LU93175B1 - Sensor - Google Patents

Abstract

This document teaches a piezoresistive device comprising an upper contact and a lower contact with an upper piezoresistive layer in contact with the upper contact and a lower piezoresistive layer in contact with the lower contact. A spacer separates the upper piezoresistive layer from the lower piezoresistive layer. An air gap is located between the two spacer. Figure for publication with 1B 93175

Description

Description

Title:_Sensor [0001] The invention relates to a sensor for measuring a range of pressures and forces.

Background to the Invention [0002] A sensor measures pressure (gases or liquids), forces or impact applied to a surface of the sensor. The pressure is an expression of the force that is required to stop the fluid from expanding, and is usually measured in terms of a force per unit area. The sensor usually acts as a transducer and generates a change in an electrical signal as a function of the pressure imposed on its surface.

[0003] The sensors can be used for control and monitoring in numerous applications, as is set out below.

Prior Art [0004] Sensors known in the art use many types of technologies. The design chosen is based on performance, suitability for the particular application as well as cost. One example of the sensors is a piezoresistive force sensor. Such piezoresistive force sensors use the piezoresistive effect of bonded or formed strain gauges to detect strain due to applied pressure and resistance of a pressure sensitive changing as the applied pressure deforms the pressure sensitive material. The pressure sensitive materials include but are not limited to monocrystalline silicon, polysilicon thin film, bonded metal foils, thick films, and sputtered thin film. Previously, such strain gauges were connected in one arm of a Wheatstone bridge circuit to maximize the output of the pressure sensor and to reduce sensitivity to errors. More recently, such sensors can be connected directly to a microprocessor.

[0005] The piezoresistive sensors have the disadvantage that they have a limited dynamic range which depends on the type of pressure sensitive material used and its composition. The piezoresistive sensors can be used, for example, for measuring large forces with a low degree of precision, or weak forces with a high degree of precision, but not both at the same time. Such sensors have therefore a limited range of uses.

[0006] Numerous patent documents are known which describe pressure sensors and force sensors. For example, European Patent No. 0 549 807 teaches a sensor which uses a plurality of components to measure in multi-dimensional directions.

[0007] International Patent Application No. WO 2016/102689 (Haydale Graphene Industries) discloses a piezoresistive device and pressure sensors which incorporate such devices. The piezoresistive device comprises a piezoresistive material positioned between an upper conductive layer and a lower conductive layer. The piezoresistive material comprises carbon nanoparticles, such as graphene nanoplatelets, graphene or carbon nanotubes, dispersed in a polymer matrix material.

[0008] There is a need to develop a sensor which has a wider dynamic range than prior art sensors.

Summary of the Invention [0009] This doscument teaches a piezoresistive device comprising an upper contact and a lower contact with an upper piezoresistive layer in contact with the upper contact and a lower piezoresistive layer in contact with the lower contact. A spacer separates the upper piezoresistive layer from the lower piezoresistive layer. An air gap is located between the two spacers.

[0010] This document teaches also a piezoresistive sensor comprising a substrate having a planar surface and a plurality of piezoresistive layers (as detection elements) having differing properties arranged on the planar surface. The piezoresistive layers are connected to a processor, which uses the changes in electrical signals generated by the piezoresistive layers to calculate the force on the sensor and can therefore also calculate a pressure. The sensor has therefore a much wider range of detection than prior art sensors as the different piezoresistive sensors can measure different dynamic ranges.

[0011] In one aspect, the piezoresistive sensor has the plurality of piezoresistive detection elements arranged in a stack and in another aspect, the plurality of piezoresistive detection elements are laterally disposed over the planar surface.

[0012] The piezoresistive layer is made from a material such as, but not limited to, carbon black, graphene or carbon nanotubes embedded in a polymer matrix.

Description of the Figures [0013] Figs. 1A and IB show two versions of a piezoresistive sensor.

[0014] Figs. 2A and 2B show a sensor made with a stack.

[0015] Figs. 3 A and 3B show a sensor with distributed sensor materials.

[0016] Fig 4 shows a further aspect of the sensor.

[0017] Fig. 5 shows the results of a force/resistance measurement of the piezoresistive sensor of Fig. IB.

Detailed Description of the Invention [0018] The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention.

[0019] Fig. 1A shows a basic piezoresistive sensor 10 as used in this sensor of this description. The piezoresistive sensor 10 has a pressure sensitive layer 20 sandwiched between two contacts 30a and 30b. The piezoresistive effect causes a change in the electric signal due to a change in resistance between the two contacts 30a and 30b which can be measured by a measuring device 40, which could be incorporated into a computer or another processor. The measured value of the potential difference indicates the force applied to the pressure sensitive layer 20. Tables in the measuring device 40 allow the force to be calculated and displayed on a display device 50.

[0020] Another type of piezoresistive sensor 10 is shown in Fig. IB. This piezoresistive sensor 10 differs from the piezoresistive sensor 10 of Fig. 1A in that the pressure sensitive layer 20 is in fact formed of two pressure sensitive layers 20a and 20b. The upper pressure sensitive layer 20a is connected to the upper contact 30a and the lower pressure sensitive layer 20b is connected to the lower contact 30b. The upper pressure sensitive layer 20a is separated from the lower sensitive layer 20b by a spacer 25. The spacer 25 is, for example, ring-shaped, rectangular shaped or square shaped, but this shape is not limiting of the invention. The size of the inner area 26 of the spacer 25 controls the active area of the piezoresistive sensor 10. An air space 27 is formed between the spacers 25. This air space 27 has been found by the inventors to increase the sensitivity of the piezoresistive sensor 10.

