Read-Through Metal Tag and Methods of Making and Using the Same

Embodiments of the disclosure pertain to a wireless communication device and a method of reading a wireless communication device in which the magnitude of electromagnetically-induced currents in a metal-containing substrate is reduced. The metal-containing substrate has one or more openings therethrough. The device includes an antenna configured to (i) receive one or more first wireless signals from a reader and (ii) transmit or broadcast one or more second wireless signals and an integrated circuit coupled to the antenna. The antenna overlaps with at least one of the one or more openings.

FIELD OF THE INVENTION

The present invention generally relates to the field(s) of wireless communication, identification and/or security devices (e.g., wireless communication tags, such as radio-frequency identification [RFID] tags, electronic article surveillance [EAS] tags, and near-field communication [NFC] tags). More specifically, embodiments of the present invention pertain to a wireless communication device including an antenna and a metal structure, such as a metal foil or blanket-deposited metal layer. The metal structure includes cuts or slits configured to reduce the effect of eddy currents in the metal structure on the magnetic flux of signals transmitted and received by the antenna.

DISCUSSION OF THE BACKGROUND

Wireless communication tags, such as RFID and/or security tags, may include labels with printed electronics. The printed electronics may comprise an integrated circuit and an antenna, among other components. The integrated circuit may include a processor and a read-only memory (ROM), and may be attached to a substrate (e.g., a thin metal foil or other mechanical support structure).

Wireless communication tags typically cannot be encapsulated with or be in close-proximity to a metal sheet or foil (e.g., aluminum or steel), since eddy currents in the metal prevent RF communication with the antenna. A magnetic field emanating from the antenna induces the eddy currents, which in turn result in a magnetic field emanating from the metal sheet or foil. The magnetic field emanating from the metal sheet or foil opposes the magnetic field from the antenna (e.g., according to Lenz's law), thus compromising the performance of the antenna by decreasing magnetic flux and increasing the resonant frequency of the antenna.

In one solution, the metal sheet or foil may be used as an antenna for the wireless tag (e.g., by shaping it in a spiral form). However, this solution is not economically viable due to precision design rules for and stringent manufacturing tolerances of such spiral antennas. In another solution, a material that limits the interference of the metal sheet or foil (e.g., a ferrite) may be used. However, such a material may be too expensive to produce and/or use on a mass scale. Thus, it is desirable to find a less expensive and/or less onerous solution to reduce the effects of eddy currents in the metal sheet or foil, and consequently improve the performance of wireless tag antennas encapsulated with and/or behind a metal sheet or foil.

This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.

SUMMARY OF THE INVENTION

To solve the problems outlined in the background, cuts or slits may be created in the metal-containing substrate to prevent the eddy currents (e.g., by rerouting moving electrons around the cuts or slits), thus improving performance of the antenna and allowing the wireless tag to be readable.

In one aspect, the present invention concerns a method of reading a wireless communication device, comprising placing a reader proximate to a first side of the wireless communication device, and transmitting or broadcasting one or more wireless signals to the wireless communication device. The wireless communication device comprises an antenna, a metal-containing substrate, and an integrated circuit on the metal-containing substrate and electrically coupled to the antenna. The first side of the wireless communication device contains the metal-containing substrate and is away from a second side of the wireless communication device that contains the antenna. The metal-containing substrate contains one or more openings therethrough. The opening(s) improve a readability of the wireless communication device and/or reduce a magnitude of electromagnetically-induced currents (e.g., eddy currents) in the metal-containing substrate. For example, the eddy currents may be reduced relative to an otherwise identical metal-containing substrate without the one or more openings. The antenna overlaps with at least one of the openings.

In some embodiments, the antenna is not co-planar with the metal-containing substrate. For example, the antenna may be parallel with the metal-containing substrate. However, in some examples, the antenna may not be more than 10 mm away from the metal-containing substrate. In some cases, the antenna is not more than 5 mm or more than 3 mm away from the metal-containing substrate.

In some embodiments, the one or more openings comprise a plurality of openings. For example, the plurality of openings may comprise at least 3 or 4 openings. In some cases, the plurality of openings comprises a pattern of openings, such as a radial pattern of cuts or slits. The radial pattern may, in some examples, further comprise an uncut center or hub, configured to maintain at least some mechanical integrity of the metal-containing substrate. In other or further examples, the metal-containing substrate further comprises one or more cross-cuts connecting at least one opening with the outermost edge of the metal-containing substrate.

