Composite material, method for its production and use, and piezoelectric sensor

Abstract

The application discloses a composite material, a preparation method and application thereof, and a piezoelectric sensor. The composite material comprises polyvinylidene fluoride microspheres and a flexible matrix material; the polyvinylidene fluoride microspheres are dispersed in the flexible matrix material. The composite material has low modulus and excellent piezoelectric performance.

Description

Technical Field

[0001] This invention relates to a composite material, its preparation method and uses, and a piezoelectric sensor. Background Technology

[0002] Flexible piezoelectric sensors based on polyvinylidene fluoride (PVDF) have broad application prospects in fields such as artificial intelligence and the Internet of Things (IoT). However, compared with inorganic piezoelectric materials, piezoelectric polymers exhibit low piezoelectric properties, resulting in low sensitivity of the fabricated piezoelectric sensors, which limits the application of flexible piezoelectric sensors.

[0003] CN114539601A discloses a method for preparing a three-dimensional porous polyvinylidene fluoride (PVDF) piezoelectric film. A homogeneous transparent solution containing PVDF is allowed to stand to remove air bubbles, yielding a casting liquid. The casting liquid is then cast into a mold to form a liquid film. Micron-sized water mist is sprayed onto the surface of the liquid film, causing initial sedimentation of PVDF molecules and forming a porous PVDF surface layer. The entire mold is then immersed in deionized water, which passes through the porous PVDF surface layer into the PVDF liquid film and exchanges with the organic solvent, forming a three-dimensional porous PVDF film. The three-dimensional porous PVDF film is then soaked in deionized water and air-dried to obtain the three-dimensional porous PVDF piezoelectric film. The PVDF obtained by this method exhibits poor piezoelectric properties.

[0004] CN114507365A discloses a method for preparing a piezoelectric three-phase composite material based on the synergy of piezoelectric particles and carbon nanotubes. PVDF polymer is poured into a DMF solution until the solution is completely transparent. CNTs are added to the PVDF solution, ultrasonicated, and stirred to disperse the CNTs in the solution. Highly dispersed BCZT powder prepared by the molten salt method is added to the mixed solution at different pulp ratios, ultrasonicated, and stirred to obtain a mixed solution. The mixed solution is poured into deionized water and stirred, resulting in a white flocculent substance. This white flocculent substance is dried; the dried sample is pressed into a disc, placed in a parallel plate mold, and subjected to natural stretching and hot pressing to obtain the piezoelectric three-phase composite material. This piezoelectric material requires a large number of CNTs, resulting in high cost.

[0005] There are some existing methods for preparing polyvinylidene fluoride (PVDF) particles, but none suggest using PVDF particles to prepare piezoelectric materials. Summary of the Invention

[0006] In view of this, one object of the present invention is to provide a composite material having a low modulus and excellent piezoelectric properties. Furthermore, the composite material has a low cost. Another object of the present invention is to provide a simple method for preparing the above-mentioned composite material. A further object of the present invention is to provide uses for the above-mentioned composite material. Yet another object of the present invention is to provide a piezoelectric sensor.

[0007] The above objectives are achieved through the following technical solutions.

[0008] On one hand, the present invention provides a composite material comprising polyvinylidene fluoride microspheres and a flexible matrix material; wherein the polyvinylidene fluoride microspheres are dispersed in the flexible matrix material.

[0009] According to the composite material of the present invention, preferably, based on 100 parts by weight of flexible matrix material, the content of polyvinylidene fluoride microspheres is 10 to 40 parts by weight; the flexible matrix material is selected from one or more of polydimethylsiloxane, styrene block copolymers, and polyurethane thermoplastic elastomers.

[0010] According to the composite material of the present invention, preferably, the polyvinylidene fluoride microspheres are obtained by annealing a polyvinylidene fluoride microsphere preform at 80-200°C to obtain polyvinylidene fluoride microspheres.

[0011] According to the composite material of the present invention, preferably, the polyvinylidene fluoride microsphere preform is obtained by phase separation method.

[0012] According to the composite material of the present invention, preferably, the polyvinylidene fluoride microsphere preform is obtained by the following method:

[0013] A first solution, comprising polyvinyl alcohol and polyvinylidene fluoride (PVDF) as poor solvents, is added dropwise to a second solution, comprising polyvinyl alcohol, PVDF, and PVDF as good solvents, which is stirred. The temperature of the second solution is 30–98°C.

