TECHNICAL FIELD

The present invention belongs to the technical field of pressure sensor, and in particular relates to a piezoresistive pressure sensor.

BACKGROUND ART

Pressure sensors are widely used for detecting pressure. In some situations, it is not only needed to detect the existence of pressure, but also needed to detect the exact position where the pressure is exerted. In order to achieve this function, piezocapacitive pressure sensors, which are generally used, should be arranged into pressure sensor arrays. Commercially available piezocapacitive pressure sensor arrays of thin-film type have a 2D-patterned (two dimensional-patterned) thin-film capacitive material layer and electrode layers attached thereto to form an array. Such a structure, however, could only be obtained through an expensive production process, since the production of 2D-patterned thin-film costs much labor and time.

It has been proposed to use polymeric material in pressure sensors to improve the flexibility. For example, US2017/0199095A1 has described a piezocapacitive pressure sensor, in which a foam layer is used between the electrode layers, wherein the foam layer can be made from polymers such as polyurethane. The disclosed pressure sensor is based on the capacitance of the two electrodes and applies polyurethane foam having an average cell size of about 50 to 250 micrometers. Such small cell size is difficult to control, and the manufacturing cost is very high, even though it may provide improved sensitivity.

Although commercial polymeric materials can be used in pressure sensors, those polymeric materials, such as artificial leather, have poor translucency (usually less than 3%) and do not have piezoresistive pressure sensing function. Pressure or touch sensing sensor arrays underneath are usually thin film type or capacitance touch functioned display panel with a 2D-patterned thin-film piezoresistive layer structure or more complex vacuum processed thin film device. Owing to those structures, the manufacturing cost is usually expensive. In addition, owing to limited translucency of polymeric materials and carbon black used, thin film pressure sensor and other component for control system and current system are difficult to combine information display, touch sensor or pressure sensor with backlight system underneath. For example, WO2018/013557A1 discloses vehicle interior component comprising a composite structure consisting of a sensor, a display, a cover and a functional layer, wherein the sensor is configured to detect input from the vehicle occupant at the cover; the display is configured to provide illumination visible through the translucent cover. However, the foam used in the composite structure is only for comfort and detection is only on/off control by using display panel.

In addition, it still remains a great challenge to make pressure sensors with large area. For example, current available pressure sensors with large area usually show low sensitivity, even though such matter may be overcome by applying sophisticated algorithm.

Therefore, it is still desired to provide pressure sensors which can detect pressure and the exerting position while having sufficient sensitivity and reliability and good translucency, and can be produced by inexpensive processes at the same time.

CONTENT OF THE PRESENT INVENTION

It is an objective of the invention to provide a piezoresistive pressure sensor, comprising a piezoresistive fabric layer; and an electrode array layer comprising a plurality of electrodes, which is disposed on a first side of the piezoresistive fabric layer; wherein the piezoresistive fabric layer is made of fabric doped with conductive particles, wherein the conductive particles are present in a liquid composition in an amount from 0.05 to 4 wt%, based on total weight of the liquid composition.

Thus, this invention can provide cost-efficient pressure sensor by using cheap and commercially available materials to form piezoresistive material layer and employing cost-efficient fabrication processes like printing and coating.

It is another objective of the invention to provide an electronic control system, comprising a piezoresistive pressure sensor, which is configured for receiving a touch from a user and generating a signal in response to the touch from the user; an executing unit; and an electronic control unit, which is coupled to the piezoresistive pressure sensor and the executing unit respectively, wherein the electronic control unit is configured to regulate the executing unit in response to the signal generated by the piezoresistive pressure sensor. Thus, the user can control the control system more precisely.

The present invention further provides a process for producing the piezoresistive pressure sensor, comprising: a) preparing an electrode array layer comprising a plurality of electrodes and a piezoresistive fabric layer, respectively; and b) disposing the electrode array layer on a first side of the piezoresistive fabric layer, wherein the piezoresistive fabric layer is made of fabric doped with conductive particles, wherein the conductive particles are present in a liquid composition in an amount from 0.05 to 4 wt%, based on total weight of the liquid composition. It has been surprisingly found that by using conductive materials doped fabric layer as the piezoresistive layer of the pressure sensor, the pressure sensor can provide overall 2D-pressure mapping in a large area. Since the pressure sensor does not need to have a 2D-patterned piezoresistive structure and can be constructed by cheap and commercially available materials, it can be prepared at a substantially reduced production cost. Moreover, the conductive materials doped fabric layer imparts to the pressure sensor good sensitivity and reliability and good translucency.

