Preparation method and application of adjustable gradient random micro-cone structure capacitance flexible pressure sensor

Abstract

The invention relates to the technical field of flexible pressure sensors, in particular to a preparation method and application of a capacitance flexible pressure sensor with an adjustable gradient random micro-cone structure, and the sensor comprises an upper electrode and a lower electrode which are transparent indium tin oxide conductive films (PET / ITO); the packaging layer is a polyimide (PI) adhesive tape and covers the outer side of the electrode; the flexible isolation layer is polydimethylsiloxane (PDMS) with a hollow structure, and is positioned between the upper electrode and the lower electrode; the dielectric layer of a gradient random micro-cone structure is located in the flexible isolation layer and is formed by compounding polyvinyl alcohol (PVA) and phosphoric acid (H3PO4) according to the mass ratio of 1: 1; the gradient micro-cone structure and the ionization effect are combined, the electric double layer effect grading phenomenon occurs, and the gradient micro-cone sensor has the advantages of being high in sensitivity, wide in detection range, capable of keeping linearity under large pressure, short in response time and good in cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible pressure sensors, and in particular to a preparation method and application of a capacitive flexible pressure sensor with an adjustable gradient random micro-cone structure. Background Art

[0002] With the rapid development of the Internet of Things, artificial intelligence, and wearable technology, flexible electronics, as an emerging electronics technology, is attracting widespread attention. As a key component of flexible electronics, capacitive flexible sensors, with their advantages such as high sensitivity, fast response, low power consumption, and good flexibility, have shown great application potential in various fields. In recent years, researchers have made numerous innovations in material selection, structural design, and manufacturing processes, greatly promoting the development of capacitive flexible sensors.

[0003] However, there is a mutual constraint between the sensitivity and detection range of flexible pressure sensors, which cannot meet the detection conditions that require high sensitivity and wide range. The dielectric layer with gradient microstructure is an effective improvement method. Although the stepped capacitance flexible sensor has made significant progress, it still faces some challenges. How to further improve the sensitivity, response speed and durability of the sensor while maintaining a wide range of detection capabilities remains an important issue. Many researchers use a stepped structure to ensure the high sensitivity and wide detection range of flexible pressure sensors. In order to achieve a stepped structure, researchers have proposed a variety of innovative solutions in structural design. For example, patent number CN116989918A designs a flexible sensor with a gradient micro-cone structure array, which achieves different sensor performance by controlling the height and spacing of the micro-cone structure. When the detection pressure is 0-40kPa, the sensitivity of the flexible sensor is 0.082kPa -1 When the detection pressure is 40-400kPa, the sensitivity of the flexible sensor is 0.0113kPa -1 When the detection pressure is 400-1500kPa, the sensitivity of the flexible sensor is 0.007kPa -1 Although this structure has a wide detection range, it has low sensitivity and does not maintain linearity under high pressure. Therefore, it is of great significance to manufacture a flexible sensor with a wide detection range, high sensitivity and linearity under high pressure. Summary of the Invention

[0004] The present invention aims to provide a method for preparing and applying a capacitive flexible pressure sensor with a tunable gradient random microcone structure. This sensor combines the gradient microcone structure with the ionization effect, resulting in a graded double-layer effect. The sensor exhibits high sensitivity, a wide detection range, linearity under high pressures, a short response time, and good cyclic stability. Furthermore, the preparation method is simple and requires low material costs. The sensor can be used in fields such as human motion monitoring, health monitoring, and human-computer interaction.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0006] A capacitive flexible pressure sensor with an adjustable gradient random micro-cone structure, comprising:

[0007] Upper and lower electrodes, wherein the electrodes are transparent indium tin oxide conductive film (PET / ITO);

[0008] The packaging layer is a polyimide (PI) tape covering the outside of the electrode;

[0009] A flexible isolation layer, wherein the flexible isolation layer is a hollow polydimethylsiloxane (PDMS) and is located between the upper and lower electrodes;

[0010] The dielectric layer with a gradient random micro-cone structure is located inside the flexible isolation layer and is composed of polyvinyl alcohol (PVA) and phosphoric acid (H3PO4) in a mass ratio of 1:1;