In some alternative embodiments, the plurality of openings comprises a plurality of parallel cuts or slits. Such a pattern may, in some examples, further comprise one or more cross-cuts connecting (i) at least two of the parallel cuts or slits, or (ii) at least one of the parallel cuts or slits with an outermost edge of the metal-containing substrate. For example, the pattern may comprise at least three parallel cuts or slits, and the cross-cut(s) may connect each of the parallel cuts or slits with the outermost edge of the metal-containing substrate.

In some embodiments, the reader comprises a near field communication (NFC) reader. In other or further embodiments, the integrated circuit is configured to (i) receive and process one or more first signals from the antenna and (ii) generate and transmit one or more second signals to the antenna.

Another aspect of the present invention concerns a wireless communication device, comprising an antenna, an integrated circuit configured to receive one or more first wireless signals from the antenna and to transmit or broadcast one or more second wireless signals using the antenna, and a metal-containing substrate having one or more openings therethrough. The antenna overlaps with at least one of the opening(s).

In some embodiments, the opening(s) are configured to reduce and/or change a direction of eddy currents in the metal-containing substrate. The eddy currents may be reduced or directionally changed relative to an otherwise identical metal-containing substrate without the opening(s).

In other or further embodiments, the opening(s) comprise a pattern. For example, the pattern may comprise a radial pattern of cuts or slits. In some cases, the radial pattern further comprises an uncut center or hub, configured to maintain at least some mechanical integrity of the metal-containing substrate. Alternatively, the pattern may comprise a plurality of parallel cuts or slits. In some cases, the pattern further comprises one or more cross-cuts connecting (i) at least two of the parallel cuts or slits, or (ii) at least one of the parallel cuts or slits with an outermost edge of the metal-containing substrate. For example, the pattern may comprise at least three parallel cuts or slits, and the cross-cut(s) connect each of the parallel cuts or slits with the outermost edge of the metal-containing substrate. The metal-containing substrate may comprise such cross-cut(s) connecting at least one of the opening(s) with the outermost edge of the metal-containing substrate independent of any pattern of the opening(s).

A still further aspect of the present invention concerns a method of making a wireless communication device, comprising forming an integrated circuit on a metal-containing substrate, forming one or more openings through the metal-containing substrate, and coupling an antenna to the integrated circuit and placing the antenna so that the antenna overlaps with at least one of the opening(s). The opening(s) improve a readability of the wireless communication device and/or reduce a magnitude of electromagnetically-induced currents in the metal-containing substrate. In some embodiments, (i) the readability of the wireless communication device is improved and/or (ii) the magnitude of electromagnetically-induced currents in the metal-containing substrate is reduced relative to an otherwise identical metal-containing substrate without the opening(s).

As for the method of reading and the device, the antenna may be parallel with the metal-containing substrate and/or may be not more than 10 mm away from the metal-containing substrate. In various examples, the antenna is not more than 5 mm or 3 mm away from the metal-containing substrate.

In various embodiments, the opening(s) comprise a plurality of openings, and the openings may comprise a pattern. In some embodiments, forming the plurality of openings comprises cutting the metal of the metal-containing substrate. For example, cutting the metal of the metal-containing substrate may comprise stamping, laser-cutting, or patterning the metal-containing substrate.

In some examples, forming the plurality of openings comprises forming a radial pattern of cuts or slits in the metal-containing substrate. The radial pattern may further comprise an uncut center or hub, configured to maintain at least some mechanical integrity of the metal-containing substrate. Alternatively, forming the plurality of openings may comprise forming a plurality of parallel cuts or slits in the metal-containing substrate. In additional embodiments, forming the plurality of openings further comprises forming one or more cross-cuts connecting (i) at least two of the parallel cuts or slits and/or (ii) at least one of the parallel cuts or slits with an outermost edge of the metal-containing substrate. For example, the plurality of openings may comprise at least three parallel cuts or slits, and the cross-cut(s) may connect each of the parallel cuts or slits with the outermost edge of the metal-containing substrate. However regardless of the number or pattern of the openings, the method may further comprise forming one or more cross-cuts connecting at least one of the opening(s) with the outermost edge of the metal-containing substrate.

