A wire-type stretchable piezoelectric tactile sensor and a method of manufacturing the same

Abstract

The application discloses a wire type stretchable piezoelectric tactile sensor and a preparation method thereof. The stretchable piezoelectric tactile sensor comprises a conductive rubber inner electrode layer, a piezoelectric sensitive layer, an insulating isolation layer, a stretchable outer electrode layer and a flexible encapsulation layer. The piezoelectric sensitive layer wraps the conductive rubber inner electrode layer. The insulating isolation layer wraps the piezoelectric sensitive layer. The stretchable structure outer electrode layer is spirally wound on the piezoelectric sensitive layer. The flexible encapsulation layer wraps the stretchable structure outer electrode layer. The insulating isolation layer and the flexible encapsulation layer are both polydimethylsiloxane films. The tactile sensor has high sensitivity, high resolution, high flexibility, high stability, good stretchability and on-site weaving, and can be widely applied to medical health monitoring, bionic robots, wearable electronic devices and other fields.

Description

Technical Field

[0001] This invention relates to the field of sensors, specifically to a wire-type stretchable piezoelectric tactile sensor and its fabrication method. Background Technology

[0002] According to World Health Statistics, cardiovascular disease is a leading cause of death and disability worldwide. Because cardiovascular disease patients often begin in a sub-healthy state with mild or no obvious symptoms, health monitoring and diagnosis of this population are essential. In medical monitoring systems, pulse and blood pressure are crucial health monitoring parameters. Real-time and accurate monitoring of pulse and blood pressure is vital for disease prevention, diagnosis, and treatment.

[0003] Piezoelectric tactile sensors are electronic devices that use the piezoelectric effect of materials to sense external tactile information. They typically consist of a sandwich-like structure composed of upper and lower electrodes and a piezoelectric sensitive layer. Because piezoelectric materials generate a piezoelectric effect when subjected to pressure, opposite charges are generated on the two opposing surfaces of the material, and the amount of charge is positively correlated with the force applied to the material. This allows for pressure data collection without the need for an external power source. The biggest advantage of flexible piezoelectric tactile sensors over traditional ones is that they maintain high sensitivity and rapid dynamic response characteristics even when bent, folded, twisted, compressed, stretched, or even deformed into arbitrary shapes. Flexible, stretchable, wearable, and breathable piezoelectric sensors sense subtle changes in subcutaneous pulse, providing solutions for personalized healthcare.

[0004] Flexible electrodes are the biggest difference between piezoelectric tactile sensors and traditional tactile sensors, possessing characteristics such as lightweight, flexibility, and stretchability. They are generally assembled using polymer-mixed silver nanowires or ITO conductive films, but ITO conductive films are expensive, difficult to manufacture, and have low flexibility; the preparation of silver nanowires requires a large amount of organic solvents and has a complex process, resulting in low production efficiency. Conductive rubber composites are prepared by adding one or more conductive fillers (carbon black, graphite, metal particles, etc.) to a rubber matrix. They possess excellent tensile strength, adjustable conductivity, high corrosion resistance, and low processing cost, making them ideal electrode materials for flexible piezoelectric tactile sensors.

[0005] The flexible piezoelectric sensitive layer is a key material for flexible piezoelectric tactile sensors, determining the detection of pressure changes. This material needs to meet requirements such as high stiffness, good linearity, fast response, and high sensitivity. Traditional lead zirconate titanate (PZT) piezoelectric ceramics have high piezoelectric coefficients, but their extremely poor toughness makes them unsuitable for flexible sensor applications. Organic piezoelectric materials such as polyvinylidene fluoride (PDVF) have good flexibility, but their piezoelectric coefficients are relatively low (d33 is approximately 10-20 pC / N). Nano-ZnO, however, combines the advantages of high flexibility and high piezoelectric coefficients. Its piezoelectric properties can be further enhanced by doping with elements such as In, Al, and V, or by combining it with PDVF. Furthermore, the morphology-controlled synthesis process for ZnO nanostructures is relatively mature; only process parameters need to be adjusted to obtain surface nanostructures such as ZnO nanorods, nanotubes, and nanoneedles. Moreover, ZnO / PVDF has a higher elastic modulus than human skin (18.8 MPa), making it suitable for wearable tactile sensors.

