Sensor mat

Abstract

A sensor mat is disclosed which is suitable for measuring temperature, pressure and other parameters and is configured to adhere to the shape of a human, animal of object. The mat comprises a sensor l

Description

TECHNICAL FIELD The following specification relates to sensor mats for applications such as temperature or pressure monitoring. BACKGROUND Sensor arrays have a wide variety of applications including medical monitoring (for humans or other animals), consumer services, as well as more industrial settings such as aerospace and / or aircraft applications, vehicle applications, and monitoring power infrastructure. For example, in clinical settings, continuous monitoring of a patient's skin temperature can provide data forthe investigation of many health conditions such as pressure ulcers, infections, shock, breast cancer and peripheral arterial disease. Similarly, many other types of sensors such as pressure, humidity, piezoelectric and capacitance sensors can be used when investigating the possibility of various health conditions. Sensor mats, where sensors are provided on or in a substrate, can be provided for a variety of the above purposes. In order for such a mat to conform to the contours of a target object (which may be an irregularly shaped object, such as a patient’s body), the mat is desirably stretchy and flexible. This can also allow the mat to retain contact with the target object as the target object moves, and, in human or animal applications, can improve comfort for the subject as they are interacting with the mat. Traditional sensors are often rigid and uncomfortable. In some known examples, the rigidness of traditional sensors has been offset by the layering of additional materials between the sensors and the target object to ensure a smooth surface is in contact with the target object. However, this process adds additional complexity in the manufacturing process. Additionally, it is often necessary to understand if or how the materials used in the additional layers may interfere with or modify sensor readings. This may also add additional cost to the final product. In view of the above, it is desirable to devise an alternative sensor mat which is flexible and / or stretchable. SUMMARY According to a first aspect, the following specification provides a sensor mat comprising a sensor layer and a fabric layer. The sensor layer comprises an array of sensor elements, each sensor element corresponding to a location in the sensor mat, and each sensor element comprising one or more sensor components. The sensor layer has a mesh configuration including circuit portions and hole portions, the circuit portions comprising the sensor elements and the circuit portions being connected to form the mesh via flexible joints. The sensor layer further comprises read circuitry for reading the array of sensor elements. By incorporating a mesh configuration, the sensor layer is able to stretch by deforming the mesh, without applying strain to individual sensor components. This means that the sensor mat can tolerate stretching while reducing or eliminating the impact on accuracy or durability of the sensor components. Additionally, the mesh configuration is porous, enabling the sensor mat to support air flow through the sensor layer. Optionally, the flexible joints are flexible PCB portions. This means that it is less necessary to provide alternative wired connections within the sensor layer. Optionally, the circuit portions are also flexible PCB portions. This means that the sensor layer can be constructed from larger circuit portions of similar materials, and manufacturing of the sensor mat can be simplified. Optionally, the sensor layer comprises one or more flexible PCB meshes, wherein each flexible PCB mesh is a single flexible PCB comprising circuit portions, hole portions and flexible joints. Alternatively, the sensor layer may be printed onto the fabric layer. This may allow for more dynamic configuration of the sensor layer for different applications of the sensor mat. Furthermore, printed circuitry may be more recyclable and biodegradable. In some embodiments, the sensor elements are temperature sensor elements. In such embodiments, a thermal conductivity of the fabric layer may be greater in a direction perpendicular to the fabric layer than in a direction within the fabric layer. This has the effect of improving accuracy of results, by improving thermal isolation between individual sensor elements. The sensor mat may further comprise a data element configured to obtaining data from the array of addressable sensor elements. For example, the data element may be used as an interface for supplying sensor readings to external devices and / orthe data element may be configured to store sensor readings over time. The sensor mat may further comprise one or more electrical connectors for connecting to a second sensor mat. In this way, the sensor mat can support modular construction of mats of different sizes. The sensor mat may, for example, be suitable for monitoring a patient. For example, the materials of the fabric layer may be chosen so that they are comfortable for being in contact with a human patient for an extended period of time. According to a second aspect, the following specification provides a monitoring system comprising a sensor mat according to the first aspect and an external data device in communication with the sensor mat, wherein the external data device is configured to obtain a plurality of sensor readings from the sensor mat. Such a monitoring system may have a variety of applications, including simple collection and display of readings; triggering of alerts based on the sensor readings; and / or automatic control of a system such as a patient comfort device (such as a bed movement to reduce the risk of a pressure ulcer), a medical treatment device, ora cooling system (in the context of either human or animal devices and / or industrial applications). According to a third aspect, the following specification provides a method