[0021] It will be appreciated that the structures shown in Figs. 1A und IB are only representative of the invention. Other sensors structures can be used with differing dimensions, and shapes to change or increase the range of sensitivity of the piezoresistive sensor 10. It will also be appreciated that the shape, size and structure of the sensitive layer 20 also results in changes in the range of operation and the sensitivity of the piezoresistive sensor 10.

[0022] Figs. 2A and 2B show a side view of a first aspect of the sensor of this document in which multiple layers of pressure sensitive layers 20a-d are stacked on top of each other in the form of a stack 35 on a substrate 15 and are separated by contacts 30a-e. In Fig. 2A the pressure sensitive layers 20a-d have the same shape and size, whereas in Fig. 2B the pressure sensitive layers 20a-d have different shapes, sizes and thicknesses. In both Figs. 2A and 2B four of the pressure sensitive layers 20a-d are shown, but this is not limiting of the invention.

[0023] Another aspect of the piezoresistive sensor 10 is shown in Figs. 3A and 3B in which a top view of the substrate 15 is shown on which a plurality of piezoresistive sensors lOa-d of similar size or a further plurality of pressure sensitive layers lOe-h having different sizes and thicknesses are disposed. The piezoresistive sensors lOa-h can be either of the design shown in Fig. 1A or IB.

[0024] Fig. 4 shows a further aspect of the sensor incorporating the stack 35 of Figs. 2A and 2B with the lateral disposition of the pressure sensitive layers shown in Figs. 3A and 3B.

[0025] The substrate 15 is in one aspect of the sensor a polymer substrate, such as but not limited to polyimide (PI), polyethylene naphthalate (PEN) or polyethylene terephthalate (PET). The substrate 15 could be a silicon substrate or a glass substrate.

[0026] The pressure sensitive layers 20a-d are from carbon black in a polymer matrix, such as PU, PDMS or PVDF but not limited to . It would also be possible to use as a pressure sensitive layer 20a-d made from graphene nanoplatelets, graphene or carbon nanotubes, embedded with a polymer matrix material, such as but not limited to a vinyl polymer matrix.

[0027] The contacts 30 are made of silver, copper or other conductive materials.

[0028] The piezoresistive sensor 10 is - for example - produced by a roll-to-roll printing process using screen printing or/and flexographic printing or sheet-to-sheet printing. The contacts 30 can be printed, evaporated or coated. It will be appreciated that other methods of manufacturing the piezoresistive sensor 10 are known and can be employed without limitation.

Examples [0029] The piezoresistive sensor 10 as shown in Fig. IB was constructed with contacts 30a and 30d made of silver and a having a thickness of 3pm. The pressure sensitive layers 20a and 20b are made of carbon black embedded in the polymer matrix and have a thickness of approx. 8 pm. The spacer 25 is square-shaped with a dimension of lxl mm and a width of 200 pm so that the active inner area of the spacer 25 was limited to 800x800 pm. The spacer 25 is made of a PET film with a thickness of approx. 23 pm.

[0030] Fig. 5 shows a result of the force / resistance measurement of this piezoresistive sensor 10.

[0031] Examples for the uses of such sensor, in addition to monitoring applications, include use in boxing to monitor force and pressure, the monitoring of correct posture by weight-lifting. Such sensors can also be placed in athletic footwear or medical devices to measure motion and pressure exerted as well as on rowing blade, skis, baseball bats, cricket bats, golf clubs, etc. The sensors are also used in logistics for monitoring the weight and load distribution of goods.

Reference Numerals 10 Piezoresistive sensor 15 Substrate 20a-d Pressure sensitive layer 25 Spacer 26 Inner area 27 Air space 30a-d Contacts 35 Stack 40 Measuring device 50 Display device

Claims (8)

Claims 1. A piezoresistive device (10) comprising: an upper contact (30a) and a lower (30b) contact; an upper piezoresistive layer (20a) in contact with the upper contact (30a); a lower piezoresistive layer (20b) in contact with the lower contact (30b); a spacer (25) separating the upper piezoresistive layer (20a) from the lower piezoresistive layer. 2. The piezoresistive device according to claim 1, wherein at least one of the upper piezoresistive layers (20a) or the lower piezoresistive layers (20b) is made of a group of piezoresistive materials consisting of carbon black, graphene or carbon nanotubes in a polymer matrix. A piezoresistive sensor (10) comprising: a substrate (15) having a planar surface; a plurality of piezoresistive sensing elements (20a-d) interposed between contact layers (30a-e), wherein one or more of the plurality of piezoresistive sensing elements (20a-d) have different characteristics and are disposed on the planar surface of the substrate (15) are. The sensor (10) of claim 3, wherein the plurality of piezoresistive sensing elements (20a-d) are arranged in a stack (35). The sensor (10) of claim 3 or 4, wherein the plurality of piezoresistive sensing elements (30a-3) are disposed laterally over the planar surface (15). The sensor (10) of any one of claims 3 to 5, wherein the substrate (15) is a polymer substrate. The sensor (10) of any one of claims 3 to 6, wherein the piezoresistive sensing elements (20a-d) are selected from a group of piezoresistive elements consisting of carbon black, graphene or carbon nanotubes in a polymer matrix. The sensor (10) of any one of claims 3 to 7, further comprising at least one spacer (25) disposed between two of the piezoresistive sensing elements (20a-d) to form an air gap (27).