A piezoresistive sensor and a method of manufacturing the same

Abstract

The application relates to the field of pressure sensors, in particular to a piezoresistive sensor and a preparation method thereof. The piezoresistive sensor comprises a sensor body, the sensor body comprises a flexible substrate, electrode sheets located at both ends of the flexible substrate, and a detection net located on the flexible substrate, the end of the detection net is located on the electrode sheet, the sensor body further comprises an elastic thermal expansion layer located on the surface of the detection net, and the elastic thermal expansion layer is dispersed with graphene particles; the piezoresistive sensor further comprises a heat generation mechanism for supplying heat to the elastic thermal expansion layer, the heat generation mechanism is located outside the sensor body, the heat generation mechanism comprises an electric control switch, a power supply and an electric heating wire, the electric control switch, the power supply and the electric heating wire are electrically connected in series, and a heat transfer component is connected between the electric heating wire and the elastic thermal expansion layer. The application further discloses a preparation method of the piezoresistive sensor. The scheme solves the problem that the flexible substrate and the detection net are not easy to recover after being subjected to pressure in a low-temperature environment, and improves the accuracy of the sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pressure sensor, in particular to a piezoresistive sensor and a preparation method thereof. BACKGROUND

[0002] The pressure sensor is a device or apparatus that can sense the pressure signal and convert the pressure signal into an electrical signal according to certain rules. There are many types of pressure sensors, among which the piezoresistive pressure sensor has the advantages of high sensitivity, large measurement range, simple structure, etc.

[0003] As shown in Figure 1 and Figure 2 , it is a piezoresistive pressure sensor in the prior art (for example, a piezoresistive pressure sensor with high sensitivity and a preparation method thereof disclosed in the invention patent with the patent application number 201510624235.2), which includes a flexible substrate 1, electrode sheets 3 located at both ends of the flexible substrate 1, and a detection net 2 located on the surface of the flexible substrate 1, and the ends of the detection net 2 are located on the electrode sheets 3. When the flexible substrate 1 of the pressure sensor is subjected to pressure, it deforms, and the flexible substrate 1 drives the detection net 2 to deform, which in turn causes a change in the resistance of the detection net 2. The change in the resistance of the detection net 2 is output through the electrode sheets 3 on both sides. The output resistance value is calibrated with the external applied pressure value, and finally the purpose of measuring the external pressure value is achieved.

[0004] The detection of the above-mentioned pressure sensor is realized by the bending deformation of the flexible substrate 1 and the detection net 2. However, in some cold environments, such as in high-altitude cold regions or in winter, in these low-temperature environments, when the flexible substrate 1 and the detection net 2 are deformed by pressure, their elastic recovery ability becomes poor. In this way, the flexible substrate 1 and the detection net 2 cannot immediately recover to their original shape and remain in a bent state, thereby affecting the normal detection of subsequent pressure and the subsequent use of the pressure sensor, and also affecting the accuracy of subsequent detection. SUMMARY

[0005] The present application aims to provide a piezoresistive sensor and a preparation method thereof to solve the problem that the flexible substrate and the detection net are not easy to recover after being subjected to pressure in a low-temperature environment.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solution: a piezoresistive sensor, comprising a sensor body, the sensor body comprising a flexible substrate, electrode sheets located at both ends of the flexible substrate, and a detection net located on the flexible substrate, the ends of the detection net being located on the electrode sheets, the sensor body further comprising an elastic thermal expansion layer located on the surface of the detection net, and the elastic thermal expansion layer containing dispersed graphene particles.

[0007] The piezoresistive sensor further comprises a heat generating mechanism for supplying heat to the elastic thermal expansion layer, the heat generating mechanism being located outside the sensor body, the heat generating mechanism comprising an electrically controlled switch, a power supply and an electric heating wire, the electrically controlled switch, the power supply and the electric heating wire being electrically connected in series, and a heat transfer component being connected between the electric heating wire and the elastic thermal expansion layer.

