Textile thermal sensors

Abstract

A wearable textile thermal sensor 100. The textile thermal sensor comprises first and second electrically conductive threads 108, 110 on an interior surface 104 (fig 1) of a fabric substrate layer 102, comprising different electrically conductive materials. The first and second electrically conductive threads are electrically connected at a first thermal sensing junction on the fabric interior surface. A securing thread 114 (fig 1) extends through the fabric substrate layer and secures the electrically conductive threads on the interior surface of the fabric substrate layer. There may be three or more electrically conductive threads / yarns connected at a plurality of thermal sensing junctions which maybe arranged in an array or straight line. The textile thermal sensor maybe a patch sensor for securing to an external article e.g. clothing.

Description

FIELD OF THE INVENTION Embodiments of the present invention relate to textile thermal sensors. In particular, but not exclusively, they relate to embroidered textile thermal sensors configured as thermocouples. BACKGROUND TO THE INVENTION The need for accurate and non-invasive temperature monitoring is prevalent in extreme environments, such as scuba diving or working in hot work environments. A similar need exists for monitoring the health conditions of patients. BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION According to various, but not necessarily all, embodiments of the invention there is provided a wearable article comprising a textile thermal sensor, the textile thermal sensor comprising: a fabric substrate layer having an interior surface and an exterior surface opposite the interior surface; a first electrically conductive thread on the interior surface, comprising a first electrically conductive material; a second electrically conductive thread on the interior surface, comprising a second electrically conductive material different from the first electrically conductive material, wherein the first and second electrically conductive threads are electrically connected at a first thermal sensing junction on the interior surface; and a securing thread arrangement extending through the fabric substrate layer and comprising securing stitches which secure the first and second 1 electrically conductive threads on the interior surface of the fabric substrate layer. This creates a thermocouple mounted to the interior skin-facing surface of a textile (the fabric substrate layer). A textile-mounted thermocouple is advantageous for non-invasive axillary body temperature monitoring. Use cases include monitoring a diver’s body temperature, monitoring a worker’s body temperature in a hot / hazardous environment, monitoring patient body temperature in hospital care, monitoring body temperature during recreational activity, monitoring body temperature of military personnel, and for general environmental monitoring, among other uses. Since the conductive threads are surface-mounted, the thermocouple is advantageously adaptable for a wide range of conductive thread stiffnesses, including generally inelastic threads such as threads substantially consisting of large-diameter solid core wires. This is because the conductive threads are embroidered onto the interior surface of the fabric substrate layer rather than forming a warp, weft, or course of the fabric substrate layer, and without being pulled into the fabric substrate layer by the securing stitches of securing thread, both of which would require more flexible but less durable conductive threads. The ability to use durable inelastic wires as the conductive threads improves durability, and suitability for harsh environments such as wet / underwater environments. According to various, but not necessarily all, embodiments of the invention there is provided a method of manufacturing the wearable article, the method comprising causing an automated stitching machine to secure the first and second electrically conductive threads onto the interior surface of the fabric substrate layer by the securing thread arrangement, wherein the securing thread arrangement is a top thread above the exterior surface, wherein the first and second electrically conductive threads are bobbin threads beneath the interior surface. Optionally, the automated stitching machine is an automated embroidery machine. An advantage of using an automated embroidery machine or automated sewing machine is enabling precise control of stitch patterns and stitch densities of the securing thread arrangement. An embroidery machine would have the further advantage regarding the uniformity of thread tensions, and the potential for high tension capabilities. The conductive threads (first and second electrically conductive threads) can follow complex shapes and still be mounted quickly and accurately. Complex shapes can be useful for increasing pull-out strength of the conductive threads. According to various, but not necessarily all, embodiments of the invention there is provided wearable article comprising a textile thermal sensor, the textile thermal sensor comprising: a fabric substrate layer having an interior surface and an exterior surface opposite the interior surface; a first electrically conductive thread comprising a first electrically conductive material; a second electrically conductive thread comprising a second electrically conductive material different than the first electrically conductive material, wherein the first and second electrically conductive threads are electrically connected at a first thermal sensing junction; and a securing thread arrangement extending through the fabric substrate layer and comprising securing stitches which secure the first and second electrically conductive threads to the fabric substrate layer, wherein one of or each of the first and second electrically conductive threads follows a path comprising a plurality of curves, wherein at least one of the curves extends through one or more of the securing stitches. An advantage of the secured curves is that pull-out strength of the conductive threads is improved relative to an arrangement of straight and linear conductive threads. The securing stitches along the curves provide lateral resistance against pull-out. They also allow the fabric substrate layer to be stretched in one or more directions without tensioning or breaking the conductive threads. According to various, but not necessarily all, embodiments of the invention there is provided a method of manufacturing the wearable article, the method comprising causing an automated stitching machine to secure the first and second electrically conductive threads onto the interior surface of the fabric substrate layer by the securing thread arrangement, wherein the method comprises causing the automated stitching machine to automatically form the plurality of curves, wherein the securing thread arrangement is a top thread above the exterior surface, wherein the first and second electrically conductive threads are bobbin threads beneath the interior surface. For repeatable patterns (in which the curvature of the patterns relates to the functionality of the sensor), the automated machine can be used to repeatably produce a pre-defined pattern comprising curves. Furthermore, the