Self-powered pressure sensor and method of manufacturing the same

Abstract

The application discloses a self-powered pressure sensor and a preparation method thereof, and the self-powered pressure sensor comprises a zinc electrode, a copper electrode, an ionic gel electrolyte film and a packaging layer provided with a gas escape gap, the upper surface of the ionic gel electrolyte film is provided with a hemispherical microstructure array, and the lower surface is provided with a microgroove or micro-pit array. The self-powered pressure sensor provided by the application solves the problems of low output performance and insufficient cycle durability caused by the deep coupling of energy supply and sensing function in traditional electrochemical self-powered sensors by means of the ionic gel electrolyte film with double-layer interlocking microstructures, high conductivity and good mechanical properties, and realizes the balance between high-sensitivity pressure sensing and high-power energy output. The self-powered pressure monitoring system constructed on the basis of the sensor can work independently without an external power supply, and can realize accurate identification of human motion rehabilitation actions in combination with a convolutional neural network model.

Description

Technical Field

[0001] This invention relates to the field of flexible pressure sensor technology, and in particular to a self-powered pressure sensor and its fabrication method. Background Technology

[0002] Flexible pressure sensors can convert external mechanical stimuli into analyzable electrical signals, and have broad application prospects in wearable health monitoring, human-computer interaction, and sports rehabilitation. Based on their working mechanisms, flexible pressure sensors are mainly classified into capacitive, piezoresistive, triboelectric, and piezoelectric types. Among them, capacitive and piezoresistive sensors have advantages such as high sensitivity and wide sensing range, but both rely on external power supplies, making it difficult to meet the miniaturization and continuous operation requirements of wearable devices. While triboelectric and piezoelectric sensors can be self-powered, they cannot detect static pressure, limiting their application in scenarios requiring continuous pressure monitoring.

[0003] To overcome the aforementioned limitations, an electrochemically self-powered pressure sensor based on the principle of a galvanic cell has been proposed. This type of sensor utilizes the electrochemical reaction within the battery system to convert chemical energy into electrical energy, providing the sensor's operating power. Simultaneously, by adjusting the battery's internal resistance or the electrode-electrolyte contact area under pressure, the output electrical signal changes with the applied pressure, thus achieving static and dynamic pressure detection without the need for an external power source.

[0004] However, existing electrochemical self-powered pressure sensors still have the following key problems that need to be solved in practical applications.

[0005] First, long-term cycling durability is insufficient. In the traditional integrated sandwich structure of electrochemically self-powered pressure sensors, the ionogel electrolyte membrane simultaneously serves as both the electrochemical reaction medium and the piezoresistive sensing layer. In many studies, the mechanical strength of the ionogel is not particularly outstanding. During thousands of compression cycles, problems such as microstructural creep, water extrusion, and adhesion of the gel material to the electrode surface may occur, leading to a continuous decrease in sensing sensitivity and output power.

[0006] Secondly, it is difficult to simultaneously achieve high sensing sensitivity and high output power. To achieve high sensing sensitivity, microstructures need to be designed on the surface of the ionogel electrolyte to increase the rate of change of output current during compression. However, these microstructures also reduce the electrode-electrolyte contact area, limiting electrochemical reactions and thus reducing output power. On the other hand, to achieve high output power, the ion concentration inside the ionogel needs to be increased to enlarge the ion conduction paths. However, denser conduction paths reduce the rate of change of output current during compression, resulting in lower sensing sensitivity.

[0007] Therefore, there is an urgent need for a new electrochemical self-powered pressure sensor that addresses the coupling contradiction between power supply and sensing performance in terms of material selection, concentration ratio, and structural parameters, while possessing high-stability sensing characteristics, long-cycle durability, and high-power energy output. Summary of the Invention

[0008] To address the technical problems existing in the background art, this invention proposes a self-powered pressure sensor and its preparation method.

[0009] The present invention proposes a self-powered pressure sensor, comprising: A zinc electrode is used as the negative electrode; A copper electrode, serving as the positive electrode, is positioned opposite the zinc electrode; An ion gel electrolyte membrane is disposed between a zinc electrode and a copper electrode. The zinc electrode, the ion gel electrolyte membrane, and the copper electrode together form a stacked structure. The ion gel electrolyte membrane has a first microstructure array transferred by a 3D printing template on the upper surface facing the copper electrode. The first microstructure array is a uniformly arranged hemispherical microstructure. The ion gel electrolyte membrane has a second microstructure array on the lower surface of the zinc electrode. The second microstructure array is a microgroove array or a micropit array, which is used to store electrolyte to maintain the interfacial ion concentration and form a physical interlock with the zinc electrode to prevent lateral slippage during compression cycling. An encapsulation layer with venting gaps encapsulates the stacked structure, allowing the zinc electrode, ion gel electrolyte membrane, and copper electrode to fit tightly together, and allowing hydrogen gas generated by the electrochemical reaction to be discharged through the venting gaps.

