Capacitive pressure sensor and preparation method thereof

Abstract

The invention discloses a capacitive pressure sensor and a preparation method thereof. The capacitive pressure sensor comprises a dielectric layer, an upper electrode and a lower electrode, wherein the dielectric layer is composed of a three-dimensional periodic lattice structure fabric and ionic gel; the three-dimensional periodic lattice structure fabric is composed of a plurality of C-shaped elastic filaments, an upper-layer mesh fabric and a lower-layer mesh fabric, and the elastic filaments are arranged between the upper-layer mesh fabric and the lower-layer mesh fabric as longitudinal supports; the ionic gel is compounded with the lower-layer mesh fabric, and a gap exists between the top of the ionic gel and the upper-layer mesh fabric; the upper electrode and the lower electrode are foam nickel electrodes with three-dimensional mesh structures, the upper electrode is arranged at the top of the upper-layer mesh fabric, and the lower electrode is arranged at the bottom of the ionic gel. The sensor provided by the invention is provided with the dielectric layer with a special structure, and can maintain high-sensitivity linear sensing in a large pressure detection range.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitive pressure sensors, and in particular to a capacitive pressure sensor and a preparation method thereof. Background Art

[0002] Flexible capacitive pressure sensors are usually composed of two flexible electrodes and an elastic matrix dielectric layer in the middle, and pressure sensing is achieved through the capacitance change caused by the deformation of the dielectric layer under pressure. At present, the main sensing mechanisms of capacitive pressure sensors are divided into two categories, one is traditional capacitive pressure sensing, and the other is ionic capacitive pressure sensing; however, sensors of these two sensing mechanisms generally have the problem of difficulty in balancing high sensitivity and wide sensing range.

[0003] Sensitivity and pressure sensing range are important indicators for evaluating sensor performance. Sensitivity refers to the ratio of the change in capacitance of the sensor output signal to the change in input pressure (S=(Δ C / C 0 ) / Δ P ), reflects the sensor's ability to respond to pressure changes. The pressure sensing range is the pressure range that the sensor can accurately measure, which determines the pressure range that the sensor can measure.

[0004] Traditional capacitive pressure sensor, capacitance value Since the pressure is generally applied vertically downward, the area facing each other is A ORD Usually unchanged, the capacitance change is mainly affected by the distance between the two electrodes d ORD and the effective dielectric constant Influence, at this time, the pressure sensing is mainly achieved by the change of capacitance caused by the longitudinal compression of the dielectric layer. Ion capacitive pressure sensor, capacitance value ,in and d EDL The change in the total capacitance value during the sensor compression process is not obvious, so the contact area between the electrode and the polymer electrolyte dielectric layer ( A EDL ) is the dominant factor in capacitance change.

[0005] For different types of sensors, the strategies to improve sensing performance are also different. Traditional capacitive pressure sensors usually make holes in the elastic dielectric layer or add conductive fillers / dielectric fillers, and use the lower elastic modulus and larger dielectric constant change of the porous elastic matrix under pressure to improve sensitivity. Ionic capacitive pressure sensors usually use polymer electrolytes with high ionic conductivity and excellent mechanical properties as the dielectric layer, and use the polymer electrolyte to form an electric double layer (EDL) capacitor with extremely high surface capacitance with the electrode surface. The sensitivity is improved by increasing the variable contact area between the dielectric layer and the electrode surface under pressure (that is, the area that can form EDL) through surface microstructure design of the dielectric layer and the electrode.

[0006] For traditional capacitive pressure sensors, the low Young's modulus and limited variable electrode spacing limit the sensor's detection range, which is often less than 200 kPa, making it difficult to meet the needs of daily human body monitoring. For ionic capacitive pressure sensors, the large initial capacitance value also restricts the continued improvement of sensitivity. The sensitivity tends to gradually decrease with increasing pressure, showing a piecewise linear pattern, making it difficult to ensure stable output of signals over a large pressure range, increasing the need for calibration and maintenance.