[0008] The principle and advantages of the present application are that when pressure acts on the flexible substrate, the flexible substrate and the detection net are bent upward, the bending of the flexible substrate and the detection net presses the elastic thermal expansion layer, the elastic thermal expansion layer shrinks due to its elasticity, so that the deformation of the flexible substrate and the detection net is not affected, and the pressure sensor can normally detect pressure.

[0009] After the pressure detection is completed, in a low-temperature environment, the elasticity of the flexible substrate and the detection net is reduced due to the low temperature, and the recovery ability of the elastic material is poor, so that the flexible substrate and the detection net are difficult to recover after deformation. At this time, the electrically controlled switch is closed, the power supply supplies power to the electric heating wire, the electric heating wire generates heat, and the heat is transferred to the elastic thermal expansion layer through the heat transfer component. Since the elastic thermal expansion layer contains graphene particles inside, the thermal conductivity of graphene is good, so the graphene particles can quickly accept heat and transfer inside the elastic thermal expansion layer, so that the inside of the elastic thermal expansion layer can be heated. According to the principle of thermal expansion and contraction, the parts of the elastic thermal expansion layer that are pressed and recessed expand after being heated, thereby pushing the deformed parts of the flexible substrate and the detection net to reset and recover. At the same time, the elastic thermal expansion layer uniformly transfers heat to the detection net and the flexible substrate, so that the temperature of the detection net and the flexible substrate is raised, and the elastic recovery ability of the detection net and the flexible substrate is also improved. Thus, through the present application, the pressure sensor can be reset as soon as possible to facilitate subsequent normal detection of pressure, without affecting the subsequent use of the pressure sensor, and also avoiding the problem of low detection accuracy caused by the difficulty of the flexible substrate and the detection net to recover after deformation.

[0010] In the present scheme, the elastic thermal expansion layer is provided, and the elastic thermal expansion layer is heated instead of directly heating the flexible substrate and the detection net, because: on the one hand, although the flexible substrate and the detection net can be heated and the elastic recovery ability is good, the flexible substrate and the detection net can only reset according to the elastic deformation of the flexible substrate and the detection net, and cannot be pushed by the outside, so the elastic thermal expansion layer has a pushing effect on the reset of the flexible substrate and the detection net in the present scheme, so that the pressure sensor has better and more timely deformation recovery effect. On the other hand, in the present scheme, after the elastic thermal expansion layer is heated, the heat is rapidly transferred horizontally on the elastic thermal expansion layer due to the good thermal conductivity of the graphene particles, and is also transferred downward to the detection net and the flexible substrate, so that the entire surface of the detection net can be heated at the same time and uniformly, and the entire surface of the flexible substrate can also be heated at the same time and uniformly, avoiding that the detection net and the flexible substrate are always heated at a certain local part, and avoiding that a certain local part is damaged due to early aging after a long time, so as to ensure the physical performance consistency of the entire material of the detection net and the entire material of the flexible substrate, and be beneficial to ensuring the detection accuracy and the service life.

[0011] The heat generating mechanism is located outside the sensor body, and the heat generated by the heating wire is not directly transferred to the elastic thermal expansion layer, but is transferred through the heat transfer component, so that the heat is emitted to the outside during the transfer process, and the temperature of the elastic thermal expansion layer after the heat transfer will not be too high, avoiding that the temperature of the elastic thermal expansion layer transferred is too high and causing damage to the pressure sensor.

[0012] Preferably, as an improvement, the heat transfer component includes a heat transfer plug, and a heat conducting wire is connected between the heat transfer plug and the heating wire. Thus, the heat generated by the heating wire is transferred to the heat conducting wire, and the heat conducting wire transfers the heat to the heat transfer plug, and the heat transfer plug transfers the heat to the elastic thermal expansion layer. The heat transfer component of this structure is simple in structure.