tension would be consistent in the machine due to the machine-control, as opposed to human-control, despite the substantial difference in stiffnesses between the conductive threads and the securing thread. By contrast, manual stitching can take place on a manual sewing machine, or a manual sewing machine (with the appropriate embroidery foot). However, the nature of the pattern is then manually determined by the operator moving the fabric in x and y directions to get the desired pattern. The uniformity of the pattern and the tension would be difficult to control. Optionally, the first and second electrically conductive threads are sewn (e.g., embroidered) to the interior surface of the fabric substrate layer by the securing thread arrangement. For example, a sewing machine or embroidery machine can be used. Optionally, the wearable article is a garment. Optionally, the garment is in the form of a vest, shirt, hat, undergarment, or coverall. Optionally, the textile thermal sensor is located at an underarm region, head region, groin region, and / or limb region of the garment. Alternatively, the wearable article is a stretchable wearable band comprising the textile thermal sensor, such as a headband, chest band, or limb band. Alternatively, the wearable article is a wound dressing. Optionally, the securing stitches of the securing thread arrangement secure the first and second electrically conductive threads at stitches which protrude from the interior surface of the fabric substrate layer. Optionally, the first and second electrically conductive threads extend in a common substantially flat plane which is parallel to a plane of the interior surface. Optionally, the first and second electrically conductive threads are continuously located on the interior surface of the fabric substrate layer as they pass through a plurality of, or each of, the securing stitches. Optionally, a bending stiffness of each of the first and second electrically conductive threads is greater than a bending stiffness of the securing thread arrangement. Optionally, a tensile strength of each of the first and second 5 electrically conductive threads is greater than a tensile strength of the securing thread arrangement. Optionally, the first thermal sensing junction is a skin contact junction. At the junction, the most accurate temperature reading will happen when in direct contact with the skin of the wearer. The other parts of the conductive wires do not need to make conductor-on-skin contact between the electrically conductive material and the skin. Optionally, the first and second electrically conductive threads are coated skin contact threads, which are at least partially uncoated at the first thermal sensing junction. The threads may be coated for example by an oxidisation-resistant insulation. The coating can help to prevent a skin reaction to certain metals in the conductive threads, such as Nickel. Optionally, the interior surface of the fabric substrate layer is a skin contact surface. This assumes that most or all of any stabiliser which was added during manufacture has been tom off, cut off, or dissolved away. In other examples, a stabiliser layer may be left in-situ. For example, the presence of stabiliser may offer structural support without compromising the ability of the sensor to take accurate temperature readings. Optionally, one of or each of the first and second electrically conductive threads follows a path comprising a plurality of curves. An advantage is that pull-out strength of the conductive threads is improved. Optionally, at least one of the curves extends through one or more of the securing stitches. Optionally, each curve extends through a plurality of the securing stitches. Optionally, the plurality of securing stitches are non-parallel to each other, and cross the respective curve. An advantage is that the securing stitches provide lateral resistance against pull-out. Optionally, the plurality of curves are opposite-facing curves. An advantage of opposite-facing curves is improved pull-out strength. Optionally, the plurality of curves define at least one sinusoid. Optionally, one of or each of the first and second electrically conductive threads follows a path comprising a first curve set located to a first side of the first thermal sensing junction. Optionally, the path comprises a second curve set located to a second side of the first thermal sensing junction. Each curve set comprises one or more curves. Optionally, the first curve set comprises a first curve in a first direction and a second curve in a second opposite direction. Optionally, the second curve set comprises a first curve in a first direction and a second curve in a second opposite direction. Optionally, each of the first and second curves of each curve set of each of the first and second electrically conductive threads extends through a separate plurality of the securing stitches. Optionally, the first and second curves define a sinusoid. Optionally, the first curve set defines a plurality of the sinusoids. Optionally, the second curve set defines a plurality of the sinusoids. Optionally, one of or each of the first and second electrically conductive threads is continuously curved through the first thermal sensing junction. An advantage is improving pull-out resistance and ensuring elasticity of the fabric substrate 7 layer is maintained, without placing the conductive threads in tension and causing breakages. Optionally, the first thermal sensing junction is at a sinusoid centre of each of the first and second electrically conductive threads. The sinusoid centre refers to the central region of a sinusoid between adjacent peaks and troughs. An advantage is improving pull-out resistance and ensuring elasticity of the fabric substrate layer is maintained, without placing the conductive threads in tension and causing breakages. Optionally, the first thermal sensing junction is an X-shaped junction, with the first and second electrically conductive threads extending to both sides of the X-shaped junction. An advantage is ensuring that the junction region is fully secured and held in stitching from both sides. Alternatively, the first thermal sensing junction is a V-shaped junction, with the first and second electrically conductive threads terminating at the V-shaped junction. Optionally, the textile thermal sensor comprises a plurality of thermal sensing junctions. Optionally, the textile thermal sensor comprises three or more electrically conductive threads of two or more different electrically conductive materials, electrically connected at a plurality of thermal sensing junctions. Optionally, the textile thermal sensor comprises circuitry configured to determine a spatially averaged temperature based on signal measurements from the plurality of thermal sensing junctions. Optionally, the three or more electrically conductive threads comprise the first and second electrically conductive threads, and a third electrically conductive thread on the interior surface, wherein the plurality of thermal sensing junctions comprise the first thermal sensing junction and a second thermal sensing junction, wherein the third electrically conductive thread comprises an 8 electrically conductive material different than the first electrically conductive