A flexible capacitive pressure sensor and a method of manufacturing the same

Abstract

The present application relates to the technical field of flexible electronic sensor, in particular to a flexible capacitive pressure sensor and a preparation method thereof, which comprises a top aerogel layer, a bottom aerogel layer, a three-dimensional porous network structure dielectric layer arranged between the two aerogel layers, and flexible electrodes respectively directly attached to the upper surface and the lower surface of the dielectric layer. The dielectric layer is composed of a polyvinyl alcohol matrix and two-dimensional transition metal carbonitride and spherical zirconium oxide dispersed therein, and the porous structure is introduced by mechanical foaming and locked by in-situ crosslinking. The electrode adopts a spray gun to directly spray silver conductive ink to form a conformal contact with the dielectric layer surface without an interface air gap. The aerogel layer is prepared by electrospinning and high-temperature sintering process, and the temperature resistance is not less than 200 DEG C. The sensor has a sensitivity of 105.4 kPa ‑1 , a response time of 36 ms, and a detection lower limit of 2 Pa, and has a wide application prospect in the field of extreme environment monitoring and wearable devices.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic sensor technology, specifically to a flexible capacitive pressure sensor and its fabrication method. Background Technology

[0002] Flexible capacitive pressure sensors possess advantages such as simple structure and good flexibility, making them highly promising for health monitoring and wearable devices. However, existing technologies face numerous challenges in balancing high sensitivity, low cost, and adaptability to complex operating conditions. Traditional methods for improving sensitivity often rely on expensive micro-nano fabrication processes like photolithography to construct surface microstructures in the dielectric layer. This not only hinders large-scale mass production but also makes the microstructures prone to collapse under high pressure, severely impacting the device's linearity and stability. Therefore, introducing polymers with three-dimensional porous network structures as dielectric layers offers a low-cost alternative, as the internal air pores significantly improve the compressibility of the dielectric layer. However, the low dielectric constant of pure polymer porous frameworks limits the initial capacitance and capacitance change rate of the device. While this can be improved by doping with conductive nanomaterials or high-dielectric inorganic particles, multidimensional nanofillers are extremely difficult to disperse uniformly in the matrix, and the foamed porous structure is prone to rupture before curing, making it difficult to maintain fatigue resistance and resilience under long-term repeated pressure. Compared to other sensors that rely on complex castings, achieving low-cost, rapid prototyping, and high-performance porous dielectric layers remains a fundamental problem that urgently needs to be solved.

[0003] Besides the core dielectric layer, existing sensors also suffer from serious defects in encapsulation protection and electrode interface assembly. Currently, most mainstream devices use polyimide (PI) tape or similar polymer films as the upper and lower protective substrates. These traditional materials have poor air permeability and extremely weak high-temperature resistance, making them prone to thermal degradation and failure in extreme industrial or harsh environments such as 200°C, severely limiting their application scenarios. Furthermore, traditional processes typically involve physical lamination of the flexible electrode to the dielectric layer. This non-conformal contact inevitably creates microscopic air gaps between the layers. These gaps not only increase interfacial impedance but also easily lead to relative slippage when the device is bent or subjected to pressure, causing severe hysteresis and drift in the sensing signal. Therefore, there is an urgent need to develop a novel flexible capacitive pressure sensor that can overcome the temperature resistance limits of traditional PI tape, eliminate assembly interface air gaps, and simultaneously achieve ultra-high sensitivity and adaptability to harsh environments, thereby completely solving the application bottlenecks of existing technologies. Summary of the Invention

[0004] The purpose of this invention is to provide a flexible capacitive pressure sensor and its preparation method, which uses mechanical foaming to construct a porous dielectric layer, combined with a direct-injection electrode and a high-temperature resistant aerogel protective layer to achieve high sensitivity and high-temperature resistance.

[0005] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: A flexible capacitive pressure sensor includes: Top aerogel layer and bottom aerogel layer; A three-dimensional porous network dielectric layer is disposed between the top aerogel layer and the bottom aerogel layer. The dielectric layer comprises a flexible polymer matrix, conductive nanomaterials dispersed in the matrix, and inorganic filler particles, and has an interconnected porous network structure with a pore size of 1 micrometer to 500 micrometers inside. And, respectively, a top flexible electrode and a bottom flexible electrode directly attached to the upper and lower surfaces of the dielectric layer.