[0013] Preferably, as an improvement, the heat transfer component includes a heat conducting sheet, the heat conducting sheet is located above the elastic thermal expansion layer, and the heat conducting sheet and the elastic thermal expansion layer have a gap therebetween; a plurality of graphene heat conducting protrusions are coated on the surface of the elastic thermal expansion layer, and the graphene heat conducting protrusions are opposite to the heat conducting sheet.

[0014] When the flexible substrate is subjected to pressure, the flexible substrate is bent upward and arches, the stress point of the flexible substrate has the highest arching height, the elastic thermal expansion layer is extruded by the part of the flexible substrate bent upward and arched, the elastic thermal expansion layer is bent upward to make the graphene heat conducting protrusions of the corresponding part move upward, the graphene heat conducting protrusions contact the heat conducting sheet, the heat is transferred from the heat conducting sheet to the graphene heat conducting protrusions, and the graphene heat conducting protrusions transfer the heat to the elastic thermal expansion layer, thereby transferring the heat downward to the detection net and the flexible substrate, and at the same time, the elastic thermal expansion layer is heated and expanded to push the flexible substrate and the detection net to reset downward.

[0015] The heat transfer component with the structure is adopted because the stress points on the flexible substrate are not fixed when the pressure is detected, and thus the positions of the flexible substrate that are bent upward are not fixed. However, no matter where the stress points are, the stress points of the flexible substrate are the positions of the flexible substrate that are bent upward the most, and the upward bending degree of the surrounding area of the stress points is smaller than that of the stress points, and thus the upward bending degree of the position of the elastic thermal expansion layer corresponding to the stress points of the flexible substrate is the largest. In this way, the graphite heat conduction protrusions corresponding to the position of the elastic thermal expansion layer that is bent upward the most can be in contact with the heat conduction sheet, so that the graphite heat conduction protrusions of the position of the elastic thermal expansion layer that is bent upward the most are in contact with the heat conduction sheet and receive heat. The positions of the flexible substrate that are pressed are different, and thus the positions of the elastic thermal expansion layer that are bent upward are different, and the graphite heat conduction protrusions that are in contact with the heat conduction sheet are different, so that the positions of the elastic thermal expansion layer that receive heat are different each time. Compared with the mode in which the heat transfer plug transmits heat to the elastic thermal expansion layer, the positions of the elastic thermal expansion layer that receive heat are not fixed and unique in the present application, and the phenomenon that the local position of the elastic thermal expansion layer is directly heated and is damaged due to long-term heating is avoided, and the service life of the elastic thermal expansion layer is improved.

[0016] Preferably, as an improvement, the bottom of the elastic thermal expansion layer is provided with a plurality of grooves, and the grooves are opposite to the mesh holes of the detection net. In this way, the elastic thermal expansion layer will not be filled into the mesh holes, and the elastic thermal expansion layer is prevented from blocking the mesh holes.

[0017] Preferably, as an improvement, the electrode sheet is made of one of gold, silver, copper, aluminum, platinum or titanium.

[0018] Preferably, as an improvement, the elastic thermal expansion layer is made of one of polydimethylsiloxane, polyethylene terephthalate or polyimide.

[0019] Preferably, as an improvement, the flexible substrate is made of one of polyethylene (PE), polyvinyl chloride (PVC) or LCP.

[0020] To achieve the above object, the present application also adopts the following technical scheme: a preparation method of a piezoresistive sensor, comprising the following steps:

[0021] Step 1, preparing an electrode sheet on a flexible substrate: coating a metal layer on the flexible substrate, and etching the metal layer by using a photolithography technology, so as to prepare an electrode sheet at the end of the flexible substrate;

[0022] Step 2, preparing a detection net: coating a graphene oxide film layer on the surface of the flexible substrate and the electrode sheet, and preparing a grid-shaped graphene oxide film layer by using a photolithography technology; then heating to reduce the grid-shaped graphene oxide film layer, so as to form a grid-shaped graphene net;

[0023] Step 3, preparing the elastic thermal expansion layer: mixing the flexible material, graphene powder particles and dispersant uniformly to form a first slurry, filling the first slurry into the cavity of the mold, drying and shaping and demolding to form the elastic thermal expansion layer;

[0024] Step 4, bonding the elastic thermal expansion layer on the surface of the detection net.