[0011] The gradient dielectric layer comprises three stepped structures, which are prepared by laser engraving a mold formed by sandpaper of different mesh sizes, and the sandpaper mesh size combination of the stepped structure is selected from one of the following:

[0012] The first step structure is formed by 100 mesh, 200 mesh, 280 mesh or 500 mesh sandpaper casting;

[0013] The second step structure is formed by 500 mesh, 1000 mesh or 1500 mesh sandpaper casting;

[0014] The third step structure is formed by 1000 mesh, 1500 mesh, 2000 mesh or 5000 mesh sandpaper casting;

[0015] The three step structures are arranged in order from low to high according to the sandpaper mesh number, and the difference in the sandpaper mesh number of adjacent steps is ≥200 meshes. When under pressure, the double electric layer effect is triggered step by step to achieve a graded capacitance response.

[0016] On the other hand, the present invention provides a method for preparing the above-mentioned capacitive flexible pressure sensor, comprising the following steps:

[0017] S1: Preparation of mold precursor solution: Mix silicone elastomer A and silicone elastomer B in a mass ratio of 1:1, stir, and then vacuum degas.

[0018] Step 2: Step mold preparation: Use a laser to engrave sandpaper into rectangular patterns with a width of <1 mm and affix them to a glass substrate in a stepped pattern (low mesh / medium mesh / high mesh). Pour the precursor solution from step S1 into the mold, cure at 40°C for 24 hours, and then peel off to obtain an Ecoflex mold with a stepped structure.

[0019] S3: Preparation of dielectric layer solution: 3 g of polyvinyl alcohol (PVA) was dissolved in 27 g of deionized water, stirred at 90 °C for 2.5 hours, and then cooled to room temperature. 3 g of phosphoric acid solution was added and stirred for 2 hours.

[0020] S4: Dielectric layer molding: inject the PVA / phosphoric acid solution from step S3 into the mold from step S2, cure at room temperature for 24 hours, and peel off to obtain a dielectric layer with a gradient random micro-cone structure;

[0021] S5: Sensor assembly: Place the dielectric layer inside the PDMS flexible isolation layer, attach the PET / ITO electrode, and encapsulate the outer layer with PI tape.

[0022] Furthermore, the preparation of the stepped mold includes a non-step mold, a non-step mold, a two-step mold, and a three-step mold; the specific preparation includes the following sub-steps:

[0023] S2.1: Take a 2*2cm piece of sandpaper with a mesh size of 360, fix it to a glass sheet of the same size with 3M tape, and place it on the bottom of a culture dish with the sandpaper side facing up. The non-sandpaper side of the glass sheet is also fixed to the culture dish with 3M tape. Pour the Ecoflex precursor solution prepared in S1 into the culture dish and place it on a magnetic stirrer set at 40°C to dry for 24 hours. After drying, peel off the Ecoflex containing the cured 360-grit sandpaper structure from the culture dish to obtain an Ecoflex membrane with a step-free structure.

[0024] S2.2: First, use a laser to carve a large number of rectangular patterns less than 1 mm wide on sandpaper of different mesh sizes (200 / 500 / 1000 / 2000). Then, use a scalpel to cut the sandpaper along the patterns. Then, systematically assemble the sandpaper of different mesh sizes onto a glass slide in the following combinations: 200 / 1000, 500 / 1000, and 1000 / 2000. Use 3M tape to secure the slide to a glass slide of the same size. Place the slide at the bottom of a Petri dish, with the stepped sandpaper facing up. The unsandpapered side of the glass slide is also secured to the Petri dish with 3M tape. Pour the Ecoflex precursor solution prepared in S1 into the Petri dish and dry it on a magnetic stirrer set at 40°C for 24 hours. After drying, the Ecoflex containing the cured 200 / 1000, 500 / 1000, and 1000 / 2000 sandpaper structures was peeled off from the culture dish to obtain an Ecoflex film with two step structures;