[0006] Furthermore, the flexible polymer matrix is ​​polyvinyl alcohol, the conductive nanomaterial is a two-dimensional transition metal carbonitride, and the inorganic filler particles are spherical zirconium oxide.

[0007] Furthermore, the two-dimensional transition metal carbonitrides are attached to the surface of the polymer skeleton constituting the interconnected porous network structure in the form of nanosheets, and the spacing between them decreases when the skeleton is compressed; the spherical zirconium oxides are uniformly dispersed in the polymer skeleton, with a particle size of 0.5 μm to 5 μm.

[0008] Furthermore, the top aerogel layer and the bottom aerogel layer are inorganic composite aerogel layers prepared by electrospinning and high-temperature sintering processes. They have a short fiber three-dimensional network structure, a thickness of 100 μm to 1000 μm, and a porosity of 80% to 95%.

[0009] Furthermore, the top flexible electrode and the bottom flexible electrode are silver electrodes, and the silver electrodes are conformally bonded to the surface of the dielectric layer.

[0010] On the other hand, the present invention proposes a method for manufacturing the above-mentioned flexible capacitive pressure sensor, comprising: S1: Provides a high-temperature resistant aerogel protective layer; S2: Inorganic filler particles, anionic foaming agent and conductive nanomaterials are added to the aqueous solution of flexible polymer matrix and mixed evenly to obtain dielectric layer precursor mixture; S3: The precursor mixture is stirred and foamed at high speed using a mechanical stirring device to expand its volume and produce a uniform foam structure. S4: Add a crosslinking agent to the foamed system and stir, then heat to cure, so as to lock the foam structure in situ and form a three-dimensional porous network structure dielectric layer. S5: Flexible electrodes are directly formed on the upper and lower surfaces of the dielectric layer of the three-dimensional porous network structure, respectively. Then, the high-temperature resistant aerogel protective layer is attached to the upper and lower sides of the dielectric layer with the flexible electrodes to obtain the flexible capacitive pressure sensor.

[0011] Furthermore, step S1 specifically includes: Zirconium oxychloride octahydrate and aluminum nitrate nonahydrate are dissolved in a polyvinyl alcohol solution to form a precursor. The precursor is electrospun to form a composite fiber film. The composite fiber film is broken into short fibers and freeze-dried to form a short fiber skeleton. The short fiber skeleton is subjected to staged high-temperature treatment in an autoclave. First, it is treated at 200°C to remove the polyvinyl alcohol matrix, then at 800°C, and finally sintered at 1000°C to obtain the high-temperature resistant aerogel protective layer.

[0012] Furthermore, step S2 specifically includes: The aqueous solution of the flexible polymer matrix has a mass concentration of 5% to 15%; the inorganic filler particles are spherical zirconia, and the mass ratio of the filler particles to polyvinyl alcohol is 1:20 to 1:5; the anionic foaming agent is sodium dodecyl sulfate, and the mass ratio of the filler particles to polyvinyl alcohol is 1:200 to 1:20; the conductive nanomaterial is MXene, and the mass ratio of the conductive nanomaterial to polyvinyl alcohol is 1:200 to 1:10.

[0013] Furthermore, in step S4, the crosslinking agent is boric acid, and the heating curing conditions are heating at 30°C to 60°C for 15 to 60 minutes; in step S5, the flexible electrode is directly formed by spraying silver conductive ink evenly onto the upper and lower surfaces of the dielectric layer using a spray gun, and then curing it to form the top flexible electrode and the bottom flexible electrode.

[0014] Furthermore, in step S2, the specific dosage ratio of each raw material is as follows: 0.5g of spherical zirconium oxide is added to every 10mL of 10% polyvinyl alcohol aqueous solution, and after ultrasonic dispersion, 0.07g of sodium dodecyl sulfate and 0.05g of MXene are added; in step S4, the specific conditions for heating and curing are heating at 40°C for 30 minutes in a constant temperature and humidity chamber.