[0025] Therefore, the preparation of the piezoresistive sensor in the present application is realized by using the method, and the sensor with the structure in the present application does not exist in the prior art, so the preparation method is also unique and creative, and therefore the preparation method is also protected by a patent.

[0026] Preferably, as an improvement, in step 3, before drying, a heat transfer plug is inserted into the cavity of the mold; after the first slurry is dried and shaped, the heat transfer plug and the elastic thermal expansion layer are connected together. Therefore, before drying, the first slurry is liquid, the heat transfer plug can be inserted, and after drying, the first slurry is solidified into a solid state, thereby realizing the connection of the heat transfer plug and the elastic thermal expansion layer.

[0027] Preferably, as an improvement, in step 3, after the elastic thermal expansion layer is demolded, a layer of template is provided on the surface of the elastic thermal expansion layer, the template is provided with a plurality of through holes, and a second slurry is coated on the template, the second slurry including carbon black, graphene powder and dispersant;

[0028] After the second slurry is coated on the template, preliminary drying is performed, the drying time is 30 min, and the drying temperature is 30℃; after preliminary drying, the template is removed, and re-drying is performed, the drying time is 30 min, and the drying temperature is 65℃. Therefore, a plurality of graphene heat-conducting protrusions are realized on the surface of the elastic thermal expansion layer at one time. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 FIG. 4 is a vertical sectional view of a piezoresistive sensor in the prior art.

[0030] Figure 2 FIG. 5 is a top view of a piezoresistive sensor in the prior art.

[0031] Figure 3 FIG. 6 is a vertical sectional view of a piezoresistive sensor in Example 1.

[0032] Figure 4 FIG. 7 is a vertical sectional view of a piezoresistive sensor in Example 2.

[0033] Figure 5 FIG. 8 is a top view of a template in Example 2. DETAILED DESCRIPTION

[0034] The following will be further described in detail through specific embodiments:

[0035] The reference signs in the attached drawings of the specification include: flexible substrate 1, detection net 2, electrode sheet 3, second carrier 4, heat conduction sheet 5, first carrier 6, elastic thermal expansion layer 7, graphene particle 8, graphene heat conduction bump 9, template 10, through hole 11, heat transfer plug 12.

[0036] Embodiment 1

[0037] The pressure resistance sensor basically as shown in the attached Figure 3 The pressure resistance sensor basically as shown in the attached Figure 2 The pressure resistance sensor basically as shown in the attached

[0038] The pressure resistance sensor further includes a heat generating mechanism (not shown in the figure) for supplying heat to the elastic thermal expansion layer 7, which is located outside the sensor body. The heat generating mechanism includes an electrically controlled switch, a power supply and an electric heating wire, which are electrically connected in series. In actual application, the heat generating mechanism is far away from the sensor body, for example, the distance is controlled between 10-20 cm. A heat transfer component is connected between the electric heating wire and the elastic thermal expansion layer 7, through which the heat generated by the electric heating wire can be transferred to the elastic thermal expansion layer 7.

[0039] The heat transfer component in this embodiment includes a metal heat transfer plug 12, which is inserted into the elastic thermal expansion layer 7. A heat conduction wire (not shown in the figure) is connected between the heat transfer plug 12 and the electric heating wire. Since the distance between the heat generating mechanism and the sensor body is between 10-20 cm, the length of the heat conduction wire is also between 10-20 cm. Thus, after the electric heating wire generates heat, the heat is transferred to the heat conduction wire, which in turn transfers the heat to the heat transfer plug 12. The heat transfer plug 12 transfers the heat to the elastic thermal expansion layer 7, and the heat is transferred through the graphene particles 8 in the elastic thermal expansion layer 7 to disperse in the elastic thermal expansion layer 7.