material, wherein the first electrically conductive thread is electrically connected to the third electrically conductive thread at the second thermal sensing junction on the interior surface, spaced along the interior surface from the first thermal sensing junction. Optionally, the third electrically conductive thread has any one or more of the features of the second electrically conductive thread described herein. Optionally, the second thermal sensing junction has any one or more of the features of the first thermal sensing junction described herein. Optionally, the third electrically conductive thread extends generally parallel to the second electrically conductive thread. Optionally, the first electrically conductive thread is curved between the first and second thermal sensing junctions. Optionally, the first electrically conductive thread comprises opposite-facing curves between the first and second thermal sensing junctions. Optionally, each thermal sensing junction is proximal to each other thermal sensing junction. Optionally, the plurality of thermal sensing junctions are arranged in an array or a line. Optionally, the textile thermal sensor comprises circuitry configured to determine a spatially averaged temperature based on signal measurements from the first and second thermal sensing junctions. Optionally, the three or more electrically conductive threads further comprise one or more further electrically conductive threads on the interior surface in 9 addition to the third electrically conductive thread, wherein the plurality of thermal sensing junctions further comprise one or more further thermal sensing junctions in addition to the first and a second thermal sensing junctions, wherein the first electrically conductive thread is further electrically connected to each of the one or more further electrically conductive threads at a respective one of the further thermal sensing junctions on the interior surface, spaced along the interior surface from the first and second thermal sensing junctions. Optionally, each one or more further electrically conductive thread has any one or more of the features of the second and / or third electrically conductive threads described herein. Optionally, the respective one or more further thermal sensing junctions comprise any one or more of the features of the first and second thermal sensing junction described herein. Optionally, the one or more further electrically conductive threads extend generally parallel to the second and third electrically conductive threads. Optionally, the spatially averaged temperature is based on signal measurements from the first, second, and one or more further sensing junctions. Optionally, one of or each of the first and second electrically conductive threads substantially consists of a solid core or monofilament wire formed from the respective electrically conductive material. The term ‘substantially consists’ means a thread either consisting only of an uncoated monofilament wire, or consisting of a solid core wire coated by thin oxidisation-resistant insulation. An advantage of using monofilament is that it is electrically conductive at any point around its circumference, which makes it easier to create electrical contact between the threads. Optionally, one of or each of the first and second electrically conductive threads comprises oxidisation-resistant insulation, wherein the oxidisation-resistant insulation has a discontinuity at the first thermal sensing junction. For example, the insulation may be scraped off. Alternatively, one or of each of the first and second electrically conductive threads is an uncoated thread, having an electrically conductive exposed surface along most or all its length. Optionally, one of or each of the first and second electrically conductive threads comprises a polymer core coated with the respective electrically conductive material. Optionally, one of or each of the first and second electrically conductive threads comprises a twisted mix of polymer fibres and at least one electrically conductive fibre of the respective electrically conductive material. Optionally, the textile thermal sensor further comprises a detector (the circuitry) to complete an electrical circuit with the first and second electrically conductive threads, wherein the detector is configured to read an electric potential difference between the first and second electrically conductive threads. Optionally, the detector is implemented by a processor. Optionally, the detector is mounted to a different body than the fabric substrate layer. Optionally, the different body comprises a circuit board. Optionally, the different body comprises a flexible circuit board. Optionally, the textile thermal sensor comprises a thermocouple amplifier to amplify the electric potential difference and provide the amplified electric 11 potential difference to the detector. Optionally, the thermocouple amplifier is mounted to a different body than the fabric substrate layer. Optionally, the thermocouple amplifier is operably connected to the first and second electrically conductive threads via a user-releasable connector arrangement (e.g., screw terminal, plug-socket, press-stud, or magnetic). An advantage of mounting the electronics to a separate body or bodies, which are user-releasably connected to the conductive threads, is that one or more circuit boards can be removed while the wearable article (e.g., garment) is washed. The conductive threads and thermal sensing junction(s) can potentially remain secured to the wearable article. Optionally, the textile thermal sensor comprises an output interface to output readings from the detector, and / or a memory to store readings from the detector. Optionally, the output interface comprises a wireless communication interface. Optionally, the output interface is mounted to a different body than the fabric substrate layer. Optionally, the textile thermal sensor comprises a battery. Optionally, the battery is mounted to a different body than the fabric substrate layer. Optionally, the different bodies referred to above are the same circuit board or a plurality of circuit boards. Optionally, the textile thermal sensor comprises a reference junction to which the electrically conductive threads are electrically connected, and which is remote from the thermal sensing junction(s). The reference junction may be mounted to a different body than the fabric substrate layer, for example. The reference junction may be a cold junction. Optionally, the fabric substrate layer is permanently attached to the wearable article and a detection apparatus of the textile thermal sensor is user-removably attached to the wearable article. The term ‘permanently’ would be understood 12 to cover sewing or similar techniques, even though stitches can be unpicked. Optionally, the detection apparatus comprises one or more circuit boards collectively comprising one or more of: the detector; the thermocouple amplifier; the output interface; the battery; the processor. Optionally, the detection apparatus is operably connected to the first and second electrically conductive threads via a user-releasable connector arrangement (e.g., as above). Optionally, the fabric substrate layer is a non-sensing layer. Optionally, the fabric substrate