comprising: obtaining a plurality of sensor readings from a sensor mat according to the first aspect. The method may additionally include processing the sensor readings and taking one or more actions based on the sensor readings. In some embodiments, each sensor reading comprises a sensor element address. In other words, each sensor reading may include a sensed value (e.g. a temperature value) together with a location in the mat from which the reading was obtained. The sensor element address may, for example, correspond to a two dimensional position in the sensor mat. In some embodiments, each sensor reading additionally or alternatively comprises a timestamp. In some embodiments, the method further comprises monitoring the position of a patient, based on the plurality of sensor readings. For example, where the sensor mat comprises temperature sensors, the position of the patient may be monitored by detecting a location of sensor readings which are likely to be associated with a human skin temperature. This may, for example, be used to detect when a patient is moving and / or when a patient is absent. The method of the third aspect may be performed within the sensor mat, or may be performed externally. For example, if the sensor mat further comprises a data element for obtaining data from the array of addressable sensor elements, the method is performed by the data element. Additionally or alternatively, the method may be performed in a system comprising a sensor mat according to the first aspect and an external data device in communication with the sensor mat, wherein the external data device is configured to obtain a plurality of sensor readings from the sensor mat. Computer program instructions defining any of the above methods may be written in any language (including compiled, interpreted or scripted languages). Such instructions may be copied onto a suitable computing device for execution, may be stored on a storage medium (such as a flash memory) and / or may be communicated over a network (such as the internet). According to a fourth aspect, the following specification provides a method of manufacturing a sensor mat, the method comprising attaching a sensor layer to a fabric layer, wherein the sensor layer comprises an array of sensor elements, each sensor element corresponding to a location in the sensor mat, and each sensor element comprising one or more sensor components, and wherein the sensor layer has a mesh configuration including circuit portions and hole portions , the circuit portions comprising the sensor elements and the circuit portions being connected to form the mesh via flexible joints, the sensor layer further comprising read circuitry for reading the array of sensor elements. In some embodiments of the fourth aspect, the method further comprises constructing the sensor layer by: obtaining a plurality of circuit portions; and attaching the plurality of circuit portions together using flexible joints. Furthermore, the flexible joints may comprise wires and / or flexible PCB portions. In general, methods according to the fourth aspect may be used to produce any of the sensor mats according to the first aspect. BRIEF DESCRIPTION OF DRAWINGS Fig. 1A is a schematic cross-section diagram illustrating layers of a sensor mat; Fig. 1B is a schematic block diagram illustrating elements of a sensor layer; Fig. 1C is schematic block diagram illustrating an enlarged portion of the sensor layer; Fig. 2 is a schematic PCB layout diagram partially illustrating a sensor layer embodiment; Fig. 3 is a schematic PCB layout diagram partially illustrating another sensor layer embodiment; Fig. 4 schematically illustrates a use case for a sensor mat; Fig. 5 is a block diagram schematically illustrating a monitoring system; Fig. 6 is a flow chart schematically illustrating alternative monitoring methods; Fig. 7 is a block diagram schematically illustrating processing apparatus and storage media. DETAILED DESCRIPTION Many sensor mats according to this specification are particularly suitable for use with human patients. However, the sensor mats are generally suitable for sensing purposes where it is necessary to obtain measurements at different locations in an area that can be covered by the mat or can be adjacent to the mat. For example, they are equally applicable to monitoring animal patients or monitoring inorganic objects. It is envisaged that the described sensor mats may, for example, have many other applications for monitoring properties (such as temperature) of components and systems in contexts such as aerospace and / or aircraft applications, vehicle applications, and monitoring power infrastructure (e.g. battery elements of electric cars). The sensor mats may be particularly suited to monitoring irregular objects, where the mat is required to conform to an irregular surface of the object. Herein, stretching and flexing properties may refer to either or both of inherent stretching / flexing properties of a material (for example due to elasticity) and / or macro stretching / flexing properties arising from a structure (e.g. deformation of a mesh structure, by changing angles within the structure without necessarily changing the length of any elements in the structure). Fig. 1A is a schematic cross-section diagram illustrating layers of a sensor mat 100. Referring to Fig. 1 A, the mat comprises a sensor layer 1 and a fabric layer 2, each of which is discussed below, starting with the sensor layer 1 which is shown in greater detail in Figs. 1B and 1C. Referring to Fig. 1B, the sensor layer 1 comprises an array of sensor elements 3, each sensor element corresponding to a location in the sensor mat 100. More specifically, the sensor mat 100 typically has a flexible planar shape, and each sensor element 3 corresponds to a location in the planar shape. The location of a sensor element 3 may change relative to a target object (such as a patient) as the mat bends or folds, but the location is at least defined within the mat. Additionally, as shown in Fig. 1B, the sensor layer 1 may