Sustainable radio-frequency identification

Abstract

A method of manufacture of a radio-frequency identification (RFID) component comprises providing at least one carbon-containing substrate and applying a laser beam to each substrate to generate a lase

Description

Field

[0001] The present invention relates to apparatus and methods for radiofrequency identification. Background

[0002] Radio-frequency identification (RFID) systems are efficient non-contact automatic identification systems. RFID systems use electromagnetic (EM) radiation, usually in the radio wave or microwave part of the EM spectrum to identify and track objects.

[0003] RFID systems are used in a wide range of applications, including tracking parts during production within assembly lines, tracking livestock and pets, and tracking items within shops to prevent theft of items or to expedite the sale and check out of the items.

[0004] A common form of RFID system includes an integrated circuit in each RFID tag, arranged to provide a characteristic response to an EM field generated by a reader. The characteristics of the response can then be assessed in order to identify the tag.

[0005] RFID systems may be classified depending on whether the reader and the tag comprise a power source, such as a battery or other power supply. In the nomenclature of the technical field, a component with its own power supply is called "active", while a component without its own power supply is called "passive". Passive components use the energy transferred by the signal received from the other component in the system to power themselves and, therefore be able to function. In general, while passive tags may be smaller and cheaper than active tags, they require illumination with a modulated EM field at a much higher power level in order to function with the same utility as active tags.

[0006] RFID systems have many advantages over, for example, optical identification systems, such as those based on, for example, bar codes or QR-codes. They are efficient in that they allow multiples tags to be identified and tracked at the same time. Moreover, they are relatively durable, reliable, and do not require direct line of sight to the tag. However, a notable disadvantage of RFID systems is the cost. The requirement of installing a chip into every tag that is to be associated with an item means that the overall cost of the RFID system may be excessively high, especially in applications involving low-cost items or in applications involving a large number of items.

[0007] The cost and complexity of traditional RFID systems has led to the development of chipless RFID technology, in which tags do not require an integrated circuit or chip to function. As described in Herrojo et al. ("Chipless-RFID: A Review and Recent Developments", 2019, Sensors, 19(15), 3385; https: / / doi.org / 10.3390 / sl9153385), chipless RFID systems may be classified as time domain systems, or frequency domain systems (including those based on resonant frequencies). Moreover, frequency domain systems are further classified as retransmission-based and backscattered-based, depending on the type of interaction between the interrogation signal transmitted by the reader and the tag.

[0008] In general, chipless RFID tags comprise one or more resonant, conductive, elements, and the interaction of these elements with the incident EM field provides the characteristic response which allows the tag to be identified. The resonant elements commonly comprise metallic materials (such as copper, gold, or silver) or graphite that have been dissolved in a water-based or organic solvent to produce a conductive ink. However, the use of such materials generally adds to the cost of the manufacture of the tag. Moreover, the use of metallic materials makes the tags, which in many applications (e.g. in shops) are disposed of after use, less sustainable and less environmentally-friendly.

[0009] The costs and environmental impact of RFID tags, whether active, passive, chipped or chipless, remain challenging for their sustainable adoption in many use cases. Summary

[0010] According to a first aspect of the present disclosure, there is provided a method of manufacture of a radio-frequency identification (RFID) component. The method comprises: providing at least one carbon-containing substrate and applying a laser beam to each substrate to generate a laser-induced graphene (LIG) pattern on the substrate, wherein the LIG pattern encodes identification information.

[0011] As such, the method may allow for the provision of chipless RFID components (in particular, chipless RFID tags) for use in RFID systems that are simple to manufacture, cost efficient, environmentally friendly and / or sustainable.

[0012] In some examples, each substrate is biodegradable, which may further reduce the environmental impact of the RFID components.

[0013] Additionally or alternatively, each carbon-containing substrate may comprise aromatic polymers and / or lignocellulose materials, which may allow the efficient and / or sufficient generation of LIG on the substrate.

[0014] In particular, each carbon-containing substrate may be a fibrous substrate and, optionally, the substrate may be a paper substrate. Such materials are widely available and may be sourced relatively effortlessly and at reasonable cost.

[0015] In some examples, the step of providing a substrate comprises: forming a pulp from a carbon-containing material and generating a sheet of the substrate from the pulp. This method allows for the provision of substrate that may be simply manufactured.

[0016] Optionally, the pulp may be formed from newsprint paper, which is widely available at reasonable cost. Furthermore, the newsprint paper may be sourced from paper recycling centres, which may allow for an environmentally sustainable method.

[0017] In some examples, the step of applying the laser beam comprises: charring the substrate, and converting at least a portion of the charred substrate into graphene.

[0018] Optionally, during the charring of the substrate the laser beam may be less focussed on the substrate than during converting at least a portion of the charred substrate into graphene. Such steps may allow for an efficient generation of LIG on each substrate.

[0019] In some examples, the method further comprises adhering a first substrate to a second substrate such that the LIG pattern formed on each substrate are conductively coupled. The resulting RFID component produced in such a manner would have more conductive material than each one of the substrates on their own. This may help ensure a stronger response from the resulting RFID component upon its EM field interrogation, and, thereby, allow for a more efficient and more reliable system.

[0020] In some examples, the laser beam is applied using a carbon dioxide laser. Carbon dioxide lasers are versatile, widely available, and low-cost lasers.

[0021] In some examples, the laser beam is applied at an operational irradiation power greater than 1W, and optionally, the operational irradiation power is at least 3W. Additionally or alternatively, in some examples, the substrate has a thickness of at least 0.5mm. Such power settings and / or thicknesses may allow for an efficient generation of LIG on each substrate.

