GB2621213A - A sensor device and a method of forming a sensor device - Google Patents

Abstract

A sensor device (10) comprising an array of sensors (15, Fig. 3), wherein each sensor of the array (15, Fig. 3) is formed from a piezoresistive ink (1) that is applied to a substrate (2). The substrate (2) may be a biodegradable material. Substrate (2) may be one or more of a polymer, a polycarbonate, a polyvinyl, bamboo, hemp, and a polyvinylalcohol polymer. The substrate (2) may be configured to serve as a carrier that dissolves when water is applied; and the layer of piezoresistive ink (1) may be configured to serve as a sensor when the substrate (2) has been removed. Another aspect is a method of forming a sensor device (10) comprising an array of sensors (15, Fig. 3), wherein each sensor of the array (15, Fig. 3) is formed from a layer of piezoresistive ink (1), the method comprising applying the piezoresistive ink (1) to a substrate (2).

Description

A sensor device and a method of forming a sensor device

Technical Field

The present disclosure generally relates to sensors.

In particular, the present disclosure relates to a pressure, tension and torsion sensor that comprises ink applied to a surface or substrate. The ink may be printed or transferred onto the surface or substrate. The ink may be a piezo electric ink, a resistive ink, or a conductive ink. The surface or substrate may be dissolvable, compostable, biodegradable, marine safe, and stronger than polyethylene. The surface or substrate may comprise polymer, hemp or bamboo.

Depending on the application, the surface or substrate can be metallised, for example with copper or aluminium utilising a conventional metallisation process, to provide heat dispersal or reflection and antimicrobial characteristics. At their end of life, the sensors are fully recyclable or biodegradable, leaving no microplastics or toxic residues, and being completely marine safe.

The disclosed sensors can be applied in transport, security, engineering sports, leisure, retail, equine and healthcare applications, amongst others. Applications of the sensors include load detection and monitoring. -2 -

Background

Pressure, tension and torsion sensors exist in many formats, some utilising conductive or resistive inks, the challenge being what happens at end of life; this is particularly of issue for short term sensing requirements. Components can be difficult and energy intensive to recycle with the problem of plastic components possibly ending up as micro-plastics.

The most common plastics are polyethylene based (C2H4); these products are not readily biodegradable and are breaking down to micro-plastics. More recently, a polyvinylalcohol based polymer has been described in US201515513195, WO-2022043405-A1, and US2022064860(A1), which is dissolvable in water (fresh and saline), biodegradable, compostable (domestic and industrial), edible and recyclable breaking down into CO2 and harmless marine safe minerals. It is also 15% stronger than polyethylene based films.

A challenge with their applications in protective gear is that they can be bulky or be uncomfortable for the wearer. Utilising a piezoresisfive polymer-based ink patent EP3397702 Al describes a sensor printed on the complete surface of the headgear, either internally or externally, coupled with a small transmitter. This enables impact data to be assessed immediately, protecting the user from further severe head injury and enables the medical teams to assess potential injury from specific impacts.

The piezoresistive inks that are utilised are described by W02017/114978. The specific attributes relating to the present disclosure are that they are polymer composites inks based on thermoplastic elastomers from the styrene-butadiene-styrene family and carbon or metal nanostructures that have demonstrated their potential as high performance or multifunctional materials and have become one of the most attractive domains in material science. Through the incorporation of carbon nanostructures into the polymers, the main characteristics of the polymer matrix such as easy processing, tailorable mechanical properties including reversible large deformation stretchability, can be combined with the excellent mechanical, thermal and electrical properties of the nanostructures. Due the overall properties of the composites matrices strong efforts have been carried out on the development of polymer composite inks that can be processed by different printing technologies, allowing economic and efficient sensor development and simple integration into devices. -3 -

Piezoresistive behaviour can be described as a mechanical stimulus that induces in the sensor a change in electrical resistivity. This is mentioned in US2951817, which describes a polyvinyl chloride polymer matrix with manganese dioxide as filler, where the electrical resistance changes throughout a very wide range of values in response to very small deformations. Resistive deformable sensors touch screens for application in electronic devices are presented in US20100123686A. Piezoresistive pressure sensors chips that are exposed to the external pressure medium directly have been disclosed in US8567256B2, as well as pressure sensors for the measurement of compression and tension of materials in different applications, which are disclosed in WO 2007044307 Al.