[0014] In the composite material according to the present invention, preferably, the poor solvent for polyvinylidene fluoride is water, and the good solvent for polyvinylidene fluoride is selected from one or more of N,N-dimethylformamide and N,N-dimethylacetamide.

[0015] On the other hand, the present invention provides a method for preparing the above-mentioned composite material, comprising the following steps:

[0016] Raw materials including flexible matrix material and polyvinylidene fluoride microspheres are mixed to obtain a first mixture; the first mixture is mixed with a curing agent to obtain a second mixture; the second mixture is cast and then cured to obtain a composite material.

[0017] According to the preparation method of the present invention, preferably, the curing agent is selected from one or more of methylvinylcyclosiloxane, tetra(butenyl)palladium(O) and photosensitizer; the mass ratio of flexible matrix material to curing agent is 10:(0.2-2); and the curing temperature is 60-95℃.

[0018] In another aspect, the present invention provides the use of the above-mentioned composite material in the preparation of piezoelectric sensors.

[0019] In another aspect, the present invention provides a piezoelectric sensor, comprising a first electrode, a second electrode, the aforementioned composite material, and a flexible encapsulation housing;

[0020] The composite material has a first surface and a second surface that are disposed opposite to each other;

[0021] The first electrode is attached to the first surface of the composite material, and the second electrode is attached to the second surface of the composite material. Wires are respectively provided on the first electrode and the second electrode.

[0022] The first electrode, the second electrode, and the composite material are located within the flexible encapsulation housing, and the wire extends from the flexible encapsulation housing.

[0023] This invention disperses polyvinylidene fluoride (PVDF) microspheres in a flexible matrix material to form a composite material. This improves the piezoelectric properties of PVDF and provides a lower modulus, enabling its application in various piezoelectric sensors, particularly flexible piezoelectric sensors. Attached Figure Description

[0024] Figure 1 The diagram shows the piezoelectric properties of the membrane product obtained in Example 1.

[0025] Figure 2 The piezoelectric properties of the membrane product obtained for comparison are shown in the diagram. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] <Composite Materials>

[0028] The composite material of the present invention comprises polyvinylidene fluoride (PVDF) microspheres and a flexible matrix material. The PVDF microspheres are dispersed in the flexible matrix material. In some embodiments, the composite material consists of PVDF microspheres and a flexible matrix material. PVDF is dispersed in the flexible matrix material in the form of microspheres, thus forming a composite material with high piezoelectric properties and a low modulus. The composite material of the present invention achieves good piezoelectric properties without the use of inorganic piezoelectric materials. This may be because the piezoelectric polymer has a low modulus, and under external force, the composite deforms significantly, generating more additional polarization, thereby producing excellent piezoelectric properties.

[0029] The flexible matrix material of this invention is a flexible polymer material. The flexible matrix material can be selected from one or more of polydimethylsiloxane, styrene-based block copolymers, and polyurethane-based thermoplastic elastomers. In some embodiments, the flexible matrix material is polydimethylsiloxane.

[0030] Based on 100 parts by weight of flexible matrix material, the content of polyvinylidene fluoride (PVDF) microspheres is 10–40 parts by weight; preferably, the content of PVDF microspheres is 15–35 parts by weight; more preferably, the content of PVDF microspheres is 25–35 parts by weight. The content of PVDF microspheres has a certain influence on the piezoelectric properties of the composite material. This may be because the PVDF microspheres in the flexible matrix material can be considered as dispersed dipoles. Below a certain doping amount, the modulus of the composite does not change significantly. As the content of PVDF microspheres increases, the dipole content increases. Under a certain external force, the low modulus leads to an increase in the amount of additional polarization, resulting in a large voltage. When the content of PVDF microspheres exceeds the optimal value, the dipole content further increases, but the modulus of the composite increases, resulting in a decrease in the deformation of the composite under the same external force, leading to a decrease in the amount of additional polarization, and thus a low piezoelectric output.

[0031] In addition to polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PVDF) microspheres may also contain a certain amount of piezoelectric ceramics and / or conductive materials. Examples of piezoelectric ceramics include, but are not limited to, barium titanate, lead zirconate titanate, and zinc oxide. Examples of conductive materials include, but are not limited to, silver nanowires, carbon nanotubes, graphene, and graphene oxide.