In addition, by adopting different types of piezoresistive material layer and/or cover layer with specific structure and properties, such as fabric structure and translucency, the inventive piezoresistive pressure sensor is especially suitable for usage in a control system of dashboard, a center console, a middle console, or a car horn.

BRIEF DESCRIPTION OF FIGURES

The present invention will be described with reference to the figures, which are not intended to limit the present invention.

Fig. 1 shows the electrode set design at one point of the pressure sensor according to an embodiment of the present invention, wherein the electrode set comprises 5 pairs of electrodes and one pair of electrodes is shown in the dashed box.

Fig. 2 is the partial view of the electrode set showing distance between the edges of two neighboring electrodes in an electrode set.

Fig. 3 is a schematic diagram of transparent electrode consisting of transparent PEDOT:PSS electrode and Ag electrode line.

Fig. 4 is a schematic diagram of the distance between two neighboring electrode sets.

MODE OF CARRYING OUT THE INVENTION

Unless defined otherwise, all terms used herein have the meaning commonly understood by a person skilled in the art to which the invention belongs.

In the present invention, the term “electrode set” means the single structural unit for forming the electrode array, as shown in Fig. 1. The electrode set can comprise a plurality of electrodes, arranged in certain geometric pattern.

In the present invention, as shown in Fig. 2, the term “distance between the edges of two neighboring electrodes in an electrode set” means the vertical separation distance between the two closest electrodes, as denoted as DO. In the present invention, the term “a neighboring electrode set” means any of surrounding electrode sets relative to the central electrode set, i.e. , an electrode set located at upper, left, right, bottom, upper-right corner, upper-left corner, bottom-right corner, or bottom-left corner of the central electrode set. For example, as shown in Fig. 4, when electrode set 412 is regarded as a central electrode set, the term “the distance between two neighboring electrode sets” means the vertical separation distance D1 between the two adjacent electrode sets 412 and 432 in the horizontal direction, or the vertical separation distance D2 between the two adjacent electrode sets 412 and 414 in the vertical direction on the base layer 400. The vertical separation distance D1 and D2 may be the same or different according to actual requirement.

The abbreviation PEDOT is short for poly(3,4-ethylenedioxythiophene).

The abbreviation PSS is short for poly(styrenesulfonate).

The abbreviation PEDOT: PSS means poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, a polymer mixture of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate).

In one aspect, the invention provides a piezoresistive pressure sensor, comprising a piezoresistive pressure sensor, comprising a piezoresistive fabric layer; and an electrode array layer comprising a plurality of electrodes, which is disposed on a first side of the piezoresistive fabric layer; wherein the piezoresistive fabric layer is made of fabric doped with conductive particles, wherein the conductive particles are present in a liquid composition in an amount from 0.05 to 4 wt%, based on total weight of the liquid composition.

In a preferred embodiment, the piezoresistive pressure sensor comprises an artificial leather layer as a cover layer, disposed on a second side of the piezoresistive fabric layer.

Usually, the artificial leather layer conventionally used comprises a base layer. Preferably, in the present invention, the base layer in the artificial leather layer can be omitted and replaced with the piezoresistive fabric layer. In this case, the piezoresistive pressure sensor will comprise an artificial leather layer in which the piezoresistive fabric layer serves the function of the original base layer, as well as an electrode array layer, which is disposed on the other side of the piezoresistive fabric layer. Thus, piezoresistive pressure sensor can be constructed by cheap and commercially available materials.

In a preferred embodiment, in the liquid composition containing conductive particles, the conductive particles are present in an amount from 0.1 to 2 wt%, preferably in an amount from 0.1 to 0.6 wt%, still preferably in an amount from 0.15 to 0.35 wt%, based on total weight of the liquid composition.