[0025] S2.3: First, use a laser to carve a large number of rectangular patterns less than 1 mm wide on sandpaper of different mesh sizes (100 / 280 / 360 / 500 / 1000 / 2000 / 5000). Then, use a scalpel to cut the sandpaper along the patterns. Then, systematically assemble the sandpaper of different mesh sizes onto a glass slide (the following combinations are: 280 / 360 / 500, 100 / 500 / 1000, 100 / 1000 / 1500, 500 / 1000 / 1500, and 1000 / 2000 / 5000). Secure the slide to a glass slide of the same size using 3M tape and place it on the bottom of a Petri dish with the stepped sandpaper facing up. The unsandpapered side of the glass slide is also secured to the Petri dish using 3M tape. Pour the Ecoflex precursor solution prepared in S1 into the Petri dish and dry it on a magnetic stirrer set at 40°C for 24 hours. After drying, the Ecoflex containing the cured sandpaper structures of 280 / 360 / 500, 100 / 500 / 1000, 100 / 1000 / 1500, 500 / 1000 / 1500, and 1000 / 2000 / 5000 was peeled off from the culture dish to obtain an Ecoflex film with three step structures;

[0026] On the other hand, the present invention proposes the application of the above-mentioned capacitive flexible pressure sensor in customized sensors for medical monitoring and human-computer interaction.

[0027] Beneficial effects of the present invention:

[0028] The present invention triggers multi-level capacitance response at different pressure stages through the hierarchical contact mechanism of gradient random microcone structure, combined with the ionization effect. In the low-pressure stage, the tip of the high-mesh microcone contacts the electrode first, and its tiny contact area deforms rapidly under the action of pressure, significantly improving the double-layer capacitance change rate under unit pressure, achieving high sensitivity; in the medium-pressure stage, the medium-mesh microcones bend to form surface contact, and the exponential growth of the contact area is superimposed on the EDL effect, so that the sensitivity remains stable; in the high-pressure stage, the wide base structure of the low-mesh microcones expands the contact area through elastic compression, and the randomly distributed microcones avoid stress concentration, ensuring that the capacitance change rate maintains a linear response within a wide pressure range. It breaks through the contradiction between the sensitivity and detection range of traditional sensors. For example, Example 7 can still maintain a near-ideal linearity (R 2 =0.99).

[0029] The gradient step structure of the present invention avoids premature saturation of a single structure under high pressure by carrying pressure in a graded manner. The wide base of the low-mesh microcones combined with the high elastic modulus of the PVA / phosphoric acid composite material provides mechanical support under high pressure, slows down the increase in contact area, and makes the capacitance change rate linearly related to pressure. The ionic conductivity of phosphoric acid enhances the stability of the double-layer capacitor and suppresses signal drift caused by polarization effects. Example 7 maintains a stable capacitance response after cycling for 2200 seconds under a pressure of 100kPa, verifying its durability under high-load environments. In addition, the low Young's modulus of the PDMS encapsulation layer matches the elasticity of the dielectric layer, further reducing interfacial stress concentration and extending device life.

[0030] The low viscoelastic properties of the PVA / phosphoric acid dielectric layer of the present invention and the elastic retraction properties of the microcone structure work synergistically to give the sensor rapid recovery capabilities. After the external force is removed, the microcone quickly recovers its deformation by relying on the elastic microstructure replicated by the Ecoflex mold, reducing viscous resistance. At the same time, the high ion concentration of phosphoric acid accelerates the migration and rearrangement of ions at the electrode-dielectric layer interface, making the response speed of the double-layer capacitor close to the tactile limit of human skin. This allows the sensor to capture dynamic physiological signals in real time, such as the successful identification of the "CPS" characteristic peak of throat vocalization in Example 7, demonstrating its applicability in biological signal detection such as speech recognition.

[0031] The present invention is based on the laser engraving of sandpaper templates and the Ecoflex molding process, which realizes low-cost and accurate replication of gradient micro-cone structures. By combining sandpapers of different mesh sizes (such as 280 / 360 / 500 mesh in Example 4 and 1000 / 2000 / 5000 mesh in Example 8), the density and height of the stepped structure can be flexibly adjusted to adapt to different sensitivity and range requirements. The room temperature film-forming properties of PVA / phosphoric acid solution simplifies the process flow, and the thickness of the dielectric layer is controlled within 300μm. Combined with the flexible substrate of PET / ITO electrodes, the sensor can be fitted to complex curved surfaces (such as joints and throats). It provides a technical basis for the development of customized sensors for scenarios such as medical monitoring and human-computer interaction.