Many applications utilise a composite multilayer conductive material often a fabric such as W0202188305 Al, GB201910547 DO and GB201912281 DO, others such as helmet sensors have a small number of sensors positioned within the helmet US20160050999. In addition, patient pressure sensing features include the whole bed or mattress DE202017102653, when for hygiene and cleaning purposes disposable is appropriate.

Sensor devices are available for the detection of impact forces. Such sensors may be integrated into protective equipment which can be worn by a user, to determine whether the user has been subject to impact forces. There is a demand to improve the precision of such sensor devices at determining a location of an impact force.

Aspects of the present invention address technical problems within existing applications.

Summary

Aspects of the present invention are set out by the claims. Further aspects are also described. Thus, disclosure is provided of printed sensors on a dissolvable substrate. Applications of the sensor includes providing detection and alerts for the prevention of injury, pressure ulcers, and the reduction of damage in trauma injuries and sports performance enhancement. The substrate may be formed from polymer, hemp, or bamboo. -4 -

In a first aspect, there is provided a sensor device (10) comprising an array of sensors (15), wherein each sensor of the array (15) is formed from a piezoresistive ink (1) that is applied to a substrate (2). Each sensor of the array (15) is configured to detect impact forces, which enables a determination of how the impact forces are distributed across the sensor device.

In a second aspect, there is provided a system comprising: the sensor device (10) according to the first aspect; a data collection unit (23) configured to store data corresponding to signals received from the sensor device (10); and a processor (25) configured to interpret the data stored by the data collection unit. Accordingly, the system is configured to sense impact forces, collect data from the sensor device, and interpret this data which has been collected by the sensor device.

In a third aspect, there is provided a method of forming a sensor device (10) comprising an array of sensors (15), wherein each sensor of the array (15) is formed from a layer of piezoresistive ink (1), the method comprising applying a layer of the piezoresistive ink (1) to a biodegradable substrate (2). Accordingly, the sensor device is manufactured from ink, to provide an array of sensors that are configured to detect impact forces.

In a fourth independent aspect, there is provided a sensor that is printed on a surface or substrate, preferably a polyvinylalcohol polymer base substrate.

In a fifth independent aspect, a method comprises applying piezoresistive ink to a surface or substrate, preferably a polyvinylalcohol polymer base substrate.

In a sixth independent aspect, a method comprises applying carbon based ink to a surface or substrate, preferably a polyvinylalcohol polymer base substrate.

Optionally, the surface or substrate is metalised.

Optionally, the surface or substrate is biodegradable.

Advantageously, the sensors are fully recyclable and suitable for single use applications.

Surprisingly, combining a piezoresistive polymer-based ink (EP3397702 Al) with a polyvinylalcohol based polymer substrate produces sensors that have several applications and are completely recyclable at end of life. -5 -

Aspects provide a sensor which can cover the whole substrate surface (e.g. a sheet), by printing the surface with piezoelectric ink or piezoresisfive ink. In particular, the present disclosure relates to a pressure, tension and torsion sensor that comprises piezoelectric, resistive and/or conductive ink. Ink(s) are applied externally to a substrate surface. This disclosure can be applied in healthcare, animal healthcare, homecare and engineers, amongst others.

In a further independent aspect, there is provided a protective device comprising a sensor, wherein the sensor is formed by printing piezoresistive ink on a substrate surface, creating a device. In dependent aspects, the sensor is printed on a substrate surface, external polycarbonate or other substrate, respectively.

Brief Description of the Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: * Figure 1 provides a cross section view of a sensor arrangement that includes a sensor; * Figure 2 provides a schematic view of a system that implements the sensor; * Figure 3 provides a schematic that illustrates the sensor arrangement; * Figure 4 provides an image of a first example of a sensor arrangement; and 25 * Figure 5 provides an image of a second example of a sensor arrangement.

Detailed Description

Various exemplary embodiments, features, and aspects are described in detail below with reference to the drawings. In an example, one or more sensor 1 is printed on any form of surface, such as a surface of a substrate 2. The substrate 2 may be formed from a biodegradable material. For example, the substrate 2 is formed from one or more of: a polymer, a polycarbonate, a polyvinyl, bamboo, hemp, fabric, concrete, and metal. The substrate 2 may comprise a polyvinylalcohol polymer surface or substrate, such as -6 -HydropolTm (as described for example in WO-2022043405-A1, US201515513195, and US2022064860). A non-exhaustive list of substrate 2 configurations include film, thermoformed objects, foam and non-woven material.