[0022] In some examples, the LIG pattern comprises one or more circular elements that form a circular design, and optionally, the circular design comprises a plurality of concentric circles positioned at predefined radii. Circular LIG patterns may be particularly simply generated by the method provided herein. Optionally, the positioning of the concentric circles at predefined radii is one particularly simple approach for encoding identification information within the LIG pattern.

[0023] Optionally, the one or more circles of the circular design may comprise a slit. The provision of a slit in the design may improve the response capability of the LIG pattern upon its EM field interrogation.

[0024] In some examples, subsequent to generating the LIG pattern on each substrate, the method further comprises applying a film of silicone to the LIG pattern and / or adhering a layer of paper on top of the LIG pattern. Such a further step may help ensure that the LIG pattern is protected from damage and is more durable, thereby extending the operational life of the RFID component and increasing its reliability.

[0025] A second aspect of the present disclosure provides for an RFID tag comprising a substrate and an LIG pattern formed on the substrate, the LIG pattern encoding identification information. Further aspects of the present disclosure provide for an RFID tag manufactured according to the method of the first aspect.

[0026] Also disclosed herein is a chipless RFID system comprising an RFID reader and the RFID tag of the second aspect. In operation, the RFID reader is configured to emit a radio frequency (RF) signal that is incident on the RFID tag, receive the RF signal reflected by the RFID tag, and analyse the RF signature of the RFID tag by comparing the received RF signal reflected by the RFID tag with the emitted RF signal.

[0027] A method of manufacture of a radio-frequency identification (RFID) component, the method comprising: providing at least one carbon-containing substrate layer; applying a laser beam to each substrate layer to generate an antenna, the antenna comprising a laser-induced graphene (LIG) pattern on the substrate layer; and electrically coupling an integrated circuit to the antenna.

[0028] Such a method may advantageously contain less metal than a conventional RFID system, while remaining compatible with existing RFID infrastructure, such as existing RFID readers 110 and software.

[0029] In particular, a significant burden when producing conventional RFID tags may be associated with the printing of the antenna, which is generally metallic. The sourcing and use of a metallic material for the antenna may contribute a significant cost relative to the overall cost of the production of the RFID tag. Furthermore, the use of metal rather than a carbon-containing material may be less environmentally friendly and / or sustainable.

[0030] Therefore, the method may allow for the provision of RFID components (in particular, LIG antennas) for use in RFID systems that are simple to manufacture, cost efficient, environmentally friendly and / or sustainable.

[0031] In some examples, each substrate layer is biodegradable, which may further reduce the environmental impact of the RFID components.

[0032] Additionally or alternatively, each carbon-containing substrate layer may comprise aromatic polymers and / or lignocellulose materials, which may allow the efficient and / or sufficient generation of LIG on the substrate.

[0033] In particular, each carbon-containing substrate layer may be a fibrous substrate and, optionally, the substrate layer may be a paper substrate. Such materials are widely available and may be sourced relatively effortlessly and at reasonable cost.

[0034] In some examples, the step of providing a substrate layer comprises: forming a pulp from a carbon-containing material and generating a sheet of the substrate from the pulp. This method allows for the provision of substrate that may be simply manufactured.

[0035] Optionally, the pulp may be formed from newsprint paper, which is widely available at reasonable cost. Furthermore, the newsprint paper may be sourced from paper recycling centres, which may allow for an environmentally sustainable method.

[0036] In some examples, the step of applying the laser beam comprises: charring the substrate, and converting at least a portion of the charred substrate into graphene.

[0037] Optionally, during the charring of the substrate the laser beam may be less focussed on the substrate than during converting at least a portion of the charred substrate into graphene. Such steps may allow for an efficient generation of LIG on each substrate layer.

[0038] In some examples, the method further comprises adhering a first substrate layer to a second substrate layer such that the LIG pattern formed on each substrate layer are conductively coupled. The resulting RFID component produced in such a manner would have more conductive material than each one of the substrate layers on their own. This may help ensure that the LIG pattern may serve as a more efficient and more reliable antenna, and, thereby, allow for a more efficient and more reliable system.

[0039] In some examples, the laser beam is applied using a carbon dioxide laser. Carbon dioxide lasers are versatile, widely available, and low-cost lasers.

[0040] In some examples, the laser beam is applied at an operational irradiation power greater than 1W, and optionally, the operational irradiation power is at least 3W. Additionally or alternatively, in some examples, the substrate has a thickness of at least 0.5mm. Such power settings and / or thicknesses may allow for an efficient generation of LIG on each substrate.

[0041] In some examples, the LIG pattern comprises the shape of a conventional RFID tag antenna. This may help ensure that the RFID component produced by the method is compatible with existing RFID infrastructure.

[0042] In some examples, subsequent to generating the LIG pattern on each substrate layer, the method further comprises applying a film of silicone to the LIG pattern and / or adhering a layer of paper on top of the LIG pattern. Such a further step may help ensure that the LIG pattern is protected from damage and is more durable, thereby extending the operational life of the RFID component and increasing its reliability.

[0043] A yet further aspect of the present disclosure provides for an RFID tag comprising a substrate with at least one antenna comprising an LIG pattern formed on the substrate. The RFID tag also comprises an integrated circuit and the at least one LIG pattern and the integrated circuit are electrically connected.

[0044] The RFID tag disclosed in the paragraph above may be used as a component of an RFID system that includes in addition a conventional RFID reader. Brief description of the figures

[0045] Figure 1 provides a schematic illustration of an RFID system.

[0046] Figure 2 provides a schematic illustration of a chipless RFID system.

[0047] Figure 3 is flowchart showing example operations for the manufacture of a chipless RFID component using LIG.

[0048] Figure 4 provides a schematic illustration of a chipless RFID tag with an example circular design pattern.