In a preferred embodiment, the doping amount of conductive particles is 1x10 ^-7 g/mm ³ to 1x1 O' ⁵ g/mm ³ , preferably 3x1 O' ⁶ g/mm ³ to 8x1 O' ⁶ g/mm ³ , and more preferably 5x1 O' ⁶ g/mm ³ to 7x1 O' ⁶ g/mm ³ , based on the size of the fabric to be doped with conductive particles. The unit of g/mm ³ means weight of conductive particles in gram per volume of fabric in mm ³ .

Many conductive materials may be used for the present invention as conductive particles. For example, the conductive material may be selected from the group consisting of Au, Ag, Cu, Ni, carbon nano tube (CNT), carbon black, graphene, a ceramic material, and an organic conductive material. In the present invention, the conductive material is preferably chosen from organic conductive materials. Many organic conductive materials may be used, such as polyaniline, polypyrrole, polythiophene, polyphenylene vinylene, polyphenylene, polyacene, or the derivatives thereof, or a copolymer of those materials. In a preferred embodiment, the conductive particles are preferably conductive polymer particles, for example, made by PEDOT: PSS.

The processes of doping the fabric include the deposition of the conductive material to the surface and inner surface of the fabric which yields the piezo-resistive fabric. Many processes may be used for such deposition of the conductive material to the fabric. Preferable are all liquid-applied processes including printing and coating processes (e.g., dip coating, spray coating, etc.) as those processes are readily available, cost-efficient and applicable to small to large areas.

In a preferred embodiment, the conductive materials can be applied in liquid form to the fabric. In a preferred embodiment, the conductive material is PEDOT:PSS. PEDOT:PSS doped fabric is commercially available, or can be produced by methods known in the art. For example, doping of commercially available fabrics with PEDOT:PSS can be conducted via standard coating methods (e.g. dip coating, spray coating, etc.). Many of the commercially available PEDOT:PSS products may be used for the present invention, such as those from Heraeus, Merck or Sigma-Aldrich. In a preferred embodiment, the conductive particles comprise PEDOT and PSS. Those PEDOT: PSS materials may be available with different concentration or grades, such as 1.0 wt% (in H2O), 1.3 wt% (in H2O), 2.8 wt% (in H2O), 3.5 wt% (in H2O), 5.0 wt% (in H2O), etc.. The PEDOT:PSS materials can be diluted by any conventional thinner, such as water, according to actual requirement, so as to obtain desired concentration. In one embodiment, the liquid composition containing conductive particles has a conductivity of no less than 1 mS/cm, preferably no less than 1.5 mS/cm, and more preferably a no less than 2 mS/cm.

For pressure sensor applications, it is important to control the current leakage of piezoresistive layer on the electrode array so that it is not higher than the noise. To control the current leakage, it is preferred that the surface resistance of the doped fabric, without any external pressure, is adjusted to more than 4 GQ/mm, preferably more than 5 GQ/mm. In this way, electrical short-circuit between neighboring electrode sets can substantially be prevented and the accuracy of the pressure sensor can be improved. The surface resistance can be adjusted by the doping amount or conductivity of the conductive material. When PEDOT:PSS is used as the conductive material, the doping amount of liquid composition containing PEDOT:PSS polymer particles is 1x1 O' ⁷ g/mm ³ to 1x1 O' ⁵ g/mm ³ , preferably 3x1 O' ⁶ g/mm ³ to 8x1 O' ⁶ g/mm ³ , and more preferably 5x1 O' ⁶ g/mm ³ to 7x1 O' ⁶ g/mm ³ , based on the size of the fabric to be doped.

The fabric in the present invention refers to woven fabric, knitted fabric or non-woven fabric, preferably woven fabric, such as plain woven fabric and stockinette stitch woven fabric, preferably stockinette stitch woven fabric. The fabric comprises, for example, polyester fiber, polyamide fiber, polyurethane fiber, polyimide fiber, polyacrylonitrile fiber, polypropylene fiber, polyvinyl chloride fiber, polyvinyl alcohol fiber, or polyvinyl acetate fiber, or the combination thereof; preferably polyester fiber, such as polyethylene terephthalate and polybutylene terephthalate fiber.