comprise a data element 4. Alternatively, the data element 4 may be connected to the sensor layer 1 without being a part of the sensor layer 1. The data element 4 may be configured to collect measurements from the sensor elements 3, to store measurements, and / or to communicate with an external data device 530 (see Fig. 5 as discussed below) Fig. 1C shows additional detail of a portion of the array of sensor elements 3 (as indicated using dashed boxes and lines in Figs. 1B and 1C). Referring to Fig. 1C, the sensor layer has a mesh configuration including circuit portions 5 and hole portions 7. The circuit portions comprise sensor components 8 (labelled in the more specific examples of Figs. 2 and 3) and also comprise flexible joints 6. As discussed below, circuit portions 5 may be entirely flexible, and / or may have enhanced flexibility at the joints 6. The use of flexible joints enables the mesh configuration to stretch as a whole, by bending the joints, without applying strain uniformly to all components of the sensor layer. This particularly helps to reduce the strain on sensor components, which could otherwise result in reduced accuracy or damage to the sensor components. Preferably, this enables the mesh structure to stretch by at least 10% in directions within the plane of the sensor mat, without applying significant strain on sensor components. Additionally, the holes 7 in the mesh structure provide locations for airflow. The holes 7 may have further advantages including reducing a thermal mass of the sensor layer 1 and / or increasing the flexibility of the sensor layer 1 in a direction perpendicular to the plane of the sensor mat, allowing greater conformability to the contours of a patient or another irregular surface of a target object. Although these portions 7 are described as holes in the sensor layer, they may be filled with other materials. For example, a portion of the fabric layer 2 may naturally fill the holes 7 due to the adjacency of the layers of the sensor mat. The fabric layer 2 itself is preferably breathable, allowing airflowthrough the holes 7 even in the aforementioned case. Sensor elements Each sensor element 3 comprises one or more sensor components 8 and corresponds to a location in the sensor mat 100. For example, each sensor element 3 may comprise a single sensor component configured to obtain readings for a point location in the sensor mat. Alternatively, each sensor element 3 may comprise a plurality of sensor components 8 configured to obtain readings for an area of the sensor mat. The readings from the sensor elements 3 are preferably unaffected by stretching of the overall mat. This may be due to the flexible joints 6 discussed above. However, the sensor elements 3 are preferably themselves tolerant of stretching. For example, sensor elements 3 may comprise a strain gauge that can be used to compensate for any effect that stretching has on readings from a main sensor component. Each sensor element 3 may comprise one or more different types of sensor component 8. For example, a sensor element may comprise a plurality of different sensor technologies in order to confirm a sensor reading. Each sensor element may further comprise logical or processing circuitry. For example, the sensor element may comprise circuitry to obtain an average of readings from multiple sensor components, and / or to apply a strain compensation based on a strain gauge. Furthermore, the sensor element may comprise circuitry to detect a failed sensor component, and may be configured to exclude a reading from the failed sensor component. Failure may, for example, be detected when a reading for a sensor component falls outside a predetermined range, or when a reading for a sensor component is significantly different from readings for other sensor components in the same sensor element. Depending on the configuration of layers in the mat 100, the sensing elements 3 may be calibrated for direct contact with a subject (e.g. a patient), and / or may be calibrated for obtaining measurements via the fabric layer 2. Sensor components In many embodiments, the sensor components 8 comprise temperature sensor components. For example, the sensors may comprise thermistors and / or infrared light sensors. As further examples, some temperature sensor components may be negative temperature coefficient (NTC) thermistors, positive temperature coefficient (PTC) thermistors, resistance temperature detectors (RTDs), thermocouples, and semiconductor-based integrated (IC) sensors, printed temperature sensors, infrared, silicon diodes or transistors. The sensor components are not limited to temperature sensors. In addition to or alternative to temperature sensor components, the sensor components may be configured to measure one or more of humidity, capacitance, pressure, tension, compression, torsion, electromyographical (EMG) response, chemistry. The sensor components may comprise thin film transistors, photovoltaic, active and passive components, interconnects, batteries, piezoelectric, capacitive, OTFTs, biosensors, load cells and / or EMG sensors. Chemistry applications may, for example, include detecting when fluid such as urine is present in the sensor mat, by detecting a specific chemical property of the fluid such as pH. There is no limit to the type of sensor components which may be used on the mat. Sensor array configuration As described above, the sensor layer 1 has a mesh configuration including the circuit portions 5 and the hole portions 7. The mesh configuration may comprise a regular two-dimensional grid section. For example, a square or rectangular grid as shown in Figs. 1C and 3, or a hexagonal grid as shown in Fig. 2. Additionally or alternatively, the mesh configuration may comprise sensor arrangements including any polygonal and / or serpentine configuration of sensor elements. Notably, the sensor configuration may be different from the PCB substrate structure. For example, the configuration shown in Fig. 2 includes a PCB substrate having hexagonal cells. However, the configuration