Conductive textile

Abstract

A conductive textile (6) is disclosed, comprising: a matrix material (14); and at least one conductive fibre (12) configured to enable electric current to flow between a first part of the matrix material and a second part of the matrix material; wherein the at least one conductive fibre is coupled to the matrix material with slack (18) between the first part and the second part to enable stretching of the matrix material while minimising tension applied to the at least one conductive fibre.

Description

[0001] CONDUCTIVE TEXTILE

[0002] FIELD OF THE INVENTION

[0003] The invention relates to conductive textiles. In particular, the invention relates to conductive textiles for use with wearable devices.

[0004] BACKGROUND

[0005] Conductive textiles have a wide variety of applications, particularly where it would be desirable for an electronic system to be flexible or to conform to other shapes and surfaces.

[0006] One key application of conductive textiles is to facilitate wearable technology in various fields, such as health monitoring, sport and fitness, and professional performance. Conductive textiles need to conduct electricity effectively while also exhibiting properties expected of regular textiles, namely: comfort, flexibility, and durability. In particular, user comfort presents one impediment to the adoption of wearable technology. Consequently, there is a need for a textile that can serve as a reliable conduit for both power and data while conforming to the human body's contours and movements, without sacrificing comfort.

[0007] Further, as wearable devices develop towards more sophisticated applications like real-time health diagnostics and location-independent professional communications, the demand for conductivity fidelity is also increasing. It is desirable for the fabric to maintain consistent electrical properties despite the mechanical stresses of daily activity, including extensive stretching and flexing. Additionally, the consumer expectation that smart garments should be as washable and durable as traditional clothing has presented a substantial challenge to the industry. Such garments should ideally be able to withstand repeated laundering without degradation in conductive performance, ensuring the longevity of the garment's electronic functions.

[0008] One existing approach involves the use of conductive tracks made from nylon yarn plated with metal, such as silver, copper, or gold. These conductive tracks have a relatively high electrical resistance that limits their usefulness for facilitating devices involving high power or weak signals. The conductive tracks can become deformed when stretched, which changes their electrical resistance and negatively affects the operation of a connected device. Additionally, the conductive tracks can be susceptible to oxidation or other chemical reactions that degrade performance. Alternative approaches also suffer from a lack of stretchability, durability, and an inability to convey high power signals safely. Conductive inks are one such approach typically comprising metallic nanoparticles suspended in a polymer binder. Under stretching, the polymer matrix can elongate, but this also increases the distance between conductive particles, leading to cracks or breaks in the conductive paths. This impacts the textile's ability to maintain conductivity under cyclical stretching and can lead to a permanent increase in resistance or outright failure of the conductive pathways.

[0009] In general, degradation due to stretching can occur due to a lack of elastic deformability of the conductive material (e.g., of a metal or conductive ink). Stretching can make conductive pathways longer and thinner, effectively increasing the electrical resistance. In more severe cases, it can break these pathways. Ideally, conductive elements would maintain a consistent resistance value over their stretchable range to ensure reliable power and signal transmission. However, current materials and designs often fail to achieve this, especially under extensive or repeated stretching. This issue can be exacerbated when the conductive material is embedded in a substrate material that is more elastically deformable than the conductive material. Everyday wearing and washing of the textile can stretch the textiles to an extent sufficient to cause a performance degradation. There is therefore a demand for a conductive textile that can be stretched without causing a change in performance.

[0010] Repeated washing also introduces chemical exposure, which can degrade conductive materials. For textiles incorporating metal fibres or particles, oxidation can lead to a gradual loss of conductivity. Similarly, conductive inks face the risk of being washed away or further cracked, compounding the issues introduced by stretching. Conductive textiles currently face limitations in safely carrying high currents due to inadequate heat dissipation capabilities and the risk of overheating, which could cause bums or fire hazards. The relatively high electrical resistance of some textiles compared to conventional wires means that more power is lost as heat. This limits their ability to support high-power devices.

[0011] The detection and transmission of ultra-low voltage signals, such as those generated by muscle (electromyography, EMG) or brain activity (electroencephalography, EEG), require materials with very low inherent electrical noise and high conductivity. Current conductive textiles often have too high a baseline resistance and electrical noise, making them unsuitable for accurately capturing these signals without significant signal amplification and processing.

[0012] It is an object of the invention to address these demands.

[0013] SUMMARY OF INVENTION

[0014] According to a first aspect of the present invention, there is provided a conductive textile, comprising: a matrix material; and at least one conductive fibre configured to enable electric current to flow between a first part of the matrix material and a second part of the matrix material; wherein the at least one conductive fibre is coupled to the matrix material with slack between the first part and the second part to enable stretching of the conductive textile while minimising tension applied to the at least one conductive fibre.

[0015] In this way, the material can be stretched (e.g., during washing or while being worn) while minimising tension on the conductive fibre. The conductive fibre can be coupled to the matrix material with slack in any suitable manner, such as using loops or a circuitous path, to allow the conductive fibre to straighten without deforming, thus maintaining the conductive pathways' integrity. This avoids stress being placed on the conductive fibre during everyday usage, which can otherwise cause the conductive fibre to permanently elongate and its resistance to change, leading to degraded electrical performance. In other words, this approach minimizes the mechanical stress on individual conductive fibres, preserving their conductive properties and structural integrity over time, even under repeated stretching.

[0016] The function of the slack between the first part and the second part can also be described alternatively as preventing an amount of tension sufficient to cause a permanent deformation, such as a change in fibre thickness, of the at least one conductive fibre. Such a permanent or inelastic deformation may be detectable by a permanent change in resistance of more than 10% ± 2%, preferably 5% ± 2% (i.e. , permanent in that the resistance does not return to a previous value when the conductive textile is returned to a relaxed state).

[0017] An amount of slack may be provided that is sufficient to enable stretching of the conductive textile along at least one axis, preferably along two perpendicular axes, by (in order of increasing preference) 20%, 30%, 40%, or 50% of its length along those axes without causing a permanent change in resistance in the at least one conductive fibre. An amount of slack may be provided to enable stretching of the conductive textile to the elastic limit of the matrix material without causing a permanent change in resistance (or only causing a minimal change in resistance, e.g., of at most 10% ± 2% or preferably 5% ± 2%).