layer is substantially non-electrically conductive. Optionally, the fabric substrate layer substantially consists of electrically insulating yarns, e.g., polymeric yarns or natural fibre (cotton / silk) yarns. Optionally, the fabric substrate layer is a woven or knit fabric. If a knit fabric, the first and second electrically conductive threads may extend over a plurality of courses of the knit fabric, the courses defining at least the interior surface of the knit fabric. If a woven fabric, the first and second electrically conductive threads may extend over a plurality of warps and wefts of the woven fabric, the warps and wefts defining at least the interior surface of the woven fabric. The first and second electrically conductive threads may extend in a direction non-parallel to the respective courses or warps and wefts, and continuously to an interior side of the courses or warps and wefts without looping or interweaving with any of the courses or warps and wefts. Optionally, the woven or knit fabric of the fabric substrate layer comprises a plurality of yarn loops, wherein one of or each of the first and second electrically conductive threads is curved and has a minimum radius of curvature that is multiple times greater than a maximum radius of curvature of the yam loops of the fabric substrate layer. According to various, but not necessarily all, embodiments of the invention there is provided a textile thermal sensor comprising: a fabric substrate layer having a first surface and a second surface opposite the first surface; a first electrically conductive thread on the first surface, comprising a first electrically conductive material; a second electrically conductive thread on the first surface, comprising a second electrically conductive material different from the first electrically conductive material, wherein the first and second electrically conductive threads are electrically connected at a first thermal sensing junction on the first surface; and a securing thread arrangement extending through the fabric substrate layer and comprising securing stitches which secure the first and second electrically conductive threads at the stitches on the first surface of the fabric substrate layer. According to various, but not necessarily all, embodiments of the invention there is provided a textile thermal sensor comprising: a fabric substrate layer having a first surface and a second surface opposite the first surface; a first electrically conductive thread comprising a first electrically conductive material; a second electrically conductive thread comprising a second electrically conductive material different than the first electrically conductive material, wherein the first and second electrically conductive threads are electrically connected at a first thermal sensing junction; and a securing thread arrangement extending through the fabric substrate layer and comprising securing stitches which secure the first and second electrically conductive threads to the fabric substrate layer, wherein one of or each of the first and second electrically conductive threads follows a path comprising a plurality of curves, wherein at least one of the curves extends through one or more of the securing stitches. Optionally, the textile thermal sensor is a patch sensor, wherein the fabric substrate layer is a patch for securing to an external article. Optionally, the patch comprises the first thermal sensing junction and one or more further thermal sensing junctions, collectively defining a plurality of thermocouples. Optionally, the patch is mechanically fixed to an external article such as the wearable article. Optionally, the patch is mechanically fixed to the external article by stitches. Alternatively, the patch is user-removably fixed to the external article, for example by a hook and loop fastener system or snap buttons. An advantage that the patch can be removed for cleaning of the external article, and then reapplied. Optionally, the external article is a wearable article. Alternatively, the patch may comprise a skin adhesive layer to adhere the patch to the external article, wherein the external article is skin. Optionally, the patch is a wound dressing. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of various examples of embodiments of the present invention reference will now be made by way of example only to the accompanying drawings in which: FIG. 1 illustrates an example cross-section view of part of a textile thermal sensor; FIGS. 2A-2D illustrate example electrically conductive thread patterns and a graph of peak pullout force; FIG. 3 illustrates an example electrically conductive thread pattern comprising multiple thermal sensing junctions; FIGS. 4A-4B illustrate example electrically conductive thread patterns; FIG. 5 illustrates an example textile thermal sensor including a circuit board; and FIG. 6 illustrates an example wearable article comprising the textile thermal sensor. DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION The Figures illustrate examples of a wearable article 1 comprising a textile thermal sensor 100, the textile thermal sensor 100 comprising: a fabric substrate layer 102 having an interior surface 104 and an exterior surface 106 opposite the interior surface 104; a first electrically conductive thread 108 on the interior surface 104, comprising a first electrically conductive material; a second electrically conductive thread 110 on the interior surface 104, comprising a second electrically conductive material different from the first electrically conductive material, wherein the first and second electrically conductive threads 108, 110 are electrically connected at a first thermal sensing junction 112 on the interior surface 104; and a securing thread arrangement 114 extending through the fabric substrate layer 102 and comprising securing stitches 116 which secure the first and second electrically conductive threads 108,110 to the fabric substrate layer 102. An optional stabiliser material layer (not shown) may further be included on one of both surfaces 104, 106 during manufacture, such as a nonwoven polymeric sheet material (e.g., comprising polyester). The stabiliser material on the exterior surface 106 may be removed after manufacture. The stabiliser material on the interior surface 104 may be removed or left in-situ to offer structural support. The stabiliser material may comprise a tearaway, washaway, or heataway stabiliser material. Integrating textile thermocouple sensors 100 into wearable garments, particularly for monitoring temperatures in extreme environments like scuba diving, presents several unique challenges. A significant challenge lies in identifying materials that are conductive enough for effective temperature measurement while also being compatible with the embroidery process. Conductive materials traditionally used in such applications often do not lend themselves easily to sewing / embroidery, necessitating innovative approaches to create conductive threads that retain their electrical properties and physical integrity when embroidered. Some embodiments provide a way of sewing / embroidering solid copper and constantan electrically conductive threads 108, 110 into fabric substrate layer 102, creating a T-type thermocouple or multiple