[0010] Preferably, the radius of a single hemispherical microstructure ranges from 1 mm to 2.5 mm.

[0011] Preferably, the ionogel electrolyte membrane is formed by cross-linking raw materials comprising the following mass fractions through freeze-thaw cycles: 8%-12% polyvinyl alcohol, 0.4%-0.8% cellulose nanofibers, 0.3%-0.9% multi-walled carbon nanotubes, 0.5%-1% phosphoric acid, and 90.8%-85.3% deionized water.

[0012] Preferably, both the zinc electrode and the copper electrode are metal sheets with a thickness of 0.3 mm to 0.6 mm and a purity of 98% or higher, and their surfaces are treated with phosphoric acid solution to remove the oxide layer.

[0013] Preferably, the encapsulation layer with venting gaps is a polyimide tape, which wraps around the laminated structure. During wrapping, a gap is reserved between two adjacent turns of tape along the wrapping direction to form venting gaps.

[0014] Preferably, the sensitivity S of the sensor is defined as S=ΔI / ΔP; where ΔI is the difference between the output current with and without a pressure load; and ΔP is the pressure change applied to the sensor.

[0015] The present invention provides a method for fabricating a self-powered pressure sensor, applicable to any of the self-powered pressure sensors described above, the method comprising the following steps: S1. Add multi-walled carbon nanotubes and cellulose nanofibers to deionized water, disperse them ultrasonically at room temperature and stir for 1 hour to obtain a uniform suspension. S2. Add polyvinyl alcohol powder to a uniform suspension, stir continuously in a water bath at 90℃-100℃ for 2-3 hours, cool to room temperature, add phosphoric acid and stir to mix evenly to obtain an ion gel precursor solution. S3. Pour the ion gel precursor solution into a polytetrafluoroethylene mold. The top of the polytetrafluoroethylene mold has an array of pits that complements the hemispherical microstructure, and the bottom has an array of raised patterns that complement the microgroove array or micropit array. S4. Transfer the polytetrafluoroethylene mold containing the ion gel precursor solution to an environment of -30°C to -20°C and freeze for 12-18 hours. Then thaw at room temperature for 2-3 hours and repeat this freeze-thaw cycle 2-3 times to allow the ion gel precursor solution to crosslink and solidify in situ, forming an ion gel electrolyte membrane with a hemispherical microstructure array on the upper surface and a microgroove array or micropit array on the lower surface. S5. Take the ion gel electrolyte membrane out of the polytetrafluoroethylene mold, attach its lower surface to the zinc electrode which has been treated with phosphoric acid solution to remove the oxide layer, and attach its upper surface to the copper electrode which has been treated with phosphoric acid solution to remove the oxide layer, to form a stacked structure. S6. A polyimide tape is used to wrap a multilayer structure. During the wrapping process, a gap is reserved between two adjacent turns of polyimide tape along the wrapping direction to form an air venting gap, ultimately resulting in a self-powered pressure sensor.

[0016] This invention proposes a self-powered pressure monitoring system, applied to a self-powered pressure sensor as described in any of the preceding claims, the system comprising: A self-powered pressure sensor serves as both the system power source and the pressure-sensitive element, with its output providing both electrical energy and a current signal carrying pressure information. The voltage conditioning circuit has its input terminal electrically connected to the output terminal of the self-powered pressure sensor. It is used to convert the current signal carrying pressure information into a voltage signal and filter and amplify it to generate a conditioned voltage signal. The microcontroller has an analog-to-digital converter interface that is electrically connected to the output of the voltage conditioning circuit to convert the conditioned voltage signal into digital pressure data. The wireless transmission module is electrically connected to the communication interface of the microcontroller and is used to transmit digital pressure data to the host computer wirelessly. The voltage conditioning circuit, microcontroller, and wireless transmission module are all powered independently by the self-powered pressure sensor.

[0017] Preferably, both the microcontroller and the wireless transmission module are configured with a low-power operating mode. When the current signal output by the self-powered pressure sensor is lower than a preset threshold, the microcontroller controls the wireless transmission module to enter a sleep state to reduce the static power consumption of the system.

[0018] The present invention proposes a method for monitoring human movement rehabilitation, applied to a self-powered pressure monitoring system as described in any of the above claims, the method comprising the following steps: A1. Attach the self-powered pressure sensor to the joint area of ​​the human body to be monitored; A2. The self-powered pressure sensor generates a current signal in response to preset rehabilitation training movements. The current signal serves as both the power source for the system and the sensing signal source carrying joint movement pressure information. A3. The voltage conditioning circuit converts the current signal into a conditioning voltage signal and filters and amplifies it to generate a conditioning voltage signal that is proportional to the joint movement pressure. A4. The microcontroller acquires the conditioning voltage signal at a preset sampling frequency, quantizes the analog voltage value into a digital pressure data sequence, and sends it through the wireless transmission module. A5. The host computer inputs the received digital stress data sequence into the pre-trained convolutional neural network model, extracts the spatiotemporal features of the digital stress data sequence, identifies the corresponding rehabilitation action category, and obtains the motion posture recognition result.