[0032] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 This is a structural diagram of the capacitive flexible sensor of the present invention and a schematic diagram of the pressure process; 1-polyimide (PI), 2-transparent indium tin oxide conductive film PET / ITO, 3-500 mesh sandpaper molded PVA / H3PO4 dielectric layer film, 4-1000 mesh sandpaper molded PVA / H3PO4 dielectric layer film, 5-1500 mesh sandpaper molded PVA / H3PO4 dielectric layer film, 6-polydimethylsiloxane (PDMS).

[0035] Figure 2 Schematic diagram of the cross-section of the dielectric layer of the capacitive flexible sensor of the present invention; schematic diagram of the PVA / H3PO4 dielectric layer film molded with 3-500 mesh sandpaper, schematic diagram of the PVA / H3PO4 dielectric layer film molded with 4-1000 mesh sandpaper, schematic diagram of the PVA / H3PO4 dielectric layer film molded with 5-1500 mesh sandpaper.

[0036] Figure 3Flow chart for preparing the capacitive flexible sensor with a ladder structure of the present invention; 7-PVA powder, 8-beaker, 9-deionized water, 10-rotor, 11-magnetic stirrer, 12-PVA / H3PO4 solution, 13-500 mesh sandpaper, 14-1500 mesh sandpaper, 15-1000 mesh sandpaper, 16-laser, 17-assembled ladder, 18-polydimethylsiloxane (PDMS), 19-spinner, 20-glass slide, 21-syringe, 22-phosphoric acid solution (H3PO4).

[0037] Figure 4 These are the sensitivity curves of Comparative Example 1, Example 1, Example 2, and Example 3 of the prepared capacitive flexible sensor.

[0038] Figure 5 These are the sensitivity curves of the prepared capacitive flexible pressure sensor embodiments 4 and 5.

[0039] Figure 6 These are the sensitivity curves of the prepared capacitive flexible pressure sensor embodiments 6 and 8.

[0040] Figure 7 These are the sensitivity curves of the prepared capacitive flexible pressure sensors of Example 1, Example 2, and Example 7.

[0041] Figure 8 This is the capacitance change rate of the capacitive flexible pressure sensor of Example 7 of the present invention after cycling for 2200 seconds under a pressure of 100 kPa.

[0042] Figure 9 The response speed and recovery speed of the capacitive flexible pressure sensor prepared in Example 7 of the present invention.

[0043] Figure 10 This is the capacitive response of the capacitive flexible pressure sensor prepared in Example 7 of the present invention when it is attached to the throat of a volunteer and the person says "CPS". DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0045] Example 1

[0046] As described in this embodiment, a capacitive flexible pressure sensor with an adjustable gradient random micro-cone structure comprises two electrodes, an encapsulation layer, a flexible isolation layer, and a polyvinyl alcohol and phosphate dielectric layer with an adjustable gradient random micro-cone structure. The adjustable gradient adopts a three-step cycle of high, medium, and low levels, and different gradient structures are achieved by changing the combination. The contact between the gradient dielectric layer and the electrode occurs in three stages. Under low pressure, due to the presence of the spacer layer, only a small portion of the electrode contacts the tip protrusions of the first-stage stepped structure, resulting in a small area change in the dielectric layer and the emergence of a double-layer effect. Upon application of greater pressure, the second-stage stepped structure begins to buckle and forms surface contact with the electrode, resulting in a large change in contact area and a significant double-layer effect. Finally, the addition of the third stage creates a larger surface contact area and a more pronounced double-layer effect. Consequently, the double-layer effect is generated in stages under different pressures, achieving a stable capacitance change rate. The flexible isolation layer is hollow polydimethylsiloxane; the stepped dielectric layer is within the flexible isolation layer, and the upper and lower electrodes do not contact the dielectric layer.

[0047] In this embodiment, further verification is performed using different orders, specifically including the following steps:

[0048] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 200-grit and 500-grit sandpaper. Then use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 200 / 500-grit sandpaper into a glass slide in a regular pattern and place it at the bottom of a culture dish with the sandpaper side facing up.