[0040] The electrode sheet 3 in this embodiment is made of one of gold, silver, copper, aluminum, platinum or titanium.

[0041] The elastic thermal expansion layer 7 in this embodiment is made of one of polydimethylsiloxane, polyethylene terephthalate or polyimide.

[0042] The flexible substrate 1 in the embodiment is a sheet made of one of polyethylene (PE), polyvinyl chloride (PVC) or LCP.

[0043] Figure 3 The first carrier 6 for supporting and fixing the sensor is also shown in the figure (the first carrier 6 does not belong to the sensor part).

[0044] Meanwhile, the embodiment also discloses a preparation method of the piezoresistive sensor, mainly a preparation method of the sensor body, which comprises the following steps:

[0045] Step 1: Preparing the electrode sheet 3 on the flexible substrate 1: coating a metal layer on the flexible substrate 1, coating photoresist layers on both ends of the metal layer respectively, and patterning; then etching the metal layer not covered by the photoresist layers; then removing the photoresist layers, and the metal layer directly below the photoresist layers forms the electrode sheet 3. In the embodiment, the electrode sheet 3 is located at both ends of the top surface of the flexible substrate 1.

[0046] Step 2: Preparing the detection net 2: coating a graphene oxide film layer on the surface of the flexible substrate 1 and the electrode sheet 3, and preparing a grid-shaped graphene oxide film layer by using a photoetching technology. The specific preparation steps are as follows: coating photoresist layers on the top surface of the flexible substrate 1 and the top surface of the electrode sheet 3 respectively, and patterning; the photoresist layers are distributed in an array on the top surface of the flexible substrate 1, and have gaps between adjacent photoresist layers; then spin-coating a graphene oxide film layer on the exposed electrode sheet 3, the surface of the flexible substrate 1 and the photoresist layers respectively; then removing the photoresist layers and the graphene oxide film layers on the photoresist layers, so as to prepare a grid-shaped graphene oxide film layer on the flexible substrate 1.

[0047] Finally, heating is performed to reduce the grid-shaped graphene oxide film layer to form a grid-shaped graphene net. Nitrogen is used as a protective gas during the reduction operation, which can prevent the graphene oxide from being not reduced thoroughly and the metal electrodes at both ends from being oxidized.

[0048] Step 3, preparation of the elastic thermal expansion layer 7: the flexible material (one of polydimethylsiloxane, polyethylene terephthalate or polyimide, and the preferred material in this embodiment is polydimethylsiloxane), graphene powder particles and dispersant are mixed and stirred uniformly to form a first slurry (the weight ratio of the flexible material, graphene powder particles and dispersant is 90:5:5), the first slurry is filled into the cavity of the mold for preparing the elastic thermal expansion layer 7, and the heat transfer plug 12 is inserted into the mold cavity (it is easily understood that in order to avoid the heat transfer plug 12 from tilting in the mold and to ensure the vertical state, the inner wall of the mold cavity is provided with a limiting slot for fixing the heat transfer plug 12), and then the mold is dried and demolded, the drying temperature is 50°C, and the drying time is 2h, thereby the elastic thermal expansion layer 7 is prepared. Since the heat transfer plug 12 is inserted into the mold, the heat transfer plug 12 is connected together after the elastic thermal expansion layer 7 is dried and solidified.

[0049] Step 4, the bottom of the elastic thermal expansion layer 7 is adhered to the surface of the detection net 2 using a glue solution.

[0050] The sensor is applied to a robot working in a low-temperature environment, and the robot is installed with the sensor at the first carrier 6. After the sensor is installed, a heat generating mechanism is installed on the robot, and a heat conducting wire is connected between the heating wire and the heat transfer plug 12.