[0018] The slack may enable the conductive textile to be stretched by (in order of increasing preference) 20%, 30%, 40%, or 50% of its length, while causing a maximum temporary change in resistance (i.e., temporary in that the resistance returns to a previous value when the conductive textile is returned to a relaxed state) that is substantially zero or is minimal, e.g., 10% ± 2% or preferably 5% ± 2%.

[0019] The at least one conductive fibre may have a resistance of less than 5 ohms per metre, preferably less than 3 Ohms per metre, most preferably less than 1 Ohm per metre.

[0020] The at least one conductive fibre may comprise a plurality of conductive fibres combined (e.g., spun) into a conductive yam. The at least one conductive fibre need not be continuous. That is, a plurality of individual, discrete threads of the at least one conductive may be coupled between regions of the matrix material. In other embodiments, the at least one conductive fibre can be continuous (e.g., formed from a single spool) throughout the conductive textile.

[0021] The matrix material is preferably non-conductive and preferably also elastic, i.e. , more elastically deformable than the at least one conductive fibre. The matrix material may comprise nylon in one example, however any other suitable material may be used in other embodiments, such as cotton, polyurethane, or latex fibres.

[0022] Preferably, the at least one conductive fibre is coupled to the matrix material with slack between the first part and the second part to enable stretching of the conductive textile along a first axis and (preferably perpendicular) a second axis while minimising tension applied to the at least one conductive fibre. This can be achieved in various ways. In one example, the at least one conductive fibre may be arranged with slack portions configured to provide surplus length along the first axis and the matrix material can comprise an elastic portion configured to elongate to enable stretching of the conductive textile along the second axis. In another example, the at least one conductive fibre can be arranged with slack portions having different orientations that straighten when the conductive textile is stretched along the first axis or the second axis. In any case, minimising the tension along two different axes provides a more resilient textile because in practice fabrics are likely to experience pulling or stretching along more than one axis.

[0023] Preferably, the at least one conductive fibre comprises a first conductive fibre and a second conductive fibre, respectively comprising a first conductive material and a second conductive material that is different from the first conductive material. In this way, the at least one conductive fibre can benefit from the properties of two different materials. For instance, the at least one conductive fibre can be made more resilient because different materials tend to degrade at different rates in response to different environmental stresses. In one example, detergent may degrade one of the materials more rapidly than the other, meaning that overall the at least one conductive fibre is more resilient to corrosion.

[0024] Preferably, the first conductive fibre comprises silver-plated nylon. Silver-plated nylon is relatively low resistance while also having a soft fabric-like feel that is comfortable to the user. The silver-plated nylon may be formed by electroplating a nylon fibre.

[0025] Preferably, the second conductive fibre comprises one or more copper fibres. As copper has a particularly low electrical resistance, this reduces the electrical losses when the at least one conductive fibre is used to transmit electrical current.

[0026] Preferably, the one or more copper fibres are tin-plated. In this way, the copper fibres can be protected from corrosion and the at least one conductive fibre can be more easily soldered to other electrical components.

[0027] Preferably, each of the one or more copper fibres have a thickness of less than 0.15 mm, preferably, less than 0.1 mm, more preferably less than 0.8 mm, most preferably of 0.05 mm or less. In this way, the copper fibres are particularly flexible, which provides the conductive textile with a soft feel that is comfortable for the user. Preferably, a plurality of copper fibres of 0.05 mm are provided, which maximises user comfort.

[0028] Preferably, the first conductive fibre and the second conductive fibre are arranged adjacently in the matrix material. In this way, the first conductive fibre and the second conductive fibre provide redundant connections between parts of the matrix material so that if one of the fibres fails the other fibre is also present and can provide an alternative path for current to flow. The first conductive fibre and the second conductive fibre may be co-located throughout the conductive textile for maximum electrical redundancy.

[0029] Preferably, the first conductive fibre and the second conductive fibre are arranged twisted about one another, or otherwise combined into a single conductive yam. In this way, a conductive yam can be formed. It has been found that forming a composite yam in this way makes the conductive textile easier to manufacture because snapping or knotting of different types of fibre coupled separately to the matrix material can be avoided. Twisting the fibres about one another in this way also ensures a redundant electrical connection is provided between the first part and the second part of the matrix material.

[0030] Preferably, the at least one conductive fibre is arranged with one or more slack portions configured to straighten when pulled, wherein the one or more slack portions are configured to straighten by a combined length corresponding to at least half of, or preferably about equal to or greater than, a change in distance between the first part and the second part when the matrix material is maximally stretched (e.g., to an elastic limit) along an axis bisecting the first part and the second part. In this way, the at least one conductive fibre has sufficient surplus length to allow stretching of the material without causing a permanent or inelastic deformation of the at least one conductive fibre. The one or more slack portions may be tuck loops in a knitted structure in one example. In another example, the one or more slack portions may be a holding stich. Generally, the one or more slack portions can be any part of the at least one conductive fibre configured to provide surplus length to enable straightening of the at least one conductive fibre when pulled.

[0031] Preferably, the at least one conductive fibre has a length that is at least half of, or preferably about equal to or greater than, a distance between the first part and the second part when the material is maximally stretched along an axis bisecting the first part and the second part.

[0032] Preferably, the at least one conductive fibre is coupled to the matrix material such that the at least one conductive fibre can slide with respect to the matrix material. In this way, the at least one conductive fibre can move freely when the conductive textile is flexed or pulled without experiencing an inelastic deformation.

[0033] Preferably, at least one conductive fibre is arranged to form one or more loops. The loops may be part of a knitted structure. Alternatively, the loops may be part of a stitched pattern. The loops may be stitched intentionally loosely to the matrix material to provide the slack. Preferably, the at least one conductive fibre is arranged in a circuitous path between the first part and the second part. In this way, the at least one conductive fibre is arranged with surplus length that can provide a slack portion.

[0034] Preferably, the at least one conductive fibre is threaded through the matrix material. In other embodiments, the at least one conductive fibre can be coupled to the matrix material in any other suitable manner. For instance, the at least one conductive fibre can be arranged on a surface of the matrix material and attached to the matrix material by stitching, which may be loose to enable the at least one conductive fibre to straighten when pulled.

[0035] Preferably, the matrix material and the at least one conductive fibre are arranged to form a knitted structure. In this way, the at least one conductive fibre can be arranged in a regular pattern throughout the conductive textile to ensure consistent and homogenous electrical properties of the conductive textile across different regions.