The present invention advantageously allows one to make a wireless tag on a metal substrate and read the wireless tag through the metal substrate, without significantly adversely affecting the read range of the tag in some cases. These and other advantages of the present invention will become readily apparent from the detailed description of various embodiments below.

DETAILED DESCRIPTION

The technical proposal(s) of embodiments of the present invention will be fully and clearly described in conjunction with the drawings in the following embodiments. It will be understood that the descriptions are not intended to limit the invention to these embodiments. Based on the described embodiments of the present invention, other embodiments can be obtained by one skilled in the art without creative contribution and are in the scope of legal protection given to the present invention.

Furthermore, all characteristics, measures or processes disclosed in this document, except characteristics and/or processes that are mutually exclusive, can be combined in any manner and in any combination possible. Any characteristic disclosed in the present specification, claims, Abstract and Figures can be replaced by other equivalent characteristics or characteristics with similar objectives, purposes and/or functions, unless specified otherwise.

FIGS. 1A-Bshow a metal-containing substrate110having eight cuts or slits120a-hand a wireless communication tag115attached to the substrate110. The wireless tag115may comprise an antenna130, an integrated circuit150(which may include a processor, one or more sensors, a battery and/or a memory, etc.), and connection pads140a-bthat connect the outer end of the antenna130to the integrated circuit. A trace135connects the inner end of the antenna130to the integrated circuit150. Another trace (not shown) under the antenna130connects the connection pads140ato the connection pad140b, and may be insulated from the antenna130by a dielectric layer between the trace and the antenna130. The processor may include a microprocessor, a signal processor, a controller, etc. The memory may store an identification number and overhead data or information.

The metal-containing substrate110may comprise a metal foil or layer (e.g., comprising aluminum, an aluminum alloy, or stainless steel). The cuts or slits120a-hare configured to reduce eddy currents in the metal-containing substrate110when a wireless signal is transmitted or received by the antenna130. The cuts or slits120a-hmay be made by milling, stamping, laser cutting, photolithographic patterning and etching, etc. Each of the cuts or slits120a-hmay have a length of from 5 to 50 mm (or any length or range of lengths of from 5 to 50 mm, e.g., 20 mm) and a width of from 0.5 to 5 mm (or any width or range of widths of from 0.5 to 5 mm, e.g., 2 mm). Metal may be retained in the center of the cuts or slits120a-hin the substrate110for structural integrity, although having less metal overlapping with the wireless tag115may increase the readability of the wireless tag. The cuts or slits120a-hmay be cut to or beyond the periphery of the substrate110, which further decreases eddy currents in the substrate110relative to cuts or slits that don't extend to the periphery of the substrate110.

Table 1 shows the results of testing the readability (e.g., the maximum distance from which the reader may transmit and receive a signal to and from the wireless tag115) of the wireless tag115when unattached and when attached to the substrate110(which, in the example shown inFIGS. 1A-B, comprises aluminum). An external capacitance across the antenna terminals of the tag115(shown in Table 1) was used to retune the tag115to the correct operating frequency.

The tag115was read through the substrate110by three different readers, including the Google Nexus 5X and Nexus 6 smartphones and the Apple iPhone 7 smartphone. The capacitance of the wireless tag115attached to the substrate110is 82 picofarads. The aluminum substrate110decreases the read range of the wireless tag115by 9.5 mm using the Nexus 5X, by 4.5 mm using the Nexus 6, and by 16.0 mm using the iPhone 7. Thus, the wireless tag115is still adequately readable, even when attached to the metal-containing substrate110.

FIG. 2is a simulation (e.g., using electromagnetic simulation software from Computer Simulation Technology GmbH, Darmstadt, Germany) that shows the eddy currents (represented by arrows) induced in the patterned substrate210by the wireless signal from an NFC reader. The frequency of the wireless signal is 13.56 MHz. The paths of the eddy currents are broken by the cuts or slits220a-h, and the paths along the periphery of adjacent sections of the substrate210across the cuts or slits220a-htend to be in different directions, essentially offsetting each other. A color key on the right shows the magnitude of the current per unit length (A/m) for each arrow. The maximum current in the substrate210is 10 A/m.