[0032] The polyvinylidene fluoride (PVDF) content in the PVDF microspheres is greater than or equal to 50 wt%. In some embodiments, the PVDF content is greater than or equal to 70 wt%. In other embodiments, the PVDF content is greater than or equal to 95 wt%.

[0033] According to one embodiment of the present invention, the polyvinylidene fluoride microspheres do not contain any other piezoelectric or conductive materials other than polyvinylidene fluoride.

[0034] The composite material of the present invention may further include fillers. The fillers may be selected from one or more of piezoelectric ceramics and conductive materials. Examples of piezoelectric ceramics include, but are not limited to, barium titanate, lead zirconate titanate, and zinc oxide. Examples of conductive materials include, but are not limited to, silver nanowires, carbon nanotubes, graphene, and graphene oxide.

[0035] The amount of filler used can be less than or equal to 30% of the mass of the flexible matrix material. In some embodiments, the amount of filler used is less than or equal to 20% of the mass of the flexible matrix material. In other embodiments, the amount of filler used is less than or equal to 10% of the mass of the flexible matrix material.

[0036] Polyvinylidene fluoride microspheres and fillers are dispersed in a flexible matrix material.

[0037] Polyvinylidene fluoride (PVDF) microspheres can be obtained by annealing a PVDF microsphere preform at 80–200°C. This process improves the crystallinity of the PVDF microspheres and enhances the piezoelectric properties of the composite material.

[0038] The annealing temperature is preferably 90–155°C; more preferably 110–150°C.

[0039] The annealing time can be 1 to 8 hours; preferably 2 to 6 hours; more preferably 3 to 5 hours.

[0040] Polyvinylidene fluoride (PVDF) microsphere preforms can be obtained through phase separation. Specifically, a first solution comprising polyvinyl alcohol (PVA) and PVDF (a poor solvent) is added dropwise to a second solution comprising PVA, PVDF, and PVDF (a good solvent) under stirring. The temperature of the second solution is 30–98°C. In some embodiments, the first solution may also contain piezoelectric ceramics and / or conductive materials. Examples of piezoelectric ceramics include, but are not limited to, barium titanate, lead zirconate titanate, and zinc oxide. Examples of conductive materials include, but are not limited to, silver nanowires, carbon nanotubes, graphene, and graphene oxide.

[0041] Water is a poor solvent for polyvinylidene fluoride.

[0042] In the first solution, the concentration of polyvinyl alcohol can be 5–50 mg / mL; preferably 10–40 mg / mL; more preferably 15–30 mg / mL. The molecular weight of polyvinyl alcohol can be 500,000–1,000,000; preferably 600,000–900,000; more preferably 700,000–850,000.

[0043] In some embodiments, the first solution consists of polyvinyl alcohol and polyvinylidene fluoride as poor solvents.

[0044] The good solvent for polyvinylidene fluoride (PVDF) can be selected from one or more of N,N-dimethylformamide and N,N-dimethylacetamide. In some embodiments, N,N-dimethylformamide is the good solvent for PVDF. In other embodiments, N,N-dimethylacetamide is the good solvent for PVDF.

[0045] In the second solution, the concentration of polyvinylidene fluoride (PVDF) can be 20–60 mg / mL; preferably 30–50 mg / mL; more preferably 40–45 mg / mL. The molecular weight of PVDF can be 350,000–700,000. In some embodiments, the molecular weight of PVDF is 400,000–600,000. In other embodiments, the molecular weight of PVDF is 500,000–550,000.

[0046] In the second solution, the concentration of polyvinyl alcohol can be 5–50 mg / mL; preferably 10–40 mg / mL; more preferably 15–30 mg / mL. The molecular weight of polyvinyl alcohol is 500,000–1,000,000; preferably 600,000–900,000; more preferably 700,000–850,000.

[0047] In some embodiments, the second solution is composed of polyvinyl alcohol, polyvinylidene fluoride, and a good solvent for polyvinylidene fluoride.

[0048] The stirring speed of the stirring device for stirring the second solution can be 150 to 700 rpm; preferably 200 to 500 rpm; more preferably 300 to 400 rpm.

[0049] The temperature of the second solution can be 30–98°C; preferably 50–98°C; more preferably 80–95°C.