[0036] Preferably, the matrix material comprises an elastic yarn that is more elastically deformable than the at least one conductive fibre. The elastic yam is preferably non-conductive. In this way, the elastic yam can provide added stretchability to the conductive textile.

[0037] Preferably, the matrix material and the at least one conductive fibre are arranged in alternating interlocking rows. In this way, rows of conductive fibre can be positioned between rows of matrix material, which is typically more stretchy than the at least one conductive fibre. This can enable the conductive textile to be stretchable along two different axes.

[0038] Preferably, the knitted structure is configured to enable the matrix material to elongate when the conductive textile is stretched along a first axis and to enable one or more slack portions of the at least one conductive fibre to straighten when the conductive textile is stretched along a second axis that is different to the first axis. In this way, the one or more slack portions can straighten to enable stretchability of the conductive textile along one axis while the matrix material can elastically extend to provide stretchability along a different, preferably perpendicular axis.

[0039] Preferably, the at least one conductive fibre interlocks with the matrix material in a plurality of first loops and a plurality of second loops, wherein the second loops are less confined than the first loops to provide slack. For example, each of the plurality of second loops may interlock with three other loops, thereby providing greater freedom (i.e., less confinement) along one direction, whereas the first loops may interlock with two loops, resulting in greater confinement of the first loops. In this way, the second loops can provide slack portions of the at least one conductive fibre.

[0040] Preferably, the knitted structure is configured to enable the matrix material to elongate when the conductive textile is stretched along a first axis and to enable the second loops to straighten when the conductive textile is stretched along a second axis that is different to the first axis. In this way, the second loops portions can straighten to enable stretchability of the conductive textile along one axis while the matrix material can elastically extend to provide stretchability along a different, preferably perpendicular axis.

[0041] Preferably, each of the first loops are positioned between second loops such that the first loops and the second loops form an alternating pattern. In this way, each of the second loops can straighten around each of the first loops, enabling the knitted structure to expand while minimising tension on the first loops.

[0042] Preferably, the second loops are tuck loops. In this way, horizontal (i.e., along the direction of extension of a particular conductive fibre) extendability is provided by the second loops. In other examples, any other type of knitting or stitching loop that enables increased extendability can be used in the knitted structure in place of or in addition to tuck loops.

[0043] Preferably, each of the first loops are adjacently surrounded by loops of the matrix material. In this way, loops of the matrix material can straighten or elongate around each of the first loops, enabling the knitted structure to expand while minimising tension applied to the first loops.

[0044] Preferably, the at least one conductive fibre is arranged in a plurality of discontinuous parallel rows. In this way, the conductive textile can be used to connect electrical components in parallel across the discontinuous parallel rows, which lowers the effective resistance of the coupling, compared to coupling electrical components with a single continuous conductive thread.

[0045] Preferably, the conductive textile comprises a connector configured to provide an electrical connection between the discontinuous parallel rows of the knitted structure. A first and a second connector (or “terminal connectors”) can be provided at opposite ends of the rows, which may be configured to enable attachment to an electronic device or a seating configured to receive an electronic device. This facilitates an electrically parallel connection (as distinct from an electrically in-series connection) between electronic components using the conductive textile.

[0046] Preferably, the conductive textile comprises a polymer layer configured to provide electrical insulation to the at least one conductive fibre. In this way, electrical insulation is provided to protect a user during use.

[0047] Preferably, the polymer layer is arranged on both sides of the conductive textile. In this way, users can be more completely protected.

[0048] Preferably, the polymer layer is more thermally conductive than the matrix material. In this way, the polymer layer can reduce the formation of hotspots on the conductive textile because heat can be more efficiently diffused throughout the extent of the fabric, thereby improving the safety of the conductive textile.

[0049] Preferably, the polymer layer is more elastically deformable than a conductive material of the at least one conductive fibre. The polymer layer may be configured to be more elastically deformable than the matrix material. In this way, the polymer layer does not inhibit the stretchability of the matrix material or the conductive textile overall. Preferably, the polymer layer comprises a printing ink, which may comprise silicone and / or polyurethane. The polymer preferably comprises one or more additives such as Boron Nitride, Aluminium Oxide, and / or Silica to make the polymer layer thermally conductive, electrically insulating, and stretchable.

[0050] Preferably, the conductive textile further comprises a first terminal connector at the first part and a second terminal connector at the second part, wherein the at least one conductive fibre is electrically connected to the first terminal and the second terminal to enable current flow between the first and second terminals.

[0051] Preferably, the at least one conductive fibre is arranged in a plurality of discontinuous rows, more preferably wherein each of the plurality of discontinuous rows are connected across the first terminal connector and the second terminal connector to form a plurality of electrically parallel connections. In this way, the conductive textile can facilitate electrical connection between the terminals (and hence between electronic components in use) with a lower effective resistance. The at least one conductive fibre may be arranged in at least 6 discontinuous rows. This has been found to provide an acceptably low resistance for many applications. In other examples, the at least one conductive fibre may be arranged in at least 8, 10, 12, 15 or 20 discontinuous rows to provide lower resistances.

[0052] Parallel connection in this manner can drastically reduce the resistance of the conductive textile to enable ultra-low voltage or power signals, such as EMG or EEG signals, which require low electrical noise, to be transmitted effectively through the conductive textile.

[0053] Preferably, at least one of the first and second terminal connectors comprise conductive epoxy. In this way, the terminal connectors can, simultaneously, bind with the matrix material while also providing an electrical connection with the at least one conductive fibre.

[0054] Preferably, the conductive textile comprises conductive epoxy configured to provide a terminal connection. According to a second aspect of the present invention, there is provided a garment, comprising the conductive textile of any of the embodiments of the first aspect of the invention. The garment can be any kind of worn item, such as clothing items like T-shirts, trousers, or leggings, as well as apparel, such as a harness or hat.

[0055] Preferably, the garment comprises a first terminal connector and a second terminal connector, wherein the at least one conductive fibre electrically connects the first terminal connector to the second terminal connector to enable current flow therebetween. In this way, electronic components such as sensors, batteries, stimulators and the like can be attached to the terminal connectors.