In the present invention, the woven fabric is made of yarns comprising at least one fiber with a diameter of 0.01-0.5 mm, wherein the yarn has a diameter of 0.01-10.0 mm, preferably 0.1-5 mm, more preferably 0.2-2 mm, especially 0.3-1.2 mm and has a twist number of 10-50 twist/10 cm, preferably 20-40 twist/10 cm, for example, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34 or 35 twist/10 cm. For example, the yarns consist of more than two fibers, preferably 4- 20 fibers, more preferably 4-16 fibers, even more preferably 6-14 fibers, wherein the fiber has a diameter of 0.01-0.5 mm, preferably 0.05-0.4 mm, more preferably 0.1-0.3 mm. Not bound by any theory, it is found that the diameter of the yarn is related to the sensitivity of the final sensor. If the diameter of the yarn is too small, the sensitivity becomes poor; and if the diameter of the yarn falls within the above scope, the sensitivity is excellent. It is also found that the twist number of the yarn has an effect on the sensitivity and reliability of the final sensor. If the twist number of the yarn is too small, the sensitivity becomes poor; and if the twist number of the yarn is too large, the reliability would be degraded. When the twist number of the yarn falls within the above scope, the sensitivity and reliability are excellent. In the present invention, the non-woven fabric is made of fibers which have a diameter of 0.01-1.0 mm, preferably 0.02-0.8 mm, more preferably 0.02-0.5 mm. The methods for forming non-woven fabric are known to those skilled in the art, such as thermal bonding, chemical bonding and melt blown process.

In the present invention, the piezoresistive fabric layer is a single layer or multilayered structure, preferably a single layer structure. The thickness of the fabric layer can be varied within a relatively large range, such as 0.1-200 mm or 0.1 to 30 mm, according to the actual requirements. In a preferred embodiment, the thickness of the fabric layer is 0.1-20 mm, preferably 0.1-10 mm, more preferably 0.2-5 mm, especially 0.3-3 mm.

In the present invention, the piezoresistive fabric layer is continuous or discontinuous layer, preferably continuous layer. The continuous piezoresistive fabric layer can be manufactured more easily and can be adjusted size easily. The size of continuous piezoresistive fabric layer can be varied within a relatively large range, and can be any size according to the actual requirements. For example, the continuous piezoresistive fabric layer can have small size and can be used for preparing smaller sensor for car interior application, for example, for smart horn, middle console and dashboard.

In a preferred embodiment, the fabric is made of the plain woven fabric and the stockinette stitch woven fabric which is made of yarns having has a diameter of 0.01- 10.0 mm, preferably 0.1-5mm, more preferably 0.2-2 mm, especially 0.3-1.2 mm and has a twist number of 10-50 twist/10 cm, preferably 20-40 twist/10 cm.

In the present invention, the artificial leather can be any commercial materials suitable for manufacturing piezoresistive pressure sensor. In a preferred embodiment of the present invention, the artificial leather is based on polyurethanes, such as artificial leather under the trademark Haptex®. Advantageously, the artificial leathers used in the present invention comprise a base layer which thus can be constituted by a piezoresistive fabric layer.

In electrode array layer of the present invention, the distance between any of the edges of two neighboring electrodes in an electrode set may be adjusted to meet the requirement of different application. In the present invention, an electrode set refers to a couple of electrodes that are connected together, as shown in Fig. 1. According to the present invention, the distance must be in the range of 0.1 to 8 mm, preferably in the range of 0.2 to 6 mm, and more preferably in the range of 0.5 to 5 mm. In addition, the number of electrode sets can be selected as needed. For pressure sensor applications, it is desired to use more than one electrode in the electrode sets to improve the sensitivity of the sensor. For example, in the present invention, it is preferable to have at least 3 pairs of electrodes in each electrode set, preferably at least 4 pairs of electrodes in each electrode set, and more preferably at least 5 pairs of electrodes in each electrode set. As shown in Fig. 1 , there are 5 pairs of electrodes in the electrode set. Moreover, it’s important to set the distance between two electrode sets in such a way that it is at least 2 times, preferably at least 3 times and more preferably at least 4 times of the distance between any of the edges of two neighboring electrodes in an electrode set. Otherwise, the sensor may show leakage current (i.e. , the current may flow between two different electrode sets). Pressure sensor meeting this requirement shows high sensitivity and low leakage current. Meanwhile, when the distance between two electrode sets is too large, the sensitivity of the senor will be decreased, for there will not be enough electrodes spread over the sensor. Therefore, it is important to set the distance between two electrode sets in such a way that it is no more than 10 times, preferably no more than 8 times and more preferably no more than 6 times of the distance between any of the edges of two neighboring electrodes in an electrode set.