[0049] Figures 5A-C illustrate an example set of patterns and the corresponding backscattered EM fields and binary numbers associated with the example patterns.

[0050] Figures 6A-L illustrate example patterns.

[0051] Figure 7A provides a schematic drawing of an experimental set up that may be used to test the performance of samples.

[0052] Figure 7B depicts the experimental result of a test performed on an example embodiment LIG sample and a control copper sample.

[0053] Figure 8 provides a schematic illustration of a hybrid RFID system with an RFID tag that comprises an integrated circuit and an LIG-formed antenna. Detailed description

[0054] Figure 1 provides a schematic illustration of an example RFID system. With reference to Figure 1, an example RFID system 100 comprises a reader 110 and a tag 120, which is configured to be attached to, fixed on to, or embedded within an object of interest that is to be identified or tracked. The reader 110 includes an antenna 112 and a processor or decoder 114. Moreover, the reader 110 may also include a memory storage unit 116 that may contain a database. Additionally, or alternatively, the reader 110 may be connected via a (wired or wireless) network connection to a remote computing device with a memory storage unit comprising a database. The tag 120 comprises a substrate 122, an integrated circuit (or simply "chip") 124 and an antenna 126.

[0055] In operation, the reader continuously broadcasts a modulated EM field 130 ("interrogation signal") via the antenna 112 using a predefined communication protocol. Should the tag 120 be within a functional range of the reader 110, the tag 120 is able to receive the modulated EM field 130 via antenna 126 and to process the modulated EM field 130 using the integrated circuit 124. Once the modulated EM field 130 has been processed, the tag 120 will decide, based on the processing of the modulated EM field 130, whether to respond to the reader 110. In some alternative examples, the tag 120 always responds to the reader 110 upon receiving and processing the modulated EM field 130. The tag 120 is configured to respond to the reader 110 using a modulated EM field 140 ("response signal") generated by the integrated circuit 124. In operation, the reader 110 receives the modulated EM field 140 via antenna 112 (or another receiver antenna of the reader 110), processes the modulated EM field 140 via decoder 114, and, optionally, stores the data acquired from the processing of the modulated EM field 140 within the memory storage unit 116. The decoder 114 may also access the database within the memory storage unit 116 in order to further process the modulated EM field 140.

[0056] In a "chipless" RFID system, the integrated circuit 124 of Figure 1 is not required, and instead the tag is hard-coded to issue a characteristic response to facilitate identification. The present disclosure provides methods and devices particularly suited to chipless RFID systems. Figure 2 provides a schematic illustration of an example chipless RFID system. With reference to Figure 2, the example chipless RFID system 200 comprises a reader 210 and a tag 220 as with RFID system 100. Similarly, the reader 210 comprises a decoder 214, and optionally, a memory storage unit 216, which may comprise a database. In addition, the chipless RFID reader 210 comprises one or more antennas 212a-c. Each of the one or more antennas 212a-c may be tuned to a different frequency or an individual antenna may be used to monitor across a range of frequencies. The tag 220 comprises a substrate 222 and a target 224. The target 224 comprises a material that is configured to interact with EM fields. The material that constitutes the target 224 may be, for example, a dielectric, magnetic, or electrically conductive material. In this example, the target 224 comprises one or more resonant, (electrically) conductive, elements with resonant frequencies that correspond to the operational frequencies of antennas 212a-c. In other words, each resonant element functions to interact characteristically with EM signals at its particular resonant frequency. Note that in contrast to the tag 120, the chipless RFID tag 220 does not comprise an integrated circuit 124 or separate driven antenna 126. In a set of chipless RFID tags 220, each individual tag is distinguished by the combination of resonant elements provided (and thus by the associated combination of resonant frequencies).

[0057] In operation, the reader 210 generates a frequency sweep signal, or an "interrogation signal" 230 that comprises an EM field. Should the tag 220 be within a functional range of the reader 210, the interrogation signal 230 backscatters off the target 224, interacting with the one or more resonant elements in the target 224. The backscattered signal 240 from the tag 220, which encodes the response information of the tag 220, is then received by the one or more antennas 212a-c. The decoder 214 analyses the backscattered signal 240 received by the antennas 212a-c and identifies the information stored in the tag 220. The information received by the reader 210 may be optionally transmitted for storage in a memory storage unit 216. The decoder 214 may also access the database within the memory storage unit in order to further process the backscattered signal 240. Additionally, or alternatively, the reader 210 may transmit the information acquired from the backscattered signal 240 via a (wired or wireless) network connection to a remote computing device for further processing.

[0058] In general, chipless RFID systems may be classified as time domain systems, or frequency domain (including hybrid) systems. Moreover, frequency domain systems are further classified as retransmission-based and backscattered-based, depending on the type of interaction between the interrogation signal transmitted by the reader and the tag. The embodiment described above in the context of Figure 2 is a (planar) backscattered-based frequency domain chipless RFID system.

[0059] As explained in the example above, a key role is played by the one or more resonant, conductive, elements of the target 224. According to the present disclosure, such elements 224 may be formed through a laser-induced graphene (LIG) process. The use of LIG avoids the need for the use of metallic materials (such as copper, gold, or silver) or conductive ink in order to form the elements 224, and therefore may provide a cost-effective solution which is biodegradable and / or readily recyclable, and thus meaningfully more environmentally sustainable. This may be particularly important in use cases in which large numbers of disposable tags are produced (for example, as price and / or security tags on items in a retail environment).

[0060] It will be understood that while antennae may be depicted as being arranged external to a given device in Figures 1 and 2, this is purely schematic. Antennae may be arranged internally or externally to any device. Method of Manufacture

[0061] In this subsection, an example method of manufacture according to one aspect of the disclosure is provided. Utilising this method, a paper-based, LIG, chipless RFID tag has been manufactured which shows the necessary properties to function.