[0006] Currently, flexible piezoelectric tactile sensors generally employ a sandwich structure (Flexible Self-Powered Tactile Sensors).

[0007] Based on hydrothermally grown ZnO nanorods (Zhang, Guangpan Lu, Ming Chen, Yurong Liu, and Ruohe Yao), it is still not possible to adaptively adjust the sensor according to the signal strength of different detection objects and different detection environments. Improving the flexibility and applicability of the sensor, preparing electrode materials with high elasticity and excellent conductivity, and optimizing and enhancing the piezoelectric properties, processing methods, and preparation procedures of piezoelectric materials remain key scientific and technological problems that need to be solved. Summary of the Invention

[0008] To address the technical problems existing in the prior art, the purpose of this invention is to provide a wire-type stretchable piezoelectric tactile sensor and its fabrication method. The stretchable piezoelectric tactile sensor of this invention utilizes linear conductive rubber as the inner electrode, a spirally wound conductive film as the stretchable outer electrode, a stretchable piezoelectric material as the piezoelectric sensitive layer, and a flexible material as the insulating and encapsulating layer, thus achieving the stretchability of the sensor. The wire-type structure has a high aspect ratio, better air permeability, and can be woven into different shapes on-site according to different application scenarios. Furthermore, it can be better integrated with textiles, effectively improving the sensor's sensitivity, adaptability, and flexibility.

[0009] The present invention is achieved by at least one of the following technical solutions.

[0010] A wire-type stretchable piezoelectric tactile sensor includes a conductive rubber inner electrode layer, a piezoelectric sensitive layer, an insulating layer, a stretchable outer electrode layer, and a flexible encapsulation layer; the piezoelectric sensitive layer encapsulates the conductive rubber inner electrode layer; the insulating layer encapsulates the piezoelectric sensitive layer; the stretchable outer electrode layer is spirally wound around the piezoelectric sensitive layer; and the flexible encapsulation layer encapsulates the stretchable outer electrode layer.

[0011] Furthermore, the conductive rubber inner electrode layer is an elastic linear conductive rubber with a diameter of 1-5 mm.

[0012] Furthermore, the material of the stretchable outer electrode layer is one of silver, gold, and copper.

[0013] Furthermore, the piezoelectric sensitive layer is a composite piezoelectric film with a ZnO nanostructure and a thickness of 2-5 μm.

[0014] Furthermore, both the insulating isolation layer and the flexible encapsulation layer are 100-500nm polydimethylsiloxane (PDMS) films.

[0015] The method for fabricating a wire-type stretchable piezoelectric tactile sensor includes the following steps:

[0016] Conductive rubber is processed into a linear structure with a diameter of 1-5 mm to serve as the inner electrode layer of the sensor.

[0017] The conductive rubber inner electrode layer was ultrasonically cleaned with ethanol and deionized water in sequence, and then dried with nitrogen.

[0018] The conductive rubber inner electrode layer is immersed in a solution containing ZnO nanostructured composite piezoelectric material or a solution containing ZnO nanostructured composite piezoelectric material is coated onto the conductive rubber inner electrode layer and then dried to form a piezoelectric sensitive layer.

[0019] A PDMS thin film insulating and protective layer is formed around the piezoelectric sensitive layer using an immersion or coating process.

[0020] A stretchable outer electrode layer with a spiral winding structure is prepared on the piezoelectric sensitive layer using vacuum evaporation, screen printing and 3D inkjet printing processes.

[0021] A PDMS thin film layer is coated on the stretchable electrode structure as an encapsulation layer.