of Fig. 2 does not include one sensor component 8 per hexagonal cell, and instead has a repeating unit comprising one sensor component 8 for every two hexagonal cells. This can be understood when looking at Fig. 2 by identifying a sensor component 8 in a "top left" position of a pair of two horizontally adjacent cells in the PCB structure. Read configuration The sensor layer 1 may be configured to provide read access to the sensor elements using any suitable read circuitry configuration. Examples of this are illustrated in Figs. 2 and 3. For example, the sensor layer may comprise a complete network of address lines (e.g. rows and columns of read lines) for random access to any sensor element in the array of sensor elements. This is illustrated in Fig. 2 where "row" lines 91 connect to each of a plurality of row positions in the sensor element array, and "column" lines 92 connect to each of a plurality of column positions in the sensor element array. By selecting a "row" line and a "column" line, a specific sensor element 3 can be selected and read. When understanding this feature, it should be noted that Fig. 2 illustrates a single layer of a multi-layer PCB. The "column" lines 92 are only partially shown in the figure, and connect to individual sensor components 8 via lines that continue in a different layer of the PCB. Additionally or alternatively, the sensor layer may provide sequential access wherein some sensor elements can be read as part of a series of sensor elements (e.g. a row of sensor elements). For example, a series of sensor elements may be configured to form a shift register. As also shown in Fig. 2, the read circuitry configuration may include some redundancy. More specifically, in the configuration of Fig. 2, sensor components 8 are only provided at half the maximum density which could be supported by the read lines, with only half of the "row and column" combinations of read lines being connected to a sensor component 8, at every second position as you move along a row or column. In contrast, Fig. 3 shows a configuration with a maximum density of sensor components 8 supported by the read lines 91, 92, the sensor components 8 being located at every vertex of a rectangular grid. Fabric layer The fabric layer 2 is preferably flexible and / or stretchable. The fabric may for example comprise a woven or non-woven material. Suitable materials for the fabric include, for example, polymer-based, textilebased, glass-based, paper-based or metal-based materials. Suitable polymers include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PDMS (polydimethylsiloxane), TPU (thermoplastic polyurethane), rubbers, polyamides, cellulose materials and silicones. Further desirable but optional properties for the fabric layer include softness, flexibility, stretchability, transparency to IR radiation, high thermal conductivity, comfortability, low coefficient of friction, resistance to liquid water, permeability to water vapour, ease of disinfection and / or durability when exposed to disinfection agents. The fabric layer may further optionally have antibacterial, antifungal, antiviral and / or bactericidal properties. For example, the fabric layer may further comprise one or more foam cells. This may enhance pressure relieving properties and / or ease of disinfection. As another example, the fabric layer may comprise latex to enhance waterproofing. An antibacterial or antiviral agent may be added to the fabric layer 2. Suitable antibacterial and / or antiviral agents include quaternary ammonium compounds (QACs), triclosan, chitosan, polyhexamethylene biguanide (PHMB), N-halamines, and metal / inorganic nanoparticles (NPs), selenium based compounds. The thermal conductivity of the fabric layer may be modified by the use of additives such as hexagonal boride nitride, aluminium oxide and zinc oxide. The thermal conductivity of the fabric layer may be modified in some locations and not in others. For example, thermal conductivity may be enhanced in a region of the fabric layer 2 that corresponds to sensor element 3 or an individual sensor component 8 in the sensor layer 1. This may be used to provide increased thermal conductivity in a direction through the fabric layer, such that heat can conducted through the fabric layer to the sensor components. On the other hand, thermal conductivity may be reduced (or simply not enhanced) in a portion of the fabric layer that corresponds to a hole portion of the sensor layer. This may be used to provide reduced thermal conductivity within a plane of the fabric layer, in order to increase thermal isolation between sensor elements. PCB-based sensor layer In many implementations, the sensor layer 1 comprises one or more printed circuit boards. The printed circuit boards (PCBs) are preferably flexible and / or stretchable. Suitable substrate materials for PCB include, for example, polymer-based, textile-based, glass-based, paper-based or metal-based materials. Suitable polymers include polyamide (PI), PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PDMS (polydimethylsiloxane), TPU (thermoplastic polyurethane), rubbers, polyamides, cellulose materials, elastomers and silicones. Preferably the substrate materials are biodegradable. The sensor components 8 may be formed as part of the PCBs. For example, temperature sensors may be implemented using temperature-sensitive resistive sections of the PCBs. Alternatively, the sensor components 8 may be attached to the PCBs. For example, the sensor components may be attached using solder, conductive glue, conductive tape or any other appropriate method. Directly-printed sensor layer The sensor layer 1 may additionally or alternatively comprise electronics printed onto the fabric layer 2 (as opposed to being printed as part of a PCB). In the case of printed electronics, the above described effects of improved stretchability are nevertheless present due to the mesh configuration having hole portions 7, even without using printed circuit boards. In other words, while the printed circuitry may have a