[0050] The volume ratio of the first solution to the second solution can be (1.5-5):1; preferably (2-4):1; more preferably (2.5-3.5):1.

[0051] In some embodiments, the following steps are also included: after the first solution is added dropwise, stirring is continued for 7–18 hours; preferably, stirring is carried out for 10–15 hours; more preferably, stirring is carried out for 12–13 hours to obtain solid polyvinylidene fluoride. The solid polyvinylidene fluoride is washed and then dried to obtain polyvinylidene fluoride microsphere preforms.

[0052] Solid polyvinylidene fluoride (PVDF) can be washed first with water, and then washed with an alcohol. The alcohol can be selected from one or more of methanol, ethanol, propanol, and isopropanol.

[0053] The flexible matrix material can be a cured flexible matrix material. Specifically, the flexible matrix material undergoes a curing reaction with a curing agent to obtain a cured flexible matrix material. The curing agent can be selected from one or more of methylvinylcyclosiloxane, tetra(butenyl)palladium(O), and photosensitizers. Examples of photosensitizers include, but are not limited to, Irgacure 184. The mass ratio of the flexible matrix material to the curing agent is 10:(0.2-2); preferably 10:(0.5-1.5); more preferably 10:(0.8-1.2).

[0054] The composite material of this invention can be a composite membrane. The thickness and shape of the composite membrane are not limited. For example, it can be circular, rectangular, hemispherical, etc.

[0055] The Young's modulus of the composite material of the present invention can be 0.5 to 6 MPa; preferably 1 to 4 MPa. In some embodiments, it is 1.5 to 3.5 MPa. In other embodiments, it is 1.7 to 2.5 MPa.

[0056] <Preparation methods of composite materials>

[0057] The method for preparing the aluminum alloy of the present invention includes the following steps: (1) forming a first mixture; (2) forming a second mixture; and (3) casting and curing. In some embodiments, the method further includes the step of preparing polyvinylidene fluoride microspheres.

[0058] Steps for forming the first mixture

[0059] The raw materials, including a flexible matrix material and polyvinylidene fluoride microspheres, are mixed to obtain a first mixture. Specifically, the flexible matrix material and polyvinylidene fluoride microspheres are stirred at 20–35°C to obtain the first mixture.

[0060] In some embodiments, the raw materials may also include fillers. The fillers may be selected from one or more of piezoelectric ceramics and conductive materials. Examples of piezoelectric ceramics include, but are not limited to, barium titanate, lead zirconate titanate, and zinc oxide. Examples of conductive materials include, but are not limited to, silver nanowires, carbon nanotubes, graphene, and graphene oxide.

[0061] The stirring time can be 7 to 18 hours; preferably 10 to 15 hours; more preferably 12 to 13 hours.

[0062] Steps for forming the second mixture

[0063] The first mixture is mixed with a curing agent to obtain a second mixture.

[0064] The curing agent may be selected from one or more of methylvinylcyclosiloxane, tetra(butenyl)palladium(0), and photosensitizers. Examples of photosensitizers include, but are not limited to, Irgacure 184.

[0065] The mass ratio of flexible matrix material to curing agent is 10:(0.2~2); preferably 10:

[0066] (0.5 to 1.5); more preferably 10:(0.8 to 1.2).

[0067] The first mixture can be mixed with the curing agent by stirring. The stirring time can be...

[0068] The time is 2 to 30 minutes; preferably 5 to 20 minutes; more preferably 10 to 15 minutes.

[0069] After stirring, the mixture can be allowed to stand to degas. The standing time can be 15–60 min; preferably 20–50 min; more preferably 30–40 min.

[0070] Pouring and curing steps

[0071] The second mixture is poured and then cured to obtain a composite material.

[0072] The curing temperature can be 50–100°C. In some embodiments, the curing temperature is 60–90°C. In other embodiments, the curing temperature is 70–80°C.

[0073] The curing time can be 2 to 8 hours; preferably 3 to 6 hours; more preferably 4 to 5 hours.

[0074] Steps for preparing polyvinylidene fluoride microspheres

[0075] The polyvinylidene fluoride (PVDF) microsphere preform was annealed at 80–200°C to obtain PVDF microspheres. The specific annealing temperature and time were as described above and will not be repeated here.

[0076] The preparation method of polyvinylidene fluoride microsphere preforms is as described above and will not be repeated here.