[0051] When pressure acts on the flexible substrate 1, the flexible substrate 1 and the detection net 2 are deformed to bend upward, the bending of the flexible substrate 1 and the detection net 2 extrudes the elastic thermal expansion layer 7, the elastic thermal expansion layer 7 shrinks, so that the deformation of the flexible substrate 1 and the detection net 2 is not affected, and the pressure sensor can normally detect the pressure.

[0052] After the pressure test is completed, in a low-temperature environment, due to the low temperature, the elastic material has poor recovery ability. Therefore, the flexible substrate 1 and the detection mesh 2 will deform and are not easy to recover and reset. At this time, the electric control switch is closed (the electric control switch can be automatically controlled according to the temperature sensor detection and the set PLC program). The power supply supplies power to the heating wire, the heating wire generates heat, and the heat is transferred to the heat transfer plug 12 through the heat conduction wire. The heat transfer plug 12 then transfers the heat to the elastic thermal expansion layer 7. Since the elastic thermal expansion layer 7 contains graphene particles 8, the graphene... With good thermal conductivity, the graphene particles 8 can quickly absorb heat and transfer it within the elastic thermal expansion layer 7, dispersing the heat and allowing it to heat up. According to the principle of thermal expansion and contraction, the elastic thermal expansion layer 7 expands upon heating, pushing the flexible substrate 1 and the detection mesh 2 downwards to achieve their reset. Simultaneously, the elastic thermal expansion layer 7 also transfers heat to the detection mesh 2 and the flexible substrate 1, increasing their temperature and improving their elastic recovery ability. Thus, the improved elastic recovery ability of the detection mesh 2 and the flexible substrate 1 due to heating, along with the downward pushing action of the elastic thermal expansion layer 7, allows the pressure sensor to reset quickly, facilitating normal subsequent pressure detection without affecting its use. This also avoids the accuracy problems caused by the flexible substrate 1 and the detection mesh 2's deformation and difficulty in recovery.

[0053] Example 2

[0054] In Example 1, the part of the elastic thermal expansion layer 7 that receives external heat is the part where the heat transfer plug 12 is inserted. This part is always receiving heat, and over time, this part is prone to aging and damage.

[0055] Therefore, the heat transfer component in this embodiment differs from that in Embodiment 1, and is combined with... Figure 4 As shown, the heat transfer component in this embodiment includes a heat-conducting sheet 5, which is located above the elastic thermal expansion layer 7. Figure 4 The heat-conducting sheet 5 is mounted on the second carrier 4 (the second carrier 4 is not part of the structure of this sensor, but is a support structure for the heat-conducting sheet 5 on the robot). There is a gap between the heat-conducting sheet 5 and the elastic thermal expansion layer 7. Multiple graphene thermally conductive bumps 9 are coated on the surface of the elastic thermal expansion layer 7, and the graphene thermally conductive bumps 9 are opposite to the heat-conducting sheet 5.

[0056] The difference between the sensor fabrication method and the method in Example 1 lies in step 3. In step 3, after demolding the elastic thermal expansion layer 7 (at this time, the heat transfer plug 12 is not provided on the elastic thermal expansion layer 7), a template 10 is set on the surface of the elastic thermal expansion layer 7, combined with... Figure 5As shown, the template 10 is provided with a plurality of through holes 11, the aperture of the through holes 11 is 0.5mm, the second slurry is coated on the template 10, the second slurry includes carbon black, graphene powder and dispersant, the weight ratio of carbon black, graphene powder and dispersant is 75:20:5, the three are mixed and stirred to form the second slurry. After the second slurry is coated on the template 10, it is put into a drying box for preliminary drying, the drying time is 30min, and the drying temperature is 30℃, so that the graphene heat-conducting protrusions 9 are initially formed; after preliminary drying, the template 10 is taken out for re-drying, the drying time is 30min, and the drying temperature is 65℃, so that the graphene heat-conducting protrusions 9 are relatively stable on the elastic thermal expansion layer 7. Thus, a plurality of graphene heat-conducting protrusions 9 are arranged on the surface of the elastic thermal expansion layer 7.