[0007] Chen et al. used the electrospinning method (Chen Q, Yang J, Chen B, Feng J, Xiao S,Yue Q, Zhang X, Wang T. Wearable Pressure Sensors with Capacitive Responseover a Wide Dynamic Range. ACS Appl Mater Interfaces. 2022 Oct 5;14(39):44642-44651. ) to stack a layer of poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) ionic liquid (IL) mixed ion nanofiber membrane and a layer of pure P(VDF-HFP) nanofiber membrane as the dielectric layer of the sensor. The pure nanofiber membrane was used to separate the ions from one side of the electrode to reduce the initial capacitance of the sensor. The porous structure and non-viscous nature of the ion membrane can be penetrated by the mixed ion membrane under pressure, which can achieve a reversible conversion from ordinary capacitance to EDL capacitance, thereby achieving a huge change in capacitance. The sensitivity of the sensor in the pressure ranges of 0~31.11 and 31.11~66.67 kPa is 55.66 and 24.72, respectively. However, the sensor detection range is only 66.67 kPa. The dielectric layer only improves the sensitivity of the sensor, and the pressure sensing range is still difficult to meet the needs of daily human body monitoring.

[0008] Therefore, it is difficult for existing capacitive flexible pressure sensors to balance high sensitivity and linear sensing range. The preparation of flexible capacitive pressure sensors that can maintain high sensitivity linear sensing within a large pressure detection range is still a key challenge in current research. Summary of the invention

[0009] In view of the deficiencies in the prior art, the present invention provides a capacitive pressure sensor and a preparation method thereof. An elastic filament is selected as a longitudinal support, and an upper mesh fabric and a lower mesh fabric are connected to the upper and lower ends of the elastic filament respectively to obtain a three-dimensional periodic lattice structure fabric. The ion gel is then compounded with the lower mesh fabric to prepare a dielectric layer with a special structure. Finally, a capacitive pressure sensor is assembled using nickel foam electrodes. The capacitive pressure sensor can maintain high-sensitivity linear sensing within a large pressure detection range.

[0010] The first object of the present invention is to provide a capacitive pressure sensor, the capacitive pressure sensor comprising: a dielectric layer composed of a three-dimensional periodic lattice structure fabric and an ion gel, and upper and lower electrodes; The three-dimensional periodic lattice structure fabric is composed of a plurality of C-shaped elastic filaments, an upper mesh fabric and a lower mesh fabric, wherein the elastic filaments are arranged between the upper mesh fabric and the lower mesh fabric as longitudinal supports, and the upper and lower ends of each elastic filament are connected to the upper mesh fabric and the lower mesh fabric respectively; The ion gel is compounded with the lower mesh fabric and completely wraps the lower mesh fabric, and there is a gap between the top of the ion gel and the upper mesh fabric; The upper and lower electrodes are both nickel foam electrodes with a three-dimensional mesh structure, the upper electrode is arranged on the top of the upper mesh fabric, and the lower electrode is arranged on the bottom of the ion gel; When the capacitive pressure sensor is subjected to pressure, the elastic filaments gradually bend as the pressure increases, and the gap between the upper mesh fabric and the ion gel gradually decreases until the ion gel passes through the mesh holes of the upper mesh fabric and contacts the upper electrode, completing the relay between the traditional capacitive sensing mechanism and the EDL capacitive sensing mechanism.

[0011] As a further improvement of the present invention, the diameter of the elastic filament is 0.3-0.5 mm, and the compression strength is 30 MPa.

[0012] As a further improvement of the present invention, the density of the elastic filaments between the upper mesh fabric and the lower mesh fabric is 180 filaments / m 2 .

[0013] As a further improvement of the present invention, the mesh size and mesh shape of the upper mesh fabric are different from those of the lower mesh fabric.

[0014] As a further improvement of the present invention, the mesh of the upper mesh fabric is elliptical, wherein the major axis diameter of the ellipse is 4 mm, and the minor axis diameter of the ellipse is 2 mm; the mesh of the lower mesh fabric is rhombus, wherein the side length of the rhombus is 1.5 mm, and the acute angle of the inner angle is .

[0015] As a further improvement of the present invention, the initial distance between the upper mesh fabric and the lower mesh fabric is 2-3 mm.