To achieve a sensor transfer, the dissolvable polymer substrate is printed in reverse order with the addition of an adhesive as the final layer, then a removable barrier layer of polymer is applied.

When deployed, the barrier polymer is removed, the sensor sheet is applied to the surface, and warm water is applied to dissolve the substrate. Once dried, the sensor is connected to the data collection unit.

Figure 1 illustrates a sensor device 10 that includes a layer of piezoresistive ink 1 applied to a surface or substrate 2. The layer of piezoresifive ink 1 serves as one or more sensor. The substrate 2 (e.g., a biodegradable substrate) is illustrated by a polymer film 2, which provides structural integrity to the sensor arrangement 10.

A side of the substrate 2 is printed with piezo and stretchable conductive ink, which serves as the sensor 1. The one or more sensor 1 may be printed over a surface of the substrate, for example, being printed over the whole available surface. For example, the surface of the substrate 2 may comprise an array of sensors 1, each sensor of the array being formed from piezoresisfive ink.

When printed on a polymer of thickness 5mm or greater, the connection points are pins, with the data collection unit base cut into the polymer (illustrated). When printed on film or thin metal, the sensor arrangement 10 comprising conductive ink is clamped in place by a connector 3, which serves to transmit signals that are output from the sensor 1. Another side of the film 2 may be protected by a layer of metal 4.

When ink is applied to permanent hard surface such as metal or concrete, the data collection unit is affixed to the surface and thereby creating the circuit connection 7 -The polyvinylalcohol polymer 2 has a number of advantages: * The polyvinylalcohol dissolves into harmless marine safe minerals and CO2.

* The polyvinylalcohol polymer leaves no toxic or micro-plastic residue.

* In a marine environment the polyvinylalcohol polymer dissolves within 10 weeks.

* The polyvinylalcohol polymer is gas impermeable and microbe static.

i.e. pathogens neither grow or die on the a polyvinylalcohol polymer base.

* Will start to degrade when urine or moist faeces comes in to contact, meaning that an additional alert is provided for the pressure ulcer application.

In an example, a blown polyvinylalcohol film 2 is 10-50p thick. With reference to Figure 1, the polyvinylalcohol polymer blown film 2 may be a single layer.

In an exemplary method, piezoresistive ink 1 is applied to the substrate 2 using gravure printing, drop casting, spraying, screen printing, or inkjet printing.

In an example, the applied connecting circuitry comprises carbon based functional ink.

Carbon based functional ink may be applied to the substrate 2 using gravure printing, drop casting, spraying, screen printing, or inkjet printing.

Depending on application the polyvinylalcohol polymer base 2 is metalised by the disposition of aluminium or copper on the upper surface. Thus, a layer of metal 4 is provided which protects the film 2.

zo In an example, metallised substrate piezoresistive and carbon-based functional ink is applied to the non-metallised surface.

Advantageously, the sensors 1 are fully recyclable. At their end of life, the sensors 1 can be fully dissolved, composted, or mechanically recycled.

With reference to Figure 2, a system 20 is illustrated of sensors 1 on polyvinylalcohol polymer substrate 2 that are suitable for single use applications. Examples of applications that include a sensor 1 are sports shoes 21a, scales 21b, security cameras 21c, helmets 21d, and pressure sheets 21e. Each of these applications (21a-e) includes a substrate that is printed with a layer of piezo ink which serves as the sensor 1. -8 -

On flexing, the cured piezoresistive ink generates a signal when pressure / impact is applied. The signal is transmitted as a sensor output 22, via the connector 3, and is collected by the data collection unit 23.

In an example, the data collection unit 23 interprets the signal, converting it to a usable format for processing. The data collection unit 23 may be part of a microprocessor with options of communications protocols 24, including but not exclusively Bluetooth, Wi-Fi, gsm, RF, transmits to a receiver.

In some embodiments, the data collection unit 23 has an option for display for healthcare applications. In healthcare applications including pressure ulcer prevention, the data collection unit 23 includes an additional Volatile Organic Compound sensor for the detection of urine and faeces.