[0062] As illustrated in Figure 3, a process for manufacturing a chipless RFID tag is described. Figure 4 illustrates a chipless RFID tag 420 formed by such a method. The chipless RFID tag 420 comprises a main body 422 and a set of conductive elements 424 formed on the body 422. The conductive elements each have a characteristic frequency at which an incident EM field will resonate, allowing interrogation of the frequency response of the RFID tag 420 to allow a reader to identify the presence or otherwise of individual conductive elements 424.

[0063] At step 301 of Figure 3, a pattern for the conductive elements 424 is designed. This may include an overall scheme for conductive elements across a range of RFID tags, such that each tag provides a characteristic response to facilitate identification.

[0064] The method of manufacture of the example tag then proceeds in two overall steps: providing the substrate (step 303) and generating an LIG pattern on the substrate to form the conductive elements 424 (step 305).

[0065] Within the step of providing a substrate 303, a suitable substrate may be formed or created. In a particular example, the substrate is a paper substrate, but in general any carbon-containing substrate may be used. Preferably, the substrate is a biodegradable substrate. In preferred embodiments the substrate is planar and may also be flexible. The substrate may contain carbon-rich materials, such as aromatic polymers and lignocellulose material. The substrate may be a fibrous substrate and / or comprise for example lignin. The substrate is chosen to offer sufficient structural support as well as being suitable for the process of step 305 to generate a laser-induced graphene (LIG) structure thereon. In particular, a carbon precursor within the substrate that does not ablate when exposed to a CO2 laser beam and can be converted into LIG is preferably provided. High-temperature engineering plastics such as Kapton, Kevlar, polysulfones, poly(ether imide), and polyphenylene sulfide are readily converted into LIG. Cross-linked polymers such as phenolic resin and cross-linked polystyrene are also suitable substrates for LIG formation. In terms of natural substances, as well as lignin, polysaccharides such as cellulose and starch can be activated for conversion into LIG with the application of boric acid or phosphate-based fire retardants. The substrate may be constructed to be optimised both in terms of chemical composition and physical microstructure.

[0066] The second step 305 is the laser induction of a conductive carbon-based material, namely LIG, on the paper substrate using a laser cutter machine. The laser induction is performed so that the LIG forms a particular pattern on the paper substrate to form the elements 424, which pattern encodes identification information that is accessible by the EM field interrogation of the pattern.

[0067] While the specification generally refers to the use of a laser cutter machine to perform the laser induction, the skilled person will recognise that, equivalently, other laser devices which emit laser light may be used. In general, it is preferable to adopt a device with a laser head that can be controlled in two axes in order to form appropriate LIG patterns on a planar substrate. For example, a laser plotter machine or a laser engraver machine may also be used.

[0068] The two steps described above need not be performed in the same location or in quick succession and may be viewed as two independent industrial processes.

[0069] Further details of a particular method for manufacturing an RFID tag such as that shown in Figure 4 are provided below. The method described pertains to small-scale manufacture of example tags for experimental purposes. The skilled person will appreciate that the method may be simply adapted for industrial or commercial purposes.

[0070] In this example, the substrate provided is a paper substrate. At step 303, the paper substrate is formed through a number of stages. First a pulp is created: 1. Soak 2 sheets of 50g / m2 absorbent 508x381mm newsprint paper in water for a few seconds until completely wet. 2. Shred 2 sheets of wet paper into roughly A5 size and place in a commercially available blender (for example, a 350W Philips™ mini blender and smoothie maker). 3. Add 250ml water into the blender. 4. Blend the mixture on high speed (Setting 2 on the 350W Philips™ mini blender and smoothie maker) for 3.5 seconds to create the pulp.

[0071] Second, a paper sheet is formed from the pulp. 1. Pour 175ml of the pulp into a container. 2. Add 175ml water into the container and mix the solution. 3. Pour the solution from the container through a paper making deckle to create a thin 1mm layer of pulp.

[0072] Third, the paper sheet is dried to create the paper substrate. 1. Squeeze excess water out of the paper making deckle by gently tapping it with a sponge. 2. Remove the paper from the deckle by turning it upside down. 3. Place the paper on a designated area (for example, a silicon mat to help with the surface smoothness) and place multiple sheets of paper kitchen towel on top. 4. Allow the paper to dry, at room temperature, for 2-3 days. 5. Once the paper is completely dry, use a hot iron (for example, Tefal™ Aquaspeed 120) to flatten the sheet.

[0073] Finally, the paper substrate is treated. 1. Measure the thickness of the paper substrate at various locations to ensure that it is around 1mm thick consistently across the surface. 2. Treat the paper substrate by spraying it with a fire-retardant spray product (for example, Eco-Sol™ Flametect C). 3. Allow the paper substrate to dry as per the instructions of the fire-retardant spray product.

[0074] In this example, for the initial stage of creating the pulp, any paper, cardboard, or organic fibrous material (such as wood, coconut or walnut shells, cork, and cotton) may be used. In general, the pulp may be formed from any material which contains lignin - for example, the pulp may be made from a hard plant material. Lignin is a polymer that provides rigidity for plant support tissues.

[0075] Advantages of using newsprint paper include the fact that it is relatively cheap, widely available for recycling purposes, and has a high lignin content. The high lignin content in newsprint paper is due to the fact that newsprint paper is made via a mechanical pulping process rather than a chemical pulping process that would remove lignin from the pulp.