thermocouples which can sense axillary body temperature when next to the skin. The curved stitching patterns shown in FIGS. 2B, 2C, 3, 4A, and 4B keep the embroidery fixed for reliable functionality. Thermal sensing junctions 112 occur wherever the copper-constantan devices make electrical contact, for example via a solder or ultrasonic weld, each junction 112 providing a discrete temperature sensor. The discrete temperature sensors can be incorporated within the designs of clothing and may be washable with the clothing. A thermocouple amplifier 128 and processor 126 operably coupled to a thermocouple or thermopile may continuously monitor axillary body temperature. In some, but not necessarily all examples, the first electrically conductive thread 108 comprises copper and the second electrically conductive thread 110 comprises constantan (e.g.. Cu55 / Ni45). Alternatively, the first electrically conductive thread 108 comprises constantan and the second electrically conductive thread 110 comprises copper. In other examples, different metals than copper and constantan may be used. Different types have their own inherent accuracies. KType metals (chromel and alumel) are possible for lower accuracy applications (+ / - 2.2C or + / - .75% whichever is greater). Once calibrated, a variety of metal combinations may be used. An advantage of copper and constantan is that experiments found they provided the best accuracy of all the tested base metal thermocouples, of + / -1 degree Celsius, or +1- 0.75%, whichever is greater. Other variants may use non-base metal materials, to change the accuracy. T-type provides the best accuracy of the base metal combinations. Electrically conductive threads specifically used in embroidery comprise stranded fibres. Each fibre may have a diameter less than 0.1mm or less than 0.5mm. A first type of stranded wire comprises a polymer core coated with the respective electrically conductive material. This allows high flexibility and maintains conductivity around the entire cross-section perimeter of the thread 108, 110. However, it offers lower electrical conductivity due to the nanoscale or micron thickness of the conductive material. Furthermore, the different elasticities of the coating and the polymer core can lead to flaking off. Furthermore, the metallisation process of coating the threads can reduce the purity of the metals, which affects measurement accuracy. A second type of stranded wire comprises a twisted mix of non-conductive polymer fibres (e.g., polyester) and one or more solid metal electrically conductive fibres. Each solid metal fibre may have a diameter of less than 0.05mm for example. This provides a greater metal surface area than the coated polymer, and good elasticity, but the twisted structure can create intermittent regions where metal is not exposed at the surface of the thread 108, 110. This can create challenges when aligning the conductive parts at the thermal sensing junctions 112. Therefore, a plurality of conductive fibres may be used to minimise the discontinuities in electrical conductivity. In some, but not necessarily all examples, the first and second electrically conductive threads 108, 110 are thicker monofilaments each with an outside diameter of between 0.1 mm and 0.4mm. This is significantly thicker than a fibre diameter of a typical stranded wire, providing a high bending stiffness and tensile strength at least 1,5x or at least double that of the securing thread 114, for example. There are no twisted strands. Such thread stiffnesses are regarded as not for use with embroidery machines but have been shown herein to be useable. However, the embodiments described and shown in FIGS. 1-4B allow for thick inelastic threads such as these to be securely fastened to the surface of the fabric substrate layer 102, while also allowing for the thinner and more elastic twisted threads to be used instead. The ability to use thicker monofilaments allows for deployment of the textile thermal sensor 100 in high-strain environments, as well as wet or corrosive environments. One or both electrically conductive monofilaments may comprise a polyimide oxidisation-resistant insulation layer to improve durability in wet environments, and allow for washing of garments. Alternatively, an uncoated copper composition for Type T thermocouples is used. 19 The material composition of the fabric substrate layer 102 may be the same as or different than that of the rest of the wearable article 1. For example, the fabric substrate layer 102 may be an integrally formed part of the wearable article 1, or a patch secured thereto. The fabric substrate layer 102 may comprise a woven or knit material, formed from yarns such as polyester, cotton, or silk yams, or any other polymeric or natural fibres. The fibres are electrically insulating and there are no sensing / metallic fibres interwoven with the warps, wefts, or courses of the yams of the fabric substrate layer 102. The material composition of the securing thread arrangement 114 can comprise, for example, a polymeric material such as polyester. The material is thin, elastic, and easy to sew. The weight may be selected from the range 150 to 250 decitex, for example. The material is not electrically conductive to avoid short-circuits. FIG. 1 illustrates how each of the electrically conductive threads 108 (and 110) may be embroidered to a surface of the fabric substrate layer 102. The embroidery of thicker conductive threads introduces additional challenges, primarily due to their inelasticity, which complicates their handling by standard embroidery machines without causing damage to the thread, the conductive material, or the machine itself. To address this, the embroidery process was inverted. This adaptation allows the use of standard polyester securing thread 114 for the top pattern component (typically visible externally), subject to the machine's extensive tension control and directional changes. The conductive thread 108 is placed in the lower bobbin on the pattern's underside, encountering minimal tension and handling. Machine settings are then adjusted to accommodate this unconventional setup, ensuring the successful integration of conductive threads into the embroidered pattern without compromising the material's integrity or the embroidery quality. As shown in FIG. 1, the securing thread 114 extends through the fabric substrate layer 102 from its exterior surface 106 to its interior surface 104. At the exterior surface 106 forming an outer visible surface of the wearable article 1, the securing thread 114 provides an externally visible pattern which may be combined with other embroidered threads (not shown) to create an aesthetic pattern. At the interior surface 104, the securing thread 114 comprises stitches 116 under the electrically conductive thread 108. These stitches 116 are referred to as securing stitches. The thread 108 extends through the securing stitches 116. As shown, the inelasticity and tension of the bottom bobbin of electrically conductive thread 108 means that it is not dragged into the body of the fabric substrate layer 102 by the tension of the embroidery machine. Therefore, the electrically conductive thread 108 extends planarly along the interior surface 104 of the fabric substrate layer 102, and the securing