[0056] Preferably, the conductive textile comprises a plurality of discontinuous rows of the at least one conductive fibre, wherein each of the plurality of discontinuous rows are connected across the first terminal connector and the second terminal connector to form a plurality of electrically parallel connections. In this way, the effective resistance of the electrical connection provided by the conductive textile is reduced, compared to a single strand of the at least one conductive fibre connecting the first and second terminal connectors. The reduction in resistance can be sufficient to enable the effective transmission of particularly weak signals, such as EMG or EEG signals.

[0057] Prefreably, the garment further comprises an electronic device attached to the first terminal connector. The electronic device can be any kind of device configured to be used on or near a wearer’s body. Any other kind of electronic component can be attached to the first terminal connector in other examples.

[0058] Preferably, the electronic device comprises one or more of a sensor, a stimulator, and a processor.

[0059] Preferably, the garment comprises an electrical energy storage component (such as a battery or supercapacitor) connected to the second terminal connector, or wherein the second terminal connector is electrically connected to a seat configured to receive an electrical energy storage component. According to a third aspect of the present invention, there is provided a kit, comprising the conductive textile of any of the embodiments of the first aspect of the invention. The kit may comprise one or more strips of pre-defined length and width configured to provide a specific resistance or power rating for one or more intended application. For example, the kit can comprise a strip of the conductive textile that is particularly wide, comprising a many parallel connections of the at least one conductive fibre, to enable compatibility with high power devices that require low resistance electrical conduits. The kit may comprise strips of different lengths and widths to provide different options for incorporation into different usage scenarios.

[0060] Preferably, the kit comprises one or more coupling connectors configured to enable attachment of the conductive textile to a garment. In one example, the coupling connectors can comprise a clamp. In another example, the coupling connector can comprise a conductive pad, such as a copper pad, and a conductive adhesive. The conductive pad can provide a conductive surface for soldering of electronic components. The conductive adhesive can be used to connect the conductive pad to the at least one conductive fibre of the conductive textile.

[0061] According to a fourth aspect of the present invention, there is provided a method of manufacturing a conductive textile, comprising: forming a conductive yam by combining two or more conductive fibres; and coupling the conductive yarn to a matrix material. In this way, coupling of the conductive yam to the matrix material can be carried out more efficiently with less errors, as the composite conductive yam is less likely to knot or snag compared to process that couple two or more conductive fibres to a matrix material individually.

[0062] The conductive textile can correspond to any of the embodiments of the first aspect of the invention discussed above.

[0063] Preferably, the conductive yam is coupled to the matrix material with slack between a first part of the matrix material and a second part of the matrix material to enable stretching of the conductive textile while minimising tension applied to the conductive yarn.

[0064] Preferably, the two or more conductive fibres comprise different materials.

[0065] Preferably, coupling the conductive yam to a matrix material comprises knitting the conductive yam with a non-conductive yam to form a knitted structure.

[0066] Prefreably, the knitted structure comprises a plurality of rows of conductive yam formed by a continuous piece of conductive yam, preferably further comprising, subsequently, cutting portions of the knitted structure to form a plurality of discontinuous rows of conductive yam. By first forming the conductive textile with a continuous piece of conductive yam, the conductive textile can be manufactured efficiently using a single spool of yam. Subsequently, the conductive textile can be cut at edge regions (also referred to herein as “ladder regions”) to efficiently separate the connected rows, forming discontinuous rows that are useful for forming low-resistance electrically parallel connections between electrical components.

[0067] BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 shows a schematic diagram of a garment according to an embodiment of the invention;

[0069] Figure 2 shows a cross-sectional schematic diagram of a conductive textile according to an embodiment of the invention;

[0070] Figure 3 shows a schematic diagram of a conductive textile according to an embodiment of the invention;

[0071] Figure 4 shows a schematic diagram of a conductive textile according to an embodiment of the invention;

[0072] Figure 5 shows a schematic diagram of a conductive textile according to an embodiment of the invention; Figure 6 shows a photographic image of a conductive textile according to an embodiment of the invention in a relaxed state;

[0073] Figure 7 shows a photographic image of a conductive textile according to an embodiment of the invention in a stretched state;

[0074] Figure 8 shows a photographic image of a conductive textile according to an embodiment of the invention in a stretched state;

[0075] Figure 9 shows a simplified schematic diagram of a conductive textile according to an embodiment of the invention;

[0076] Figure 10 shows a simplified schematic diagram of a conductive textile according to an embodiment of the invention incorporated into a circuit; and

[0077] Figure 11 shows a flowchart of a method of forming a conductive textile according to an embodiment of the invention.

[0078] DETAILED DESCRIPTION

[0079] Figure 1 shows a schematic diagram of garment comprising a conductive textile according to an embodiment of the invention.

[0080] A garment in the form of a T-shirt 1 is provided. An electronic device 2 is attached to a first part of the T-shirt 1 . The electronic device 2 is electrically connected to a battery 4 positioned at a second part of the T-shirt 1 by a strip of conductive textile 6. The conductive textile 6 is configured to transmit electrical current from the battery 4 to the electronic device 2 to power the electronic device 2 and is described in greater detail below.

[0081] The T-shirt 1 can be any other type of garment or wearable item in other embodiments, such as a harness, trousers, leggings, or underwear.

[0082] The electronic device 2 can be any kind of device configured to receive or transmit electronic signals to perform a function. In one example, the electronic device 2 can be a stimulator configured to transmit a stimulation signal to a wearer’s body. In another example, the electronic device 2 can be a sensor configured to perform a measurement on the wearer’s body. In this case, the electronic device 2 may transmit sensor readings to a remote device, such as the wearer’s smartphone, using a suitable wireless interface. Alternatively, the sensor can be configured to transmit a signal through the conductive textile 6 to an amplification circuit or microprocessor for subsequent processing. The conductive textile 6 of the present invention can be configured to have a sufficiently low resistance that enables suitability for transmitting ultra-low voltage signals, such as EMG (electromyography) or EEG (electroencephalogram) signals. Thus, the electronic device 2 can also be a sensor configured to measure one of these signals or any other low voltage (or low power) signals.

[0083] The electronic device 2 can comprise at least one processor and a memory for executing and storing instructions, respectively, for operating the electronic device 2. Alternatively, the processor and memory may be provided elsewhere and connected to the electronic device 2 by the conductive textile 6.

[0084] The electronic device 2 may be permanently attached to the garment 1 , in which case the electronic device 2 may be provided in a sealed casing to prevent damage during washing. Alternatively, the electronic device 2 may be removably attached to a device seating (not shown) comprising an electrical connection that is connected to the conductive textile 6.