[0022] Furthermore, the ZnO nanostructure composite piezoelectric material contains one of ZnO, Sn-doped ZnO, Mg-doped ZnO, and V-doped ZnO, and the nanostructure is one of nanoflowers, nanowires, nanorods, and nanosheets, and the ZnO nanostructure is obtained by hydrothermal or high-temperature sintering methods.

[0023] Furthermore, the solution containing the ZnO nanostructure composite piezoelectric material is a mixture of ZnO nanostructure and PDMS.

[0024] Furthermore, the preparation method of the hydrothermal precursor solution for ZnO nanostructures is as follows: 0.05-0.1 mol / L zinc nitrate hexahydrate, 0.05-0.1 mol / L hexamethylenetetramine and 0.01-0.05 mol / L dopant solution are added to deionized water and magnetically stirred for 40 min to mix evenly, thus preparing the precursor solution for the hydrothermal reaction; the dopant solution is one of SnCl4·4H2O, (Mg(NO3)2·6H2O) and VOSO4.

[0025] Furthermore, the preparation method of the ZnO nanostructure and PDMS mixture is as follows: First, mix PDMS and curing agent in a ratio of 10:1-20:1. After mixing evenly, place the mixture in a vacuum drying oven and vacuum to eliminate air bubbles in the PDMS solution. Then, mix ZnO nanostructure and the evenly stirred PDMS solution in a mass ratio of 20-40%, and stir with a glass rod for 10-30 minutes. After stirring, let it stand for later use.

[0026] Compared with existing technologies, the present invention has at least the following beneficial effects:

[0027] (1) The present invention has a wire-type stretchable piezoelectric tactile sensor, which uses conductive rubber as the inner electrode material, which has excellent flexibility and excellent conductivity. Compared with PDMS and PI, conductive rubber has better stretchability. At the same time, the outer electrode is a spirally wound conductive film, with stretchable piezoelectric material as the piezoelectric sensitive layer and flexible material as the insulating isolation layer and encapsulation layer, thus realizing the stretchability of the sensor.

[0028] (2) This invention features a wire-type stretchable piezoelectric tactile sensor with a spiral-wound outer electrode structure to achieve stretchability while minimizing the reduction in piezoelectric charge collection area. The wire-type structure has a high aspect ratio and better air permeability, and can be woven into different shapes on-site according to different application scenarios. It can also be better integrated with textiles, improving the sensor's sensitivity, adaptability, and flexibility.

[0029] (3) The present invention has a wire-type stretchable piezoelectric tactile sensor with PDMS encapsulation material. Compared with PI and epoxy resin, the PDMS-encapsulated sensor will produce a larger deformation and output a larger output voltage under the same external pressure, making it more suitable for pulse detection.

[0030] (4) The tactile sensor described in this invention has the advantages of high sensitivity, high resolution, high flexibility, high stability, good tensile strength and field weaving, and simple process, low cost and easy mass production. It can be widely used in many fields such as medical health monitoring, bionic robots and wearable electronic devices. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of a flexible piezoelectric tactile sensor with a stretchable electrode structure according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the fabrication process of a flexible piezoelectric tactile sensor with a stretchable electrode structure according to an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram illustrating a specific application scenario of an embodiment of the present invention;

[0034] Explanation of reference numerals in the attached figures: 10, conductive rubber inner electrode layer; 20, piezoelectric sensitive layer composed of ZnO nanorod array; 30, insulating isolation layer; 40, stretchable outer electrode layer; 50, flexible encapsulation layer. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0036] like Figures 1-2 As shown, this embodiment of the invention provides a wire-type stretchable piezoelectric tactile sensor. The sensor includes a conductive rubber inner electrode layer 10, a stretchable piezoelectric sensitive layer 20, an insulating layer 30, a stretchable outer electrode layer 40, and a flexible encapsulation layer 50. The piezoelectric sensitive layer 20 encapsulates the conductive rubber inner electrode layer 10; the insulating layer 30 encapsulates the piezoelectric sensitive layer 20; the stretchable outer electrode layer 40 is attached to the stretchable outer electrode layer 20; and the encapsulation layer 50 encapsulates the stretchable outer electrode layer 40.