[0015] The beneficial effects of this invention are: The interconnected porous network structure introduced by mechanical foaming and locked in situ through cross-linking in the dielectric layer of this invention, synergistically with the two-dimensional transition metal carbonitrides and spherical zirconium oxide dispersed in the polymer framework, enables the sensor to possess both high sensitivity and a low detection limit. The micron-scale air pores constructed within the dielectric layer by mechanical foaming significantly reduce the elastic modulus of the dielectric layer, making it prone to macroscopic compressive deformation under pressure. The two-dimensional transition metal carbonitride nanosheets uniformly distributed in the polyvinyl alcohol framework constitute a microcapacitor network. When the porous framework is compressed, the narrowing of the nanosheet spacing induces interfacial polarization and microcapacitor permeation effects, causing the equivalent dielectric constant of the dielectric layer to increase sharply with increasing pressure, endowing the sensor with a pressure range of 0 to 1000 kPa.-1 The sensitivity is high. At the same time, the spherical zirconia particles are uniformly dispersed in the framework as micro-stress concentration points. When the macroscopic deformation is not yet significant, local framework compression is induced around the particles, triggering the polarization response between adjacent nanosheets. This enables the sensor to generate a distinguishable capacitive step signal in response to a small pressure of 2 Pa, achieving an extremely low detection limit.

[0016] The direct adhesion structure between the electrode and the dielectric layer, along with the high-temperature resistant inorganic composite aerogel protective layer, jointly improve the sensor's response speed, signal stability, and temperature resistance. Silver conductive ink is directly sprayed onto the surface of the porous dielectric layer using a spray gun and cured to form the electrode. The silver ink, in a fluid form, penetrates and adapts to the microscopic undulations of the dielectric layer surface. After curing, it forms a conformal contact with the dielectric layer without interface gaps, eliminating the increased interfacial impedance caused by interface gaps and the relative slippage between the electrode and the dielectric layer under pressure, as seen in traditional physical laminated structures. This shortens the sensor response time to 36 ms and the recovery time to 24 ms, effectively suppressing signal hysteresis and baseline drift. An inorganic composite aerogel layer prepared by electrospinning and high-temperature sintering is used as the top and bottom protective layers. The aerogel is made by spinning, crushing, freeze drying and sintering in stages at a maximum temperature of 1000 °C, using zirconium oxychloride octahydrate and aluminum nitrate nonahydrate as precursors. Its low thermal conductivity structure provides effective thermal insulation for the internal dielectric layer, enabling the sensor to maintain a stable capacitive response output at a high temperature of 200 °C, breaking through the temperature limit of traditional polyimide tapes that will shrink and fail at 120 °C.

[0017] The entire preparation process of this invention does not require photolithography or high-temperature vacuum deposition. The dielectric layer and electrode assembly can be completed by mechanical foaming with a whisk, in-situ crosslinking of boric acid, spraying silver ink with a spray gun, and constant temperature curing. The electrospinning and high-temperature sintering of the aerogel layer are also mature industrial technologies. The raw materials are all bulk chemicals. The overall equipment threshold and material cost of the process are significantly lower than the existing solutions that rely on micro-nano processing, and it has industrial feasibility for large-scale preparation.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1This is a schematic diagram of the flexible pressure sensor based on a three-dimensional porous network structure with an aerogel protective layer as described in Embodiment 1 of the present invention; 1. Aerogel layer; 2. Top and bottom flexible silver electrodes directly sprayed onto the surface of the dielectric layer; 3. Three-dimensional porous network structure dielectric layer; 4. Spherical zirconia particles in the three-dimensional porous network structure dielectric layer; 5. MXene nanosheets in the three-dimensional porous network structure dielectric layer.

[0021] Figure 2 The sensing mechanism and equivalent circuit diagram of the flexible capacitive pressure sensor prepared in Example 1 of the present invention are shown in (a) and (b) respectively. (a) is a diagram of the microscopic mechanism changes during the pressure process.

[0022] Figure 3 This is a flowchart illustrating the preparation of the three-dimensional porous network structure composite dielectric layer and the direct electrode assembly process described in Embodiment 1 of the present invention. 6. Polyvinyl alcohol (PVA), 7. Beaker, 8. Deionized water, 9. Spherical zirconia particles, 10. PVA / spherical zirconia particle mixed solution, 11. Magnetic stirrer, 12. Ultrasonic instrument, 13. Sodium dodecyl sulfate (SDS), 14. Precursor mixture, 15. MXene, 16. Egg beater, 17. Borax, 18. Constant temperature and humidity chamber, 19. Spray gun, 20. Silver conductive ink.