[0085] The battery 4 can be any suitable kind of battery and may be replaceable or rechargeable. The battery 4 may be permanently attached to the garment 1 , in which case the battery 4 may be provided in a sealed casing to prevent damage during washing. Alternatively, the battery 4 may be removably attached to a battery seating (not shown) comprising an electrical connection that is connected to the conductive textile 6.

[0086] The arrangement of Figure 1 provides a comfortable system for wearable technology having a wide range of applications, depending on the choice of electronic device 2. It would be understood that in other embodiments various other electronic components can be interconnected by strips of the conductive textile 6, in addition or alternatively to the electronic device 2 and the battery 4. For instance, the conductive textile 6 can also be used to transmit digital control signals or sensor signals between a control unit and the electronic device 2 located distantly on the garment 1 .

[0087] In other embodiments, the conductive textile 6 is suitable for various other applications, such as for use with electrodes for discerning muscle action potentials. In yet further applications, the conductive textile 6 need not be incorporated into a garment. For example, the conductive textile 6 can be used within home textiles such as curtains, rugs and duvets for smart devices and smart home functions, or use within automobile textiles, such as seat upholstery to be used for applications such as heated seats or means to transfer sensor data without wiring.

[0088] Figure 2 shows a cross-sectional schematic diagram of the conductive textile 6 according to an example embodiment. As shown, the conductive textile comprises 6 a conductive layer 8 covered on both sides by a polymer layer 10. The polymer layer 10 electrically insulates the wearer from the conductive layer 8.

[0089] One issue with known conductive textiles is that they cannot be stretched without the current carrying portions becoming permanently deformed in a manner that changes the electrical resistance of the current carrying portions. To address this issue, the conductive layer 8 of the present invention comprises a matrix material and one or more conductive fibres coupled between two regions of the matrix material with surplus length that provides additional slack. This allows the conductive textile 6 to be stretched without applying tension that is sufficient to permanently deform the conductive fibres, thereby preserving their electrical properties. The one or more conductive fibres are preferably combined in to a conductive yam, and thus will generally be referred to as a conductive yam in the following description.

[0090] An amount of slack can be provided in the conductive layer 8 so that when the matrix material is stretched to an elastic limit of its constituent materials, minimal tension is applied to the conductive yarn so that permanent deformation of the conductive yam is avoided.

[0091] The conductive textile 6 may be stretchable by (in order of increasing preference) 20%, 30%, 40%, or 50% of its total length, without causing a permanent change (or causing a negligible change of less than 5%) of resistance of the conductive yam. The conductive textile 6 may be stretchable by the same proportions without causing a temporary change in resistance, or by causing only minimal or negligible temporary change in resistance of 10% or less.

[0092] The slack in the conductive layer 8 can be provided in various ways, for instance by arranging the conductive yam in a circuitous path and with freedom to move or slide relative to the matrix material. In this example, the conductive layer 8 is formed by a knitted structure and is discussed below in greater detail. However, in other embodiments, the conductive textile 6 need not be provided as a knitted structure. For instance, an individual or several threads of conductive yam can be stitched between two parts of an ordinary fabric or textile. In this case, some of the stiches can be intentionally loose so that the conductive yam can slide in and out of the ordinary fabric during movement or stretching of the fabric. This can also be described as coupling the conductive yam to the matrix material with a holding stich.

[0093] Each strand of conductive yam in the conductive layer 8 comprises a plurality of conductive fibres. In this example, the conductive yam comprises one or more silver-plated (e.g., electroplated) nylon fibres and a plurality of tin-plated copper fibres, each tin-plated copper fibre having a thickness of about 0.05 mm. The silver electroplated fibres are particularly soft and suitable for direct skin contact. The tin-plated copper fibres have a lower resistance on aggregate compared to the silver-plated nylon fibres, which reduces the overall resistance of the conductive yam to minimise electrical losses. The tin coating on the copper fibres protects against corrosion and facilitates easier integration into electronic systems through improved solderability. The copper fibres are about 0.05 mm thick so that the copper is sufficiently flexible and feels soft like an ordinary fabric. As sole copper wires of 0.05 have a relatively high resistance, a plurality of tin-plated copper fibres are used in parallel to provide a lower effective resistance. It has been found that a parallel connection of 6 rows of the conductive yam comprised of silver-plated nylon fibres and tin-plated copper fibres has a resistance of less than 1 ohm per metre.

[0094] The tin-plated copper fibres and the silver-plated nylon fibres are spun together to form a composite conductive yam prior to forming the knitted structure of Figure 3. This prevents the conductive yam from snapping or knotting in the knitting process. Combining two types of conductive fibre in this way incorporates the advantages of both materials in the conductive yam, while also providing increased redundancy in case of the failure of one type of fibre. For instance, the two types of conductive fibre may corrode at different rates in response to exposure to a particular detergent during washing of the conductive textile 6. The slower-corroding fibre then enables the conductive textile 6 to be more resilient to washing.

[0095] In other embodiments, the conductive textile 6 can comprise any other suitable type of conductive fibre alternatively or in addition, such as gold-based fibres.

[0096] The polymer layer 10 is preferably configured to be relatively thermally conductive while remaining electrically insulating. This avoids the formation of hotspots because heat generated in one region of the conductive textile 6 can be efficiently diffused to other regions. Providing a thermally conductive polymer layer enables the conductive textile 6 to be used in applications requiring sustained electrical activity, or in high-power applications, ensuring that the conductive textile 6 can be used safely against the skin. The polymer layer 10 may have a thermal conductivity between 1-10 W m-1K"1.

[0097] The polymer layer 10 also provides a barrier that protects the conductive layer 8 from abrasion, moisture, or chemical contaminants. This has been found to significantly increasing the durability of the conductive textile 6 in practice, helping to ensure the electrical properties of the conductive textile 6 remain constant over the course of repeated use. The polymer layer 10 can comprise any suitable material. In this example, the polymer layer 10 comprises a silicone- and polyurethane-based screen-printing ink, comprising an additive, such as one or more of Boron Nitride, Aluminium Oxide, or Silica. These additives may be powdered. These exemplary additives give the polymer layer 10 relatively high thermal conductivity while retaining low electrical conductivity; however, it would be understood that any other suitable additive may be used alternatively or in addition. These materials also allow the polymer layer 10 to be stretchable, i.e. at least more elastically deformable than the conductive yam, for increased user comfort.