[0076] In general, any material with a higher carbon content (e.g. a higher lignin content) performs better, as far as the production of LIG is concerned, than materials with a lower carbon content. This also means that papers with enriched lignin content are particularly suitable for yielding LIG. Increasing the lignin content of the paper, however, also reduces the material's lifespan, as it causes the paper to turn brittle and yellow when exposed to air or sunlight. As a result, an optimal lignin content is required to balance structural strength and durability on the one hand with potential conductivity-yielding properties on the other. In some preferred embodiments, the lignin content of the substrate is at least 10% and preferably at least 15%. In general, lignin content between 10% to 40% may provide a suitable combination of conductivity and material strength, although in some preferred embodiments a range of 15% to 35 % may be utilised.

[0077] Additional factors that are borne in mind when making the substrate are as follows. The substrate should be thick enough to support the laser-induced circuitry (at least until potentially reinforced after the LIG process). For this reason, the substrate thickness may be at least 0.5mm and preferably around 1mm or above. The ideal thickness of the paper substrate is just under 1mm. It is also crucial for the laser-induction process to yield an even layer of LIG that the paper substrate surface is as flat and smooth as possible. Additionally, the microstructure of the paper may be optimised for yielding LIG by creating a suitable level of porosity within the paper material. In a preferred embodiment, the density of the substrate is around 240.5kg / m3 and more generally may be in the range 200kg / m3 to 300kg / m3, more preferably 240kg / m3 to 260kg / m3.

[0078] The fire-retardant spray that is used to treat the paper substrate functions as a dehydration spray and is used to further dry the paper substrate.

[0079] Step 305 for generating the LIG on the substrate is now described in greater detail. Firstly, the paper substrate is prepared: 1. Measure the thickness of the paper substrate to ensure that it is the desired thickness evenly across the surface (in this case around 1mm thick) and treat it with fire-retardant spray if it has not already been treated so at the paper substrate making step. 2. Place the paper substrate on the bed of a laser cutter machine or other laser machine (for example, Universal Laser Systems™ VLS3.50 - 10.6pm CO2 laser). 3. Secure the edges of the paper substrate to the bed of the laser cutter machine using masking tape making sure that the paper substrate lies as flat as possible on the bed.

[0080] Second, generating the LIG itself: 1. Import the files of the required pattern into the memory storage unit of the laser cutter machine. 2. Tune the settings of the laser cutter machine to a power of 3.25W (6.5% on the Universal Laser Systems™ VLS3.50 - 10.6pm CO2 laser), speed of 10% (or 133mm / s) on the Universal Laser Systems™ VLS3.50 - 10.6pm CO2 laser, and pulses per inch (PPI) of 1000. 3. Run the laser cutter machine with Z-axis value of 11mm to char the paper substrate at the sight of the pattern. At this stage, the charring process is carried out with the laser beam unfocussed on the substrate. 4. Run the laser cutter machine for the second time with Z-axis value of 1mm to convert the charred substrate material into a material that comprises of a combination of graphite and graphene. This second state is operated with the laser beam more focussed on the substrate than at step 3 above.

[0081] Techniques for providing LIG have been described in US 2017 / 0062821 and Lin et al. ("Laser-induced porous graphene films from commercial polymers", 2014, Nature Communications, 5, 5714; https: / / doi.org / 10.1038 / ncomms6714), which both describe a method of inducing a film of graphene on commercial polymers using a CO2 laser. The resulting laser-induced graphene (LIG) exhibits high electrical conductivity. Moreover, Kulyk et al. ("Laser-Induced Graphene from Paper for Mechanical Sensing", 2021, ACS Appl. Mater. Interfaces, 13, 8, 10210-10221; https: / / doi.org / 10.1021 / acsami.0c20270) describes producing LIG on a paper using a CO2 laser.

[0082] The skilled person will recognise that the particular parameters adopted in the example context above may be varied according to practical needs.

[0083] Once the LIG patterns 424 have been generated at step 305, the component may be treated for durability. 1. Handle the resulting sample with care. 2. Treat the sample with silicone spray, laminate, and / or adhere a layer of paper (or another planar substrate) on top of the LIG pattern in order to ensure the LIG pattern is more durable and less susceptible to damage.

[0084] Silicon spray may be used for prototyping purposes, while, adhering a layer of paper on top of the LIG pattern may be the preferred method for commercial purposes, since it is more environmentally friendly and sustainable. The adhesive used to fix a layer of paper on top of the LIG paper may be a recycling-compatible adhesive.

[0085] In some embodiments, multiple substrates will have LIG patterns formed thereon. The substrates can then be adhered to one another in such a way that the corresponding LIG patterns on each substrate are conductively coupled (i.e. so that the two adjacent patterns form a single conductive element). In this manner, once the two substrates are combined, the two LIG patterns on the two respective paper layers overlap so as to create a conductive structure that is twice as thick as the original LIG pattern on each individual substrate. Such a technique may be used to increase the conductivity of the tag, and thereby increase the efficacy of the system. LIG Pattern

[0086] The LIG pattern that is generated on the substrate encodes identification information about the tag that comprises the LIG pattern. The irradiation of the tag by an EM field and the backscattering of the EM field allows the chipless RFID reader to decode the information stored in the LIG pattern upon the processing of the backscattered EM field. The non-trivial backscattered EM field from the tag is generated by the conductive property of the LIG pattern, which property allows its constituent parts (the "resonant elements") to act as antennas.

[0087] Figures 5A-C provide a schematic illustration of three sets of LIG patterns 510a-c, the corresponding backscattered EM field 240 generated by the respective LIG patterns 520a-c, as received by the chipless RFID reader 210 and processed by the decoder 214, and the corresponding pre-defined binary numbers 530a-c associated with the LIG patterns.