[0057] In actual use, the stress position on the flexible substrate 1 is not fixed. No matter where the stress position of the flexible substrate 1 is, the stress position of the flexible substrate 1 is the highest position of the upward arching of the flexible substrate 1, and the upward arching degree of the area around the stress position is smaller than that of the stress position. In this embodiment, since the upward arching of the flexible substrate 1 extrudes the elastic thermal expansion layer 7, the upward arching degree of the part of the elastic thermal expansion layer 7 corresponding to the stress point of the flexible substrate 1 is also the largest. Thus, the graphene heat-conducting protrusions 9 corresponding to the part of the elastic thermal expansion layer 7 with the largest upward arching can contact the heat-conducting sheet 5, so that the graphene heat-conducting protrusions 9 of the part of the elastic thermal expansion layer 7 with the largest upward arching contact the heat-conducting sheet 5 and receive heat. When the flexible substrate 1 is extruded at different positions, the part of the elastic thermal expansion layer 7 that arches upward is also different, and the graphene heat-conducting protrusions 9 that contact the heat-conducting sheet 5 are also different, so that the part of the elastic thermal expansion layer 7 that receives heat is also different each time. Compared with the mode in which the heat transfer plug 12 transfers heat to the elastic thermal expansion layer 7 in embodiment 1, the part of the elastic thermal expansion layer 7 that receives heat in this scheme is not fixed and unique, and the upper surface of the entire elastic thermal expansion layer 7 can receive heat, which avoids the phenomenon that the elastic thermal expansion layer 7 is always fixed to receive heat and is damaged by long-term heating, and improves the service life of the elastic thermal expansion layer 7.

[0058] Embodiment 3

[0059] The bottom of the elastic thermal expansion layer 7 in this embodiment is provided with a plurality of grooves (not shown in the figure), and the grooves are opposite to the mesh holes of the detection net 2. Thus, the part of the detection net 2 provided with mesh holes is not provided with the elastic thermal expansion layer 7, the elastic thermal expansion layer 7 will not be filled into the mesh holes of the detection net 2, which avoids the elastic thermal expansion layer 7 from blocking the mesh holes, ensures the normal bending and deformation of the detection net 2, and reduces the influence on the pressure detection of the detection net 2.

[0060] The structure in this embodiment is prepared by a method different from that in embodiments 1-2, and the specific preparation method is as follows:

[0061] Step 1, preparing electrode sheet 3 on flexible substrate 1: same as step 1 in example 1.

[0062] Step 2, preparing elastic thermal expansion layer 7: same as step 3 in example 1 or example 2.

[0063] Step 3, preparing detection net 2: applying graphene oxide film layer on the bottom of elastic thermal expansion layer 7, heating, reducing graphene oxide film layer to form graphene layer. During the reducing operation, nitrogen is used as protective gas to prevent graphene oxide from not being reduced thoroughly and the metal electrodes at both ends from being oxidized.

[0064] Then, multiple holes are processed on the bottom of elastic thermal expansion layer 7 by laser drilling (the depth of the holes is greater than the thickness of graphene layer and less than the total thickness of graphene layer and elastic thermal expansion layer 7), the holes are located on graphene layer to form mesh holes, thus multiple mesh holes are processed on graphene layer to form graphene net. Since the depth of the holes is less than the total thickness of graphene layer and elastic thermal expansion layer 7, the holes pass through the bottom of elastic thermal expansion layer 7 without drilling through the whole elastic thermal expansion layer 7, thus forming grooves. Since the mesh holes and grooves are formed at the same time, the grooves are opposite to the mesh holes.

[0065] Step 4, using glue to bond the lower side of elastic thermal expansion layer 7 provided with detection net 2 to the upper surface of flexible substrate 1, and the end of detection net 2 is located on electrode sheet 3.