stitches 116similarly protrude from the interior surface 104 of the fabric substrate layer 102. The electrically conductive thread 108 does not interact (interweave I loop) with the warps, wefts, or courses (not shown) of the fabric substrate layer 102. Optionally, the securing thread arrangement 114 defines a running stitch pattern or zigzag pattern. Optionally, the securing thread arrangement 114 has a stitch spacing between the securing stitches 116, selected from the range 1mm to 2mm, or from 0.8mm to 3mm. So our stitches typically occur every 2mm in this design but this can be changed. I sometimes vary it and have 1mm between each stitch and then a bigger gap at the crossover to allow for soldering. FIGS. 2A-2D illustrate example electrically conductive thread patterns as would be visible on the interior surface 104 of the fabric substrate layer 102, as well as a graph of peak pullout force for the patterns depicted in FIGS. 2A-2C. Peak 21 pullout force represents the force at which either pullout or breakage occurred. The securing stitches 116 of the securing thread arrangement 114 are not shown. FIGS. 2A-2C each show the first and second electrically conductive threads 108, 110 extending generally perpendicularly to each other and meeting at an X-shaped thermal sensing junction 112, except in FIG. 2A the threads are straight whereas in FIGS. 2B-2C they are continuously curved in a sinusoidal pattern (pairs of opposite-direction curves 120, 122). In FIG. 2B, each of the four legs of the electrically conductive threads 108, 110 comprises at least one complete sinusoid 120, 122 (i.e., two sinusoids per thread 108, 110) between the thermal sensing junction 112 and the end of the curved region of the thread 108, 110. By contrast, in FIG. 2C, each leg comprises multiple complete sinusoids 120, 122. The pullout force graph of FIG. 2D illustrates that the ‘multiple sinusoids’ layout of FIG. 2C achieved double the peak force before pullout or breakage, compared to the straight thread patterns of FIG. 2A. The weakest result for ‘multiple sinusoids’ still achieved a greater peak force than the strongest result for the ‘single sinusoid’, indicating that a highly curved geometry is beneficial. The sinusoid pattern allows the fabric 102 to be stretched in the direction of each of the sinusoidal lines, without tensioning or breaking the conductive threads 108, 110. The variance bars also demonstrate that the sinusoid results had less variance than the straight line results, which suggests they are more tolerant to manufacturing variations. Optionally, the first thermal sensing junction 112 comprises a weld or solder electrically connecting the first and second electrically conductive threads 108, 110. FIG. 3 illustrates an example electrically conductive thread pattern comprising multiple thermal sensing junctions 112 in an array or line formation, defining a plurality of thermocouples sharing a common cathode (or common anode). In applications which require high measurement accuracy such as medical treatment, an ensemble average reading for the thermal sensing junctions 112 spaced close to each other can be obtained by a processor 126 (FIG. 5). Alternatively, the reading may be a different measure of central tendency such as median or mode. Alternatively, a temperature gradient may be measured by incorporating individual thermocouple / thermopile units in an array or line formation. Measuring temperature gradients have important applications in assessing athletic performance in sports, monitoring recovery after injuries, monitoring chronic conditions, etc. In FIG. 3, the multiple thermal sensing junctions 112 are achieved with a plurality of threads 110 of a second metal extending transversely to a single thread 108 of a first metal, making electrical contact with the latter at respective thermal sensing junctions 112. One of the metals may be copper and the other constantan, for example. In examples, the single thread 108 of first metal is a common cathode (e.g., constantan), otherwise the electronics of FIG. 5 may need to be modified to allow for the polarity of the voltage. Another embodiment involves the first electrically conductive thread 108 not being shared. Each thermal sensing junction 112 is formed by a different pair of electrically conductive threads. Where an average is taken, the multiple thermal sensing junctions 112 may all be within 1cm, or within 3cm, or within 5cm, or within 10cm of each other. The exact proximity depends on how localised of a temperature reading is required. Furthermore, the first electrically conductive thread 108 may comprise one or more curves between each thermal sensing junction 112, to further secure the thread 108 and protect against movement which may damage the electrical connections at the junctions 112. FIGS. 4A-4B illustrate that the curvature of the embroidery pattern is not restricted to sinusoids, and can be varied either for aesthetic or location convenience purposes. Furthermore, the functional threads 108, 110 can be combined with non-functional aesthetic threads (e.g., polymer threads) for aesthetic reasons. FIG. 4A illustrates the visible securing thread arrangement 114 on the exterior surface 106 of the fabric substrate layer 102 which extends in the same path as the electrically conductive threads 108, 110 (not visible). A further polyester thread 124 is shown, which forms a decorative pattern along with the securing threads 114. Multiple layers of embroidery are possible for protection / aesthetic reasons. In this instance, the conductive threads 108, 110 could either be provided in conjunction with other running stitch patterns in polyester 114, or the conductive threads 108, 110 could be embroidered onto the interior surface 104 of layer 102 using a running stitch and then hidden / protected using standard stitches on top using a zigzag stitch of securing thread 114. This would protect the conductive threads 108, 110 but would make direct contact between the junction point 112 and the skin more difficult. The junction 112 could be modified at the soldering stage. Furthermore, if a stabiliser layer (not shown) is left in-situ on the interior surface 104, the junction 112 would be configured to be between the stabiliser layer and the skin, so that the junction 112 is still able to contact skin directly. FIG. 4B also shows a variant of FIGS. 2A-2C where the electrically conductive wires meet each other at an oblique angle rather than a generally perpendicular angle. The angle may vary from 1 degree to 90 degrees. Alternatively, although not shown, the thermal sensing junctions 112 may be V-shaped junctions rather than X-shaped junctions, with the first and second electrically conductive threads 108, 110 terminating at the V-shaped junction. FIG. 5 illustrates a textile thermal sensor 100 comprising a patch of the fabric substrate layer 102, and a separate circuit board 124 comprising a processor 126 and memory 127 configured as a controller / microcontroller or similar, the memory 127 comprising computer-readable instructions which when executed by the processor 126 implement a detector. The circuit board 124 also comprises a thermocouple amplifier 128 to amplify signals from the temperature sensing junction 112, a battery 134, and a wireless