The paths of the eddy currents in patterned substrate210are broken or at least redirected by the cuts or slits220a-h. The eddy currents also have different, and in some cases opposing, directions near the cuts or slits220a-hand elsewhere in the substrate210. The eddy currents are generally weaker in areas or regions of the substrate210that overlap with the antenna230and/or that are along the cuts or slits220a-hthan in other areas or regions of the substrate210.

FIG. 3is a simulation made using the electromagnetic simulation software from Computer Simulation Technology GmbH (CST) that shows the magnetic field in a plane normal to the metal-containing substrate210when the eddy currents are induced by the 13.56 MHz wireless signal. The antenna230(part of which is obscured by the legend at the far right side ofFIG. 3) surrounds the slits220a,220band220h. Thus, the center of this cross-section of the substrate210and slits220a,220band220hshown inFIG. 3is from a region inside the antenna230(FIG. 2). The horizontal line240inFIG. 3depicts the substrate on which the antenna is formed. The magnetic field vectors at the slits220a,220band220hindicate magnetic flux through the slits. Thus, a wireless signal from a reader is readable by the antenna. One objective of the present invention is to maximize the normal (i.e., perpendicular) component of the magnetic field (and therefore flux) in locations at or near the antenna. The slit geometry shown inFIGS. 1-2provides at least in part such a magnetic field and flux. Widening the cuts or slits220a-hand reducing the diameter of the hub increases readability (e.g., the read range) due to an increase in the normal component of the magnetic field, but may compromise mechanical integrity.

FIG. 4is a simulation made using the electromagnetic simulation software from CST that shows eddy currents (represented by arrows) induced in a patterned substrate310by the 13.56 MHz wireless signal from an NFC reader. The substrate310may be similar or substantially identical to the substrate210shown inFIG. 2, except that the cuts or slits320a-kforms a serpentine pattern in the substrate310. The cuts or slits320a-kare parallel to each other and/or in a grating pattern, and may be staggered and/or offset at opposite ends. A key on the right shows the magnitude of the current per unit length (A/m) for each arrow. The maximum current in the substrate310is 10 A/m.

The paths of the eddy currents in patterned substrate310are broken by the cuts or slits320a-k. In addition, the eddy currents have different, and frequently opposing, directions, both near the cuts or slits320a-kand elsewhere in the substrate310. In some parts of the metal substrate310near or between the cuts or slits320a-k, particularly inside the antenna330(the inner and outer outlines of which are designated by the dashed lines), the eddy currents partially or completely offset each other. While the eddy currents in areas or regions of the substrate310that overlap with the antenna330are stronger than in other areas or regions of the substrate310the region inside the antenna330has relatively weak eddy currents, similar in weakness to those in the region of the substrate310away from the antenna. In the region inside and surrounded by the antenna330, the slits320d-320hweaken the eddy currents in the substrate310. The areas outside the antenna330also show relatively weak eddy currents, compared to the region of overlap between the antenna330and the substrate310. The slits320a-kreduce eddy current strength in the substrate310in the areas inside and outside of the antenna330.

Each of the cuts or slits320a-kmay have a width of from 0.1% to 10% of the length of the substrate310(or any width or range of widths between 0.1% and 10% of the length of the substrate310, e.g., 2%), and a length of from 50% to 95% of the width of the substrate310(or any length or range of lengths between 50% to 95% of the width of the substrate, e.g., 90%). The cuts or slits320a-kmay be cut to the periphery or edge on either or both of the opposing sides of the substrate310. In alternative embodiments, the cuts or slits320a-kmay not be cut to the periphery of the substrate310, and/or narrow cuts may be made parallel to the length of the substrate (e.g., in a direction perpendicular to the cuts of slits320a-k.

FIG. 5is a simulation made using the electromagnetic simulation software from CST that shows the magnetic field in a plane normal to the metal-containing substrate310when the eddy currents are induced by a 13.56 MHz wireless signal from the reader (not shown). The reader is located at the bottom of the image (i.e., below the substrate310), and the tag antenna (not shown) is located above the substrate310. The normal component of the field is weakest above and below the uncut region of the substrate310. However, a significant normal component of the field exists in the cut regions320cto320i. Although readability performance (e.g., read distance) is improved compared to the metal-containing substrate210shown inFIGS. 2 and 3, mechanical integrity is not as good.