greater stiffness than the fabric layer 2, the mesh configuration can distribute strain in the sensor layer 1 so that the strain is applied to the flexible joints in the mesh. This can therefore reduce strain on sensor components 8. Printed electronics can be used to reduce the cost and environmental footprint of electronics manufacturing. Printed electronics may be referred to as directly-printed electronics, as a way of distinguishing from PCB printing. Advantages of printed electronics include simplified processing, greater cost efficiency, and faster manufacturing. Printed electronics can be produced with a flexible or stretchable form factor, clean room facilities are not required and there can be greater flexibility with the designs, material and integration of a final product. For example, circuit components such as temperature sensors can be printed using conductive inks or pastes that exhibit stable resistance characteristics. Inks can include but are not limited to silver nanoparticles, carbon, carbon nanotubes, conductive polymers; metallic particles such as silver (Ag), copper (Cu) or gold (Au); functional ink, nanowires, nanosheets, graphenes, MXenes, graphite, dielectric inks and polymeric inks. A process of producing printed electronics components may, for example, involve aerosol jet printing, screen printing, flexography, laser direct writing, gravure printing or soft lithography. The process may also or alternatively involve available wet deposition techniques, such as spin, spray, dip and bar coating. The process may further or alternatively involve various printing methods such as inkjet or piezoelectric inkjet printing and 3D printing. Additionally or alternatively, printed electronics components may be produced by a sintering process. This may comprise any of thermal, laser / IPL, electrical, microwave, photonic, microwave, plasma or chemical sintering. The sensor layer 1 may be constructed from any combination of directly-printed components, PCB-printed components (including solid state components) and / or free-standing components, or may be entirely constructed using a single one of these component types. Sensor layer coating The sensor layer 1 may additionally comprise a coating. The coating may, for example, be deposited on a surface of the sensor layer 1 that is opposite to the fabric Iayer2, or may be deposited between the fabric Iayer2 and the sensor layer 1 (priorto assembling the layers). For example, a coating such as a CNF (carbon nano fibre) coating can be used to improve electrical properties, a waterproof coating may be used to protect the sensor layer, and / or a barrier coating may be used to protect against moisture, dust and / or EMR (electromagnetic interference). Manufacturing process The sensor mat 100 may be manufactured using any suitable method. For example, the sensor layer 1 may be constructed from individual circuit portion components 5. The circuit portion components 5 may be separately manufactured, and attached together to form the mesh structure using flexible joints. The flexible joints may comprise wires, flexible PCB portion components, and or a mixture of flexible joint components. Alternatively, the sensor layer 1 may be manufactured in additional stages. For example, one or more circuit portions 5 and flexible joints 6 may be assembled into a sensor layer module, and the sensor layer 1 may be constructed by attaching a plurality of sensor layer modules together. For example, a sensor layer module may correspond to one or more repeating units of the mesh structure, including one or more of the hole portions 7. In the case of a directly-printed sensor layer 1, a printer may be configured to print individual circuit portion components and / or sensor layer modules, as an addition or alternative to printing individual sensor components and circuitry connections. Data element Referring again to Fig. 1B, the data element 4 may, for example, comprise a simple external connector for accessing read lines 91, 92 connected to the array of sensor elements. The data element 4 may connect to the array of sensor elements at a single location, as shown in Fig. 2, where there are separate groups of "row" connections 41 and "column" connections 42. Alternatively, the data element 4 may connect to the array of sensor elements via block access points 41, 42 connected to blocks of "row" lines 91 and "column" lines 92 as shown in Fig. 3. The block connection configuration of Fig. 3 has the advantage of scalability, because it does not require a large number of read lines to connect to a single location in the circuit. The data element 4 may additionally or alternatively comprise some processing capability, rather than being a passive connector. For example, the data element 4 may comprise a communication element configured to obtain readings from the array of sensor elements 3 and transmit readings to an external entity 530 (see also Fig. 5). For example, the data element 4 may operate as a server configured to receive and fulfil external requests for data. Alternatively or additionally, the data element 4 may comprise a memory and may be configured to automatically store readings from the array of sensor elements. The memory may be a removable memory such as a flash memory. In such an embodiment, readings may alternatively be obtained from the sensor mat 100 and used externally by physically extracting the memory from the data element 4, without requiring that the sensor may 100 has means for external communication. The data element 4 may also be configured to analyse readings. For example, the data element 4 may be configured to detect when a sensor element fails. For example, some printed sensors are liable to change their effectiveness, or become ineffective, due to tension or compression beyond a limit. As another example, the data element 4 may be configured to detect whether or not a target object is present and / or whether mat has been arranged in a sensor-facing orientation (i.e. sensor layer 1 is closest) or a fabric-facing