For example, the sensor arrangement 10 may plug into the data collection unit 23 with easy-to-use clip-on or a plug arrangement 3.

In some embodiments, the data is sent to a cloud 25 or an on-premise receiver. The cloud and/or an on-premise based platform 25 may interpret the data, trigger alarms and alerts (26a, 26b). The platform 25 may broker data to users' existing analytics engine (27a, 27b).

At end of life, the polyvinylalcohol polymer sensor can be placed in washing machine, sink or sluice and dissolved at 700, advantageously leaving no harmful or micro-plastic residue.

In an example, the polyvinylalcohol polymer 2 meets the following specifications: a. Determination of biobased content: CEN/TS 16137; ASTM D6866 b. Composability: EN 14995; EN13432; ASTM D6400; ISO 17088; AS4736; IS018606; ASTM D6868 c. Anaerobic Digestion: ISO 15985; ASTM D5511 d. Soil: ISO 17556 e. Freshwater: ISO 13975; EN14987 f. Landfill: ASTM D 5526 g. Aerobic wastewater and sewage sludge: EN14851; EN14852 h. Anaerobic wastewater: EN14853 i. Marine: ASTM 06691; OK Marine; ISO 18830 (floating); ISO 19679 (sediment) j. Recycling: ISO 15270 (Guidelines for the recovery and recycling of plastics waste) -9 -k. Plastic waste: EN15347 Figure 3 illustrates a typical electrical circuitry of a sensor arrangement 10. The electrical circuitry is configured to form an electrical connection with the layer of piezoresistive ink 1. The electrical circuitry is itself formed from ink.

In the example shown in Figure 3, the layer of piezoresistive ink 1 comprises an array of sensors 15, each sensor of the array 15 being formed from the piezoresistive ink 1. For the arrangement shown in Figure 3, the array 15(x,y) is a 10 by 11 array of sensors.

Each of the sensors 15 of the layer of piezoresistive ink 1 can be addressed by (x,y) coordinates. A determination of the location of the force can be achieved by separately detecting the x-location and the y-location. Electrical contacts 16x address the location along the x-axis of array 15(x,y), each of these electrical contacts 16x being connected to wires 17x. Electrical contacts 18y address the location along the y-axis of array 15(x,y), each of these electrical contacts 18y being connected to wires 19y.

If the layer of piezoresistive ink 1 receives a force, then this changes the resistivity of the layer of ink 1. Wien this force is removed, the elastomeric property of the ink results in the layer of ink 1 resuming its original shape, thus returning its resistivity to its previous value. The sensor arrangement 10 is calibrated so that the amount of force can be calculated by measuring the resistance to current that is received via the electrical circuitry. The location of the force is determined based upon which part of the array 15(x,y) detects the change in resistivity of the layer of ink 1.

Figure 4 illustrates a first example of such a sensor arrangement 10. and Figure 5 illustrates a second example of such a sensor arrangement 10. The sensor arrangement 10 shown in Figure 4 provides a 10 by 11 array, so corresponds to the schematic diagram shown in Figure 3. The sensor arrangement 10 shown in Figure 5 provides a 4 by 4 array.

In both of Figure 4 and Figure 5, each sensor arrangement 10 includes an array of sensors 15, with each of these sensors being formed from piezoresistive ink 1. Each of the sensors is shown connected to electrical contacts (16, 17), with these electrical contacts connected to wires (18, 19). These electrical connections can also be printed onto the substrate 2.

Thus, the array of sensors is can be used to precisely identify the location at which a force is detected by the sensor.

-10 -Applications By way of example, a number of applications are envisaged: 1) Prevention of pressure ulcers * Piezo electric ink sensors are printed in blocks and lines covering the whole sheet * Advantages include single use, maximum 24 hours or 72 hours, or to sheet soiled whichever is the sooner.

* In an example, a sheet of substrate 2 which may be formed from polyvinylalcohol polymer (e.g., HydropolTM) 20-25p thick with dimensions 200cm x 130cm is printed with a piezo resistive functional ink (patent application no. W02017114978A1) and a conductive carbon ink for the circuitry.

* A fabric material sheet may be printed with piezo resistive functional ink (patent application no. W020171 14978A1).

* It may supplied on a roll, being perforated between sheets on the roll.

* Another embodiment may have one side metallised with copper for antimicrobial and heat dispersal properties.