[0023] Figure 4 This is a flowchart illustrating the preparation process of the thermal insulation aerogel described in Example 1 of the present invention (including electrospinning, short fiber treatment, freeze-drying, and high-temperature sintering processes). 21. Zirconium oxychloride octahydrate, 22. 10% PVA solution, 23. Aluminum nitrate nonahydrate, 24. Electrospinning precursor solution, 25. Electrospinning machine, 26. Electrospinning receiving plate, 27. Aerogel spun film, 28. Surgical scissors, 29. Cut aerogel spun film piece, 30. Deionized water, 31. Tert-butanol, 32. Ultrasonic instrument, 33. Mold, 34. Freeze dryer, 35. Autoclave, 36. Aerogel.

[0024] Figure 5 The sensitivity curve of the flexible capacitive pressure sensor prepared in Example 1 of the present invention.

[0025] Figure 6 The response time and recovery time performance test diagrams of the flexible capacitive pressure sensor prepared in Example 1 of the present invention are shown.

[0026] Figure 7 The sensing performance test diagram shows the minimum pressure detection resolution (2 Pa) of the flexible capacitive pressure sensor prepared in Example 1 of the present invention.

[0027] Figure 8The flexible capacitive pressure sensor prepared in Example 1 of the present invention accurately captures and outputs the pulse signal response curve when it is attached to the human body surface.

[0028] Figure 9 A comparison of the sensitivity performance of the flexible capacitive pressure sensor prepared in Example 1 of the present invention under normal temperature and high temperature conditions of 180°C. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a flexible capacitive pressure sensor and its fabrication method.

[0032] like Figure 1 As shown, the flexible pressure sensor comprises, from top to bottom: a top aerogel layer 1, a top silver electrode 2, a three-dimensional porous network dielectric layer 3, a bottom silver electrode 2, and the bottom aerogel layer 1. The three-dimensional porous network dielectric layer 3 contains spherical zirconia particles 4 and MXene nanosheets 5. The top and bottom silver electrodes are directly attached to the upper and lower surfaces of the dielectric layer, respectively, forming a conformal contact without interface gaps. This completely eliminates the microscopic gaps and the resulting increase in interface impedance and signal drift problems present in traditional physical lamination processes.

[0033] In this embodiment, the three-dimensional porous network dielectric layer is composed of polyvinyl alcohol as a flexible polymer matrix, two-dimensional transition metal carbonitrides as conductive nanomaterials, and spherical zirconium oxide as inorganic filler particles. The dielectric layer contains an interconnected porous network structure introduced by mechanical foaming and locked in situ through cross-linking. The two-dimensional transition metal carbonitrides are distributed within the polymer framework constituting this interconnected porous network structure, forming a microcapacitor network that exhibits interfacial polarization due to reduced interlayer spacing under pressure. The spherical zirconium oxide, acting as a high-dielectric filler and micro-stress concentration point, is uniformly dispersed within the framework. This effectively compensates for the initial capacitance reduction caused by the high air content in the porous structure, and also acts as a micro-stress concentration point when the sensor is under pressure, further promoting local compression deformation of the porous polymer framework and significantly improving the device's detection resolution for minute pressures.

[0034] The sensor fabrication method in this embodiment includes: First, the high-temperature resistant aerogel protective layer is prepared, and the complete process flow is as follows: Figure 4 As shown. In a 10% polyvinyl alcohol solution 22, zirconium oxychloride octahydrate 21 and aluminum nitrate nonahydrate 23 were added as inorganic precursor sources. The mixture was stirred continuously at room temperature for 12 h using a magnetic stirrer to ensure that the metal salts were fully dissolved and mixed evenly, resulting in an electrospinning precursor solution 24. Subsequently, the precursor solution was transferred to an electrospinning apparatus 25, with the solution feed rate set at 0.8 mL / h, the applied voltage at 18 kV, and the receiving distance at 17 cm. Electrospinning was performed at room temperature, and an aerogel spun film 27 was collected on the receiving plate 26. Next, the obtained spun film was removed and preliminarily cut into small pieces 29 using surgical scissors 28. These small pieces were then placed in an ultrasonic instrument 32 containing deionized water 30 and tert-butanol 31 for high-power ultrasonic treatment. The mechanical shearing action of the ultrasound was used to completely break down the long fibers, forming a uniform short fiber dispersion. The short fiber dispersion was poured into mold 33 and placed in freeze dryer 34 at -80 °C for 48 h to allow direct sublimation of water, thereby constructing a three-dimensional short fiber skeleton with high porosity. Finally, the freeze-dried aerogel preform was placed in autoclave 35 and subjected to a staged high-temperature treatment process: first, heating at 200 °C for 2 h to completely thermally degrade and remove the polyvinyl alcohol organic component serving as a flexible template; then, further heating to 800 °C for 2 h; and finally, high-temperature sintering at 1000 °C for 2 h. After natural cooling, an inorganic composite aerogel 36 with a temperature resistance of not less than 200 °C was obtained.