orientation (i.e. fabric layer 2 is closest) relative to the target object. For example, if a mat has been designed for use with specific types of target objects(e.g. patient) or even for use with specific body parts of a patient, such analysis may be performed based on known properties such as expected temperature ranges / distributions. Furthermore, the data element 4 may be configured to control a level of activity (e.g. a rate of obtaining readings) depending on factors such as whether a target object is present and whether the readings fall within expected ranges. Modular mats Referring again to Fig. 2, the sensor layer 1 may additionally comprise electrical connectors 93 for connecting two or more of the sensor mats 100 together, in order to form a combined mat with a greater area. This enables modular expansion of the sensor mat 100 to a variety of sizes. These electrical connectors 93 may be arranged along one or more edges of the sensor layer 1 of the sensor mat 100. Preferably the sensor mat also comprises one or more physical connectors for attaching multiple sensor mats together, with the electrical connectors 93 being appropriately positioned. In an embodiment where the sensor mat 100 is configured to connect with one or more additional sensor mats 100, each sensor mat 100 may have its own respective data element 4 for obtaining, storing and or communicating sensor readings. Alternatively, the read circuitry and the data element 4 may be configured to support data gathering over an extensible array of sensor elements 3. For example, in a scenario where multiple sensor mats 100 are connected using electrical connectors 93, the data element 4 and the read lines 91, 92 may be configured to support multiplexing in order to select and read data from a specific one of the multiple sensor mats 100. Extra layers As illustrated in Fig. 1A, the sensor mat 100 comprises at least a sensor layer 1 and a fabric layer 2. The mat may further comprise additional layers. For example, the sensor layer 1 may be sandwiched between two fabric layers 2. In such embodiments, the two fabric layers 2 may have different properties. For example, a fabric layer 2 that is intended to be in contact with a target object may have increased thermal conductivity and airflow, and an opposing fabric layer 2, intended to be away from the target object, may have increased thermal insulation. As another example, the sensor mat 100 may comprise multiple sensor layers 1. The overall structure may alternate between sensor layers 1 and fabric layers 2, or may have multiple adjacent sensor layers 1. The use of multiple sensor layers 1 may have various advantages. For example, multiple sensor layers 1 provide redundancy in case sensor components 8 become damaged. Additionally, multiple sensor layers may be used to add a third dimension (depth) to the sensor measurements. Applications Fig. 4 schematically illustrates an example use case for a sensor mat. The sensor mat 100 may be arranged in various positions relative to a target object. For example the target object may lie directly on top of the sensor mat 100. Alternatively, the sensor mat 100 may cover a part of the target object. More generally, the sensor mat 100 may be provided in any suitable form and configuration for the target object. For example, when the target object is a patient, the sensor mat 100 may form all or part of a bed sheet, quilt, clothing, or furniture upholstery. Referring to Fig. 4, a sensor mat 100 may be deployed in a patient bed. In the specific example shown, the sensor mat 100 is arranged between a mattress 430 and a bed sheet 410, with the intention that the patient will lie on top of the bed sheet 410. Equally, the sensor mat 100 may be deployed above a bedsheet 410. The sensor mat 100 may be sized for covering the patient or supporting the patient from below, for example as a blanket, cover, bed cover, bed sheet. As an example, where the sensor components 8 are temperature sensors, the sensor mat 100 may be used in the configuration of Fig. 4 for the continuous monitoring of patient skin temperature. The sensor mat 100 can equally be integrated with other furniture such as chairs and / or car seats. Furthermore, the sensor mat 100 may be used without any furniture. As another alternative, the sensor mat 100 may be integrated into a wearable article such as a vest, or may itself be configured as a wearable article. The sensor mat 100 can also be used in other applications where large-area temperature monitoring is required, such as in athletic training or rehabilitation. The sensor mat 100 may also be used for many other monitoring applications such as monitoring of the risk of pressure ulcers (by monitoring pressure using the sensor components), monitoring for risk of sepsis (for example by obtaining localised temperature measurements), monitoring for risk of chest infections, and for baby monitoring. Furthermore, the sensor mat 100 may be additionally or alternatively used for other purposes including monitoring the position of a patient. For example, where the sensor mat 100 comprises temperature sensors, the position of the patient may be monitored by detecting a location of sensor readings which are likely to be associated with a human skin temperature. This may, for example, be used to detect when a patient is moving and / or when a patient is absent. Fig. 5 is a block diagram schematically illustrating a monitoring system. Referring to Fig. 5, in this example, the sensor mat 100 comprises a communication interface 510. This may be a wireless interface (such as a Bluetooth or Wi-Fi interface), or may be a wired connection. Using the communication interface 510, the sensor mat 100 may communicate with an external data device 530. For example, in a hospital context, the external data device 530 may comprise a monitoring station adjacent to a patient's bed. Alternatively, the external data device 530 may be remotely located, and may communicate with the sensor mat 100 via one or more wireless and / or wired networks 520 such as