Current leakage can be determined by measuring the resistance of sensor under the condition of without any external pressure onto the sensor. Resistance can be determined by using commercially available source measure units, such as Keithley 2636B SYSTEM sourcemeter. In the present invention, the measurement is performed with an applied voltage of 5 V and Cu foil is used as the electrode material. Distance between the edges of two neighboring electrodes in an electrode set can be determined by any suitable instruments, such as a micrometer or digital caliper.

The electrode array layer comprises a base layer and a plurality of electrode sets thereon and optionally a substrate layer below the base layer. The electrode array layer may be placed on either side of piezoresistive fabric layer. Moreover, the electrode array layer may be separately formed and then laminated with the piezoresistive fabric layer, or may be integrally formed together with the base layer and the optional substrate layer. The integration of the electrode array layer may be affected by printing, such as screen-printing, gravure printing or coating. The base layer can be any commercial materials suitable for manufacturing the electrode array layer, such as polyimide film, polyethylene terephthalate film and polyethylene naphthalate film. The substrate layer can be any commercial materials suitable for manufacturing the electrode array layer, such as flexible polymer film and artificial leather.

The material of the electrode array is known in the art, such as PEDOT:PSS, Ag, Cu, Cr, Al, Ni or the like, or any combination thereof. By way of example, PEDOT:PSS, Ag and Cu are preferably used to prepare the electrode array layer of the pressure sensor according to the present invention. In a preferred embodiment, the electrode array layer is available from screen-printing with commercial Ag or Cu inks. In another preferred embodiment, in the electrode array layer, each electrode set is transparent electrode, such as transparent PEDOT:PSS electrode with Ag electrode line.

The manufacturing process of the electrode array is well known to the skilled person in the art. The electrode array layer may have a 3-layered structure, i.e. , electrode array/insulator/electrode array. Each electrode array may have certain number of electrode sets. As an example, Fig. 1 shows the top view of the schematic diagram of the structure of one electrode set in the electrode array layer. In this example, an electrode set has five pairs of electrodes. However, there can be more or less pairs of electrodes in each electrode set.

The cover layer serves the function of protecting the layer lying under it, and may be formed from any flexible material known in the art as needed. By way of example, artificial leather under the trademark Haptex® (manufactured by BASF), which has soft touch, is preferably used to produce the cover layer of the pressure sensor according to the present invention, and provides the sensor with improved user experience, including soft and smooth surface feeling combined with sensing functionality.

In a preferred embodiment of the present invention, at least one electrode in the electrode array layer is transparent.

In a preferred embodiment of the present invention, at least one electrode is made from PEDOT:PSS and/or Ag paste.

In the present invention, the piezoresistive fabric layer and/or the artificial leather layer has a translucency of equal to or higher than 3%. In a preferred embodiment of the present invention, both the artificial leather layer and the piezoresistive fabric layer have translucency of higher than 3%, such as higher than 15%; in the electrode array layer, each electrode set is transparent electrode, such as transparent PEDOT:PSS electrode with Ag electrode line. Thus, a transparent piezoresistive pressure sensor can be achieved, so as to be suitable for sensor with backlight integration with good translucency.

In the present invention, translucency was measured by a WT81 digital lux meter from Shenzhen Wintact Electronics Co., Ltd.

In a preferred embodiment of the present invention, in the electrode array layer, each electrode in each electrode set on a base layer 310 is transparent electrode, such as transparent PEDOT:PSS electrode 320 with Ag electrode wires 332 and 334, as shown in Fig. 3. In the present invention, conductive material can be doped on a separate fabric or the base layer of the artificial leather before full integration or after integration of the artificial leather, which depends on the process condition or needs. The fabrics, such as polyester fabric, can be used alone or replace the original base layer of the artificial leather to form the piezoresistive layer.