[0049] S2: Pour the Ecoflex precursor solution into the culture dish S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the solution. If any bubbles persist, pop them with a toothpick. Dry the solution in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 200 / 500 mesh overmold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0050] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0051] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a two-step gradient microstructure containing a 200 / 500 grit sandpaper combination.

[0052] S5: A two-step gradient microstructure containing a combination of PVA phosphoric acid 200 / 500 grit sandpaper is used as the dielectric layer, and the electrode uses PET / ITO film. To reduce parasitic capacitance, the outermost layer is encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0053] Example 2

[0054] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 5000-grit and 1000-grit sandpaper. Then use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 500 / 1000-grit sandpaper into a glass slide in a regular pattern and place it at the bottom of a culture dish with the sandpaper side facing up.

[0055] S2: Pour the Ecoflex precursor solution into the culture dish in S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the mixture. If any bubbles persist, pop them with a toothpick. Dry the mixture in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 500 / 1000 mesh overmold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0056] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0057] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a two-step gradient microstructure containing a combination of 500 / 1000 grit sandpaper.

[0058] S5: A two-step gradient microstructure containing a combination of PVA phosphoric acid 500 / 1000 grit sandpaper is used as the dielectric layer, and the electrode is made of PET / ITO film. To reduce parasitic capacitance, the outermost layer is encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0059] Example 3

[0060] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 1000-grit and 2000-grit sandpaper. Then use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 1000 / 2000-grit sandpaper into a glass slide in a regular pattern and place it at the bottom of a culture dish with the sandpaper side facing up.

[0061] S2: Pour the Ecoflex precursor solution into the culture dish S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the mixture. If any bubbles persist, pop them with a toothpick. Dry the mixture in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 1000 / 2000 mesh overmold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0062] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0063] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a two-step gradient microstructure containing a combination of 1000 / 2000 grit sandpaper.

[0064] S5: A two-step gradient microstructure containing a combination of PVA phosphoric acid 1000 / 2000 grit sandpaper is used as the dielectric layer, and the electrode is made of PET / ITO film. To reduce parasitic capacitance, the outermost layer is encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0065] Comparative Example 1

[0066] S1: Take a 2*2cm piece of sandpaper with a mesh size of 360, then assemble the 360-mesh sandpaper into the glass slide and place it at the bottom of the culture dish with the sandpaper side facing up.

[0067] S2: Pour the Ecoflex precursor solution into the culture dish S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the solution. If any bubbles persist, pop them with a toothpick. Dry the solution in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 360-mesh mold from the culture dish to obtain an Ecoflex mold without the step structure.

[0068] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0069] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a two-step gradient microstructure containing a combination of 360-grit sandpaper.

[0070] S5: A two-step gradient microstructure containing a combination of PVA and 360-grit sandpaper is used as the dielectric layer, and the electrode is made of PET / ITO film. To reduce parasitic capacitance, the outermost layer is encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0071] The sensitivity curves of the prepared capacitive flexible sensor of Comparative Example 1, Example 1, Example 2, and Example 3 were compared. Figure 3 It can be found that by comparing the second-order gradients of the two mesh combinations of Example 1, Example 2, and Example 3 with the comparative example 1 without a gradient, it can be clearly seen that due to the presence of the step structure, the sensor not only has improved sensitivity but also has a wider detection range. Comparing the three second-order structures of Example 1, Example 2, and Example 3, it can be found that the largest mesh combination of 1000 / 2000 has a larger capacitance change rate and better linearity (R 2 =0.99). This is because the mesh combinations of Example 1 (200 / 1000) and Example 2 (500 / 1000) are smaller than those of Example 3, resulting in a smaller rate of change in area under pressure.

[0072] Example 4

[0073] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 280-, 360-, and 500-grit sandpaper. Then, use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 280 / 360 / 500-grit sandpaper into a regular pattern on a glass slide and place it at the bottom of a culture dish with the sandpaper side facing up.

[0074] S2: Pour the Ecoflex precursor solution into the culture dish S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the solution. If any bubbles persist, pop them with a toothpick. Dry the solution in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 280 / 360 / 500 mesh mold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0075] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0076] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2. After curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a three-step gradient microstructure containing a combination of 280 / 360 / 500 grit sandpaper.