[0098] The conductive textile 6 can also be provided without the polymer layer 10, which may not be necessary for some applications, or with the polymer layer 10 applied only to a single side of the conductive textile 6. In this case, the conductive layer 8 may form the entirety of the conductive textile 6.

[0099] Figure 3 shows a schematic diagram of a portion of the conductive layer 8 according to an example embodiment.

[0100] The conductive Iayer 8 comprises alternating rows of a conductive yam 12 and an elastic yam 14 that is more elastically deformable than the conductive yam 12. The elastic yam 14 provides a matrix material to which the conductive yam 12 is repeatedly coupled using a plurality of loops to form a knitted structure. For the purposes of illustration, only two rows of conductive yam 12 and two rows of elastic yam 14 are shown in Figure 3. It would be appreciated that a much greater number of alternating rows would often be provided in practice. Similarly, only two repeating units are shown for each of the four rows are shown in Figure 3. In practice, each row may be comprise many more repeating units of loops.

[0101] The conductive yam 12 is comprised of the same silver-plated nylon and tin-plated copperfibres as described previously with reference to Figure 2. In other example embodiments, any conductive fibre, or conductive yam comprising several conductive fibres, can be used in the knitting structure of Figure 3. The elastic yam 14 can be any suitable type of fibrous material, preferably a non-conductive material, such as nylon. Each row of conductive yarn 12 is arranged in an alternating pattern of first loops 16 and second loops 18, where each individual first loop 16 is between two second loops 18 and vice versa. Each row of elastic yam 14 is also arranged in an alternating pattern of first loops 20 and second loops 22 in a similar fashion.

[0102] Each first loop 16 is wrapped around a single first loop 20 of an adjacent row (specifically, the row above, from the perspective of Figure 3) of elastic yarn 14. Similarly, each first loop 20 is wrapped around a single first loop 16 of an adjacent row of conductive yam 12. This causes the tip of each first loop 16 to constrain the base of a first loop 20 of the row above. Equally, the tip of each first loop 20 constrains the base of a first loop 16 of the row above.

[0103] Each second loop 18 differs from the first loops 16 in that each second loop 18 is coupled at its respective base between two adjacent first loops 20 of the elastic yam 14. At its tip, each second loop 18 is wrapped about the base of a second loop 22 of the elastic yam 14. Each second loop 18 is confined to a less narrow horizontal region compared to each first loop 16, due to the coupling of the second loop 18 across two adjacent first loops 20 of elastic yam 14. This lower degree of confinement provides a slack portion between each first loop 16 of the conductive yam 12 that can extend more freely when the conductive textile 6 is stretched along the axis X shown in Figure s (i.e., horizontally from the illustrated perspective). Thus, when the knitted structure is pulled along the X axis, each second loop 18 has freedom to straighten, such that the distance between successive first loops 16 can increase, without applying significant stress on the conductive yam 12. This enables the conductive textile 6 to accommodate the stretching along its horizontal axis without applying an amount of tension to the conductive yam 12 that is sufficient to cause a permanent deformation (e.g., reduction in thickness) and resulting permanent change of electrical resistance.

[0104] Each second loop 22 is coupled to the base of a different second loop 22 in the nearest preceding row of elastic yam 14. In other words, the second loops 22 are coupled to one another in vertical columns. This creates a vertical chain (that is, vertical from the perspective of Figure 3) of elastic yam 14 that allows the knitted structure to stretch in the vertical direction, shown by the Y axis in Figure 3. When pulled vertically, the vertical chains of second loops 22 stretch preferentially to the rows of conductive yam 12. Preferential stretching of the elastic yam 14 is also aided by the alternating pattern of rows of conductive yam 12 and elastic yam 14, which means that each row of conductive yam 12 is surrounded by rows of elastic yam 14. This allows the rows of elastic yam 14 to elastically elongate between the rows of conductive yam 12 when stretched vertically. In this way, the knitted structure minimises the tension applied to the conductive yam 12 when the conductive textile 6 is stretched vertically, to avoid permanent deformation of the conductive yam 12.

[0105] Overall, the slack provided by the second loops 18 together with the stretchability of the chains of second loops 22 allows the knitted structure to be stretched along two perpendicular axes without applying damaging stress to the conductive yam 12.

[0106] More specifically, each second loop 18 is configured as a “tuck loop”, or equivalently each conductive yam 12 can be described as implemented using a “tuck stitch”. These terms refer in part to each second loop 18 overlying a second loop 22 of the elastic yam 14 at an overlap region 24. Each second loop 22 can also be referred to as a “held loop” or a “held stitch”. Implementing a tuck stich in this manner provides increased horizontal stretchability, compared to a more homogenous knitted structure comprised only of rows of first loops 16 and first loops 20, for instance.

[0107] In other example embodiments, other knitted structures incorporating other types of stitches or loops can be implemented. The conductive yam 12 can be arranged using any type of loop or stitch that provides additional slack that enables a greater freedom of movement when stretched along a particular axis. In one example, the conductive yam 12 can also be arranged in a “holding stitch” coupled to the elastic yam.

[0108] Figure 4 shows a schematic diagram illustrating the knitted structure of Figure 3 at a larger scale from a front perspective. Figure 5 shows a schematic diagram illustrating the knitted structure of Figure 3 at a larger scale from a back perspective. In the interest of clarity, only single loop of each type and each yam has been labelled. As the tip of each second loop 18 is tucked behind a respective tip of a second loop 22, the second loops 18 are mostly obscured in the front view of Figure 4. Similarly, the tips of the second loops 22 are tucked behind the second loops 18 and thus are not visible in the back view of Figure 5.

[0109] At edge regions of the conductive layer 8, the knitted structure may have a different arrangement. At the horizontal periphery of the structure (i.e. at the left and right sides of the structure when the parallel rows of yam are arranged horizontally), each row of conductive yam 12 and elastic yam 14 can trail without interlocking or forming a loop (also referred to as “missed stitches”). This forms a ladder region 26, along which the knitted structure can be cut to facilitate integration into an electrical circuit. The ladder region 26 is described in more detail below with respect to Figures 9 and 10.