[0088] Figure 5A depicts a pattern 510a with three equally spaced concentric conductive circles. The backscattered EM signal 240 when processed by the decoder 214 of the chipless RFID reader 210 is schematically of the form 520a. Note that the y-axis, labelled "response", corresponds to the absolute value of the radar cross-section (RCS) measured in decibels relative to a square metre (dBsm). The resonant frequency of the three concentric conductive circles translates to three peaks in the frequency response plot 520a. In practical implementations, the resonant frequencies are generally of the order of 1 GHz. A larger radius for the circle translates to a lower frequency in the response. Therefore, the lowest frequency peak in the response graph 520a corresponds to the largest radius circle in the pattern 510a and vice-versa with the middle frequency peak corresponding to the circle with radius between that of the lowest and highest radii.

[0089] In the example illustrated in Figures 5A-C, there may be at most three concentric circles positioned at predefined radii appearing in the pattern. Therefore, one expects at most three peaks at particular (predefined) frequencies (corresponding to the predefined radii) appearing in the response graph.

[0090] The appearance of a peak in the response at a particular predefined frequency may be represented by a binary code of "1" and the absence of a peak at that frequency may be represented by a binary code of "0". This is the encoding adopted in the examples illustrated in Figures 5A-C. Alternatively, the opposite encoding may be adopted; namely, the appearance of a peak is represented by a binary code of "0" and the absence of the peak by a binary code of "1".

[0091] Moreover, the particular frequency of the peak may correspond to a particular digit of a binary number. The correspondence between the particular frequency and the particular digit of the binary number 530a-c may be chosen as desired. For example, in the examples illustrated in Figures 5A-C, a convention is adopted whereby the inner circles (corresponding to higher frequencies) correspond to lower digits. However, alternative conventions are self-evident and may be adopted.

[0092] In summary, the set of patterns constructed from three concentric circles, examples of which are depicted in Figures 5A-C, may be used to encode 3 bits of information or equivalently eight states.

[0093] Therefore, in Figure 5A, there appears a pattern 510a with three concentric circles. This leads to a response 520a with three peaks and translates to a binary number 530a, "111".

[0094] Similarly, in Figure 5B, the pattern 510b has the two outer circles but not the inner most circle. This leads to a response 520b with the two lowest peaks appearing and therefore, adopting the convention chosen in this example, translates to a binary number 530b, "110".

[0095] Finally, in Figure 5C, the pattern 510c has the two inner circles but not the outer most circle. This leads to a response 520c with the two highest peaks appearing and therefore, translates to a binary number 530c, "Oil".

[0096] The patterns depicted in Figures 5A-C are simple examples used to demonstrate the encoding principle. Other patterns may be adopted depending on many factors, such as the amount of information that needs to be encoded, the environment in which the tag is likely to be used, the paper substrate on which the LIG pattern will be formed, the strength and position of the chipless RFID reader that is to be used, and / or other aesthetic considerations.

[0097] Figures 6A-L illustrate some other example pattern designs that may be used to encode the information.

[0098] The LIG pattern may comprise one or more circles 602 (as depicted in Figure 6A), ovals 604 (as depicted in Figure 6B) or ellipses, where each resonant element of the pattern corresponds to a circle, oval, or ellipse. Alternatively, the one or more resonant elements that constitute the LIG pattern may correspond to other closed shapes, such as squares 606 (as depicted in Figure 6C), rectangles, or other polygons. Furthermore, the resonant elements may be positioned in a concentric arrangement. This allows the LIG pattern to be more compact, thereby facilitating the encoding of higher number of bits of information per unit area, hence allowing for a smaller tag.

[0099] Alternatively, the resonant elements may correspond to open shapes 608, as depicted in Figure 6D. For example, each resonant element may be formed by two straight lines meeting at an angle. The angle may be, for example, 90°. Alternatively, each resonant element may be C-shaped 610, as depicted in Figure 6E. As with the closed shapes, resonant elements corresponding to open shapes may also be arranged in a packed, or concentric manner.

[00100] Another possibility is to encode the information in areas of LIG absence 612, as depicted in Figure 6F. The absence of LIG from an area that is otherwise conductive due to the presence of LIG will affect the backscattered signal. In this case, the response in the frequency associated with such an element would be the opposite of that for the inverse patterns illustrated in Figures 6A to 6E, and this may be used to encode a bit of information.

[00101] As depicted in Figures 6G and 6H, the resonant elements may be grouped into sets 614, 616 with similar resonant frequencies so that more than one resonant element corresponds to a particular encoding. The presence of two or more resonant elements with similar resonant frequencies may be used to increase the sensitivity of a detection. For example, if either frequency is detected by the reader, then the presence of both resonant elements is inferred. Alternatively, such a configuration may be used to increase the accuracy of a detection. For example, only if both frequencies associated with the resonant elements are detected by the reader does a positive detection register.

[00102] As depicted in Figures 6I-K, the resonant elements may also be furnished with small slits or gaps, that may themselves be arranged in a suitable pattern. The slits may allow for a better backscattered signal, thereby increasing the performance of the chipless RFID system. It has been found that slits (or gaps) of this kind can reduce unwanted harmonic resonances. For brevity, patterns with slits may be referred to using the name of the corresponding closed shape. Therefore, the pattern in Figure 61 may be referred to as a "circular" pattern 618, the pattern in Figure 6J, as an "ovular" pattern 620 and the pattern in Figure 6K as a "hexagonal" pattern 622.

[00103] Finally, the pattern 624 depicted in Figure 6L is indicative that a variety of combinations and options are available to the skilled person for encoding information using LIG-generated patterns. In particular, any combination of the examples presented above may be utilised where appropriate. Results

[00104] The performance of an example embodiment with a LIG circular design pattern manufactured according to the technique described above has been tested against the performance of a control sample with the same circular design pattern made of copper.