FIGS. 6A-Bshow a metal substrate410having sixteen cuts or slits420a-pmade using a surgical knife or scalpel in a radial pattern extending from a center or hub415and a wireless communication tag430secured to the substrate410with tape440a-b. The substrate410is aluminum foil having a thickness of 30 μm, but other metal foils or sheets and other thicknesses are also suitable. The cuts or slits420a-pcan also be made with an exacto knife, a box cutter, a razor blade, etc., which may be drawn along a straight edge (e.g., a ruler).FIG. 6Ashows the front side with the substrate410closer to the reader, andFIG. 6Bshows the backside with the metal foil or layer410away from the reader. The wireless tag430is attached directly to the foil or layer410.

The wireless tag430may comprise an antenna and an integrated circuit (not visible) on a plastic (e.g., polyethylene terephthalate, or PET) substrate, and may be similar or substantially identical to the wireless tag115shown inFIGS. 1A-B. As shown, the wireless tag430is face-down on the metal foil or layer410. The integrated circuit may be between the substrate410and the antenna, but other arrangements or relationships are also suitable. The metal foil or layer410as shown inFIGS. 6A-Bcomprises aluminum (e.g., an aluminum foil). Alternatively, the metal foil or layer410may comprise stainless steel, or a sputtered or evaporated layer of Al, Ti, Cr, Ni, Cu, Zn, Ag, Sn, Ta, W, Au, or an alloy thereof. Graphics may be on the front side of the metal foil or layer410. The cuts or slits420a-pare configured to reduce eddy currents in the metal-containing substrate410when a wireless signal is transmitted or received by the antenna in the wireless tag430. The cuts or slits420a-pmay be made as described herein. The metal in the center or hub415of the foil or layer410maintains structural integrity of the metal foil or layer410. The cuts or slits420a-pdo not extend all the way to the periphery of the metal foil or layer410, also to maintain structural integrity of the metal foil or layer410.

FIGS. 7A-Dshow various patterns of cuts and slits (each having a radial distribution) in a copper foil substrate. The copper foil may have a thickness of from 5 to 100 micrometers (or any thickness or range of thicknesses of from 5 to 100 micrometers, e.g., 30 micrometers). The pattern520(FIG. 7A) has eight cuts or slits525a-h. The pattern530(FIG. 7B) has sixteen cuts or slits535a-p. The pattern540(FIG. 7C) has thirty-two cuts or slits545a-af. The pattern550(FIG. 7D) has sixty-four cuts or slits555a-b1. Each of the cuts or slits525a-h,535a-p,545a-af, or555a-b1may have a length of from 5% to 48% of the substrate (or any length or range of lengths of from 5% to 48% of the substrate, e.g., 42%). As shown inFIGS. 7A-D, as the number of cuts or slits in the substrate increases, the mechanical integrity of the substrate in the center of the pattern of cuts or slits may be progressively weaker, and/or the circular or substantially circular portion of the substrate at the inner ends of the cuts or slits may be progressively larger and/or non-uniform. In alternative embodiments, any of the patterns520,530,540, and550may have a number of cuts or slits of from four to one hundred and twenty-eight.

A wireless tag attached to the copper foil with the pattern530was not readable. However, substantially identical wireless tags attached to the copper foils with the patterns540and550were readable. Therefore, the increasing the number of cuts or slits in a radial pattern in the metal substrate may increase the readability of the wireless tag.

FIG. 8shows a milling plate610having a radial pattern612thereon, an NFC tag620having a length L and a width W, and a cross-section of the milling plate610. The milling plate610is used to transfer the pattern612onto a metal foil or an exposed metal layer of a metal-containing substrate. The radial pattern has a diameter D1of from 10 to 400 mm and a center D2of from 1 to 25 mm. In one example, D1is 28 mm (i.e., the length of two colinear cuts or slits and the diameter D2of the center or hub), and D2is 3 mm, but the invention is not so limited. The thickness T of the cross-section630of the milling plate610of can be any value or range of values from 0.01 mm to 10 mm. In one example, T is about 0.3 mm.