[0037] In this embodiment, the stretchable piezoelectric sensitive layer 20 includes at least a composite piezoelectric film with a ZnO nanostructure. The ZnO may be one of ZnO, Sn-doped ZnO, Mg-doped ZnO, or V-doped ZnO. The nanostructure may be one of nanoflowers, nanowires, nanorods, or nanosheets; it may also be a stretchable piezoelectric material such as PVDF. The spirally wound conductive film, serving as the stretchable outer electrode layer 40, can be made of silver, gold, or copper. The spirally wound outer electrode structure achieves stretchability while minimizing the reduction in piezoelectric charge collection area. The wire-type structure has a high aspect ratio and better air permeability, allowing it to be woven into different shapes on-site according to different application scenarios. It can also be better integrated with textiles, improving the sensor's sensitivity, adaptability, and flexibility. The insulating layer 30 and the flexible encapsulation layer 50 are PDMS films.

[0038] When the wire-type stretchable piezoelectric tactile sensor is subjected to external pressure, the crystal structure of the stretchable piezoelectric sensitive layer 20 deforms, causing the electric dipole moment to separate. The induced charge accumulates on the electrode 40, and after being amplified by a charge amplifier, the charge signal is converted into a voltage signal and transmitted to the oscilloscope.

[0039] In one embodiment, the conductive rubber inner electrode layer 10 is an elastic linear conductive rubber with a diameter of 1-5 mm. The piezoelectric sensitive layer 20 has a thickness of 2-5 μm.

[0040] The following will be discussed in conjunction with the embodiments and appendices. Figure 2 The preparation method of the flexible piezoelectric tactile sensor with a stretchable electrode structure of the present invention is described in detail.

[0041] Example 1

[0042] Conductive rubber is processed into a linear structure with a diameter of 1-5 mm to serve as the inner electrode of the sensor. This inner electrode layer is then ultrasonically cleaned with ethanol and deionized water for 15 minutes and dried with nitrogen. The conductive rubber inner electrode layer is then immersed in a solution of ZnO nanostructured piezoelectric material, or a solution of ZnO nanostructured piezoelectric material is coated onto the conductive rubber wire. The wire is then dried at 60-80℃ to form a piezoelectric sensitive layer. A PDMS thin film insulating layer is then formed around the piezoelectric sensitive layer using an immersion or coating process. A stretchable copper outer electrode layer with a spiral winding structure is then fabricated on the piezoelectric sensitive layer using processes such as vacuum evaporation, screen printing, and 3D printing. Finally, a PDMS thin film layer is coated onto the stretchable outer electrode structure as an encapsulation layer, resulting in a flexible piezoelectric tactile sensor with a stretchable electrode structure. The PDMS-coated sensor exhibits greater deformation and output voltage under the same external pressure, making it more suitable for pulse detection.

[0043] The hydrothermal process for the ZnO nanostructure powder involves preparing a precursor solution by mixing 2.23 g of zinc nitrate hexahydrate, 1.05 g of hexamethylenetetramine, 200 μL of Mg(NO3)2·6H2O, and 100 mL of deionized water. The mixture is then magnetically stirred for 40 min to ensure homogeneity. The precursor solution is poured into a polytetrafluoroethylene-lined high-pressure reactor, and the hydrothermal reaction temperature is controlled at 90 °C for 4 h. The ZnO nanostructure powder is then filtered through a vacuum filter, washed repeatedly with deionized water three times, and finally dried in an oven at 80 °C to obtain Mg-doped ZnO nanostructure powder.

[0044] The high-temperature sintering process of the ZnO nanostructure powder is as follows: after the quartz tube furnace is heated to the required temperature, a quartz boat with a thin layer of Zn powder is pushed into the center of the tube furnace. After the reaction takes 3 minutes, the quartz boat is pulled out and the ZnO nanostructure powder is collected in layers.