In another aspect, the invention provides an electronic control system, comprising, a piezoresistive pressure sensor, which is configured for receiving a touch from a user and generating a signal in response to the touch from the user; an executing unit; and an electronic control unit, which is coupled to the piezoresistive pressure sensor and the executing unit respectively, wherein the electronic control unit is configured to regulate the executing unit in response to the signal generated by the piezoresistive pressure sensor.

In the electronic control system, piezoresistive pressure sensor is a sensor capable of converting a measured pressure change into a resistance change. When a pressure is applied to the piezoresistive pressure sensor, a contact level on the piezoresistive fabric layer or a contact area between piezoresistive fabric layer and the electrode array layer is increased, so as to make the resistance of the piezoresistive fabric layer changed. The resistance of piezoresistive fabric layer can be varied within a relatively large range according to the actual requirements. For example, the resistance of the piezoresistive fabric layer is varying from about 10 GQ to 10±5 KQ under 2kgf force with a size of 30 mm x 30 mm (length x width) on I mm gap of two Cu electrodes (Cu tape).

In the electronic control system, executing unit and electronic control unit can be purchased according to the application field of the electronic control system.

In a preferred embodiment of the present invention, the electronic control system is located within a vehicle, a household appliance, a building, a communication device, a garment, or a wearable device.

In a preferred embodiment of the present invention, the piezoresistive pressure sensor is located at a dashboard, a center console, a middle console, or a horn of the vehicle.

In another aspect, the invention provides a process for producing piezoresistive pressure sensor, comprising: a) preparing an electrode array layer comprising a plurality of electrodes and a piezoresistive fabric layer, respectively; and b) disposing the electrode array layer on a first side of the piezoresistive fabric layer, wherein the piezoresistive fabric layer is made of fabric doped with conductive particles, wherein the conductive particles are present in a liquid composition in an amount from 0.05 to 4 wt%, based on total weight of the liquid composition.

In a preferred embodiment of the present invention, the process for producing piezoresistive pressure sensor further comprises c) providing an artificial leather layer, and disposing the artificial leather layer on a second side of the piezoresistive fabric layer. In the presence of the artificial leather layer, the piezoresistive fabric layer can be formed by replacing the original base layer of an artificial leather layer.

In the present invention, the resistance (a representative parameter for the sensitivity property) of the piezoresistive fabric layer is controllable and depends on the user needs and the readout system. The sensitivity (equivalent to the resistance change) of the piezoresistive fabric is in a range of about 10 GQ to 10 kQ (higher than 10 ^A 5 order difference), which makes the piezoresistive pressure sensor sense the pressure more precisely. In a preferred embodiment of the present invention, the resistance of the piezoresistive fabric layer is varying from about 10 GQ to 10±5 kQ, which is measured under 2 kgf force with the piezoresistive fabric size of 30 mm x 30 mm (length x width) on I mm gap of two Cu electrodes (Cu tape).

The piezoresistive pressure sensor according to the present invention may have a total thickness in the range of 0.5 mm to 120 mm, preferably in the range of 1 mm to 100 mm, more preferably in the range of 1.5 mm to 60 mm, and most preferably in the range of 2 mm to 30 mm.

The above definitions and description concerning entire structure of the piezoelectric pressure sensor, the material of the electrode array layer, the continuous piezoresistive fabric layer and the cover layer also apply to the process.

The preparation of the electrode array layer may be conducted by any suitable method known in the art, for example, by printing or coating an ink containing metal particles, or cutting a metal foil.

The electrode array layer, the piezoresistive fabric layer and the cover layer can be laminated together by conventional method, for example, by using adhesive, welding, or fusing under heating. Alternatively, the electrode array layer, the piezoresistive fabric layer and the cover layer can be integrally formed together by conventional method.

The piezoresistive pressure sensor can be used in an electronic control system. The electronic control system comprises the piezoresistive pressure sensor, an executing unit, and an electronic control unit. The piezoresistive pressure sensor is configured for receiving a touch from a user and generating a signal in response to the touch from the user. The user can be a human user, e.g., a driver, a resident, an office occupant, or an operator. The user can also be an automated machine or system, e.g., a robot or a driverless vehicle system. The touch can be instant or have a duration of time. The touch can be time dependent. In some cases, the touch is a gesture. The signal can be in the form of a waveform of current, voltage, or combination thereof. The signal can be generated as a function of the pressure imposed.

