at each time. This corresponds to a more uniformly distributed current density, so that the magnetic field is generated along the transmission line loop path of the coupler. This results in a highly efficient coupling with RFID tags of various shapes. On the other hand, since the electric field strength decreases rapidly outside the area of ​​the metal structure, the magnetic field is limited only 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 different 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 coupling loops at UHF.

[0068] As can be seen, the balun 2 generally has a three-port structure, with an input terminal 1 denoted as "Port 1" and two output terminals 7 and 8 denoted as "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, the input port 1 is connected to the output port 7 via a first current path 51 and to the output port 8 via a second current path 52. In particular, the first current path 51 connects the input terminal 1 and the 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). The second current path 52 connects the input terminal 1 and the 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 the elements LLP1, LLP2, and CLP respectively form the structure of a low pass filter. Meanwhile, the label "CHP2" is used for historical reasons of development.

[0070] Based on the scheme 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), the capacitor is a high resistance path and the 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 (for clarity of illustration, power supply terminal 31, but this is not required for symmetry). Output terminal 8 ("Port 3") is connected to the other loop terminal (i.e., for clarity of illustration, power supply terminal 32), and is therefore grounded. Thus, at lower (HF) frequencies, the balun structure is in fact a single-ended solution.

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

[0073] Further 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 only an example, and does not limit the balun structures applicable within the framework of this disclosure. For example, arrangements including high-pass filters in one of the current paths, or more complex structures, would be possible as well, 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 ​​are selected to allow for a differentially fed arrangement in the high frequency range (UHF) and a single ended ground 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 in accordance with 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 number of four dielectric substrate layers (d1, d2, d3, d4) are each disposed between and "sandwiched" by two adjacent metal layers, such that each signal layer is electrically isolated, although 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 that includes the double-ended linear metallic 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] Further in the illustrated structure, layers s4, s3, s2, and s1 correspond to the first ground plane layer, the middle signal layer (optional), the second ground plane layer (optional), and the power / component layer, respectively, discussed above. The middle signal layer is realized in stripline technology and is always sandwiched between two ground plane layers, while the top layer and the component and power layers are implemented in microstrip technology and combined into a single ground plane. As mentioned above, the middle signal layer s3 and the second ground plane layer s2 are optional. Thus, in a minimal configuration, the stack-up structure 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 relevant 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] Today, both HF and UHF RFID are viable and existing technologies, allowing printer manufacturers to more streamline production.

[0084] The development towards multi-frequency concepts will drive 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 above description outlines some of the more suitable non-limiting embodiments. It will be apparent to those skilled in the art that modifications to the disclosed non-limiting embodiments can be achieved without departing from the spirit and scope thereof. Therefore, the described non-limiting embodiments should be considered merely as illustrative of some of the 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: that is, 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 understand that features, elements, and / or functions of one embodiment may be incorporated into other embodiments as appropriate, unless otherwise noted above. This description has been made with respect to a particular structure and method, but the intent and concept are suitable and applicable to other structures and applications.

[0087] In summary, 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.

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 metal structure (36) having a helical or elongated helical planar shape and comprising a plurality of looped metal trace sections (36a, 36b, 36c), each section being connected to the next section by an inductive element (L); a first terminal of the initial looped metal trace section (36a) and an end terminal of the final 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 its previous inductive element (L) and the next inductive element (L) along the current path of the linear metallic structure (36); An electromagnetic coupler structure in which each capacitance element (C) is arranged to connect between each terminal of an inductive element (L) and each terminal of an adjacent inductive element (L).

2. 2. The electromagnetic coupler structure of claim 1, having a multi-layer structure, The multi-layer 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) to which electromagnetic power is to be coupled, and in which the double-ended linear metallic 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 (L) and capacitive (C) elements 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 electromagnetic coupler structure comprising a first dielectric substrate layer (d4) disposed between said top layer (s5) and said metal ground plane layer (s4), and a second dielectric substrate layer (d1) disposed between said metal ground plane layer (s4) and said component and feed layer (s1), said inductive (L) and capacitive (C) elements being electrically connected to said double-ended linear metallic structure (36) through vias in said first and second dielectric substrate layers (d4, d1).

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) to 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); an electromagnetic coupler structure comprising: 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) and 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 metal structure (36) has an elongated spiral planar shape, the elongated spiral shape being planar, the linear metal structure (36) is wound around a fixed center point (35), each winding having straight portions arranged parallel to each other, and the first terminal of the first looped metal trace section (36a) and the end terminal of the last looped metal trace section (36c) are arranged such that at least one winding of the linear metal structure (36) is therebetween.

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

6. 6. The electromagnetic coupler structure according to claim 1, further comprising a balanced-to-unbalanced converter, 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 linear metal 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 according to claim 6, The balun (2) further comprises a third balun terminal (1) arranged to act 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 6 or claim 7, further comprising an interrogation device (40) coupled to the third balun terminal (1) and for providing electromagnetic energy coupled to the RFID inlay (60).

9. 9. An electromagnetic coupler structure according to claim 1, 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 metallic trace section (36a; 36b; 36c) does not exceed half a guided wavelength in the first frequency range.

11. 11. The electromagnetic coupler structure of any of claims 1 to 10, 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 11.

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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