[0035] The next steps involve the preparation of the dielectric layer precursor mixture, mechanical foaming, in-situ cross-linking and curing, and direct electrode assembly. The complete process flow is as follows: Figure 3 As shown. 10 mL of a 10% polyvinyl alcohol solution 6 was placed in a beaker 7, and 0.5 g of spherical zirconia particles 9 were added. The mixture was stirred thoroughly using a magnetic stirrer 11 to obtain a mixed solution 10 of polyvinyl alcohol and spherical zirconia particles, ensuring uniform dispersion of the spherical zirconia particles. The mixed solution was then sonicated for 60 min using an ultrasonicator 12. Next, 0.07 g of sodium dodecyl sulfate 13 as an anionic foaming agent and 0.05 g of a two-dimensional transition metal carbonitride 15 as a conductive nanomaterial were added sequentially. The mixture was stirred thoroughly again using a magnetic stirrer to ensure uniform dispersion of all components, ultimately yielding a uniform gray precursor mixture 14.

[0036] Mechanical foaming was then performed. Approximately 5 mL of the prepared precursor mixture was placed in a foaming container, and a standard mechanical whisk 16 was used as the mechanical stirring device to stir and foam it at high speed. Under the surfactant effect of sodium dodecyl sulfate, a large amount of air was entrained inside the mixture, causing a significant volume expansion and forming a uniform and stable foam structure.

[0037] Immediately after foaming, in-situ crosslinking and curing are performed. 0.1 g of boric acid 17 is rapidly added to the foamed system as a crosslinking agent and briefly stirred. The mixture is then poured into a mold of a specific size and placed in a constant temperature and humidity chamber 18 at 40 °C for 30 min. Boric acid undergoes a rapid dynamic crosslinking reaction with polyvinyl alcohol, instantly locking and curing the three-dimensional porous structure generated by mechanical foaming. After dehydration and molding, a composite dielectric layer with a three-dimensional porous network structure is obtained.

[0038] Finally, electrode formation and device assembly are performed. Silver conductive ink 20 is uniformly sprayed onto the upper and lower surfaces of the cured dielectric layer using a spray gun 19. After the silver ink cures, tightly adhered top and bottom flexible silver electrodes are formed directly on the dielectric layer surface. These silver electrodes form a conformal contact with the porous structure of the dielectric layer surface without interface gaps. Subsequently, pre-prepared high-temperature resistant aerogel protective layers are attached to the upper and lower sides of the dielectric layer with electrodes, completing the assembly of the entire capacitive flexible pressure sensor.

[0039] Example 2

[0040] The sensor structure and preparation method in this embodiment are basically the same as those in Embodiment 1, except that an alternative mixing ratio of the dielectric layer precursor solution is provided. In some embodiments, the relative amounts of spherical zirconium oxide, sodium dodecyl sulfate foaming agent, and two-dimensional transition metal carbonitride nanosheets can be adjusted within a certain range according to specific sensitivity and measurement range requirements, without departing from the core concept of the present invention. The sensor prepared in this embodiment can also achieve high-sensitivity pressure detection and withstand temperatures not lower than 200 °C.

[0041] Comparative Example 1 This comparative example provides a solid dielectric layer sensor without a foamed porous structure to verify the technical effect achieved by the mechanical foaming process of the present invention.