[0045] The solution containing the ZnO nanostructure composite piezoelectric material is a mixture of ZnO nanostructure and polydimethylsiloxane (PDMS). The preparation method for the ZnO nanostructure powder and PDMS mixture is as follows: First, the PDMS curing agent and prepolymer are mixed at a ratio of 5-10 wt%. After uniform mixing, the mixture is placed in a vacuum drying oven and vacuumed to eliminate air bubbles in the PDMS solution. Then, ZnO and uniformly stirred PDMS are mixed at a ratio of 20-40 wt%, and stirred with a glass rod for 10 minutes. After stirring, the mixture is allowed to stand for later use.

[0046] The process for the PDMS thin film insulating and insulating coating layer is as follows: First, the PDMS curing agent and the prepolymer are mixed at a ratio of 5-10 wt%. After the mixture is evenly mixed, it is placed in a vacuum drying oven and vacuumed to eliminate air bubbles in the PDMS solution. Then, a PDMS thin film insulating and insulating coating layer is formed on the periphery of the piezoelectric sensitive layer by means of immersion or coating.

[0047] Example 2

[0048] The ZnO nanostructure composite piezoelectric film layer in Example 1 was replaced with PVDF. Specifically, PVDF-TrFE powder and N,N-dimethylformamide (DMF) were mixed at a ratio of 10 wt%, and then magnetically stirred at 60°C for 2 h to obtain a clear PVDF solution. ZnO nanostructure powder was then mixed with the uniformly stirred PVDF solution at a ratio of 0.25-7.5 wt%. The composite solution was stirred at room temperature for 12 h and sonicated for 2 h to ensure that ZnO was uniformly mixed in the PVDF solution. The composite solution was then coated onto a conductive rubber wire and dried at 60-80°C to form a piezoelectric sensitive layer. Other steps were the same as in Example 1, resulting in a flexible piezoelectric tactile sensor with a stretchable electrode structure.

[0049] Example 3

[0050] The stretchable copper outer electrode layer in Example 1 was replaced with silver, gold, nano-silver, and nano-gold. A helical winding structure of stretchable silver, gold, nano-silver, and nano-gold outer electrode layers was prepared using processes such as vacuum evaporation, screen printing, and 3D inkjet printing. Then, a PDMS thin film layer was coated on the stretchable outer electrode structure as an encapsulation layer. Other steps were the same as in Example 1, resulting in a flexible piezoelectric tactile sensor with a stretchable electrode structure.

[0051] Example 4

[0052] In Example 1, Mg(NO3)2·6H2O was replaced with 100 μL of VOSO4. The ZnO nanostructure powder was prepared by mixing 2.23 g of zinc nitrate hexahydrate, 1.05 g of hexamethylenetetramine, 100 μL of VOSO4, and 100 mL of deionized water to form a precursor solution. The mixture was magnetically stirred for 40 min to ensure uniform mixing. The precursor solution was then poured into a polytetrafluoroethylene liner in a high-pressure reactor, and the hydrothermal reaction temperature was controlled at 90 °C for 4 h. The ZnO nanostructure powder was then filtered through a vacuum filter, washed three times with deionized water, and dried in an oven at 80 °C to obtain V (vanadium)-doped ZnO nanostructure powder. Other steps were the same as in Example 1, resulting in a flexible piezoelectric tactile sensor with a stretchable electrode structure.