[0110] At top and bottom edges 28 of the conductive layer 8, the knitted structure may be formed entirely from the elastic yam 14 and tied so that there are no loose threads or loops that could allow the knitted structure to unravel. Any suitable tying method or component to prevent unravelling can be implemented, such as a clamp.

[0111] Figure 6 shows a photographic image of the knitted structure of Figures 3 to 5 in a relaxed state. Figure 7 shows a photographic image of the same knitted structure in a horizontally stretched state (i.e., stretched along the X-axis of Figure 3, parallel to the parallel rows of elastic and conductive yams 12, 14). Figure 8 shows a photographic image of the same knitted structure in a vertically stretched state (i.e., stretched along the Y-axis of Figure 3, perpendicular to the parallel rows of elastic and conductive yams 12, 14).

[0112] Figure 9 shows a simplified schematic diagram of the conductive layer 8 in an intermediate form, prior to its integration into a circuit. Specifically, Figure 9 shows the conductive layer 8 immediately after knitting of the knitted structure and before a cutting step. It should be noted that in Figure 9 the interlocking loop structure illustrated by Figures 3 to 8 has been simplified for the purposes of illustration only to non-interlocking rows of conductive yam 12 and elastic yam 14.

[0113] The knitted structure of Figures 3 to 8 can be formed using a single spool of conductive yam 12 that is continuous between successive rows of conductive yam 12. As shown, the uppermost row of conductive yam 12 is connected to a subsequent row continuously by a connecting portion 12a of conductive yam 12 at the ladder region 26 of the knitted structure. In turn, the middle row of conductive yam 12 is connected to the lowermost row of conductive yam 12 continuously by a connecting portion 12b at the ladder region 26 on the opposite side of the knitted structure. Forming the knitted structure in this way can provide a convenient way to manufacture the conductive textile 6. Although not shown, the elastic yam 14 may be arranged continuously in a similar manner. The connecting portions may be deliberately elongated, as shown on the right-hand side of Figures 4 and 5, to facilitate easier cutting.

[0114] In some embodiments, the conductive layer 8 can remain in the uncut form of Figure 9, for instance to provide more freedom to adjust the conductive textile 6 to a particular application. Alternatively, the conductive layer 8 can be cut at the ladder regions 26 along the dashed lines 30 shown in Figure 9 to form a plurality of discontinuous parallel rows of conductive yam 12.

[0115] The arrangement of Figure 9 can also be implemented using other types of knitted structures alternatively to the structure illustrated by Figures 3 to 8.

[0116] Figure 10 shows a simplified schematic diagram of the conductive layer 8 integrated within an exemplary circuit 32 after being cut along the dashed lines 30 of Figure 9. The interlocking loop structure of the conductive Iayer8 has also been simplified in the same manner as Figure 9 for the purposes of illustration only.

[0117] The circuit 32 comprises the electronic device 2 and the battery 4. The circuit 32 also comprises two connectors 34a, 34b (which can also be described as terminals or terminal connectors) positioned at each horizontal end (following the orientation of Figure 3) of the plurality of discontinuous parallel rows of conductive yarn 12. A first connector 34a is connected to a first end of each strand of conductive yam 12. A second connector 34b is connected to a second, opposing terminal end of each strand of conductive yam 12.

[0118] The electronic device 2 is connected to the leftmost connector 34a and the battery 4 is connected to the rightmost connector 34b. In this configuration, each row of conductive yam 12 provides a parallel pathway between the electronic device 2 and the battery 4. One advantage of this arrangement is that if one of the rows becomes damaged, other rows of conductive yam 12 provide a redundant connection, so that operation of the circuit 32 can be maintained. A further advantage is that the overall resistance of the conductive layer 8 is decreased compared to connection by a single piece of conductive yam 12. Thus, depending on the function of the circuit 32, it may be advantageous to increase the number of rows of conductive yam 12, in order to further reduce the overall resistance of the conductive layer 8.

[0119] In this example, the connectors 34a, 34b comprise a conductive epoxy that provides an electrical connection with the conductive yam 12 while also bonding to the non-conductive parts of the conductive textile 6, such as the elastic yam 14 (or any other matrix material). The conductive epoxy may have a volume resistivity of 10-3to 10-5Q cm. The conductive epoxy can comprise an epoxy resin matrix and a conductive filler, such as a carbon, silver, or copper-based filler. The connectors 34a, 34b can comprise any suitable material, such as a conductive metal, in other embodiments.

[0120] The parallel arrangement of Figure 10 can also be implemented using other types of knitted or non-knitted structures alternatively to the exemplary structure of Figures 3 to 8.

[0121] In Figure 10, the circuit 32 includes the electronic device 2 and the battery 4. The conductive textile 6 can also be packaged and provided as a strip configured similarly to the circuit 32 but without the electronic device 2 and the battery 4. In this case, the strip may comprise device seatings in electrical connection with the connectors 34a, 34b, configured to receive electronic devices or power sources that can communicate with one another through the conductive layer 8 of the conductive textile 6. Alternatively, the strip can include any other suitable means at each end for connecting to electronic components. Strips of various lengths and widths (and hence of various resistances and power-ratings) can be provided for different applications.

[0122] The strip can be provided together with the seatings as a kit. For example, a plurality of detachable seatings may be provided to facilitate different devices. The kit can also include coupling devices configured to attach the strip of conductive textile to an ordinary textile or garment. The coupling devices may be configured to withstand high-temperature connection, such as soldering, in order to protect the conductive textile 6. The coupling devices can comprise a copper pad and an electrically conductive adhesive in one example, however any other suitable coupling device can be provided in other embodiments.

[0123] Figure 11 shows a flowchart of a method 100 of forming the conductive textile 6 according to an embodiment of the invention.

[0124] In step 102, a conductive yam can be formed by spinning together constituent conductive fibres. Combining the individual conductive fibres into a single composite yarn before stitching reduces the number of knitting steps required compared to attaching each conductive fibre to a matrix material separately. Additionally, it has been found a composite conductive fibre spun prior to knitting (or stitching) is less likely to snap or knot during the knitting (or stitching) process.

[0125] In one example, one or more silver-plated nylon fibres and a plurality of tin-plated copper wires can be spun together to form the conductive yam 12. In other example embodiments, a conductive yam can be formed from any other suitable conductive fibres.