* The piezoelectric ink may be printed in blocks and lines to create the sensor areas covering an area of 1.5m2.

* The connector may be a wired clip-on clamp to enable quick and easy connection to the data collection unit.

* The data collection unit may be mains powered.

* The data collection may include a volatile organic compound sensor for the detection of urine and faeces.

* A data collection unit may provide connectivity via ethernet or W-Fi.

* The system may include a display of reading on the data collection unit at end of bed for clinicians.

* Alerts/alarms may be issued if patient shows no movement for clinically specified time.

* Alerts/alarms may be issued if too much pressure shown in one area.

* Alerts/alarms may be issued on the degradation of the sheet, possibly due to urine or faeces.

* Alerts may be issued via bleeper, email, SMS or text to voice call.

* Analytics of time from alarm to movement/change of pressure may be made available.

2) Prevention of Falls Same specification as for item 1. (Prevention of pressure ulcers) * Detection of pressure changes from spread across the sheet to be concentrated in one area.

* Detection zones 600mm from edge of bed.

* Alerts/alarms may be issued if pressure reading in detection zone and sized, circa. 600x600mm.

* Alerts may be issued via bleeper, email, SMS or text to voice call.

3) Reduction of damage in trauma injuries Printed sensors in helmets * Hard helmets including motorcycle and sports.

* Soft head guards including cycles, epilepsy and rugby.

o Printed inner lining on helmet/head guard which is bonded to the helmet/ head guard.

o Piezoelectric ink sensors may be printed on to the substrate (e.g., HydropolTM) foam and film in blocks and lines covering the whole inside of the helmet/head guard.

o Professional sports option data collected in small data processing unit brokered and transmitted existing systems.

o Healthcare application option to have data brokered to the users medical notes.

o Amateur sports data transmitted to cloud and app.

o Cycle helmets and motorcycle helmets data: * impact data stored on chip * On impact data stored and transmitted to cloud via GSM * Data shows location of impact and severity of impact * Platform provides assistance with immediate diagnosis * Impact data available to first responder via OR code on helmet and via app 4) Printed sensors in clothing -12 - * Detecting muscle movement changes for professional sports ^ For example, may be used in socks, leggings and tops, to provide indications of changes in key muscle movement * Movement data may be transmitted to cloud via GSM, wi-fi, RE or Bluetooth.

* Data may show location and severity of changes in muscle response.

* A platform may provide assistance with immediate diagnosis.

5) Sizing of head protection A single use cap, with printed sensors, placed on the head then the head protection, such as helmet is donned.

* Data shows location of pressure points ^ Data can be uploaded on to the client's own database.

6) Sizing of shoes A single use socks, with printed sensors, to identify pressure points and correct sizing for performance, healthcare and general applications.

* Data shows location of pressure points * Identification of areas requiring support * Data can be uploaded on to the client's own database 7) Prevention of foot injuries Printed sensors on the sole, sides and upper of the shoe, or as a sock utilising non-woven substrate 2 which may be formed from polyvinylalcohol polymer (e.g., Hydropol TM).

Sensors are printed on to the substrate, in multiple sensor configurations (e.g., blocks and lines) covering the whole inside of the shoe * Professional sports option data collected in small data processing unit brokered and transmitted via existing systems * Healthcare application option to have data brokered to the user's medical notes * Amateur sports data transmitted to cloud and app * Data stored on chip * Transmitted to cloud by the smartphone via Bluetooth -13 - * Platform provides assistance with immediate diagnosis * Data collected o Impacts * Walking/running * Kicking e.g. a ball * Twists * Side of shoe integrity * Severity of impact o Outcomes * Changes in gait * Potential injury * Developing injury * Diagnosis assistance 8) Sensor as a Transfer Piezoresistive sensors printed in reverse on the substrate 2 which may be formed from polyvinylalcohol polymer (e.g., HydropolTm), with adhesive and removable backing. The backing may be formed from a polyvinylalcohol polymer (e.g., HydropolTm). The sensor can be placed on any surface, then water applied, so the substrate 2 carrier dissolves leaving sensors in-situ.

* Connector is a wired clip enable quick and easy connection to the data collection unit.

* Data collection unit communication designed for GSM, ethernet, Bluetooth, RF and * If used as scales temperature and humidity sensors built into data collection unit.