[0016] As a further improvement of the present invention, the ion gel is made of polyvinyl alcohol and phosphoric acid.

[0017] As a further improvement of the present invention, the material of the three-dimensional periodic lattice structure fabric is polyester.

[0018] A second object of the present invention is to provide a method for preparing a capacitive pressure sensor, characterized by comprising: Weaving three-dimensional periodic lattice structure fabrics; Add polyvinyl alcohol to deionized water, stir magnetically at 90° C. for a certain period of time until the polyvinyl alcohol is completely dissolved to obtain an initial solution, and cool the initial solution naturally to room temperature; adding phosphoric acid to the initial solution, stirring for a certain period of time to ensure that the initial solution and the phosphoric acid are fully mixed, to obtain a mixed solution; Pour the mixed solution into the mold so that it evenly covers the bottom of the mold, put the three-dimensional periodic lattice structure fabric into the mold so that the lower mesh fabric is completely immersed in the mixed solution and the upper mesh fabric is kept dry and does not contact with the mixed solution; After the mixed solution is solidified, an ion gel is formed, and after the ion gel is completely compounded with the lower mesh fabric, demoulding is performed to obtain a dielectric layer consisting of a three-dimensional periodic lattice structure fabric and the ion gel; The nickel foam electrode and the dielectric layer are cut, and the nickel foam electrode is fixed on the dielectric layer to complete the preparation of the capacitive pressure sensor.

[0019] As a further improvement of the present invention, the material ratio of polyvinyl alcohol to deionized water is 1:10; the concentration of phosphoric acid is 0.1 mol / L, and the material ratio of phosphoric acid to the initial solution is 0.17 g:1 ml.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The capacitive pressure sensor provided by the present invention has a simple preparation process. The dielectric layer of the sensor is composed of a three-dimensional periodic lattice structure fabric and an ion gel. This specific dielectric layer structure effectively expands the sensing range of the capacitive pressure sensor.

[0021] Elastic filaments in three-dimensional periodic lattice structured fabrics provide sensors with large variable electrode spacing d ORD , while the ion gel and the upper electrode are separated by elastic filaments, eliminating the negative impact of high initial capacitance values ​​on sensitivity.

[0022] The upper mesh fabric creates conditions for the ion gel to contact the upper electrode to form an EDL, and the lower mesh fabric can support the ion gel and improve the mechanical properties of the dielectric layer.

[0023] The three-dimensional porous nickel foam electrode is used as the upper and lower electrodes. It has a large specific surface area and interconnected network channels, which can not only increase the variable contact area between the electrode and the dielectric layer A EDL It also provides an efficient channel for ion diffusion, accelerates the uniform distribution of ions, and makes the sensor respond faster and have higher detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of the capacitive pressure sensor provided by the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings: This embodiment provides a capacitive pressure sensor, the structure of which is as follows Figure 1 As shown, the capacitive pressure sensor includes: a dielectric layer composed of a three-dimensional periodic lattice structure fabric and an ion gel, and upper and lower electrodes.

[0027] The three-dimensional periodic lattice structure fabric (3D periodic lattice elastomer, 3DPLE) is composed of a plurality of C-shaped elastic filaments, an upper mesh fabric and a lower mesh fabric. The material of the three-dimensional periodic lattice structure fabric is polyester.

[0028] The elastic filaments are arranged between the upper mesh fabric and the lower mesh fabric as longitudinal supports, and the upper and lower ends of each elastic filament are respectively connected to the upper mesh fabric and the lower mesh fabric, so that there is an air gap between the upper mesh fabric and the lower mesh fabric, and the initial distance between the upper mesh fabric and the lower mesh fabric is 2~3mm.

[0029] Specifically: the diameter of the elastic filament is 0.3~0.5mm, the compression strength is 30MPa, and the density of the elastic filaments between the upper mesh fabric and the lower mesh fabric is 180 filaments / m 2 .

[0030] Furthermore, the mesh size and shape of the upper mesh fabric are different from those of the lower mesh fabric. The mesh of the upper mesh fabric is elliptical, the major axis diameter of the ellipse is 4 mm, and the minor axis diameter of the ellipse is 2 mm; the mesh of the lower mesh fabric is rhombus, the side length of the rhombus is 1.5 mm, and the acute angle of the inner angle is .