[0053] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A wire-type stretchable piezoelectric tactile sensor, characterized in that, It includes a conductive rubber inner electrode layer, a piezoelectric sensitive layer, an insulating isolation layer, a stretchable outer electrode layer, and a flexible encapsulation layer; the piezoelectric sensitive layer wraps the conductive rubber inner electrode layer, the conductive rubber inner electrode layer is immersed in a solution of ZnO nanostructure composite piezoelectric material or the solution of ZnO nanostructure composite piezoelectric material is coated on the conductive rubber wire and dried to form a piezoelectric sensitive layer on the conductive rubber inner electrode layer; The insulating isolation layer encapsulates the piezoelectric sensitive layer; the stretchable outer electrode layer is spirally wound around the insulating isolation layer; the insulating isolation layer is disposed between the piezoelectric sensitive layer and the stretchable outer electrode layer; the flexible encapsulation layer encapsulates the stretchable outer electrode layer; the conductive rubber inner electrode layer is an elastic linear conductive rubber, which is prepared by adding at least one conductive filler to a rubber matrix; the piezoelectric sensitive layer is a composite piezoelectric film with a ZnO nanostructure; and both the insulating isolation layer and the flexible encapsulation layer are polydimethylsiloxane films, achieving the stretchability of the sensor.

2. The wire-type stretchable piezoelectric tactile sensor according to claim 1, characterized in that, The diameter of the conductive rubber inner electrode layer is 1-5 mm.

3. A wire-type stretchable piezoelectric tactile sensor according to claim 1, characterized in that, The material of the stretchable outer electrode layer is one of silver, gold, and copper.

4. A wire-type stretchable piezoelectric tactile sensor according to claim 1, characterized in that, The thickness of the piezoelectric sensitive layer is 2-5 μm.

5. A wire-type stretchable piezoelectric tactile sensor according to any one of claims 1 to 4, characterized in that, Both the insulating isolation layer and the flexible encapsulation layer are 100-500 nm polydimethylsiloxane (PDMS) films.

6. A method for fabricating a wire-type stretchable piezoelectric tactile sensor as described in claim 5, characterized in that, Includes the following steps: Conductive rubber is processed into a linear structure with a diameter of 1-5 mm to serve as the inner electrode layer of the sensor. The conductive rubber inner electrode layer was ultrasonically cleaned with ethanol and deionized water in sequence, and then dried with nitrogen. The conductive rubber inner electrode layer is immersed in a solution containing ZnO nanostructured composite piezoelectric material or a solution containing ZnO nanostructured composite piezoelectric material is coated onto the conductive rubber inner electrode layer and then dried to form a piezoelectric sensitive layer. A PDMS thin film insulating and protective layer is formed around the piezoelectric sensitive layer using an immersion or coating process. A stretchable outer electrode layer with a spiral winding structure is prepared on the insulating and protective wrapping layer using vacuum evaporation, screen printing and 3D inkjet printing processes. A PDMS thin film layer is coated on the stretchable electrode structure as an encapsulation layer.

7. The preparation method according to claim 6, characterized in that, The ZnO nanostructured composite piezoelectric material contains one of ZnO, Sn-doped ZnO, Mg-doped ZnO, and V-doped ZnO. The nanostructure is one of nanoflowers, nanowires, nanorods, and nanosheets. The ZnO nanostructure is obtained by hydrothermal or high-temperature sintering methods.

8. The preparation method according to claim 6, characterized in that, The solution containing the ZnO nanostructure composite piezoelectric material is a mixture of ZnO nanostructure and PDMS.

9. The preparation method according to claim 7, characterized in that, The preparation method of the hydrothermal precursor solution for ZnO nanostructures is as follows: 0.05-0.1 mol / L zinc nitrate hexahydrate, 0.05-0.1 mol / L hexamethylenetetramine and 0.01-0.05 mol / L dopant solution are added to deionized water and magnetically stirred for 40 min to mix evenly, thus preparing the precursor solution for the hydrothermal reaction; the dopant solution is one of SnCl4·4H2O, (Mg(NO3)2·6H2O) and VOSO4.

10. The preparation method according to claim 8, characterized in that, The preparation method of ZnO nanostructure and PDMS mixture is as follows: First, mix PDMS and curing agent in a ratio of 10:1-20:

1. After mixing evenly, place it in a vacuum drying oven and vacuum to eliminate air bubbles in the PDMS solution. Then, mix ZnO nanostructure and the evenly stirred PDMS solution in a mass ratio of 20-40%, and stir with a glass rod for 10-30 minutes. After stirring, let it stand for later use.

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