The length L and width W of the NFC tag620are generally (but not always) greater than the diameter D1of the radial pattern612. The length L may be of from 5 to 100 mm, and the width W may be of from 5 to 100 mm. The width W may be the same as of less than the length L. In one example, each of the length L and width W of the NFC tag620is 30 mm.

FIG. 9is a simulation made using the electromagnetic simulation software from CST that shows the eddy currents (represented by arrows) induced in a metal substrate710by the 13.56 MHz wireless signal from an NFC reader. The substrate710may be similar or substantially identical to the substrate210shown inFIGS. 2-3. The cuts or slits720a-fare parallel to each other and/or in a grating pattern, and do not extend to the edge of the substrate710. A key on the right shows the magnitude of the current per unit length (A/m) for each arrow. The maximum current in the substrate710is 5 A/m. Each of the six cuts or slits720a-fmay have the same or similar dimensions as the cuts or slits320a-kshown inFIG. 4. In alternative embodiments, there may be four, eight, or sixteen cuts or slits320a-k, etc. If more cuts or slits720are added to the same area as shown inFIG. 9, the width of each of the cuts and slits720are generally smaller than as shown.

The paths of the eddy currents in the metal substrate710are broken by cuts or slits720a-f. In addition, the eddy currents have different directions near the cuts or slits720a-f. In some parts of the metal substrate710near or between the cuts or slits720a-f, particularly near or inside the antenna730, the eddy currents partially or completely offset each other. The eddy currents are weaker (i) along the periphery of the substrate710near the cuts or slits720a-f, and (ii) in areas or regions of the substrate710that overlap with the antenna730.

FIG. 10is a simulation made using the electromagnetic simulation software from CST that shows the eddy currents (represented by arrows) induced in an alternative substrate710′ by a 13.56 MHz wireless signal from an NFC reader. The substrate710′ is similar to the substrate710shown inFIG. 9, except for the addition of narrow cross-cuts725a-fthat separate the strips of substrate710′ between the cuts or slits720a-f(and/or between the outermost cut or slit720fand the outer periphery of the substrate710′), and connect the cuts or slits720a-fto the periphery of the substrate710′ (e.g., with empty space). The narrow cross-cuts725a-fmay be in the center of the substrate710′ and/or along the length of the substrate710′ (e.g., the narrow cross-cuts725a-fmay be perpendicular to the main or primary cuts or slits720a-f). A key on the right shows the magnitude of the current per length (A/m) for each arrow. The maximum current in the substrate710is 5 A/m.

The paths of the eddy currents in the substrate710′ are further broken or redirected by the narrow cross-cuts725a-fin addition to the main or primary cuts or slits720a-f. the eddy currents have different (and in some cases, opposing) directions that at least partially offset each other. In addition to being weaker in areas or regions of the substrate710′ that overlap with the antenna730, the cross-cuts725a-falso appear to weaken the eddy currents throughout the remainder of the substrate710′. Along the narrow cross-cuts725a-f, the eddy currents are relatively strong, but in opposite directions so that they effectively offset each other.

Each of the main/primary cuts or slits720a-fmay have a width of from 0.2% to 10% of the length of the substrate810(or any width or range of widths between 0.2% and 10%; e.g., 4%), and a length of from 50% to 95% of the width of the substrate710and/or710′ (or any length or range of lengths between 50% to 95% of the width of the substrate; e.g., 85%). The narrow cross-cuts725a-fmay have a length less than or equal to the width of the strips of the substrate710′ between the main/primary cuts or slits720a-f(i.e., the cross-cuts725a-fneed not extend completely across the strips of the substrate710′ between the main/primary cuts or slits720a-f) and a width of 1-100% of the width of the main/primary cuts or slits720a-f, although the invention is not so limited.

FIG. 11is a simulation made using the electromagnetic simulation software from CST that shows the magnetic field in a plane normal to the substrate710′ (shown inFIG. 10) when the eddy currents are induced by the 13.56 MHz wireless signal. The field strength on the tag side (i.e., near the antenna730) is noticeably stronger than other geometries (e.g., of patterns of cuts or slits). The maximum magnetic field strength is 5 A/m.