the internet. For example, the external data device 530 may be configured as one or more physical servers and / or one or more cloud-based servers. The external data device 530 may perform a variety of functions based on obtaining sensor readings from the sensor mat 100. For example, the monitoring system may further include a display 540 for displaying the raw sensor readings and / or results of analysing the sensor readings. The display 540 may be a display that is specifically provided for use with a sensor mat 100 and / or may be a generic display. For example, the monitoring system may support communication with an existing display belonging to a hospital, a patient etc. The display 540 may for example be a smartphone display and / or a computer desktop display. Additionally or alternatively, the monitoring system may include an alert or notification system 550, and the external data device 530 may be configured to generate alerts or notifications based on the results of analysing sensor readings. For example, an alert may be triggered in response to a sudden change in sensor readings. In a hospital context or other care contexts, such alerts may be used to assist healthcare staff in their duties. The external device 530 may, for example, perform real-time analysis using artificial intelligence or statistical and / or logical techniques to predict or aid in any of the detection, diagnosis and / or management of health conditions. Furthermore, the external device 530 may be configured to automatically control some aspect of a patient's care or comfort or, where the target object is an inanimate object, some aspect of managing the object. For example, in an example context of reducing the risk of pressure ulcers, the external device 530 may be configured to control automated localised movement of a mattress or seat at areas to offload pressure as identified by high risk areas for pressure ulcers, based on sensor reading obtained from the sensor mat 100. Fig. 6 is a flow chart schematically illustrating alternative methods for using a sensor mat 10. The method of Fig. 6 may be implemented by any suitable device or system of devices. For example, the method may be performed within the sensor mat 100 by processing elements of a data element 4. Alternatively, the method of Fig. 6 may be performed by an external data device 530. Referring to Fig. 6, at step 610, the device obtains a plurality of sensor readings from the sensor mat 100. The sensor readings may, for example, comprise temperature readings and / or pressure readings, or readings obtained from any of the sensor types and / or comprising any of the sensor data types described in the preceding description. The sensor readings may be obtained as raw data, without initially including any metadata about where the relevant sensor element 3 was located or when the reading was obtained. In that case, the device performing the method may add metadata based on, for example, which read lines 91, 92 were active when the reading was obtained, and / or a time stamp at the device. This is particularly relevant when the method is performed by a data element 4 that is internal to the sensor mat 100. Alternatively, the sensor readings may be obtained with metadata already indicating a sensor element address in the sensor mat 100. Preferably, the sensor element address corresponds to a two dimensional position in the sensor mat 100, so that the reading can be linked to a physical position. The sensor element address may, for example, be defined in terms of active read lines 91, 92. The obtained sensor readings may further comprise a timestamp. After obtaining readings, the method may involve any of a number of alternative actions. Referring to step 620a, the obtained readings may be displayed. For example, the readings may be displayed using a display device 540 as described above. Additionally or alternatively, referring to step 620b, an alert may be triggered in response to the sensor readings. For example, an alert may be triggered at an alert or notification system 550 as described above. Additionally or alternatively, referring to step 620c, the method may comprise automatically controlling some aspect of a patient's care or comfort or, where the target object is an inanimate object, some aspect of managing the object. For example, in an example context of reducing the risk of pressure ulcers, the method may comprise controlling automated localised movement of a mattress or seat at areas to offload pressure as identified by high risk areas for pressure ulcers, based on sensor readings obtained from the sensor mat 100. Fig. 7 is a block diagram schematically illustrating processing apparatus 700 and storage media 800. The processing apparatus 700 may be implemented in any of the data element 4, the external data device 530, and so on. Referring to Fig. 7, the processing apparatus 700 comprises a processor 710, a memory 720 and a communication interface 730. The memory 720 stores instructions which can be read and executed by the processor 710. For example, the instructions may include an instruction to obtain sensor readings from an array of sensor elements 3 in a sensor mat 100. The instructions may be copied to the memory 720 from a data storage device 800, and / or copied from the memory 720 to a data storage device 800. The data storage device 800 may be a removable storage device suitable for distributing the instructions between devices. Additionally, the instructions may be sent or received over the communication interface 730 (for example via the Internet). For example, the instructions may be copied to and / or installed in the memory 720 by connecting the processing apparatus 700 to a user's personal device such as a smartphone, PC or laptop. The instructions may also be subsequently updated via any of the above-described connections. As an alternative to the configuration of Fig. 7, the above-described methods for obtaining sensor readings from a sensor mat 100 may be implemented using dedicated hardware, such as an ASIC.