9) Single Use Healthcare Scales Piezoresistive sensor printed on a polymer substrate, up to 30p substrate 2 which may be formed from polyvinylalcohol polymer (e.g., Hydropol Tm), film in blocks and lines * Easily deployed on a firm surface in home, workplace, hospital or public area such as street.

-14 - * Data collection unit (not single use) may connect to smart phone via Bluetooth.

* Connector is a wired clip on clamp to enable quick and easy connection * Once measurements taken, the sensor may be disposed in the sink or recycled.

10) Multiple Use Healthcare and Veterinary Scales Piezo resistive sensor printing on a polymer substrate * Easily deployed on a firm surface in home, workplace, farm or field.

* Connector is a wired clip on clamp to enable quick and easy connection.

* Measurement is visually displayed, with option to transmit to software platforms.

11) Security Sensors Piezoresistive Sensor printed on substrate 2 which may be formed from polyvinylalcohol polymer (e.g., HydropolTM) film in blocks and lines.

* Easily deployed on a surface, for example by doorways, windows, in trailers for detection of stowaways or thieves.

* Data collection unit communication designed for GSM, ethernet, Bluetooth, RF and VVi-Fi.

* Data collection unit mains and battery powered.

* Alarms and alerts may be issued via email, SMS or text to voice call including alerts to the police.

12) People Counting A piezoresistive sensor printed on substrate 2 which may be formed from polyvinylalcohol polymer (e.g., Hydropol Tm) can be easily deployed and redeployed on the floor, for example by doorways corridors, walkways, aisles.

* Counting footfall, dwell time.

* Security elements such as rapid changes in movement and bubbling.

In the above examples, it will be appreciated that the substrate 2 may be formed from any of a polymer, a polycarbonate, a polyvinyl, bamboo, and hemp. For example, the substrate 2 may be formed from a polyvinylalcohol polymer such as Hydropol TM -15 -Although the disclosed subject matter has been described using specific terminology relating to apparatus features and/or method features, it is to be understood that the claimed subject matter is not necessarily limited to the examples disclosed. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. The advantages disclosed may relate to several of the examples that are disclosed.

Claims (2)

1. -16 -Claims 1. A sensor device (10) comprising an array of sensors (15), wherein each sensor of the array (15) is formed from a piezoresistive ink (1) that is applied to a substrate (2).
2. 2. The sensor device (10) according to claim, wherein the piezoresistive ink (1) is applied to the substrate (2) by any one of gravure printing, drop casting, spraying, screen printing, or inkjet printing.The sensor device (10) according to claim 1 or claim 2, further comprising: a connector (3) configured to receive the substrate (2) The sensor device (10) according to any preceding claim, further comprising: connecting circuitry configured to provide an electrical connection for each sensor of the array (15).The sensor device (10) according to claim 4, wherein: the connecting circuitry comprises carbon based functional ink.6. The sensor device (10) according to claim 4 or claim 5, wherein the connecting circuitry is applied to the substrate (2) by any one of gravure printing, drop casting, spraying, screen printing, or inkjet printing.The sensor device (10) according to any preceding claim, further comprising: a metal layer (4) applied to a side of the substrate (2).The sensor device (10) according to any preceding claim, wherein: the substrate (2) comprises a biodegradable material.-17 -The sensor device (10) according to any preceding claim, wherein: the substrate (2) is configured to serve as a carrier that dissolves when water is applied; and the layer of piezoresistive ink (1) is configured to serve as a sensor when the substrate (2) has been removed.10. The sensor device (10) according to any preceding claim, wherein the substrate (2) comprises one or more of a polymer, a polycarbonate, a polyvinyl, bamboo, hemp, and a polyvinylalcohol polymer.11. A system comprising: the sensor device (10) according to any preceding claim; a data collection unit (23) configured to store data corresponding to signals received from the sensor device (10); and a processor (25) configured to interpret the data stored by the data collection unit.12. A method of forming a sensor device (10) comprising an array of sensors (15), wherein each sensor of the array (15) is formed from a layer of piezoresistive ink (1), the method comprising applying the piezoresistive ink (1) to a substrate (2).13. The method according to claim 12, further comprising: forming connecting circuitry by applying carbon based ink to the substrate (2).14. The method according to claim 12 or claim 13, wherein the substrate (2) is metalised.