The mechanical integrity and mechanical performance are comparable to embodiments shown inFIGS. 2-5, while electrical performance (e.g., the magnetic field) is considerably better. To further improve mechanical integrity, the outermost cross-cut725fcan be omitted and/or the cross-cuts725a-fcan be made only partially across the strips of the substrate between the main/primary cuts or slits720a-720fPlacement of the wireless tag inside the outermost primary cuts720aand720fcan minimize the adverse effects of the metal substrate710on signal transmission.

FIG. 12Ashows a metal-containing substrate810having three cuts or slits820a-cand a wireless communication tag attached to the substrate810. The wireless tag may be similar or substantially identical to the wireless tag115shown inFIGS. 1A-B. The wireless tag may comprise an antenna830, an integrated circuit (not visible, but which may include a processor, one or more sensors, a memory, and/or a battery, etc.), and a first connection pad840(e.g., to connect the outer end of the antenna830to the integrated circuit; a second connection pad configured to connect the outer end of the antenna830to a trace or strap that crosses the loops of the antenna830that, in turn, is connected to the first connection pad840is obscured by the substrate810). The metal-containing substrate810may comprise a metal foil or layer (not shown, but which may comprise, e.g., aluminum, an aluminum alloy, copper, a copper alloy, or stainless steel). The cuts or slits820a-bare configured to reduce eddy currents in the metal-containing substrate810when a wireless signal is transmitted or received by the antenna830in the wireless tag. Relatively narrow cross-cuts825a-bconnect each of the cuts or slits820b-cto the periphery of the substrate810and further reduce and/or change the direction of eddy currents in the substrate810.

The primary cuts or slits820a-cmay be manufactured by milling, stamping, or laser cutting. The cut or slit820cis aligned with traces of the antenna830and is shorter in length than the cuts or slits820a-b, although the invention is not so limited. The cross-cuts825a-bmay be made with a laser, a blade or a saw, and are much narrower than the primary cuts or slits820a-c, although the invention is not so limited.

Each of the primary cuts or slits820a-cmay have a width of from 0.2% to 15% of the length of the substrate810(or any width or range of widths between 0.2% and 15%; e.g., 8%), and a length of from 50% to 95% of the width of the substrate810(or any length or range of lengths between 50% to 95% of the width of the substrate; e.g., 75%). The cuts or slits820a-cdo not extend to the periphery of the substrate810. In alternative embodiments, the cuts or slits820a-cmay extend to and/or be exposed through the periphery or outermost edge of the substrate810.

FIG. 12Bshows a metal-containing substrate910similar to the substrate810inFIG. 12A, but having four main or primary cuts or slits920a-dand three narrow cross-cuts925a-ctherein. A wireless communication tag attached to the substrate910. The wireless tag may be similar or substantially identical to the wireless tag115shown inFIGS. 1A-Band the wireless tag inFIG. 12A. The wireless tagFIG. 12Bmay comprise an antenna930, an integrated circuit (not shown, but which may include a processor, one or more sensors, a memory, a battery, etc.), and connection pads940a-b(e.g., to connect the outer end of the antenna930via a trace or strap that crosses the loops of the antenna930to the integrated circuit). The metal-containing substrate910may comprise a metal foil or layer, similarly or identically to the substrate810inFIG. 12A. The cuts or slits920a-d(which may have equal dimensions) are configured to reduce eddy currents in the metal-containing substrate910when a wireless signal is transmitted or received by the antenna930in the wireless tag. The narrow cross-cuts925a-cconnect the cuts or slits920b-dto the periphery of the substrate910and further reduce and/or change the direction of the eddy currents. The cuts or slits920a-dand the cross-cuts925a-cmay be made in the same way as the cuts or slits820a-band the cross-cuts825a-binFIG. 12A.

Table 2 shows the results of testing the readability (e.g., the maximum distance from which the reader may transmit and receive a signal to and from the wireless tag) of each of the wireless tags shown inFIGS. 12A-Bwhen unattached (i.e., as a stand-alone device) and when attached to the respective substrate810or910. An external capacitance across the antenna terminals of the tag was used to retune the tag to the correct operating frequency.