[0066] The above is only an embodiment of the present application, and the specific technical solutions and / or common knowledge of characteristics in the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in this application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. A piezoresistive sensor comprising a sensor body, the sensor body comprising a flexible substrate, electrode pads at either end of the flexible substrate and a detection web on the flexible substrate, the ends of the detection web being located on the electrode pads, characterised in that: The sensor body further comprises an elastic thermal expansion layer on the surface of the detection net, and the elastic thermal expansion layer is filled with graphene particles; The piezoresistive sensor further comprises a heat generating mechanism for supplying heat to the elastic thermal expansion layer, the heat generating mechanism is located outside the sensor body, and the heat generating mechanism comprises an electrically controlled switch, a power supply and an electric heating wire, the electrically controlled switch, the power supply and the electric heating wire are electrically connected in series, and a heat transfer component is connected between the electric heating wire and the elastic thermal expansion layer; The recessed part of the elastic thermal expansion layer is expanded after being pressed, so as to push the flexible substrate and the deformed part of the detection net to reset and recover.

2. A piezoresistive sensor according to claim 1, wherein: The heat transfer component comprises a heat transfer plug, and a heat conducting wire is connected between the heat transfer plug and the electric heating wire.

3. A piezoresistive sensor according to claim 1, wherein: The heat transfer component comprises a heat conducting sheet, the heat conducting sheet is located above the elastic thermal expansion layer, and a gap is formed between the heat conducting sheet and the elastic thermal expansion layer; a plurality of graphene heat conducting protrusions are coated on the surface of the elastic thermal expansion layer, and the graphene heat conducting protrusions are opposite to the heat conducting sheet.

4. A piezoresistive sensor according to claim 1, wherein: A plurality of grooves are arranged on the bottom of the elastic thermal expansion layer, and the grooves are opposite to the mesh holes of the detection net.

5. A piezoresistive sensor according to claim 1, wherein: The electrode sheet is made of one of gold, silver, copper, aluminum, platinum or titanium.

6. A piezoresistive sensor according to claim 1, wherein: The elastic thermal expansion layer is made of one of polydimethylsiloxane, polyethylene terephthalate or polyimide.

7. A piezoresistive sensor according to claim 1, wherein: The flexible substrate is made of one of polyethylene (PE), polyvinyl chloride (PVC) or LCP.

8. The method of claim 1-7, wherein: The method comprises the following steps: Step 1: Preparing an electrode sheet on a flexible substrate: a metal layer is coated on the flexible substrate, and the metal layer is etched by using a photolithography technology, so as to prepare an electrode sheet at the end of the flexible substrate; Step 2: Preparing a detection net: a graphene oxide film layer is coated on the surface of the flexible substrate and the electrode sheet, and a grid-shaped graphene oxide film layer is prepared by using a photolithography technology; then, the grid-shaped graphene oxide film layer is reduced by heating, so as to form a grid-shaped graphene net; Step 3: Preparing an elastic thermal expansion layer: a flexible material, graphene powder particles and a dispersing agent are uniformly mixed to form a first slurry, the first slurry is filled into a cavity of a mold, and the first slurry is dried and formed, and then the first slurry is demolded, so as to prepare the elastic thermal expansion layer; Step 4: Bonding the elastic thermal expansion layer on the surface of the detection net.

9. The method of claim 8, wherein: In step 3, before drying, the heat transfer plug is inserted into the cavity of the mold; after the first slurry is dried and formed, the heat transfer plug and the elastic thermal expansion layer are connected together.

10. The method of claim 8, wherein: In step 3, after the elastic thermal expansion layer is demolded, a template is arranged on the surface of the elastic thermal expansion layer, a plurality of through holes are arranged on the template, and a second slurry is coated on the template, the second slurry comprises carbon black, graphene powder and a dispersing agent; After the second slurry is coated on the template, preliminary drying is performed, the drying time is 30 min, and the drying temperature is 30°C; after the preliminary drying, the template is removed, and re-drying is performed, the drying time is 30 min, and the drying temperature is 65°C.

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