[0077] S5: A three-step gradient microstructure containing a combination of PVA phosphoric acid 280 / 360 / 500 grit sandpaper is used as the dielectric layer, and the electrode uses PET / ITO film. To reduce parasitic capacitance, the outermost layer is encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0078] Example 5

[0079] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 100, 1000, and 1500 grit sandpaper. Then use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 100 / 1000 / 1500 grit sandpaper into a regular pattern on a glass slide and place it at the bottom of a culture dish with the sandpaper side facing up.

[0080] S2: Pour the Ecoflex precursor solution into the culture dish S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the mixture. If any bubbles persist, pop them with a toothpick. Dry the mixture in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 100 / 1000 / 1500 mesh mold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0081] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0082] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a three-step gradient microstructure containing a combination of 100 / 1000 / 1500 grit sandpaper.

[0083] S5: A three-step gradient microstructure containing a combination of PVA phosphoric acid 100 / 1000 / 1500 grit sandpaper was used as the dielectric layer, and the electrodes were made of PET / ITO film. To reduce parasitic capacitance, the outermost layer was encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0084] Figure 4 The sensitivity curves of the prepared capacitive flexible pressure sensor embodiments 4 and 5 are shown in FIG. Figure 3 Based on the above, the ladder combination is changed to 3-step. It can be found that relative to Figure 3 The second-order combination and the third-order combination have better linearity and greater capacitance change rate under high pressure (>200kPa).

[0085] Example 7

[0086] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 500, 1000, and 1500 grit sandpaper. Then use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 500 / 1000 / 1500 grit sandpaper into a regular pattern on a glass slide and place it at the bottom of a culture dish with the sandpaper side facing up.

[0087] S2: Pour the Ecoflex precursor solution into the culture dish in S1. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the solution. If any bubbles persist, pop them with a toothpick. Dry the solution in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 500 / 1000 / 1500 mesh mold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0088] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0089] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a three-step gradient microstructure containing a combination of 500 / 1000 / 1500 grit sandpaper.

[0090] S5: A three-step gradient microstructure containing a combination of PVA phosphoric acid 500 / 1000 / 1500 grit sandpaper was used as the dielectric layer, and the electrodes were made of PET / ITO film. To reduce parasitic capacitance, the outermost layer was encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0091] Example 8

[0092] S1: First, use a laser to carve rectangular patterns less than 1 mm wide on 1000, 2000, and 5000 grit sandpaper. Then use a scalpel to cut the sandpaper along the patterns. Finally, assemble the 1000 / 2000 / 5000 grit sandpaper into a regular pattern on a glass slide and place it at the bottom of a culture dish with the sandpaper side facing up.

[0093] S2: Pour the Ecoflex precursor solution into the S1 culture dish. The Ecoflex precursor solution is made by mixing Glue A (silicone elastomer) and Glue B (silicone elastomer crosslinker) in a 1:1 weight ratio. After mixing thoroughly, vacuum the mixture. If any bubbles persist, pop them with a toothpick. Dry the mixture in a magnetic stirrer set at 40°C for 36 hours. After drying, peel the Ecoflex containing the 1000 / 2000 / 5000 mesh mold from the culture dish to obtain the Ecoflex mold with a stepped structure.

[0094] S3: Dissolve 3 g of polyvinyl alcohol (PVA, Mw ~ 195,000) in 27 g of deionized water, then stir in an intelligent mixer at 90 ° C for 2.5 h until the PVA is completely dissolved. After cooling to room temperature, add phosphoric acid solution (PVA / H3PO4 = 1:1) to the solution and stir in an intelligent mixer for 2 h. After stirring and mixing evenly, pour it into a sample bottle and set it at room temperature.

[0095] S4: Pour the prepared PVA / phosphoric acid solution into the silicone mold obtained in step S2, and after curing at room temperature for 24 hours, peel off the dielectric layer of the capacitive flexible pressure sensor with a three-step gradient microstructure containing a combination of 1000 / 2000 / 5000 grit sandpaper.

[0096] S5: A three-step gradient microstructure containing a combination of PVA phosphoric acid 1000 / 2000 / 5000 grit sandpaper is used as the dielectric layer, and the electrode is made of PET / ITO film. To reduce parasitic capacitance, the outermost layer is encapsulated with PI tape to assemble a complete capacitive flexible pressure sensor.