communication output interface 132 such as a wireless transmitter / transceiver. A single circuit board 124 is illustrated, but may be replaced with multiple circuit boards in other examples. The illustrated circuit board 124 is a flexible circuit board to improve comfort for the wearer of a garment, although a non-flexible board could be used in other applications. If the electrically conductive threads 108, 110 are suitably protected from corrosion, the patch could potentially remain secured to the garment during washing. Therefore, the patch may be mechanically fixed to the wearable article 1 by stitches. Alternatively, the patch is user-removably fixed to the wearable article 1, for example by a hook and loop fastener system or snap buttons. Both the patch and the circuit board 124 may be removed prior to washing the garment. In such an example, the circuit board 124 may remain permanently attached to the patch. The illustrated circuit board 124 is connected locally to one end of each of the first and second electrically conductive threads 108, 110 via lead wires in the fabric substrate layer 102. The lead wires may be formed from the same or similar materials as those of the threads 108, 110. The lead wires may be threads extending on or in the fabric substrate layer 102. The lead wires connect to the circuit board 124 at a user-releasable connector arrangement 130, such as screw terminals, plug-socket connectors, press-stud connectors, or magnetic connectors. The connectors allow the circuit board 124 to be removed while the patch remains attached to the wearable article 1 during washing. The detector completes an electrical circuit with the first and second electrically conductive threads 108, 110, and may be configured as a voltmeter to read an electric potential difference between the first and second electrically conductive threads 108, 110. Furthermore, the circuit board 124 further comprises a reference junction 136 (cold junction) to which the electrically conductive threads 108, 110 are electrically connected, and which is remote from the thermal sensing junction(s) 112 (hot junctions). The reference junction 136 may be mounted to a different body than the fabric substrate layer 102, for example. 26 FIG. 6 illustrates an example implementation in which the wearable article 1 is a vest garment. The textile thermal sensor 100 is located at an underarm region to measure axillary body temperature. Only the securing threads 114 are visible, because the conductive threads 108, 110 are located to the interior. The circuit board 124 may be mounted elsewhere in an internal or external pocket of the garment, somewhere unobtrusive. The flexibility of the fabric substrate layer 102 substantially matches that of the material of the rest of the garment, so that the textile thermal sensor 100 is flexible, discrete, conformable, and unnoticeable next to the skin. The use of embroidery allow the top stitches of the securing threads 114 to be incorporated as part of the overall design of the garment. Depending on the implementation, the garment may comprise a vest, shirt, hat, undergarment (e.g., underpants or brassiere), or coverall such as a flight suit or diving suit. The textile thermal sensor 100 may be anywhere that can ensure a good skin contact in a body region where it is desirable to measure the temperature. In other implementations, the wearable article 1 is a stretchable (e.g., elasticated) wearable band comprising the textile thermal sensor, such as a headband, chest band, or limb band. Alternatively, the wearable article is a wound dressing. Some example use cases are described below. Scuba Diving: Scuba diving represents a prime application for this technology. The sensor's ability to withstand varying water temperatures and harsh underwater conditions while providing real-time monitoring makes it invaluable for diver safety and comfort. The textile thermal sensor 100, when integrated 27 into diving base layers or a wetsuit or drysuit would provide monitoring of axillary (or other appropriate) temperature, which also has the potential to be integrated into the existing dive computer technology (watch) to provide that information in real-time. Industrial Settings: In industries where workers are exposed to extreme temperatures or hazardous environments, such as manufacturing, construction, emergency services or mining, the textile thermal sensor 100 could be integrated into workwear to monitor temperature fluctuations and ensure worker safety. Medical Monitoring: The non-invasive nature of embroidered textile thermal sensors 100 makes them suitable for medical applications, such as continuous temperature monitoring for patients in hospitals or at home. Monitoring neonatal babies in real-time and feeding this data back to nursing staff would be of significant use. Another application would be in the monitoring of infection in wounds, where a textile thermal sensor 100 could be integrated into a wound dressing. Recreation: The textile thermal sensor 100 could also be utilised in sports medicine for monitoring athletes' body temperature during training or competitions. Embroidered wearable textile thermal sensors 100 could enhance safety and comfort in outdoor activities like hiking, camping, or mountaineering, where individuals are exposed to fluctuating environmental temperatures. Aerospace: Textile thermal sensors 100 could be integrated into aerospace suits to monitor temperatures in extreme environments, such as high altitudes, ensuring the well-being and performance of personnel. Environmental Monitoring: Beyond human applications, embroidered textile thermal sensors 100 could be used for environmental monitoring in ecosystems sensitive to temperature changes, such as coral reefs or Arctic regions, providing valuable data for research and conservation efforts. Animal or object monitoring: animal monitoring or a lab environment where a flexible temperature monitoring system is needed, or object temperature monitoring. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, if thinner and more elastic conductive threads 108, 110 are used, they may be pulled into the fabric substrate layer 102 and therefore may not reside wholly on the interior surface 104 of the fabric substrate layer 102. They may however retain the curvature. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable 29 feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A wearable article comprising a textile thermal sensor, the textile thermal sensor comprising:a fabric substrate layer having an interior surface and an exterior surface opposite the interior surface;a first electrically conductive thread on the interior surface, comprising a first electrically conductive material;a second electrically conductive thread on the interior surface, comprising a second electrically conductive material different from the first electrically conductive material, wherein the first and second electrically conductive threads are electrically connected at a first thermal sensing junction on the interior surface; anda securing thread arrangement extending through the fabric substrate layer and comprising securing stitches which secure the first and second electrically conductive threads on the interior surface of the fabric substrate layer.