The readers include the Google Nexus 5X and Nexus 6 smartphones, and the Apple iPhone 7 smartphone. The external capacitance between the wireless tag and each of the substrates810and910is 82 picofarads. The substrates810and910did not significantly decrease the readability of the wireless tags using the Nexus 5X or the Nexus 6, if at all, and the readability of the wireless tags using the iPhone 7 by was affected only slightly (about 6.7% relative to the readability of the stand-alone wireless tag, but about the same as or better than the Nexus 5X and Nexus 6). Thus, the wireless tag attached to the metal-containing substrates810and910is still about as readable as the stand-alone wireless tags.

FIGS. 13A-Bshow a metal-containing substrate1010before and after being cut in an exemplary internal pattern. The pattern1020inFIG. 13Bis somewhat random and/or arbitrary, as the actual shape of the pattern1020is largely irrelevant for purposes of explaining this aspect of the invention. The metal-containing substrate1010may comprise aluminum, an aluminum alloy, stainless steel, or another metal such as copper or a copper alloy. The uncut substrate1010inFIG. 13Aexperiences surface eddy currents when placed in an electromagnetic field.

FIG. 13Bshows the metal-containing substrate1010with a narrow cut1025(e.g., bounded by AA′-BB′) connecting a larger internal cut1020(e.g., bounded by B′C′D′E′F′A′) to the outermost edge of the substrate1010. An external magnetic field induces an electromagnetic force (EMF) in both of the loops BCDEFA and B′C′D′E′F′A′ (with polarities shown by the + signs). Since the loops BCDEFA and B′C′D′E′F′A′ are effectively in series with opposing polarities, the net surface current is determined by the difference in EMF in the loops BCDEFA and B′C′D′E′F′A′, divided by the sum of effective surface impedances in each loop BCDEFA and B′C′D′E′F′A′. The difference in EMF between the loops BCDEFA and B′C′D′E′F′A′ approaches zero when the pattern (e.g., internal cut1020) approaches the dimensions of the substrate1010. However, to preserve structural integrity of the substrate1010, a minimum amount of the substrate1010is preserved. For a given area, the irregular geometry of the loop B′C′D′E′F′A′ may be used to minimize the surface current(s). In other words, it may be desirable to find an optimum geometry for the pattern1020to (i) minimize the difference in EMF between the inner and outer loops B′C′D′E′F′A′ and BCDEFA and/or (ii) maximize the sum of the surface impedances in each of the inner and outer loops B′C′D′E′F′A′ and BCDEFA.

FIGS. 14A-Cshow exemplary metal-containing substrates each respectively having a square pattern, a cross pattern, and a grating pattern therein (i.e., the pattern of the inner cut). The area of uncut metal (and/or the area of metal removed in the pattern) is the same in each substrate. Each of the pattern geometries was tested for mitigation of surface current (e.g., by testing the readability of a wireless tag using a near field communication [NFC] reader, such as a smartphone).

FIG. 14Ashows a substrate1110including a square pattern1120and a narrow cut1125connecting the square pattern1120to the outer edge of the substrate1110.FIG. 14Bshows a substrate1111including a cross pattern1130and a narrow cut1135connecting the cross pattern1130to the outer edge of the substrate1111.FIG. 14Cshows a substrate1112including parallel main cuts or slits1140a-eand narrow cross-cuts1145a-e.

The substrate1112including the parallel main cuts or slits1140a-eand cross-cuts1145a-e(FIG. 14C) has the highest impedance, whereas the substrate1110including the square pattern1120(FIG. 14A) has the lowest impedance. After testing, the substrate1110including the square pattern1120(FIG. 14A) had the longest or largest read range, the substrate1112including the parallel main cuts or slits1140a-eand cross-cuts1145a-e(FIG. 14C) had the second longest or largest read range, and the substrate1111including the cross pattern1130(FIG. 14B) had the third longest or largest read range. The fact that the substrate1110ofFIG. 14Ahas a higher read range than the substrate1112ofFIG. 14Cmay be due to better cancellation of EMF's in the substrate1110ofFIG. 14A.

In further or alternative embodiments, the geometry of the pattern may be determined using a computer algorithm, and the geometry may be irregular or fractal in shape.