[00105] The copper control sample was manufactured as follows: 1. Print off the design pattern onto a transparent sheet of material, such as those manufactured from polyester and used in overhead projectors (commonly known as a "transparency", "viewfoil", or "viewgraph"). 2. Peel off the cover layer of a photoresist printed circuit board (PCB), and cover it with the printed pattern. One may use, for example, a Bungard™ photoresist presensitized FR4 fibreglass PCB 120306E33. 3. Expose the PCB with the designed pattern arranged on top off it to ultraviolet light for 30 seconds. 4. Take 5g of photoresist developer and dissolve it into 200mL of water. 5. Submerge the PCB board in the developer solution until the pattern appears clearly on its surface. 6. Clean the developed PCB board and submerge it into Ferric Chloride solution until the copper area outside the pattern disappears.

[00106] Figure 7A provides a schematic drawing of an experimental set up that was used to test the performance of an example embodiment LIG sample and a control copper sample.

[00107] As illustrated in Figure 7A, a vector network analyser (VNA) 702 may be used to generate a transmission signal and measure the resulting backscattered signal from the testing sample 708. An example commercially available VNA that may be used is an Agilent Technologies™ E5071B VNA. The transmission signal may be generated using a transmitting antenna 704 and the backscattered signal may be measured using a backscattering antenna 706. In particular, the two antennas (704, 706) may be near field radio frequency H-Loop antennas.

[00108] When performing the test, the two antennas (704,706) are arranged to be pointing perpendicular to the sample with an angle of about 30 degrees between them.

[00109] Figure 7B depicts the experimental result of a test performed on an example embodiment LIG sample and a control copper sample. Both samples comprise a circular design pattern 700, with three concentric circles, as depicted in Figure 7A.

[00110] In particular, Figure 7B depicts a graph of the RCS in dBsm (decibels relative to a square metre) versus the frequency measured in gigahertz for the LIG sample 710 and the copper sample 720.

[00111] Clear peaks are visible in the LIG sample response curve 710, demonstrating the viability of the proposed technique to encode identification information using LIG patterns. Further embodiment

[00112] While Figures 2-7 relate to the provision of chipless RFID tags and their use in a chipless RFID system, the techniques of the present disclosure can also be used in combination with an RFID chip. Figure 8 provides a schematic illustration of such a system 800, referred to in this disclosure as a "hybrid" system.

[00113] With reference to Figure 8, the hybrid RFID system 800 comprises a reader 110 and a tag 820. The reader 110 is as described with reference to Figure 1 and includes an antenna 112, a processor or decoder 114, and may also include a memory storage unit 116 that may contain a database. Tag 820 shares common elements with tag 120, as described with reference to Figure 1, in that it comprises a substrate822, a chip 124 and an antenna 826. However, the antenna 826 in tag 820 is formed from LIG rather than metal as is conventionally the case with antenna 126, as described with reference to Figure 1.

[00114] Antenna 826 may conform to the geometry or shape of a conventional RFID antenna 126 and may be formed on the substrate 822 using a method that comprises step 305 as described with reference to Figure 3. Similar to a conventional RFID tag antenna 126, antenna 826 may be configured in its size and / or shape to operate within any one of a number of frequency bands, including, but not limited to, LF, HF, UHF, and NFC. Therefore, antenna 826 may comprise the shape of a conventional RFID tag antenna. For example, the shape of antenna 826 may correspond to that of the antenna coil depicted in Figure 1 of Hoon et al. ("Radio Frequency Identification (RFID) Tag Antenna Design at Ultra High Frequency (UHF) Band", 2017, Indian Journal of Science and Technology, 10, 5, 1-6; doi: 10.17485 / ijst / 2017 / vl0i5 / 111270).

[00115] The LIG-formed antenna 826 may be connected to a conventional chip 124 in the same way that a conventional antenna 126 may be connected to the chip 124 in a RFID system as schematically illustrated in Figure 1. In particular, antenna 826 may be connected to chip 124 using silver paste.

[00116] The LIG-formed antenna pattern may be treated for durability as described with reference to Figure 3 above. Additionally, or alternatively, the combination of the LIG-formed antenna 826, chip 124, and the connection(s) between them may be encased by adhering a layer of paper on top of the configuration as described with reference to Figure 3.

[00117] Substrate 822 may be multi-layered substrate comprising at least one layer of integrated circuit substrate and at least one layer of a paper, or more generally carbon-containing, substrate as in one example described with reference to Figure 3. In general, the process described in Figure 3 above may be adopted in respect of one or possibly more of the paper, or carbon-containing, layers in the provision of the tag 820, and particularly to form the antenna 826.

[00118] With reference to Figure 9a, substrate 822 may comprise a first layer 822a that is formed in the same manner as substrate 122 with reference to Figure 1. Thus, layer 822a may constitute an integrated circuit substrate, such as a semiconductor material, for example silicon. Alternatively, layer 822a may be formed from a polymer or plastic material, such as polyethylene terephthalate (PET) or polyvinyl chloride (PVC). In other embodiments, layer 822a may be formed from carbon-containing material, such as paper. In yet further embodiments layer 822a may itself be a multi-layered structure comprising any one of a combination of semi-conductor material, polymer material, and / or carbon-containing material.

[00119] Substrate 822 may have a second layer 822b that is formed in the same manner as substrate 222 with reference to Figure 2. Thus, layer 822b may be a paper substrate, or more generally, a carbon-containing substrate. The LIG may be formed on layer 822b. That is, the process described in Figure 3 may be applied to layer 822b to form the antenna 826. Additionally, layer 822b may comprise a gap configured to accommodate, or simply accommodating, chip 124. Alternatively, layer 822b need not be formed so as to substantially cover layer 822a. The electrical connections between the components of the tag 820 may be formed within layer 822a and its interface with layer 822b. Alternatively, the electrical connections between the components of the tag 820 may be formed within layer 822a and on layer 822b. In yet further embodiments layer 822b may itself be a multi-layered structure comprising at least one carbon-containing layer and any number of other layers containing semi-conductor material, polymer material, and / or carbon-containing material.