The electronic control unit is coupled to the piezoresistive pressure sensor and the executing unit respectively. The electronic control unit can regulate the executing unit in response to the signal generated by the piezoresistive pressure sensor. The electronic control unit can be in the form of a multi-core processor, a microprocessor, a digital signal processor, or the like. The coupling can be wired or wireless.

According to some embodiments, the electronic control system is located within a vehicle, a household appliance, a building, a communication device, a garment, or a wearable device. The electronic control system can control environmental variables or physical quantities, e.g., humidity, temperature, pressure, wind speed, ventilation, luminance, sound, power, tension, magnitude of vibration or rotation. The electronic control system can output signals or other forms of information, such as, text, audio, video, and emergency calls.

The electronic control system can allow a user, for example, a driver, to control the vehicle. As an example, when the electronic control system is used within a vehicle, it can be located at a dashboard, a center console, a middle console, or a horn of a vehicle.

The present invention will now be described with reference to Examples and Comparative Examples, which are not intended to limit the present invention.

Example

Starting materials:

Plain woven fabric and stockinette stitch woven fabric are made from PE fibers.

Non-woven fabric is made from PE fibers by thermal bonding, from BASF SE.

PEDOT:PSS: commercial product from Heraeus, having a conductivity (dried layer) around 200 S/cm and a solid content of 3.5 wt% (liquid composition);

Base layer of the electrode array layer: commercial polyethylene terephthalate film; Ag paste: MicroPE PG-007 conductive silver ink for printed electronics from Paru Co., Ltd, South Korea.

Artificial leather layer: artificial leather Haptex®, from BASF SE.

Test Methods:

Resistance was determined by Keithley 2636B SYSTEM SourceMeter with 5 V voltage. For each resistance measurement, tests were performed three times and an average resistance was recorded as the final result.

Distance between the edges of two neighboring electrodes in an electrodes set was determined by measuring the gap of two electrodes.

I. Preparation of the pressure sensor consisting of a piezoresistive fabric layer and an electrode array layer:

Piezoresistive fabric layer was fabricated by manually applying 10 g of PEDOT:PSS solution (3.5 wt% of PEDOT:PSS in H2O, from Heraeus) via dip coating to a sheet of PE fabric. Then, the coated PE fabric was dried for 30min at 100 °C under vacuum, to obtain the piezoresistive fabric layer.

The electrode array layer was formed by coating the Ag paste on a polyethylene terephthalate film as base layer to obtain Ag wire which was connected to the electrodes of each electrodes set on the base layer. Then, the piezoresistive fabric layer and the electrode array layer were laminated by 3M ^TM Scotch-Weld™ epoxy adhesive. In the following examples, the obtained pressure sensor had 160 electrode sets in a 16 x 10 arrangement (i.e. , 16 sets in each row in 105 mm length direction and 10 sets in each row in 70 mm width direction) and the distance between the two neighboring sets was 0.5 mm. In the examples, the distance between the two electrodes was fixed at 0.5 mm.

The electrode array layer was laminated with the piezoresistive fabric layer to form a pressure sensor.

1. Translucency test of the pressure sensors having different types of piezoresistive fabric layer:

The preparation method of the piezoresistive fabric layers is similar as above. Lux meter is used to measure the translucency of the piezoresistive fabric.

In this test, Keithley 2612B SYSTEM SourceMeter was used to measure resistance with 2 kgf. 5V of voltage and 1 mm gap of Cu electrode in Keithley 2612B SYSTEM SourceMeter were applied when measuring the resistance. The translucency of the pressure sensor was measured by the Lux meter.

The resistance and the translucency measurements of the pressure sensor proceeded under the following conditions:

The above PEDOT:PSS was used as conductive material as formulation 1 (containing 3.5 wt% of conductive particles ), and the above PEDOT: PSS diluted in a PEDOT: PSS-to-thinner ratio of 1 :15 was used as formulation 2 (containing 0.23 wt% of conductive particles).

PE fabrics had a size of 30 mm x 30 mm (length x width) with different thickness, as shown in table 1.

The PE fabrics used were stockinette stitch woven fabric and non-woven fabric.

Ref light intensity = 51400 Lx

Target Min Resistance = 10±5 kQ

The results were shown in Table 1.