[0042] The difference between this comparative example and Example 1 is that sodium dodecyl sulfate foaming agent was not added to the dielectric layer precursor solution, and the mechanical foaming step was completely omitted, thus preparing a solid composite dielectric layer. Specifically, 0.5 g of spherical zirconia particles were added sequentially to 10 mL of a 10% (w / w) polyvinyl alcohol solution, magnetically stirred and dispersed, and then ultrasonically treated. Next, 0.05 g of two-dimensional transition metal carbonitride nanosheets were added and stirred until homogeneous. Then, 0.1 g of boric acid solution was directly added, and without any mechanical foaming treatment, the mixture was directly poured into a mold and heated for cross-linking and curing. Finally, silver electrodes were directly sprayed onto the upper and lower surfaces of the cured solid dielectric layer, and upper and lower aerogel protective layers were assembled.

[0043] Under the same testing conditions, the dielectric layer of the sensor prepared in this comparative example has a solid and dense structure, lacking internal micron-level air pores, and exhibits extremely high elastic modulus, making it difficult to undergo effective volume compression and deformation under external mechanical pressure. Test results show that the capacitance change rate of this solid sensor is extremely low, and its overall sensitivity is far lower than the 105.4 kPa achieved in Example 1. -1 The sensitivity index is thus demonstrated. This strongly proves that constructing a three-dimensional interconnected porous network structure using mechanical foaming technology is a key prerequisite for reducing the elastic modulus of the dielectric layer and achieving high pressure response sensitivity.

[0044] Comparative Example 2 This comparative example provides a sensor that uses traditional polyimide tape encapsulation and physical bonding assembly to verify the technical effect of the aerogel protective layer and electrode direct injection process of the present invention.

[0045] The difference between this comparative example and Example 1 is that the high-temperature resistant inorganic aerogel protective layer and the direct electrode spraying process are completely omitted. Instead, a traditional polyimide tape and physical lamination assembly method is used. Specifically, a composite dielectric film with a three-dimensional porous network structure is prepared according to the same steps as in Example 1. In the electrode assembly stage, instead of directly spraying silver electrodes onto the dielectric layer surface, a traditional process is used to spray silver conductive ink onto the inner sides of the upper and lower polyimide tapes and cure it to form electrodes. Finally, the polyimide tape with electrodes is mechanically bonded to the upper and lower surfaces of the porous dielectric layer through physical lamination to obtain a complete sensor.

[0046] Under the same room temperature testing conditions, the response time of the sensor prepared in this comparative example was significantly slower than the 36 ms response speed achieved in Example 1, and a significant signal hysteresis phenomenon was observed during pressure unloading. This is because the physical bonding between the traditional polyimide tape and the porous dielectric layer cannot achieve perfect conformal contact; the microscopic air gaps between the layers increase the interfacial impedance and lead to interfacial slippage under pressure. In extreme temperature resistance tests, when the ambient temperature rises to 120 °C or higher, the traditional polyimide tape in the comparative example undergoes severe thermal shrinkage and mechanical degradation, the electrode layer detaches, and the sensor completely fails with no signal output. In stark contrast, Example 1, benefiting from the excellent thermal stability of the inorganic composite aerogel layer and the robust conformal interface formed by direct electrode injection, can still stably output a capacitive response signal at a high temperature of 200 °C without any thermal failure. This fully demonstrates that the introduction of a high-temperature resistant aerogel protective layer and direct electrode injection process in this invention has irreplaceable technical value in eliminating interfacial air gaps, improving response speed, and breaking through the temperature resistance limits of traditional flexible sensors.

[0047] Example 1 To verify the excellent performance of the sensor prepared in Example 1 of the present invention, its sensing mechanism was analyzed and its comprehensive performance was tested.

[0048] In terms of sensing mechanism, Figure 2 The sensing mechanism and equivalent circuit of this sensor are illustrated. Among them, Figure 2 Figure 'a' represents the microscopic mechanism changes during the compression process. Figure 2 Figure b shows the corresponding equivalent circuit diagram. Because the silver electrode is directly sprayed onto the surface of the dielectric layer, the interfacial air gaps inherent in traditional physical bonding are eliminated, ensuring perfect stress transfer. Initially, the dielectric layer contains numerous air pores introduced by mechanical foaming and a composite solid framework. Under low pressure, the porous structure is easily compressed, the pore volume decreases rapidly, and the expelled air leads to a significant increase in the equivalent dielectric constant of the dielectric layer. Under high pressure, not only are the macroscopic pores further compressed, but the spacing between the two-dimensional transition metal carbonitride nanosheets distributed within the polyvinyl alcohol framework decreases sharply, forming numerous microcapacitors and triggering a strong microcapacitor percolation effect, resulting in a sharp increase in overall capacitance.