[0031] An ion gel (IG) made of polyvinyl alcohol and phosphoric acid mixed in a preset ratio is compounded with the lower mesh fabric and completely wraps the lower mesh fabric, and there is a gap between the top of the ion gel and the upper mesh fabric, thereby preparing a dielectric layer with a special structure. The large mesh holes of the upper mesh fabric provide a channel for the IG to contact the upper electrode to form an EDL, thereby realizing the relay from the traditional capacitive sensing mechanism to the EDL capacitive sensing mechanism. The sparsely arranged small coils of the lower mesh fabric play a role in supporting the IG, improving the mechanical properties of the IG.

[0032] Ion gels can also be made from other flexible substrates (such as TPU, PDMS, etc.) and other materials that can provide ions (such as hydrochloric acid, sodium chloride, ionic liquids, etc.).

[0033] The upper and lower electrodes are both nickel foam electrodes with a three-dimensional mesh structure. The upper electrode is arranged on the top of the upper mesh fabric, and the lower electrode is arranged on the bottom of the ion gel to obtain a capacitive pressure sensor combining a three-dimensional periodic lattice structure fabric and an ion gel.

[0034] The three-dimensional porous structure of nickel foam has a larger specific surface area and interconnected network channels, which not only enhances the variable contact area between the electrode and the dielectric layer, but also A EDL It also provides an effective diffusion channel for ions within the electrolyte (i.e., IG), making the ions distributed throughout the material faster and more uniform, greatly improving the overall performance of the sensor.

[0035] Longitudinal elastic filaments in 3DPLE provide large variable electrode spacing for capacitive pressure sensors d ORDIG and the upper electrode separated by the air gap in 3DPLE eliminate the negative impact of high initial capacitance on sensitivity, and the three-dimensional mesh structure of nickel foam provides a large variable contact area for EDL capacitance. When the capacitive pressure sensor is under pressure, the elastic filaments gradually bend as the pressure increases, and the gap between the upper mesh fabric and the ion gel gradually decreases until the ion gel contacts the upper electrode through the mesh of the upper mesh fabric, completing the relay of the traditional capacitive sensing mechanism and the EDL capacitive sensing mechanism, expanding the sensing range of the capacitive pressure sensor.

[0036] This embodiment provides a method for preparing a capacitive pressure sensor, comprising: Weaving a three-dimensional periodic lattice structure fabric; the manufacturing equipment is a double needle bed Raschel warp knitting machine, and the preparation process is to use the front comb and the back comb of the warp knitting machine to weave the polyester filaments into upper and lower mesh fabrics with different mesh structures, and use the middle comb of the warp knitting machine to make the C-shaped polyester monofilament reciprocate between the upper and lower mesh fabrics to connect the upper and lower mesh fabrics; Preparation of an initial solution containing a flexible matrix: PVA was added to a glass beaker containing deionized water, with the material ratio of PVA to deionized water being 1:10; magnetic stirring was performed at 90° C. for 2 h until the PVA was completely dissolved to obtain an initial solution, and the initial solution was naturally cooled to room temperature; Add H to the initial solution 3 PO 4 , H 3 PO 4 The concentration of H2O is 0.1 mol / L, and 0.17 g H2O is added to each ml of the initial solution. 3 PO 4 , and stirred for 30 min to ensure that the initial solution was 3 PO 4 Mix thoroughly to obtain a mixed solution; Weigh 1.5 g of mixed solution (PVA / H 3 PO 4 Solution), pour the mixed solution into the mold so that it evenly covers the bottom of the mold; The three-dimensional periodic lattice structure fabric is placed in a mold, so that the lower mesh fabric is completely immersed in the mixed solution, and the upper mesh fabric is kept dry and does not contact the mixed solution, the mold is placed in a 70°C constant temperature drying oven for 15 minutes, and then taken out, and then left to stand and cure at room temperature for 6 hours, and then demolded to obtain a dielectric layer composed of the three-dimensional periodic lattice structure fabric and the ion gel; The nickel foam electrode and the dielectric layer were cut, and the nickel foam electrode was fixed on the dielectric layer with PI tape to complete the preparation of the capacitive pressure sensor.