[0097] Figure 5 The sensitivity curves of the prepared capacitive flexible pressure sensor embodiments 6 and 8 are shown in FIG. 1 . The step combination is changed to 3 steps, relative to FIG. Figure 4 The third-order combination of Figure 5 The largest mesh size of the (1000 / 2000 / 5000) combination has the largest capacitance change rate, and under high pressure (>300kPa), the linearity is 1. Figure 3 ,4 It can be found that the larger the mesh number combination, the higher the linearity and the wider the range under high pressure.

[0098] Figure 7 The sensitivity curves of the prepared capacitive flexible pressure sensor are shown in Table 1, Example 2, and Example 7. To select the best combination, the mesh combinations of 1, 2, and 3 orders are compared, and the linearity is divided into two sections. Figure 3 , 4, 5, when the mesh combination is (500 / 1000 / 1500), the linearity can be maintained within the range of (>100kPa) 2 =0.99), and at the same time taking into account wide range and high sensitivity.

[0099] Figure 8 This is the capacitance change rate of the capacitive flexible pressure sensor of Example 7 of the present invention, after cycling for 2200 seconds at 100 kPa. As can be seen, with increasing pressurization times, the sensor maintains the original capacitance change curve trend, except for a slight decrease. This demonstrates that the capacitive flexible pressure sensor of the present invention has good mechanical cycling characteristics and can be used stably under high pressure (>100 kPa).

[0100] Figure 9 The response time and recovery time of the capacitive flexible pressure sensor prepared in Example 7 of the present invention are 34ms and 37.5ms, respectively. The touch response time of human skin is 30-50 milliseconds, indicating that the present invention can be used as electronic skin.

[0101] Figure 10 This is the capacitive response of the capacitive flexible pressure sensor prepared in Example 7 of the present invention when placed on a volunteer's throat and the words "CPS" are spoken. The figure shows different responses for different English letters, with "CPS" corresponding to their respective characteristic peaks. This indicates that the sensor can be used for speech recognition.

[0102] Based on the above examples 1-8 and comparative example 1, it can be concluded through comparative verification of specific examples that as the number of combined meshes increases, the capacitance change rate of the capacitive flexible sensor becomes wider; under high pressure (>100kPa), the linearity also approaches 1 as the number of orders increases. Figure 3 , 4 It can be found that the larger the mesh number combination, the higher the linearity and the wider the range under high pressure. This situation occurs because the capacitive flexible sensor of the present invention adopts a stepped structure, which allows the "EDL" effect to be generated in a graded manner. The optimal embodiment 7 adopts a three-level protruding stepped structure. First, a structure with a small mesh sandpaper mold is used as the first step, a structure with a medium mesh sandpaper mold is used as the second step, and a structure with a maximum mesh sandpaper mold is used as the third step. Compared with the first-level protruding stepped structure, the second-level stepped structure is smaller than the first, and the third level is also smaller than the second. The microstructure within each step is a randomly distributed pattern with large surface area compressibility. Due to the existence of this stepped structure, when the pressure increases from 0Pa to 1.2MPa, the contact process is divided into three stages:

[0103] 1) At low voltage, only a small portion of the electrode contacts the first-level stepped structure, resulting in small area variation and low EDL capacitance in the pF range.

[0104] 2) When greater pressure is applied, the first-level stepped structure begins to buckle and forms surface contact with the electrode, and the second-level also changes from line contact to surface contact, resulting in a significant change in contact area and a relatively high EDL capacitance.

[0105] 3) Under high-voltage conditions, the curved protruding structure of the first stage can withstand high forces, and under condition 2, the addition of the third step promotes the formation of more surface contact area, thereby increasing the capacitance of the EDL.

[0106] The graded “EDL” effect ensures high sensitivity while fully guaranteeing linearity.

[0107] The capacitive flexible pressure sensor fabricated in this invention also exhibits rapid response and recovery speeds, as well as excellent cycling stability. Compared to existing capacitive flexible sensors with stepped structures, it offers superior sensitivity and a wide detection range, strong overall performance, and a simple manufacturing process at a low cost. It also has potential applications in areas such as human motion monitoring and human-computer interaction.