[0049] Regarding sensitivity and linear range testing, Figure 5 This is a sensitivity curve of the sensor prepared in this embodiment. A wide pressure range of 0–1000 kPa was applied to the sensor, and the rate of change of capacitance was recorded. The test results show that the sensor has extremely high sensitivity over a wide pressure range, reaching 105.4 kPa. -1 It also maintained excellent linearity.

[0050] Regarding response time and recovery time testing,Figure 6 The graph shows the response and recovery time performance of the sensor prepared in this embodiment. When a pulse pressure of 100 kPa is applied instantaneously, the sensor's response time is only about 36 ms, and the recovery time after the pressure is removed is about 24 ms. This excellent transient response capability demonstrates that the cross-linked polyvinyl alcohol porous framework endows the dielectric layer with excellent viscoelasticity and rapid mechanical rebound capability, and also confirms that the direct electrode injection process completely eliminates interface slippage and signal hysteresis.

[0051] Regarding minimum detection limit testing, Figure 7 This is a test graph showing the sensing performance of the sensor prepared in this embodiment at a minimum pressure detection resolution of 2 Pa. Placing a tiny weight of only 20 mg on the sensor surface is equivalent to applying an extremely small pressure of 2 Pa, and the sensor instantly outputs a clear and highly stable capacitive step signal. This indicates that the doped spherical zirconia acts as a micro-stress concentration point, giving the sensor an extremely low detection limit and enabling it to accurately capture extremely weak external forces.

[0052] In terms of monitoring human physiological signals, Figure 8 This is a pulse signal response curve accurately captured and output by the sensor prepared in this embodiment when attached to the human body surface. The sensor was attached to the radial artery of the test subject's wrist for pulse monitoring. The sensor accurately and without delay captured the human pulse signal, producing a clear output waveform with a high signal-to-noise ratio and exhibiting perfect periodicity. The measured pulse frequency was stable at 68 beats / min, verifying its application potential in the field of wearable medical health monitoring.

[0053] In terms of extreme operating condition performance testing, Figure 9 This diagram compares the sensitivity performance of the sensor fabricated in this embodiment under normal temperature and 180°C high-temperature conditions. The sensor was placed in both normal temperature and 180°C environments for sensitivity comparison tests. The test results show that, due to the use of a high-temperature resistant inorganic aerogel protective layer, the sensor's internal three-dimensional porous dielectric layer provides excellent thermal insulation protection even at extreme temperatures of 180°C and even 200°C. The sensitivity curve at high temperatures highly overlaps with that at normal temperature, and the capacitive signal output remains stable. No signal drift or thermal failure phenomena common in traditional flexible devices were observed, demonstrating excellent stability under all operating conditions.

[0054] In summary, this invention proposes a flexible capacitive pressure sensor and its fabrication method, comprising a top aerogel layer, a bottom aerogel layer, a three-dimensional porous network dielectric layer disposed between the two aerogel layers, and flexible electrodes directly attached to the upper and lower surfaces of the dielectric layer, respectively. The dielectric layer is composed of a polyvinyl alcohol matrix and two-dimensional transition metal carbonitrides and spherical zirconium oxide dispersed therein. Its porous structure is introduced by mechanical foaming and locked in situ through cross-linking. The electrodes are formed by direct spraying of silver conductive ink using a spray gun, forming a conformal contact with the dielectric layer surface without interface gaps. The aerogel layer is prepared by electrospinning and high-temperature sintering processes, with a temperature resistance of not less than 200℃. The sensor achieves a sensitivity of 105.4 kPa. -1 With a response time of 36 ms and a detection limit of 2 Pa, it has broad application prospects in extreme environment monitoring and wearable devices.

[0055] 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 flexible capacitive pressure sensor, characterized in that, include: Top aerogel layer and bottom aerogel layer; A three-dimensional porous network dielectric layer is disposed between the top aerogel layer and the bottom aerogel layer. The dielectric layer comprises a flexible polymer matrix, conductive nanomaterials dispersed in the matrix, and inorganic filler particles, and has an interconnected porous network structure with a pore size of 1 micrometer to 500 micrometers inside. And, respectively, a top flexible electrode and a bottom flexible electrode directly attached to the upper and lower surfaces of the dielectric layer.

2. The flexible capacitive pressure sensor as described in claim 1, characterized in that, The flexible polymer matrix is ​​polyvinyl alcohol, the conductive nanomaterial is a two-dimensional transition metal carbonitride, and the inorganic filler particles are spherical zirconium oxide.

3. The flexible capacitive pressure sensor as described in claim 2, characterized in that, The two-dimensional transition metal carbonitrides are attached to the surface of the polymer skeleton constituting the interconnected porous network structure in the form of nanosheets, and the spacing between them decreases when the skeleton is compressed; the spherical zirconium oxides are uniformly dispersed in the polymer skeleton, and their particle size is 0.5 μm to 5 μm.

4. The flexible capacitive pressure sensor as described in claim 1, characterized in that, The top and bottom aerogel layers are inorganic composite aerogel layers prepared by electrospinning and high-temperature sintering processes. They have a short fiber three-dimensional network structure, a thickness of 100 μm to 1000 μm, and a porosity of 80% to 95%.

5. The flexible capacitive pressure sensor as described in claim 1, characterized in that, The top flexible electrode and the bottom flexible electrode are silver electrodes, and the silver electrodes are conformally bonded to the surface of the dielectric layer.

6. A method for manufacturing a flexible capacitive pressure sensor according to any one of claims 1 to 5, characterized in that, include: S1: Provides a high-temperature resistant aerogel protective layer; S2: Inorganic filler particles, anionic foaming agent and conductive nanomaterials are added to the aqueous solution of flexible polymer matrix and mixed evenly to obtain dielectric layer precursor mixture; S3: The precursor mixture is stirred and foamed at high speed using a mechanical stirring device to expand its volume and produce a uniform foam structure. S4: Add a crosslinking agent to the foamed system and stir, then heat to cure, so as to lock the foam structure in situ and form a three-dimensional porous network structure dielectric layer. S5: Flexible electrodes are directly formed on the upper and lower surfaces of the dielectric layer of the three-dimensional porous network structure, respectively. Then, the high-temperature resistant aerogel protective layer is attached to the upper and lower sides of the dielectric layer with the flexible electrodes to obtain the flexible capacitive pressure sensor.

7. The preparation method according to claim 6, characterized in that, Step S1 specifically includes: Zirconium oxychloride octahydrate and aluminum nitrate nonahydrate are dissolved in a polyvinyl alcohol solution to form a precursor. The precursor is electrospun to form a composite fiber film. The composite fiber film is broken into short fibers and freeze-dried to form a short fiber skeleton. The short fiber skeleton is subjected to staged high-temperature treatment in an autoclave. First, it is treated at 200°C to remove the polyvinyl alcohol matrix, then at 800°C, and finally sintered at 1000°C to obtain the high-temperature resistant aerogel protective layer.

8. The preparation method according to claim 6, characterized in that, Step S2 specifically includes: The aqueous solution of the flexible polymer matrix has a mass concentration of 5% to 15%; the inorganic filler particles are spherical zirconia, and the mass ratio of the filler particles to polyvinyl alcohol is 1:20 to 1:5; the anionic foaming agent is sodium dodecyl sulfate, and the mass ratio of the filler particles to polyvinyl alcohol is 1:200 to 1:20; the conductive nanomaterial is MXene, and the mass ratio of the conductive nanomaterial to polyvinyl alcohol is 1:200 to 1:

10.

9. The preparation method according to claim 6, characterized in that, In step S4, the crosslinking agent is boric acid, and the heating curing conditions are heating at 30°C to 60°C for 15 to 60 minutes; in step S5, the flexible electrode is formed directly by using a spray gun to uniformly spray silver conductive ink onto the upper and lower surfaces of the dielectric layer, and then curing it to form the top flexible electrode and the bottom flexible electrode.

10. The preparation method according to claim 6, characterized in that, In step S2, the specific dosage ratio of each raw material is as follows: 0.5g of spherical zirconium oxide is added to every 10mL of 10% polyvinyl alcohol aqueous solution, and after ultrasonic dispersion, 0.07g of sodium dodecyl sulfate and 0.05g of MXene are added; in step S4, the specific conditions for heating and curing are heating at 40°C for 30 minutes in a constant temperature and humidity chamber.

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