[0077] Applications of composite materials

[0078] The composite material of this invention exhibits high piezoelectric properties and low modulus. Therefore, the composite material of this invention can be used to fabricate piezoelectric sensors, and is particularly suitable for fabricating flexible piezoelectric sensors.

[0079] Depending on the application, piezoelectric sensors can be categorized into piezoelectric pressure sensors, piezoelectric strain sensors, piezoelectric vibration sensors, and piezoelectric acceleration sensors. The composite material of this invention can be applied to all of these types of piezoelectric sensors.

[0080] The working principle of a piezoelectric force sensor is: applying an external force in the vertical direction causes the piezoelectric sensor to change direction at d... 33 Piezoelectric output in a specific direction. Piezoelectric pressure sensors are mainly used for monitoring dynamic pressure, such as pulse and blood pressure, and can also be used in smart home applications, such as burglar alarms.

[0081] The working principle of a piezoelectric strain sensor is: applying a tensile force in the horizontal direction causes the piezoelectric sensor to change direction in the d direction. 31 Piezoelectric output in directional direction. Piezoelectric pressure sensors are mainly used in artificial intelligence, gesture recognition, and monitoring of human joint movement and automotive bearings.

[0082] The working principle of a piezoelectric vibration sensor is as follows: when mechanical vibration acts on the piezoelectric sensor, stress is generated, which causes uneven charge distribution in the piezoelectric material, forming an electric potential. It can be used for monitoring instrument vibration, such as in bridge and highway health inspections, and also for sound recognition.

[0083] The working principle of a piezoelectric accelerometer: Changes in acceleration cause changes in the force applied to the piezoelectric sensor, which in turn generates a change in piezoelectric potential. It has applications in industry, aerospace, and medical fields, such as vibration monitoring of industrial machinery, vibration detection of aircraft and satellites, and monitoring of sports injury rehabilitation processes.

[0084] <Piezoelectric Sensor>

[0085] The piezoelectric sensor of the present invention includes the aforementioned composite material, a first electrode, a second electrode, and a flexible encapsulation shell.

[0086] The composite material has a first surface and a second surface that are arranged opposite to each other.

[0087] The first electrode is bonded to the first surface of the composite material. The first electrode can be selected from copper foil or aluminum foil. A wire is disposed on the first electrode.

[0088] The second electrode is bonded to the second surface of the composite material. The second electrode can be selected from copper foil or aluminum foil. A wire is provided on the second electrode.

[0089] The first electrode, the second electrode, and the composite material are housed within a flexible encapsulation shell. Wires extend from the flexible encapsulation shell. The flexible encapsulation shell can be formed from materials such as thermoplastic polyurethane elastomer, polyimide tape, or polydimethylsiloxane.

[0090] The raw materials are described below:

[0091] The molecular weight of polyvinylidene fluoride is 530,000.

[0092] The molecular weight of polyvinyl alcohol is 820,000.

[0093] The curing agent is methylvinylcyclosiloxane.

[0094] Example 1

[0095] Polyvinyl alcohol and water were mixed to obtain a first solution with a polyvinyl alcohol concentration of 20 mg / mL.

[0096] Polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) were added to an N,N-dimethylacetamide solution to obtain a second solution. In the second solution, the concentration of PVDF was 40 mg / mL and the concentration of PVA was 20 mg / mL.

[0097] The first solution was added dropwise to a second solution at 95°C under stirring. The stirring speed of the device for the second solution was 300 rpm. The volume ratio of the first solution to the second solution was 3:1. After the first solution was completely added, stirring continued for 12 hours to obtain solid polyvinylidene fluoride (PVDF). The solid PVDF was washed three times with deionized water, then three times with ethanol, and dried to obtain PVDF microsphere preforms.

[0098] The polyvinylidene fluoride microsphere preform was annealed at 150°C for 4 hours to obtain polyvinylidene fluoride microspheres.

[0099] 100 parts by weight of polydimethylsiloxane and 30 parts by weight of polyvinylidene fluoride microspheres were stirred at 25°C for 12 hours to obtain a first mixture. The first mixture was then stirred with 10 parts by weight of a curing agent for 10 minutes, followed by standing for 30 minutes to obtain a second mixture. The second mixture was poured into a mold and cured at 80°C for 4 hours to obtain a composite material. The composite material is a composite film.