[0108] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A capacitive flexible pressure sensor with adjustable gradient random micro-cone structure, characterized in that: include: Upper and lower electrodes, wherein the electrodes are transparent indium tin oxide conductive films; The packaging layer is a polyimide tape covering the outside of the electrode; A flexible isolation layer, which is a hollow polydimethylsiloxane layer located between the upper and lower electrodes; The dielectric layer with gradient random micro-cone structure is located inside the flexible isolation layer and is composed of polyvinyl alcohol and phosphoric acid in a mass ratio of 1:1; The gradient dielectric layer comprises three stepped structures, which are prepared by laser engraving a mold formed by sandpaper of different mesh sizes, and the sandpaper mesh size combination of the stepped structure is selected from one of the following: The first step structure is formed by 100 mesh, 200 mesh, 280 mesh or 500 mesh sandpaper casting; The second step structure is formed by 500 mesh, 1000 mesh or 1500 mesh sandpaper casting; The third step structure is formed by 1000 mesh, 1500 mesh, 2000 mesh or 5000 mesh sandpaper casting; The three step structures are arranged in order from low to high according to the sandpaper mesh number, and the difference in the sandpaper mesh number of adjacent steps is ≥200 meshes. When under pressure, the double layer effect is triggered step by step to achieve a graded capacitance response.

2. The capacitive flexible pressure sensor according to claim 1, wherein: The sandpaper mesh combination of the gradient dielectric layer is specifically: Three-step combination: 500 mesh / 1000 mesh / 1500 mesh, 1000 mesh / 2000 mesh / 5000 mesh, 280 mesh / 360 mesh / 500 mesh, 100 mesh / 500 mesh / 1000 mesh; Two-step combinations: 200 mesh / 1000 mesh, 500 mesh / 1000 mesh, 1000 mesh / 2000 mesh.

3. The capacitive flexible pressure sensor according to claim 1, wherein: The thickness of the dielectric layer is ≤300 μm, and within the pressure range of 0-1.2 MPa, the capacitance change rate is linearly related to the pressure, and the linearity R 2 ≥0.

99.

4. The capacitive flexible pressure sensor according to claim 1, wherein: After the sensor is circulated for 2200 seconds under a pressure of 100 kPa, the capacitance change rate decays by ≤5%, the response time is ≤34 ms, and the recovery time is ≤37.5 ms.

5. A method for preparing a capacitive flexible pressure sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1: Preparation of mold precursor solution: Mix silicone elastomer A and silicone elastomer B in a mass ratio of 1:1, stir, and then vacuum degas. Step 2: Step mold preparation: Use a laser to carve sandpaper into rectangular patterns <1 mm wide and affix them to a glass substrate in a stepped arrangement. Pour the precursor solution from step S1 into the mold, cure at 40°C for 24 hours, and then peel off to obtain an Ecoflex mold with a stepped structure. S3: Preparation of dielectric layer solution: 3 g of polyvinyl alcohol was dissolved in 27 g of deionized water, stirred at 90 °C for 2.5 hours, cooled to room temperature, and 3 g of phosphoric acid solution was added, and stirred for 2 hours; S4: Dielectric layer molding: inject the PVA / phosphoric acid solution from step S3 into the mold from step S2, cure at room temperature for 24 hours, and peel off to obtain a dielectric layer with a gradient random micro-cone structure; S5: Sensor assembly: Place the dielectric layer inside the PDMS flexible isolation layer, attach the PET / ITO electrode, and encapsulate the outer layer with PI tape.

6. The preparation method according to claim 5, wherein The mesh size of the sandpaper ranges from 100 mesh to 5000 mesh, and the sandpaper combination of the step mold is selected from: Three-step combination: 500 mesh / 1000 mesh / 1500 mesh, 1000 mesh / 2000 mesh / 5000 mesh; Two-step combinations: 200 mesh / 1000 mesh, 500 mesh / 1000 mesh.

7. The preparation method according to claim 5, wherein The width of the laser engraved sandpaper lines is 0.5-1 mm, and the mesh difference between adjacent step sandpapers is ≥300 meshes.

8. Application of the capacitive flexible pressure sensor according to any one of claims 1 to 4 in customized sensors for medical monitoring and human-computer interaction.

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