2. The wearable article of claim 1, wherein the wearable article is a garment in the form of a vest, shirt, hat, undergarment, or coverall, or wherein the wearable article is a wound dressing, or wherein the wearable article is a stretchable band or a wound dressing.

3. The wearable article of claim 1 or 2, wherein the securing stitches of the securing thread arrangement secure the first and second electrically conductive threads at stitches which protrude from the interior surface of the fabric substrate layer.

4. The wearable article of claim 1, 2, or 3, wherein a bending stiffness of each of the first and second electrically conductive threads is greater than a bending stiffness of the securing thread arrangement, and / or wherein a tensile31strength of each of the first and second electrically conductive threads is greater than a tensile strength of the securing thread arrangement.

5. The wearable article of any preceding claim, wherein the first thermal sensing junction is a skin contact junction.

6. The wearable article of any preceding claim, wherein one of or each of the first and second electrically conductive threads follows a path comprising a plurality of curves.

7. The wearable article of claim 6, wherein at least one of the curves extends through one or more of the securing stitches.

8. The wearable article of claim 7, wherein at least one of the curves extends through a plurality of the securing stitches, and wherein the plurality of securing stitches through which the curves extend are non-parallel to each other, and cross the respective curve.

9. The wearable article of claim 6, 7, or 8, wherein the plurality of curves are opposite-facing curves.

10. The wearable article of any one of claims 6 to 9, wherein one of or each of the first and second electrically conductive threads follows a path comprising a first curve set located to a first side of the first thermal sensing junction, and a second curve set located to a second side of the first thermal sensing junction, each curve set comprising one or more curves.

11. The wearable article of claim 10, wherein the at least one of the curve sets comprises a first curve in a first direction and a second curve in a second opposite direction.

12. The wearable article of claim 10 or 11, wherein each of the first and second curves of each curve set of each of the first and second electrically conductive threads extends through a separate plurality of the securing stitches.

13. The wearable article of claim any preceding claim, wherein the textile thermal sensor comprises three or more electrically conductive threads of two or more different electrically conductive materials, electrically connected at a plurality of thermal sensing junctions.

14. The wearable article of claim 13, wherein the textile thermal sensor comprises circuitry configured to determine a spatially averaged temperature based on signal measurements from the plurality of thermal sensing junctions.

15. The wearable article of claim 14, wherein the three or more electrically conductive threads comprise the first and second electrically conductive threads, and a third electrically conductive thread on the interior surface, wherein the plurality of thermal sensing junctions comprise the first thermal sensing junction and a second thermal sensing junction, wherein the third electrically conductive thread comprises an electrically conductive material different than the first electrically conductive material, wherein the first electrically conductive thread is electrically connected to the third electrically conductive thread at the second thermal sensing junction on the interior surface, spaced along the interior surface from the first thermal sensing junction.

16. The wearable article of claim 13, 14, or 15, wherein each thermal sensing junction is proximal to each other thermal sensing junction.

17. The wearable article of any one of claims 13 to 16, wherein the pluralityof thermal sensing junctions are arranged in a straight line or an array.3318. The wearable article of any preceding claim, wherein one of or each of the first and second electrically conductive threads substantially consists of a monofilament wire formed from the respective electrically conductive material, orwherein one of or each of the first and second electrically conductive threads comprises a polymer core coated with the respective electrically conductive material, orwherein one of or each of the first and second electrically conductive threads comprises a twisted mix of polymer fibres and at least one electrically conductive fibre of the respective electrically conductive material.

19. The wearable article of any preceding claim, wherein one of or each of the first and second electrically conductive threads comprises oxidisationresistant insulation, wherein the oxidisation-resistant insulation has a discontinuity at the first thermal sensing junction.

20. The wearable article of any preceding claim, wherein the fabric substrate layer is permanently attached to the wearable article, and wherein a detection apparatus of the textile thermal sensor is user-removably attached to the wearable article.

21. The wearable article of any preceding claim, wherein the fabric substrate layer is a non-sensing layer.

22. A method of manufacturing the wearable article of any one of the preceding claims, the method comprising embroidering the first and second electrically conductive threads onto the interior surface of the fabric substrate layer by the securing thread arrangement, wherein the securing thread arrangement is a top thread above the exterior surface, wherein the first andsecond electrically conductive threads are bobbin threads beneath the interior surface.

23. A textile thermal sensor comprising:a fabric substrate layer having a first surface and a second surface opposite the first surface;a first electrically conductive thread on the first surface, comprising a first electrically conductive material;a second electrically conductive thread on the first surface, comprising a second electrically conductive material different from the first electrically conductive material, wherein the first and second electrically conductive threads are electrically connected at a first thermal sensing junction on the first surface; anda securing thread arrangement extending through the fabric substrate layer and comprising securing stitches which secure the first and second electrically conductive threads at the stitches on the first surface of the fabric substrate layer.

24. The textile thermal sensor of claim 23, in the form of a patch sensor, wherein the fabric substrate layer is a patch for securing to an external article.

25. The textile thermal sensor of claim 24, wherein the patch is user-removably fixed to the external article.36

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