[0126] The density of the conductive yam can be increased or decreased by adjusting the number of constituent conductive fibres, according to the particular power requirements of the intended application. In step 104, the conductive yarn is coupled to a matrix material, which can be carried out in any suitable manner, to form the conductive layer of the conductive textile of the invention. In one example, the conductive yam 12 can be knitted with the elastic yam 14 to form the knitted structure of Figures 3 to 9. In other examples, the conductive yam can be stitched to a matrix material using holding stitches or by providing slack in the conductive yam by other means. The stitching or knitting can be performed using any suitable means, such as by hand or using a suitable sewing or industrial knitting machine.

[0127] When step 104 is performed to produce a knitted structure comprised of a plurality of parallel rows of conductive yam, the conductive yam can be threaded continuously through the knitted structure, so that each row is connected with the previous row by connecting portions at each side of the structure. At least 6 rows of the conductive yam may be threaded in this way to enable a parallel connection of sufficiently low resistance. The connecting portions may form a ladder region, as described previously. The arrangement of Figure 9 shows one example for the knitted structure of Figures 3 to 8; however, types of knitted structures can also be threaded “continuously” in a similar manner. The method 100 can include a subsequent step 106 of cutting the side regions to form a plurality of disconnected parallel rows, as shown in Figure 10. This can provide a convenient and efficient way of forming a plurality of parallel rows of conductive yam in a conductive layer.

[0128] When forming a knitted structure, the maximum stitch width possible for the given stitching means can be selected to maximise the number of stitches per length of knitted structure. This increases the stretchability of the knitted structure. For some fabricating devices, including some devices that can be used to knit together the structure of Figures 3 to 10, selecting the maximum stitch with may involve selecting the maximum possible number of needles used during fabrication, which for some machines may be 699 needles.

[0129] In step 108, which can occur before step 106 in other embodiments, a polymer layer (such as the polymer layer 10) can be applied to one or both sides of the conductive layer. The polymer layer can be applied using any suitable technique, such as by screen printing or spray coating. For some applications it may be desirable not to coat the conducive layer. In this case, the conductive layer forms the entirety of the conductive textile and step 108 can be skipped.

[0130] It would be understood that additional steps can be implemented as required, such as further cutting of the conductive textile to a desired shape and size.

Claims

CLAIMS1 . A conductive textile, comprising: a matrix material; and at least one conductive fibre configured to enable electric current to flow between a first part of the matrix material and a second part of the matrix material; wherein the at least one conductive fibre is coupled to the matrix material with slack between the first part and the second part to enable stretching of the conductive textile while minimising tension applied to the at least one conductive fibre.

2. The conductive textile of any of the preceding claims, wherein the at least one conductive fibre comprises a first conductive fibre and a second conductive fibre, respectively comprising a first conductive material and a second conductive material that is different from the first conductive material.

3. The conductive textile of claim 2, wherein the first conductive fibre comprises silver-plated nylon.

4. The conductive textile of claim 2 or claim 3, wherein the second conductive fibre comprises one or more copper fibres, preferably wherein the one or more copper fibres are tin-plated.

5. The conductive textile of claim 4, wherein each of the one or more copper fibres have a thickness of less than 0.15 mm, preferably, less than 0.1 mm, more preferably less than 0.8 mm, most preferably of 0.05 mm or less.

6. The conductive textile of any of claims 2 to 5, wherein the first conductive fibre and the second conductive fibre are arranged adjacently in the matrix material, preferably wherein the first conductive fibre and the second conductive fibre are arranged twisted about one another.

7. The conductive textile of any of the preceding claims, wherein the at least one conductive fibre is arranged with one or more slack portions configured to straighten when pulled, wherein the one or more slack portions are configured tostraighten by a combined length corresponding to at least half of, or preferably about equal to or greater than, a change in distance between the first part and the second part when the matrix material is maximally stretched along an axis bisecting the first part and the second part.

8. The conductive textile of any of the preceding claims, wherein the matrix material and the at least one conductive fibre are arranged to form a knitted structure.

9. The conductive textile of claim 8, wherein the matrix material comprises an elastic yarn that is more elastically deformable than the at least one conductive fibre.

10. The conductive textile of claim 8 or claim 9, wherein the matrix material and the at least one conductive fibre are arranged in alternating interlocking rows.11 . The conductive textile of any of claims 8 to 10, wherein the at least one conductive fibre interlocks with the matrix material in a plurality of first loops and a plurality of second loops, wherein the second loops are less confined than the first loops to provide slack.

12. The conductive textile of claim 11 , wherein the knitted structure is configured to enable the matrix material to elongate when the conductive textile is stretched along a first axis and to enable the second loops to straighten when the conductive textile is stretched along a second axis that is different to the first axis.

13. The conductive textile of claim 11 or claim 12, wherein each of the first loops are positioned between second loops such that the first loops and the second loops form an alternating pattern.

14. The conductive textile of any of claims 11 to 13, wherein the second loops are tuck loops.

15. The conductive textile of any of claims 11 to 14, wherein each of the first loops are adjacently surrounded by loops of the matrix material.

16. The conductive textile of any of claims 8 to 15, wherein the at least one conductive fibre is arranged in a plurality of discontinuous parallel rows.

17. The conductive textile of any of the preceding claims, wherein the conductive textile comprises a polymer layer configured to provide electrical insulation to the at least one conductive fibre.

18. The conductive textile of claim 17, wherein the polymer layer is arranged on both sides of the conductive textile.

19. The conductive textile of claim 17 or claim 18, wherein the polymer layer is more thermally conductive than the matrix material.

20. The conductive textile of any of the preceding claims, wherein the conductive textile comprises conductive epoxy configured to provide a terminal connection.

21. A garment, comprising the conductive textile of any of the preceding claims.

22. The garment of claim 21 , further comprising: a first terminal connector and a second terminal connector; wherein the at least one conductive fibre electrically connects the first terminal connector to the second terminal connector to enable current flow therebetween.

23. The garment of claim 22, wherein the conductive textile comprises a plurality of discontinuous rows of the at least one conductive fibre, wherein each of the plurality of discontinuous rows are connected across the first terminal connector and the second terminal connector to form a plurality of electrically parallel connections.

24. The garment of claim 22 or claim 23, further comprising an electronic device attached to the first terminal connector.

25. A method of manufacturing a conductive textile, comprising:forming a conductive yarn by combining two or more conductive fibres; and coupling the conductive yam to a matrix material.

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