Claims

1. A sensor mat comprising a sensor layer and a fabric layer,wherein the sensor layer comprises an array of sensor elements, each sensor element corresponding to a location in the sensor mat, and each sensor element comprising one or more sensor components, andwherein the sensor layer has a mesh configuration including circuit portions and hole portions, the circuit portions comprising the sensor elements and the circuit portions being connected to form the mesh via flexible joints,the sensor layer further comprising read circuitry for reading the array of sensor elements.

2. A sensor mat according to claim 1, wherein the flexible joints are flexible PCB portions.

3. A sensor mat according to claim 2, wherein the circuit portions are flexible PCB portions.

4. A sensor mat according to claim 3, wherein the sensor layer comprises one or more flexible PCB meshes, wherein each flexible PCB mesh is a single flexible PCB comprising circuit portions, hole portions and flexible joints.

5. A sensor mat according to claim 1, wherein the sensor layer is printed onto the fabric layer.

6. A sensor mat according to any of claims 1 to 5, wherein the sensor elements are temperaturesensor elements.

7. A sensor mat according to claim 6, wherein a thermal conductivity of the fabric layer is greater in a direction perpendicular to the fabric layer than in a direction within the fabric layer.

8. A sensor mat according to any of claims 1 to 7, further comprising a data element configured to obtaining data from the array of addressable sensor elements.

9. A sensor mat according to any of claims 1 to 8, further comprising one or more electrical connectors for connecting to a second sensor mat.

10. A sensor mat according to any of claims 1 to 9, wherein the sensor mat is suitable for monitoring a patient.

11. A monitoring system comprising a sensor mat according to any of claims 1 to 10 and an external data device in communication with the sensor mat, wherein the external data device is configured to obtain a plurality of sensor readings from the sensor mat.

12. A method comprising: obtaining a plurality of sensor readings from a sensor mat according to any of claims 1 to 10.

13. A method according to claim 12, wherein each sensor reading comprises a sensor element address.

14. A method according to claim 13, wherein each sensor element address corresponds to a two dimensional position in the sensor mat.

15. A method according to any of claims 12 to 14, wherein each sensor reading comprises a timestamp.

16. A method according to any of claims 12 to 15, further comprising monitoring the position of a patient, based on the plurality of sensor readings.

17. A method according to any of claims 12 to 16, wherein:the sensor mat further comprises a data element for obtaining data from the array of addressable sensor elements, and the method is performed by the data element; and / orthe method is performed in a system comprising a sensor mat according to any of claims 1 to 8 and an external data device in communication with the sensor mat, wherein the external data device is configured to obtain a plurality of sensor readings from the sensor mat18. A non-transitory storage medium storing computer program instructions which, when read by a processor, cause the processor to perform a method according to any of claims 12 to 17.

19. A method of manufacturing a sensor mat, the method comprising attaching a sensor layer to a fabric layer,wherein the sensor layer comprises an array of sensor elements, each sensor element corresponding to a location in the sensor mat, and each sensor element comprising one or more sensor components, andwherein the sensor layer has a mesh configuration including circuit portions and hole portions, the circuit portions comprising the sensor elements and the circuit portions being connected to form the mesh via flexible joints,the sensor layer further comprising read circuitry for reading the array of sensor elements.

20. A method according to claim 19, further comprising constructing the sensor layer by:obtaining a plurality of circuit portions; andattaching the plurality of circuit portions together using flexible joints.

21. A method according to claim 20, wherein the flexible joints comprise wires and / or flexible PCB portions.

22. A method according to any of claims 19 to 21, wherein the sensor mat is a sensor mat according to any of claims 1 to 10.

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