[0037] The sensor prepared in this embodiment can realize 0~1550 kPa (linear sensing range accounts for 94.84%) pressure detection, and can maintain 49.76 in the entire detection range. (R 2 =0.99) high sensitivity.

[0038] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A capacitive pressure sensor, characterized in that: The capacitive pressure sensor comprises: a dielectric layer composed of a three-dimensional periodic lattice structure fabric and an ion gel, and upper and lower electrodes; The three-dimensional periodic lattice structure fabric is composed of a plurality of C-shaped elastic filaments, an upper mesh fabric and a lower mesh fabric, wherein the elastic filaments are arranged between the upper mesh fabric and the lower mesh fabric as longitudinal supports, and the upper and lower ends of each elastic filament are connected to the upper mesh fabric and the lower mesh fabric respectively; The ion gel is compounded with the lower mesh fabric and completely wraps the lower mesh fabric, and there is a gap between the top of the ion gel and the upper mesh fabric; The upper and lower electrodes are both nickel foam electrodes with a three-dimensional mesh structure. The upper electrode is arranged on the top of the upper mesh fabric, and the lower electrode is arranged on the bottom of the ion gel.

2. The capacitive pressure sensor according to claim 1, characterized in that: The diameter of the elastic filament is 0.3-0.5 mm, and the compression strength is 30 MPa.

3. The capacitive pressure sensor according to claim 1, characterized in that: The density of the elastic filaments between the upper mesh fabric and the lower mesh fabric is 180 filaments / m 2 .

4. The capacitive pressure sensor according to claim 1, characterized in that: The mesh size and mesh shape of the upper mesh fabric are different from those of the lower mesh fabric.

5. The capacitive pressure sensor according to claim 4, characterized in that: The mesh holes of the upper mesh fabric are elliptical, wherein the major axis diameter of the ellipse is 4 mm, and the minor axis diameter of the ellipse is 2 mm; the mesh holes of the lower mesh fabric are rhombus, wherein the side length of the rhombus is 1.5 mm, and the acute angle of the inner angle is .

6. The capacitive pressure sensor according to claim 1, characterized in that: The initial distance between the upper mesh fabric and the lower mesh fabric is 2-3 mm.

7. The capacitive pressure sensor according to claim 1, characterized in that: The ion gel is prepared from polyvinyl alcohol and phosphoric acid.

8. The capacitive pressure sensor according to claim 1, characterized in that: The material of the three-dimensional periodic lattice structure fabric is polyester.

9. A method for preparing a capacitive pressure sensor according to any one of claims 1 to 8, characterized in that: include: Weaving three-dimensional periodic lattice structure fabrics; Add polyvinyl alcohol to deionized water, stir magnetically at 90° C. for a certain period of time until the polyvinyl alcohol is completely dissolved to obtain an initial solution, and cool the initial solution naturally to room temperature; adding phosphoric acid to the initial solution, stirring for a certain period of time to ensure that the initial solution and the phosphoric acid are fully mixed, to obtain a mixed solution; Pour the mixed solution into the mold so that it evenly covers the bottom of the mold, put the three-dimensional periodic lattice structure fabric into the mold so that the lower mesh fabric is completely immersed in the mixed solution and the upper mesh fabric is kept dry and does not contact with the mixed solution; After the mixed solution is solidified, an ion gel is formed, and after the ion gel is completely compounded with the lower mesh fabric, demoulding is performed to obtain a dielectric layer consisting of a three-dimensional periodic lattice structure fabric and the ion gel; The nickel foam electrode and the dielectric layer are cut, and the nickel foam electrode is fixed on the dielectric layer to complete the preparation of the capacitive pressure sensor.

10. The preparation method according to claim 9, characterized in that: The material ratio of polyvinyl alcohol to deionized water is 1:10; the concentration of phosphoric acid is 0.1 mol / L, and the material ratio of phosphoric acid to the initial solution is 0.17 g:1 ml.

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