[00120] Alternatively, substrate 822 may be formed in a different configuration to that described with reference to Figure 9a. With reference to Figure 9b, substrate 822 may comprise a first layer 822b that is formed in the same manner as substrate 222 with reference to Figure 2, i.e. layer 822b may be a paper substrate, or more generally, a carbon-containing substrate. The LIG may be formed on layer 822b. That is, the process described in Figure 3 may be applied to layer 822b to form the antenna 826. Substrate 822 may have a second layer 822a that is formed in the same manner as substrate 122 with reference to Figure 1, i.e. layer 822a may be an integrated circuit substrate, such as that formed from silicon, or as explained above, may comprise any one of a combination of materials including semi-conductor material, polymer material, and / or carbon-containing material. The chip 124 may then be accommodated on layer 822a. Layer 822a may have any shape with respect to layer 822b. Layer 822a may substantially cover layer 822b or layer 822a may only cover a fraction of the surface of layer 822b. The electrical connections between the components of the tag 820 may be formed within layer 822a and its interface with layer 822b. Alternatively, the electrical connections between the components of the tag 820 may be formed within layer 822a and on a surface of layer 822b that is not covered by layer 822a. As described with reference to Figure 9a, layer 822a and / or layer 822b may themselves be multilayered. What is ultimately required is at least one carbon-containing substrate layer so that a laser beam may be applied to each of the at least one carbon-containing substrate layer to generate an antenna that comprises a LIG pattern. In the case of a plurality of such carbon-containing substrate layers, the antenna may be generated independently on each one of the plurality of carbon-containing substrate layers. Alternatively, the antenna may be generated by the cumulative effect of the application of the laser beam on each one of the plurality of carbon-containing substrate layers. That is, an antenna could not be said to be generated on any one of the plurality of carbon-containing substrate layers. However, the application of the laser beam on each of the plurality of carbon-containing substrate layers nevertheless generates an antenna on or within the plurality of the layers.

[00121] Returning to the description with reference to the Figure 8, in operation, the hybrid RFID system 800 functions in the same way as the RFID system 100 as described with reference to Figure 1. The LIG-formed antenna 826 performs the role of the conventional antenna 126 of Figure 1 in terms of receiving the modulated EM field 130 and transmitting the modulated EM field 140.

[00122] Such a hybrid system 800 may advantageously contain less metal than a conventional RFID system 100, while remaining compatible with existing RFID infrastructure, such as existing RFID readers 110 and software.

[00123] It should be realised that the foregoing embodiments are not to be construed as limiting and that other variations, modifications and equivalents will be evident to those skilled in the art and are intended to be encompassed by the claims unless expressly excluded by the claim language.

[00124] Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or in any generalisation thereof. Claims may be formulated to cover any such features and / or combination of such features derived therefrom.

Claims

1. A method of manufacture of a radio-frequency identification (RFID) component configured for use in an RFID tag, the method comprising:providing a substrate, the substrate comprising one or more of paper and cardboard; andapplying a laser beam to the substrate to generate a laser-induced graphene (LIG) pattern on the substrate, the LIG pattern encoding identification information of the RFID tag, and the encoded identification information being decodable by an RFID reader.

2. The method of claim 1, wherein the substrate is biodegradable.

3. The method of claim 1 or claim 2, wherein the substrate further comprisesaromatic polymers and / or lignocellulose materials.

4. The method of claim 3, wherein the substrate is a fibrous substrate.

5. The method of any one of the preceding claims, wherein the step ofproviding a substrate comprises:forming a pulp from a carbon-containing material, the carbon-containing material comprising one or more of paper and cardboard; andgenerating a sheet of the substrate from the pulp.

6. The method of claim 5, wherein the pulp is formed from newsprint paper.

7. The method of any one of the preceding claims, wherein the step of applyingthe laser beam comprises:charring the substrate; andconverting at least a portion of the charred substrate into graphene.

8. The method of claim 7, wherein during the charring of the substrate the laser beam is less focussed on the substrate than during converting at least a portion of the charred substrate into graphene.

9. The method of any one of the preceding claims, further comprising adhering a first substrate to a second substrate such that the LIG pattern formed on each substrate are conductively coupled.

10. The method of any one of the preceding claims, wherein the laser beam is applied using a carbon dioxide laser.

11. The method of any one of the preceding claims, wherein the laser beam is applied at an operational irradiation power greater than 1W.

12. The method of claim 11, wherein the operational irradiation power is at least 3W.

13. The method of any one of the preceding claims, wherein the substrate has a thickness of at least 0.5mm.

14. The method of any one of the preceding claims, wherein the LIG pattern comprises one or more circular elements.

15. The method of claim 14, wherein the circular elements form a circular design that comprises a plurality of concentric circles positioned at predefined radii.

16. The method of claim 15, wherein one or more of the circles comprises a slit.

17. The method of any one of the preceding claims, further comprising, subsequent to generating the LIG pattern on the substrate:applying a film of silicone to the LIG pattern; and / or adhering a layer of paper on top of the LIG pattern.

18. The method of any one of claims 1-17, wherein the step of applying a laser beam to the substrate to generate a laser-induced graphene (LIG) pattern on the substrate comprises:applying a laser beam to the substrate to generate an antenna, the antenna comprising the LIG pattern on the substrate; andelectrically coupling an integrated circuit to the antenna.

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