Table 1

From the results, it is clear that the fabric structure, the diameter of fiber for forming the fabric and the thickness of the fabric greatly affect the translucency of the pressure sensors. Thicker fabric made from fibers with a larger diameter has better translucency. In addition, it also can be seen that the doping amount of PEDOT:PSS has great influence on the translucency of the pressure sensors. By adjusting the doping amount of PEDOT: PSS in the defined scope, the pressure sensors can show good translucency.

2. Minimum resistance test of the pressure sensors having different types of piezoresistive fabric layer: The preparation method of the piezoresistive fabric layer is similar as above.

In this test, Keithley 2612B SYSTEM SourceMeter was used to measure resistance with 2 kgf or 0.1 kgf force. 5V of voltage and 1 mm gap of Cu electrode in Keithley 2612B SYSTEM SourceMeter were applied when measuring the resistance.

The resistance measurement of the pressure sensor proceeded under the following conditions:

The above PEDOT:PSS was used as conductive material as formulation 1 (containing 3.5 wt% of conductive particles), and the above PEDOT: PSS diluted in a PEDOT: PSS-to-thinner ratio of 1 :15 was used as formulation 2 (containing 0.23 wt% of conductive particles).

The PE fabrics have a fabric size of 30 mm x 30 mm (length x width) with different thickness, as shown in table 2. The PE fabrics used are plain woven fabric, stockinette stitch woven fabric and non-woven fabric.

The results were shown in Table 2.

Tab e 2

* on/off ratio means the resistance difference between slightly touch (0.1 kgf force) and strong touch (2kgf force). From the results, it can be seen that the fabric structure, the diameter of fiber for forming the fabric and the thickness of the fabric, greatly affect the sensitivity of the pressure sensors.

In addition, it is clear that the doping amount of PEDOT:PSS also has great influence on the sensitivity of the pressure sensors. By adjusting the doping amount of PEDOT : PSS to the defined scope, on/off ratio (sensitivity at 0.1 kgf 12kgf force) is lower, implying that the pressure sensors can show good sensitivity.

3. Min resistance test of the pressure sensors having piezoresistive fabric layer made from plain woven fabric with different diameter and twist of yarns

In this test, Keithley 2612B SYSTEM SourceMeter was used to measure resistance with 2 kgf force. 5 V voltage and 1 mm gap of Cu electrode in Keithley 2612B SYSTEM SourceMeter were applied when measuring the resistance.

The resistance measurement of the pressure sensor proceeded under the following conditions:

The above PEDOT: PSS was used as conductive material as formulation 1 (containing 3.5 wt% of conductive particles).

PE fabrics have a fabric size of 20 mm x 20 mm (length x width) and are made from different diameter and twist of yarns, as shown in table 3. The PE fabrics used are plain woven fabric.

The min resistance results were shown in Table3.

Table 3

From the results, it can be seen that the fabric structure, the diameter and twist of yarn for forming the fabric greatly affect the sensitivity of the pressure sensors. By adjusting the diameter and twist of yarn to the defined scope, sensitivity at 2kgf force is lower, implying that the pressure sensors can show good sensitivity. In addition, it is found that under the same diameter of the yarn, the reliability is degraded, if the twist of yarn is too large. By adjusting the diameter and twist of yarn to the defined scope, the pressure sensors can show good sensitivity and reliability.

II. Preparation of the pressure sensor comprising artificial leather layer as cover layer

The preparation methods of each piezoresistive fabric layer and each electrode array layer are the same as mentioned above under portion I.

The pressure sensor comprising an artificial leather layer as cover layer was prepared as follows: stripping the original base layer of the artificial leather layer; laminating the obtained artificial leather layer with the piezoresistive fabric layer; and laminating the electrode array layer with the piezoresistive fabric layer.

Similarly, the pressure sensors can show sufficient sensitivity and reliability in translucency test and min resistance test.

The structures, materials, compositions, and methods described herein are intended to be representative examples of the invention, and it will be understood that the scope of the invention is not limited by the scope of the examples. Those skilled in the art will recognize that the invention may be practiced with variations on the disclosed structures, materials, compositions and methods, and such variations are regarded as within the ambit of the invention. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims.