Signal-drift-free and low-lag ionizing capacitive pressure sensor and preparation method and application thereof

Abstract

The invention discloses a signal-drift-free and low-lag ionization type capacitance pressure sensor and a preparation method and application thereof. The ionization type capacitance pressure sensor comprises a capacitance medium and substrates which are attached to the upper surface and the lower surface of the capacitance medium and comprise electrodes. The capacitor medium takes silicone rubber foam as a matrix, the surface of the silicone rubber foam is uniformly coated with a layer of polydopamine, the polydopamine is combined on the surface of the silicone rubber foam through multi-covalent and non-covalent interaction, and a bis (fluorosulfonyl) imide ion layer is formed on the surface of the polydopamine through protonation and ion exchange. The ionizing capacitive pressure sensor provided by the invention shows excellent detection performance in a wider pressure range, is high in sensitivity, high in response speed, good in long-term stability, capable of working in a wider temperature range and good in high and low temperature resistance stability, and the stability is remarkably superior to that of a traditional ion electronic sensor; and a solid foundation is laid for the development of real-time physiological signal monitoring and intelligent man-machine interaction systems.

Description

Technical Field

[0001] This invention belongs to the field of force or stress measurement technology by measuring the change of ohmic resistance of solid materials or conductive fluids, and specifically relates to an ionized capacitive pressure sensor with no signal drift and low hysteresis, as well as its preparation method and application. Background Technology

[0002] With the rapid development of artificial tactile systems in robotics, autonomous driving, and wearable health monitoring, the demand for high-performance flexible pressure sensors is becoming increasingly urgent. Capacitive sensors have attracted widespread attention due to their simple structure, low power consumption, and fast response speed. However, traditional capacitive sensors based on dielectric elastomers are limited by their inherently low capacitance (on the order of picofarads) and poor material compressibility, making it difficult to simultaneously achieve high sensitivity (>10 kPa). -1 These sensors offer a wide pressure detection range (>1000 kPa). Emerging ionized capacitive pressure sensors utilize ionic conductors (such as polymer gels loaded with ionic liquids) as the dielectric layer, achieving extremely high interfacial capacitance by forming an electrical double layer (EDL) structure at the interface between the ionic and electronic conductors. The capacitance of these sensors is typically 4–6 orders of magnitude higher than that of traditional capacitive devices, significantly improving sensitivity, signal-to-noise ratio, and resolution. However, during long-term use, creep of the polymer matrix and leakage of ionic solvents can still easily lead to signal drift and measurement inaccuracies, especially under continuous pressure loads. These phenomena are mainly caused by polymer chain rearrangement and capillary-induced phase separation.

[0003] Furthermore, in practical applications, sensors often face significant environmental temperature variations. Ion migration within the sensor is affected by temperature, and the viscoelastic creep of the polymer backbone is also temperature-sensitive. Increased temperature accelerates ion migration within the electrolyte, increases the risk of leakage, and alters the electrochemical balance of the double layer. It also softens the polymer network and amplifies creep deformation. Conversely, low temperatures slow down ion transport, hinder EDL charging kinetics, and often lead to hysteresis and unstable capacitance recovery. This reduces the stability of sensor pressure detection, making drift-free operation over a wide temperature range particularly challenging.

[0004] Based on this, the present invention uses silicone rubber foam as the matrix and obtains hydrophobic ionic foam through polydopamine protonation and ion exchange. This not only makes the ions bond more firmly to the matrix and significantly reduces ion migration, but also greatly improves the stability of the sensor under different operating environments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art by providing an ionized capacitive pressure sensor with no signal drift and low hysteresis, as well as its preparation method and application. The ionized capacitive pressure sensor exhibits excellent detection performance in the pressure range of 10Pa-3000kPa, with high sensitivity, fast response speed, good long-term stability, minimal capacitance attenuation, almost no signal drift, and is applicable to a wide temperature range.

[0006] The first aspect of the present invention provides an ionized capacitive pressure sensor with no signal drift and low hysteresis, the ionized capacitive pressure sensor comprising a capacitive dielectric and a substrate containing electrodes attached to the upper and lower surfaces of the capacitive dielectric. The capacitor dielectric uses silicone rubber foam (PDMS) as the matrix, and a layer of polydopamine (PDA) is uniformly coated on the surface of the silicone rubber foam. The polydopamine is bonded to the surface of the silicone rubber foam through multiple covalent and non-covalent interactions, and a bisfluorosulfonamide (TFSI) ion layer is formed on the surface of the polydopamine through protonation and ion exchange.

[0007] According to the above scheme, the substrate containing the electrode is a polyimide (PI) film with one side covered with an electrode (silver or copper electrode), wherein the side covered with the electrode is bonded to the capacitor dielectric.

[0008] According to the above scheme, the silicone rubber foam is an ordered porous foam with an open pore structure and a face-centered cubic (FCT) structure. It is obtained by 3D printing and has a pore size of 150-600μm and a thickness of 500-900μm.

[0009] According to the above scheme, the thickness of polydopamine on the surface of the silicone rubber foam is 120-360nm.

[0010] According to the above scheme, the pressure monitoring range of the sensor is 10Pa-3000kPa, and the peak sensitivity is 20-30kPa. -1 The response time is 3-6ms.

[0011] The second aspect of this invention provides a method for fabricating the above-mentioned signal drift-free, low-hysteresis ion-capacitive pressure sensor, the specific steps of which are as follows: 1) Silicone rubber foam was prepared using 3D printing. 2) Preparation of capacitor dielectric: Trimethylolpropionate was dissolved in deionized water, and the pH of the system was adjusted to 7-9 with hydrochloric acid solution to obtain a trimethylolpropionate solution. Then, the silicone rubber foam obtained in step 1) and dopamine hydrochloride were added to the obtained trimethylolpropionate solution and stirred to react. After the reaction was completed, the silicone rubber foam was taken out, rinsed and dried to obtain PDA-coated silicone rubber foam. The obtained PDA-coated PDMS foam was placed in an acidic solution to fully protonate the PDA. Then, lithium bis(fluorosulfonyl)imide (LiTFSI) was added to it for ion exchange. Finally, it was washed and dried to obtain capacitor dielectric. 3) Fabrication of an ionized capacitive pressure sensor: Two substrates containing electrodes are attached to the upper and lower surfaces of the capacitor dielectric, and then packaged to obtain an ionized capacitive pressure sensor.

[0012] According to the above scheme, in step 1), silicone rubber foam is prepared by 3D printing. During the 3D printing process, the line spacing is set to 0.35-0.8mm, the line width is set to 0.15-0.25mm, and the number of printing layers is set to 4-8.

[0013] According to the above scheme, the concentration of the trimethylolpropionic acid solution in step 2) is 0.01-0.02 g / mL.

[0014] According to the above scheme, the mass-to-volume ratio of dopamine hydrochloride to trimethylolpropionate solution in step 2) is 1g / 230-250mL.

[0015] According to the above scheme, the stirring reaction time in step 2) is 16-24 hours.

[0016] According to the above scheme, the acidic solution in step 2) is a hydrochloric acid solution with a concentration of 0.1-0.5 mol / L. The method to fully protonate the PDA by placing it in the acidic solution is to immerse it in the acidic solution and stir for 30-60 minutes.

[0017] According to the above scheme, in step 2), the concentration of lithium bis(fluorosulfonyl)imide in the acidic solution is 0.1-0.3 mol / L.

[0018] According to the above scheme, the method for ion exchange in step 2) is: stir the reaction for 30-60 minutes.

[0019] The third aspect of the present invention provides an application of the above-mentioned non-signal drift, low hysteresis ionized capacitive pressure sensor in the field of posture correction, which provides feedback on subtle posture changes by dynamically monitoring pressure changes.

[0020] This invention utilizes direct-write 3D printing to construct silicone rubber foam with low creep characteristics and excellent pressure response performance. First, the silicone rubber foam is placed in an alkaline solution containing dopamine. Dopamine molecules self-polymerize under alkaline conditions, loading a layer of polydopamine onto the silicone rubber surface. Then, the polydopamine is protonated and ion-exchanged to form a TFSI ion layer on the polydopamine surface. TFSI ions are adsorbed onto the foam skeleton through electrostatic interaction, effectively suppressing TFSI ion leakage. This layer is then combined with an electrode to obtain a flexible ion elastomer sensing layer. Under external pressure, the elastic foam undergoes significant compression deformation, causing a change in the contact area between its ordered porous skeleton and the electrode, thereby triggering a significant change in capacitance.

[0021] The beneficial effects of this invention are as follows: 1. The ion-electrode capacitive pressure sensor provided by this invention exhibits excellent detection performance in the pressure range of 36Pa-3000kPa, with high sensitivity, fast response speed (response and recovery times are approximately 3ms and 6ms, respectively), and good long-term stability. It can operate in a wide temperature range, has good high and low temperature stability, and maintains good signal stability even under high-frequency loading. After 10,000 cycles of compression, the capacitance decay rate is as low as 0.1%. Under continuous loading at 500kPa static pressure for 24 hours, the device shows almost no signal drift, and its stability is significantly better than that of traditional ion-electrode sensors. In addition, the device can continuously and accurately identify subtle posture changes during long-term operation without any observable drift. This "drift-free" ion-electrode capacitive pressure sensor provides strong support for achieving high-precision pressure monitoring and lays a solid foundation for the development of real-time physiological signal monitoring and intelligent human-computer interaction systems. 2. The preparation method of this invention is simple, the raw materials are common and readily available, and it is suitable for industrial-scale preparation. Attached Figure Description

[0022] Figure 1 XPS full spectrum of PDA@PDMS and PPDA@PDMS prepared in Example 1 of the present invention, and high-resolution XPS spectrum of C1s, S2p, O1s, N1s and F1s in PPDA@PDMS; Figure 2 The attenuated total reflectance Fourier transform infrared spectra of PDA@PDMS and PPDA@PDMS prepared in Example 1 are shown below. Figure 3 The cross-sectional X-ray spectral elemental distribution map and elemental mapping map of Si, O, F, N, C, and S of PPDA@PDMS prepared in Example 1; Figure 4 A comparison of the static water contact angles of PDMS, PDA@PDMS, and PPDA@PDMS prepared in Example 1; Figure 5A comparison graph showing the weight change of PPDA@PDMS prepared in Example 1 over time after standing at room temperature for 7 days; Figure 6 The compressive stress-strain test diagram of the FCT-0.2-0.6-6 sensor prepared in Example 1; Figure 7 The contact area (top) and cross-sectional image (bottom) of the FCT-0.2-0.6-6 sensor prepared for Example 1 under different pressure compressive strains. Figure 8 The test graph shows the change of capacitance response over time under repeated mechanical loads for the FCT-0.2-0.6-6 sensor prepared in Example 1, and the curves showing the change of capacitance response over time under constant loads at different compression speeds. Figure 9 The graph shows the relative capacitance change of the FCT-0.2-0.6-6 sensor prepared in Example 1 after 24 hours and 10 days of static pressure testing. Figure 10 The graph shows the change in capacitance of the FCT-0.2-0.6-6 sensor prepared in Example 1 after 10,000 cycles of testing between pressures of 0 and 500 kPa. Figure 11 The chart shows the applicability test results of the FCT-0.2-0.6-6 sensor prepared in Example 1 at different temperatures. Figure 12 The graph shows the change in the relative capacitance of four identical sensors prepared for Example 1 placed under the four legs of a chair and tested over time. Figure 13 A graph showing the change of relative capacitance values ​​over time measured by four sensors when a person is in different postures on a chair. Figure 14 The compressive stress-strain curve and the relative capacitance change under different applied pressures are shown for the FCT-0.2-0.4-6 sensor prepared in Example 2. Figure 15 The compressive stress-strain curve and the relative capacitance change under different applied pressures are shown for the FCT-0.2-0.8-6 sensor prepared in Example 3. Figure 16 The compressive stress-strain curve and the relative capacitance change under different applied pressures are shown for the FCT-0.15-0.45-6 sensor prepared in Example 4. Figure 17 The compressive stress-strain curve and the relative capacitance change under different applied pressures are shown for the FCT-0.25-0.75-6 sensor prepared in Example 5. Figure 18The compressive stress-strain curve and the relative capacitance change under different applied pressures are shown for the ST-0.2-0.6-6 sensor prepared for Comparative Example 1. Figure 19 The contact area (top) and cross-sectional image (bottom) of the ST-0.2-0.6-6 sensor prepared for Comparative Example 1 under different pressure compressive strains are shown. Figure 20 The sensor prepared for Comparative Example 2 was subjected to static compression of 500 kPa for 1 hour, and the changes in the relative capacitance and strain of the sensor over time were measured. Figure 21 The graph shows the relative capacitance change of the sensor prepared for Comparative Example 2 at 50℃ and a load pressure of 500 kPa. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0024] Example 1 The specific steps of fabricating an ion-capacitive pressure sensor are as follows: 1) Preparation of silicone rubber foam using 3D printing: The base silicone (Dow Corning SE1700 PDMS silicone rubber), curing agent (Dow Corning SE1700 curing agent) and inhibitor (3-buten-1-ol) were mixed in a mass ratio of 10:1:0.1 and stirred for 5 minutes until homogeneous. The resulting mixture was then centrifuged at 8000 rpm for 5 minutes to remove air bubbles. Subsequently, it was added to the hopper of the 3D printer. After setting the FCT structure printing parameters, printing was performed with a line spacing of 600 μm, a line width of 200 μm, and a number of printing layers of 6. The printed flexible rubber foam was cured in a 150℃ oven for 1 hour to obtain silicone rubber foam, denoted as PDMS. 2) Preparation of capacitor dielectric: 0.4 g of trimethylolpropionate was dissolved in 30 mL of deionized water, and then hydrochloric acid solution (37 wt%) was slowly added dropwise until the pH of the system reached 8.5 to obtain a trimethylolpropionate solution. Then, the silicone rubber foam obtained in step 1) (cut into discs with a diameter of 6 mm and a thickness of 815 μm) and 0.13 g of dopamine hydrochloride were added to the obtained trimethylolpropionate solution, and the mixture was stirred for 16 hours. The mixture was then removed, rinsed with deionized water and ethanol in sequence, and dried at 60 °C to obtain PDA-coated silicone rubber foam (denoted as PDA@PDMS). The obtained PDA-coated silicone rubber foam was then immersed in 20 mL of hydrochloric acid solution (0.1 mol / L) and stirred for 30 min to allow the PDA to be fully protonated. Then, 0.4 g of LiTFSI was added to the acidic solution and stirred for 30 min to carry out ion exchange. Finally, the mixture was rinsed with deionized water and dried at 50 °C for 4 h to obtain the capacitor dielectric, denoted as PPDA@PDMS. 3) Fabrication of an ionized capacitive pressure sensor: Two Cu / PI sheets (commercially available, 40 μm thick) are attached to the upper and lower surfaces of the capacitor dielectric obtained in step 2), with the Cu electrode in direct contact with the surface of the capacitor dielectric. The sensor is then encapsulated with a flexible polydimethylsiloxane film to obtain an ionized capacitive pressure sensor (denoted as FCT-0.2-0.6-6).

[0025] like Figure 1 (a) shows the XPS full spectrum of PDA@PDMS and PPDA@PDMS prepared in this embodiment. (b), (c), (d), (e), and (f) are the high-resolution XPS spectra of C 1s, S 2p, O 1s, N 1s, and F 1s in PPDA@PDMS, respectively. The surface of PDA@PDMS foam contains only C, N, and O elements, while the surface of PPDA@PDMS foam also contains S and F elements in addition to the above elements. In the high-resolution spectra of C 1s, S 2p, O 1s, N 1s, and F 1s of PPDA@PDMS foam, characteristic peaks such as C=O, C–S, C–F, and S=O originating from [TFSI] ions can be clearly identified.

[0026] Figure 2 The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of PDA@PDMS and PPDA@PDMS prepared in this embodiment are shown. For PDA@PDMS foam, the value is 3374 cm⁻¹. -1 The adsorption peak at 2852 cm⁻¹ is attributed to the overlapping stretching vibrations of the N–H bond and the O–H bond of the phenolic hydroxyl group. -1 and 2923cm -1 The adsorption signal at this location is attributed to the stretching vibrations of C–H and C=C in the indole structure. (1607 cm⁻¹) -1 and 1513cm -1The adsorption peak at this location is correlated with the bending and shear vibrations of N–H, confirming the presence of numerous imine and amine groups in the PDA unit. Compared to PDA@PDMS, PPDA@PDMS exhibits a peak at 1346 cm⁻¹. -1 and 1056cm -1 The obvious peak value corresponds to the stretching vibration of S=O and C–F bonds, indicating that the PDA chains on the foam surface have been reconstructed into a polyelectrolyte rich in TFSI counterions.

[0027] Figure 3 The elemental distribution map and elemental mapping maps of Si, O, F, N, C, and S in the cross-sectional X-ray spectroscopy (EDS) of PPDA@PDMS prepared in this embodiment further verify the presence of Si, O, C, F, N, and S elements within the foam. Si and O elements are distributed within the PDMS framework, while C, F, N, and S are mainly concentrated on the foam surface, indicating that PDA and [TFSI] ions are effectively fixed on the foam framework, and that [TFSI] ions are uniformly incorporated.

[0028] Figure 4 The static water contact angle comparison diagram of PDMS, PDA@PDMS and PPDA@PDMS prepared in this embodiment shows that PDMS has high hydrophobicity, the hydrophobicity decreases after PDA is composited on the surface, and the hydrophobicity is improved after PPDA@PDMS is further generated. The water contact angle of PPDA@PDMS is 128°, which shows excellent hydrophobic performance.

[0029] The PPDA@PDMS prepared in this embodiment was left to stand at room temperature for 7 days, and its weight change was tested. Figure 5 The graph shows a comparison of the weight of the PPDA@PDMS over time, indicating that its weight has not changed significantly.

[0030] The three-dimensional microstructure of the dielectric layer has a decisive influence on the response characteristics of ion electron sensors. Traditional microstructure fabrication methods, such as template casting and photolithography, are often complex and costly. In contrast, 3D printing technology offers high structural programmability, allowing for the free design of foam microstructures by precisely controlling parameters such as filament diameter, interlayer spacing, and arrangement, thereby flexibly adjusting the sensor's response range and sensitivity.

[0031] The sensitivity S of the sensor is defined as follows:

[0032] Where C0 represents the initial capacitance value before loading, and ΔC is the change in capacitance after applying pressure P. Because the foam has a supporting structure in its initial state, there is no direct contact between the electrode and the ion layer, so the initial capacitance is extremely small (approximately 2pF).

[0033] like Figure 6 (a) shows the compressive stress-strain curve of the FCT-0.2-0.6-6 sensor prepared in this embodiment. It can be seen that the sensor can achieve a wide pressure detection range of up to 2.8 MPa. The ion sensor based on FCT-0.2-0.6-6 foam has extremely high sensitivity over a wide pressure range. Figure 6 b). Three different sensitivity ranges (S1-S3≈21.4kPa) -1 7.4 kPa -1 2.9 kPa -1 These correspond to pressure ranges of 0.01-400 kPa, 400-1500 kPa, and 1500-2800 kPa, respectively. Initially, there is no contact between the foam and the electrodes, so the capacitance is essentially an air capacitance (C0~2 pF), almost unaffected by the test frequency. After loading, the top filament layer comes into contact with the electrodes, creating an electrically double-layer (EDL) capacitance. This capacitance is frequency-sensitive, causing the capacitance to rise rapidly (C~nF) and exhibiting extremely high sensitivity at low pressures. As the pressure increases, the upper filaments gradually deform, forming more EDL capacitors in parallel, thus enhancing the total capacitance. Under high pressure, the deeper layers compress, further increasing the contact area and signal amplification. Figure 6 (c) shows the response and recovery times of the FCT-0.2-0.6-6 sensor under a pressure of 100 kPa, with a response time of 3 ms and a recovery time of 6 ms. Figure 6 (d) is the test curve of the sensor's minimum detection limit. There is no signal display below 10 Pa, indicating that the minimum detection limit is 10 Pa.

[0034] Figure 7 The contact area (top) and cross-sectional image (bottom) of the FCT-0.2-0.6-6 sensor prepared for this embodiment under compressive stresses of 5 kPa (a), 50 kPa (b), 500 kPa (c), and 2000 kPa (d), respectively. The FCT structure is arranged in an interleaved stack, which can more uniformly distribute stress. Under low pressure, the foam is more easily deformed, resulting in smaller local strain of the top fiber and lower initial sensitivity of the sensor. Under higher pressure (>500 kPa), the fibers (0.2 mm in diameter) of the second and third layers in the FCT structure can easily pass through the wide gaps of the first layer, thereby increasing the contact area with the electrode and achieving higher sensitivity.

[0035] like Figure 8(a) shows the capacitance response of the FCT-0.2-0.6-6 sensor prepared in this embodiment under repeated mechanical loads as a function of time. The load pressure range was randomly increased from 20 kPa to 2500 kPa. It can be seen that the capacitance increases accordingly with the increase of pressure, which reflects the expansion of the contact area between the foam and the electrode. This monotonically increasing trend makes it possible to reliably distinguish the applied pressure level based on the capacitance. (b) shows the capacitance response as a function of time measured by the sensor under a constant load (500 kPa) at different compression rates (randomly increased from 0.2 mm / min to 4 mm / min). The sensor maintains excellent uniformity and stability under different loading rates, highlighting its robustness under dynamic conditions.

[0036] To evaluate long-term capacitance signal drift, a static pressure (500 kPa) was applied continuously for 24 hours to the FCT-0.2-0.6-6 sensor prepared in this embodiment, and the relative capacitance change of the sensor was tested. The test results are as follows: Figure 9 As shown in (a), the sensor maintains a stable capacitance with almost no drift and recovers immediately after unloading. The capacitance was monitored daily under a fixed load of 500 kPa for ten days. Figure 9 (b) No obvious drift was found, which indicates that PPDA@PDMS has the ability to resist polymer creep and ion leakage.

[0037] The FCT-0.2-0.6-6 sensor prepared in this embodiment was subjected to a compression rate of 500 kPa at a pressure of 5 mm / s from a pressure of 0. After compression to the maximum deformation, the pressure was released at a compression rate of 5 mm / s (reducing to 0). After the sensor recovered its shape, the pressure was applied again. This compression-release process was repeated 10,000 times. The change in sensor capacitance during the compression cycle was tested, and the test results are shown in the figure. Figure 10 As shown, the sensor capacitance changes very little during 10,000 cyclic compressions (the capacitance decay rate is as low as 0.1% after 10,000 cyclic compressions), with almost no hysteresis or signal attenuation.

[0038] To evaluate the applicability of the FCT-0.2-0.6-6 sensor prepared in this embodiment under different temperatures, the relative capacitance change of the sensor under load at different temperatures (-20℃, -10℃, 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃) was tested. The test results are shown in the figure below. Figure 11As shown in the figure, a) is a comparison of the relative capacitance change curves of the sensor under different temperatures and loads ranging from 0 to 1500 kPa, indicating that at the same temperature, the relative capacitance of the sensor is still positively correlated with the load pressure. As the temperature increases, the relative capacitance of the capacitor gradually increases under the same load pressure. b) is a comparison of the relative capacitance change curves of the sensor under a continuous static load (pressure 500 kPa) for 3 hours at different temperatures, showing that the relative capacitance drift value of the sensor is exceptionally low over the entire ultra-wide temperature range, with a maximum of only 4% at 90℃, which is far superior to traditional ion gel-based sensors. The test results show that the sensor prepared in this embodiment has excellent signal stability in the temperature range of -20℃ to 90℃. This stability stems from the macroscopic load distribution and geometric constraints of the framework FCT structure and the thermally stable polyelectrolyte interface, which together suppress thermally activated chain movement, local stress relaxation, and ion migration.

[0039] To test the practical application value of the sensor prepared in this embodiment, four identical sensors were prepared using the method described in this embodiment, denoted as Sensor1, Sensor2, Sensor3, and Sensor4. The four sensors were placed under the four legs of a chair (Sensor1: front left, Sensor2: rear left, Sensor3: front right, Sensor4: rear right) for ten minutes. The change in the relative capacitance value (ΔC / C0, where C0 is the initial capacitance value) of the four sensors over time was then measured. The test results are shown below. Figure 12 The four sensors exhibited stable and consistent signals during the 10-minute load test, reflecting the structural consistency of the capacitor dielectric prepared in this embodiment.

[0040] Further, the four sensors were used to monitor the load caused by changes in posture while seated. Common sitting postures were categorized into four types: upright, leaning forward, leaning left, and leaning left-forward. The relative capacitance changes of the four sensors were tested under these four postures (the person's weight was 60kg, and they maintained the same sitting posture for 10 minutes). The test results are shown below. Figure 13Of these, only the upright posture (a) produces a uniform pressure distribution and a low peak capacitance, which is conducive to spinal health. In contrast, the forward-leaning posture (b) shifts the center of gravity forward, resulting in enhanced signals from Sensors 1 and 3, while the signals from Sensors 2 and 4 decrease. Prolonged asymmetrical loading (such as the left-leaning posture, Figure c) alters the proportions of the sensors (e.g., the signals from Sensors 1 and 2 are approximately 60% of those from Sensors 3 and 4), indicating spinal asymmetry. Simulating a left-leaning posture (d) while reading, the four sensors output different signals and remained stable over 10 minutes. Therefore, under various postures—including upright sitting, forward-leaning sitting, left-leaning sitting, and left-leaning-forward-leaning sitting—each sensor exhibits significant time-dependent capacitance changes, demonstrating its high sensitivity to subtle postural changes. Real-time tracking of these characteristics accurately distinguishes patterns of center of gravity movement and pressure distribution, providing a solid electrical foundation for posture recognition and dynamic behavior monitoring. In addition to its resistance to long-term signal drift, this sensor shows great potential for application in wearable posture correction systems, especially in sedentary environments.

[0041] Example 2 An ionized capacitive pressure sensor is prepared in a manner that differs from that of Example 1 in that: in step 1), during the 3D printing process, the line spacing is set to 400 μm, the line width is set to 200 μm, and the number of printing layers is set to 6. The remaining conditions are the same as in Example 1. The resulting sensor is denoted as FCT-0.2-0.4-6.

[0042] like Figure 14 Figure (a) shows the compressive stress-strain curve of the FCT-0.2-0.4-6 sensor prepared in this embodiment. The silicone rubber foam can withstand a pressure of 3500 kPa at 55% strain. Therefore, the detection range of the FCT-0.2-0.4-6 sensor is as high as 3500 kPa. Figure (b) shows the relative capacitance change of the sensor under different applied pressures, indicating that the sensor has high sensitivity at low strain.

[0043] Example 3 An ionized capacitive pressure sensor is prepared in a manner that differs from that of Example 1 in that: in step 1), during the 3D printing process, the line spacing is set to 800 μm, the line width is set to 200 μm, and the number of printing layers is set to 6. The remaining conditions are the same as in Example 1. The resulting sensor is denoted as FCT-0.2-0.8-6.

[0044] Figure 15Figure (a) shows the compressive stress-strain curve of the FCT-0.2-0.8-6 sensor prepared in this embodiment. The silicone rubber foam is subjected to a pressure of 2200 kPa at 90% strain. Therefore, the detection range of the FCT-0.2-0.8-6 sensor is as high as 2200 kPa. Figure (b) shows the relative capacitance change of the sensor under different applied pressures, indicating that the sensor has high sensitivity at low strain.

[0045] Example 4 An ionized capacitive pressure sensor is prepared in a manner that differs from that of Example 1 in that: in step 1), during the 3D printing process, the line spacing is set to 450 μm, the line width is set to 150 μm, and the number of printing layers is set to 6. The remaining conditions are the same as in Example 1. The resulting sensor is denoted as FCT-0.15-0.45-6.

[0046] Figure 16 (a) shows the compressive stress-strain curve of the FCT-0.15-0.45-6 sensor prepared in this embodiment. The silicone rubber foam can withstand a pressure of 2600 kPa at 60% strain. Therefore, the detection range of the FCT-0.15-0.45-6 sensor is as high as 2500 kPa. (b) is a graph showing the relative capacitance change of the sensor under different applied pressures, indicating that the sensor has high sensitivity.

[0047] Example 5 An ionized capacitive pressure sensor is prepared in a manner that differs from that of Example 1 in that: in step 1), during the 3D printing process, the line spacing is set to 750 μm, the line width is set to 250 μm, and the number of printing layers is set to 6. The remaining conditions are the same as in Example 1. The resulting sensor is denoted as FCT-0.25-0.75-6.

[0048] Figure 17 (a) shows the compressive stress-strain curve of the FCT-0.25-0.75-6 sensor prepared in this embodiment. The silicone rubber foam can withstand a pressure of 2300 kPa at 90% strain. Therefore, the detection range of the FCT-0.25-0.75-6 sensor is as high as 2300 kPa. (b) is a graph showing the relative capacitance change of the sensor under different applied pressures, indicating that the sensor has high sensitivity under higher pressures.

[0049] Comparative Example 1 An ionized capacitive pressure sensor is prepared in a manner that differs from that of Example 1 in that: in step 1), the ST structure printing parameters are set during the 3D printing process, the line spacing is set to 600μm, the line width is set to 200μm, the number of printing layers is set to 6, and the other conditions are the same as in Example 1. The resulting sensor is denoted as ST-0.2-0.6-6.

[0050] Figure 18 (a) shows the compressive stress-strain curve of the ST-0.2-0.6-6 sensor prepared in this comparative example. The silicone rubber foam can withstand a pressure of 3000 kPa at 75% strain. Therefore, the detection range of the ST-0.2-0.6-6 sensor is as high as 3000 kPa. (b) shows the relative capacitance change of the sensor under different applied pressures, indicating that the sensor has high sensitivity under higher pressures.

[0051] Figure 19 The contact area diagram (top) and cross-sectional image (bottom) of the ST-0.2-0.6-6 sensor prepared for this comparative example under compressive stresses of 5 kPa (a), 50 kPa (b), 500 kPa (c), and 2000 kPa (d) are shown. In the ST structure, the top layer initially contacts the electrode, and the stress pillars restrict overall deformation, concentrating strain in the fibers of the first layer, thus achieving high sensitivity under low pressure conditions. As the load increases (>50 kPa), uniaxial buckling deformation occurs, and the second layer begins to participate (c). When the load is further increased (>500 kPa), densification limits the increase of additional contact, thereby reducing the detection sensitivity (d).

[0052] Comparative Example 2 An ionized capacitive pressure sensor is prepared in a manner different from that in Example 1, where the silicone rubber foam used in step 1) has a disordered structure. Specifically, the preparation method involves adding 60% NaCl (by weight of the silicone rubber foam raw material) to uncured PDMS (i.e., the raw material of the silicone rubber foam in Example 1). After the silicone rubber is completely cured, the resulting block is placed in 90°C warm water and stirred for 3 hours to remove the NaCl. After drying, a disordered silicone rubber foam is obtained. The remaining preparation conditions are the same as in Example 1.

[0053] The sensor prepared in this comparative example was subjected to static compression of 500 kPa for 1 hour, and the changes in the relative capacitance and strain of the sensor over time were measured as follows: Figure 20 As shown, the sensor exhibits a 14.9% capacitance signal drift over 1 hour at 500 kPa. The main reason for the signal drift is the creep (2%) of the disordered silicone rubber foam under pressure, which increases the contact area between the electrode and the dielectric layer (ion), thereby increasing the capacitance.

[0054] The sensor prepared in this comparative example underwent a relative capacitance change at 50℃ and a load pressure of 500 kPa. The signal drift over a continuous period of 1 hour was measured to be 18.5%, as shown in the test graph. Figure 21 As shown.

[0055] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A signal drift free, low hysteresis, off-the-shelf capacitive pressure sensor, characterized in that, The off-electricity capacitive pressure sensor comprises a capacitive medium and a substrate containing electrodes attached to the upper and lower surfaces of the capacitive medium; The capacitive medium is based on a silicone rubber foam, and the surface of the silicone rubber foam is uniformly covered with a layer of polydopamine, which is combined with the surface of the silicone rubber foam through multiple covalent and non-covalent interactions, and a layer of double fluorosulfonylimide ions is formed on the surface of the polydopamine through protonation and ion exchange.

2. The signal drift free, low hysteresis, off the shelf capacitive pressure sensor of claim 1, wherein, The substrate containing electrodes is a polyimide film with an electrode on one side, and the side with the electrode is attached to the capacitive medium.

3. The signal drift free, low hysteresis, off the shelf capacitive pressure sensor of claim 1, wherein, The silicone rubber foam is an ordered porous foam with an open pore structure and a face-centered cubic structure, and is obtained by 3D printing, with a pore size of 150-600 μm and a thickness of 500-900 μm.

4. The signal drift free, low hysteresis, off the shelf capacitive pressure sensor of claim 1, wherein, The thickness of the polydopamine on the surface of the silicone rubber foam is 120-360 nm.

5. The signal drift free, low hysteresis, off the shelf capacitive pressure sensor of claim 1 wherein, The pressure monitoring range of the sensor is 10 Pa to 3000 kPa, and the peak sensitivity is 20 to 30 kPa. -1 The response time is 3-6ms.

6. A method of manufacturing a signal drift free, low hysteresis, electrostatic capacitive pressure sensor according to any one of claims 1-5, characterized in that, The specific steps are as follows: 1) Prepare the silicone rubber foam by 3D printing; 2) Prepare the capacitive medium: dissolve trimethylamine in deionized water, and adjust the pH of the system to 7-9 with hydrochloric acid solution to obtain a trimethylamine solution, then add the silicone rubber foam obtained in step 1) and dopamine hydrochloride to the obtained trimethylamine solution, stir and react, take out the silicone rubber foam after the reaction is completed, and then rinse and dry to obtain PDA-coated silicone rubber foam, place the obtained PDA-coated PDMS foam in an acidic solution to fully protonate the PDA, then add double fluorosulfonylimide lithium salt to the solution for ion exchange, and finally wash and dry to obtain the capacitive medium; 3) Prepare the off-electricity capacitive pressure sensor: attach two pieces of substrate containing electrodes to the upper and lower surfaces of the capacitive medium, and then package to obtain the off-electricity capacitive pressure sensor.

7. The method of claim 6, wherein the method further comprises the step of: In step 1), the line spacing is set to 0.35-0.8 mm, the line width is set to 0.15-0.25 mm, and the number of printing layers is set to 4-8 during 3D printing. ​ 8. The method of claim 6, wherein the method further comprises: In step 2), the concentration of the trimethylamine solution is 0.01-0.02 g / mL, and the stirring reaction time is 16-24 hours.

9. The method of claim 6, wherein the method further comprises the step of: 5 applying a thin layer of a conductive material to the surface of the dielectric material. In step 2), the acidic solution is a hydrochloric acid solution with a concentration of 0.1-0.5 mol / L; the method for placing the obtained PDA-coated PDMS foam in an acidic solution to fully protonate the PDA is to immerse it in the acidic solution and stir for 30-60 min; the concentration of double fluorosulfonylimide lithium salt in the acidic solution is 0.1-0.3 mol / L; and the ion exchange method is to stir for 30-60 min.

10. Use of a signal drift free, low hysteresis, electrostatic capacitive pressure sensor according to any one of claims 1-5 for posture correction, characterized in that, The dynamic monitoring of pressure changes can feedback subtle posture changes.

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