[0100] Comparative example

[0101] 100 parts by weight of polydimethylsiloxane and 10 parts by weight of curing agent were stirred for 10 minutes, then allowed to stand for 30 minutes to obtain a mixture. The mixture was poured into a mold and then cured at 80°C for 4 hours to obtain a polymer material. The polymer material is a polymer film.

[0102] Experimental Example

[0103] 1. The modulus was tested using the following method:

[0104] The prepared membrane product was placed in the upper jaw of a universal tensile testing machine, and then the lower jaw was moved to a suitable clamping position and the lower end of the membrane product was clamped. The universal tensile testing machine was started, and a tensile force was applied to the membrane product until the sample fractured. The stress-strain data of the membrane product were read. The Young's modulus of the membrane product was calculated from the linear part of the stress-strain. The results are shown in Table 1.

[0105] Table 1

[0106] Example 1 Comparative example Young's modulus (MPa) 1.75 1.68

[0107] 2. The piezoelectric properties of the membrane product were tested using the following method.

[0108] The prepared membrane product was placed in an oil bath for contact polarization under a 15kV electric field for 1 hour. Then, conductive copper foil was cut into 1.5×1.5cm pieces and placed on the top and bottom surfaces of the membrane product as electrodes. External connecting electrodes were prepared by connecting copper wires with silver paste. Finally, piezoelectric nanogenerators were prepared by encapsulation with thermoplastic polyurethane.

[0109] The assembled piezoelectric nanogenerator was placed on a test platform, and a linear motor was used to strike the piezoelectric nanogenerator. The motor output force was set to 20N, and piezoelectric data was collected using a 6517 electrometer.

[0110] Figure 1 and Figure 2 The piezoelectric data graphs are collected under the test conditions of this invention for piezoelectric nanogenerators prepared using different membrane products.

[0111] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A composite material, characterized in that, The composite material includes polyvinylidene fluoride microspheres and a flexible matrix material; the polyvinylidene fluoride microspheres are dispersed in the flexible matrix material; based on 100 parts by weight of flexible matrix material, the content of polyvinylidene fluoride microspheres is 10 to 40 parts by weight. The polyvinylidene fluoride microspheres are obtained by the following method: a first solution comprising polyvinyl alcohol and polyvinylidene fluoride (PVDF) as poor solvents is added dropwise to a second solution comprising polyvinyl alcohol, PVDF, and PVDF as good solvents while being stirred, to obtain a PVDF microsphere preform; the PVDF microsphere preform is annealed at 80–155°C to obtain PVDF microspheres; the temperature of the second solution is 30–98°C.

2. The composite material according to claim 1, characterized in that, Based on 100 parts by weight of flexible matrix material, the content of polyvinylidene fluoride microspheres is 15 to 35 parts by weight; the flexible matrix material is selected from one or more of polydimethylsiloxane, styrene block copolymers, and polyurethane thermoplastic elastomers.

3. The composite material according to claim 1, characterized in that, The poor solvent for polyvinylidene fluoride is water, and the good solvent for polyvinylidene fluoride is selected from one or more of N,N-dimethylformamide and N,N-dimethylacetamide.

4. The method for preparing the composite material according to any one of claims 1 to 3, characterized in that, The steps include the following: Raw materials including flexible matrix material and polyvinylidene fluoride microspheres are mixed to obtain a first mixture; the first mixture is mixed with a curing agent to obtain a second mixture; the second mixture is cast and then cured to obtain a composite material.

5. The preparation method according to claim 4, characterized in that, The curing agent is selected from one or more of methylvinylcyclosiloxane and photosensitizer; the mass ratio of flexible matrix material to curing agent is 10:(0.2~2); the curing temperature is 60~95℃.

6. Use of the composite material according to any one of claims 1 to 3 in the preparation of piezoelectric sensors.

7. A piezoelectric sensor, characterized in that, The piezoelectric sensor includes a first electrode, a second electrode, the composite material as described in any one of claims 1 to 3, and a flexible encapsulation shell; The composite material has a first surface and a second surface that are disposed opposite to each other; The first electrode is attached to the first surface of the composite material, and the second electrode is attached to the second surface of the composite material. Wires are respectively provided on the first electrode and the second electrode. The first electrode, the second electrode, and the composite material are located within the flexible encapsulation housing, and the wire extends from the flexible encapsulation housing.

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