[0019] This invention presents a self-powered pressure sensor and its fabrication method. By fabricating a hemispherical microstructure array on the upper surface of an ion gel and a microgroove or micropit array on the lower surface for storing the electrolyte and forming a physical interlock with the zinc electrode, an ion gel electrolyte with excellent mechanical and electrical properties is produced. This solves the problems of low output performance and insufficient long-term cycle durability caused by the deep coupling of power supply and sensing functions in traditional integrated structures. The microstructures on the upper and lower surfaces of the ion gel increase the rate of change of the contact area between the electrode and the electrolyte during compression, thereby improving the rate of change of the output current and thus enhancing sensitivity. The addition of appropriate mass fractions of multi-walled carbon nanotubes and phosphoric acid increases the conductivity of the ion gel electrolyte membrane, enabling the sensor to maintain high sensitivity while possessing high output power. Furthermore, the addition of appropriate mass fractions of cellulose nanofibers enhances the cross-linking network of the ion gel, improving its mechanical properties and thus enhancing the sensor's cycle stability. In addition, the design of the venting gaps ensures the smooth discharge of hydrogen, maintaining the internal pressure balance of the sensor and ensuring continuous close contact between the electrode and the electrolyte membrane. The self-powered pressure monitoring system built on this sensor can work independently without an external power source, and combined with a convolutional neural network model, it can achieve accurate recognition of human movement rehabilitation movements. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the architecture of a self-powered pressure sensor proposed in this invention; Figure 2 This is a schematic diagram illustrating the power generation principle, preparation process, and crosslinking mechanism of the ion gel electrolyte membrane of a self-powered pressure sensor proposed in this invention. Figure 3 The microstructure, elemental distribution, and spectral characterization of the ion gel electrolyte membrane are shown in one embodiment of the self-powered pressure sensor proposed in this invention. Figure 4 This is a comparison of the mechanical properties, electrical properties, and sensor sensitivity under different microstructure sizes of the ion gel electrolyte membrane under different material ratios in one embodiment of the self-powered pressure sensor proposed in this invention. Figure 5 The finite element simulation stress distribution diagrams of different types of microstructures and the schematic diagram of the piezoresistive sensing mechanism of the sensor are shown for one embodiment of the self-powered pressure sensor proposed in this invention. Figure 6 The graphs show the sensor performance test results of a self-powered pressure sensor proposed in this invention, including sensitivity, hysteresis, response time, and cycle stability. Figure 7 The diagram shows the impedance characteristics, output power, and power generation performance of the self-powered pressure sensor proposed in this invention, compared with those of existing technologies. Figure 8This invention provides an application demonstration of a driving light-emitting diode, a block diagram of a self-powered pressure sensing system, and an application diagram of human activity monitoring, representing one embodiment of a human movement rehabilitation monitoring method proposed in this invention. Figure 9 This is a diagram showing the motion posture recognition result of one embodiment of the human motion rehabilitation monitoring method proposed in this invention. Detailed Implementation

[0021] Reference Figures 1-7 The present invention proposes a self-powered pressure sensor, comprising: A zinc electrode serves as the negative electrode, and a copper electrode serves as the positive electrode, positioned opposite the zinc electrode.

[0022] It should be noted that both the zinc and copper electrodes are metal sheets with a thickness of 0.3 mm to 0.6 mm and a purity of over 98%, and their surfaces are treated with phosphoric acid solution to remove the oxide layer.

[0023] In this embodiment, as Figure 1 As shown, both the zinc electrode and the copper electrode are metal sheets with a thickness of 0.6 mm and a purity of 99%.

[0024] Specifically, both the zinc and copper electrodes are square with sides of 2 cm. Before assembly, the surfaces of both the zinc and copper electrodes are immersed in a phosphoric acid solution to remove the surface oxide layer.

[0025] An ion gel electrolyte membrane is placed between the zinc electrode and the copper electrode, and the zinc electrode, the ion gel electrolyte membrane and the copper electrode together form a stacked structure.

[0026] In this embodiment, the ionogel electrolyte membrane has a length of 2 cm, a width of 2 cm, and a height of 5 mm.

[0027] The ion gel electrolyte membrane has a first microstructure array transferred by a 3D printing template on the upper surface facing the copper electrode. The first microstructure array is a uniformly arranged hemispherical microstructure.

[0028] In this embodiment, the radius of a single hemispherical microstructure ranges from 1 mm to 2.5 mm; preferably 2.0 mm. Figure 5 As shown in a, compared with pyramid and microconical structures, the stress distribution of hemispherical microstructures is more uniform, and the stress is not concentrated at the tip, which can avoid excessive local stress during compression, thereby preventing microstructure damage and ensuring the cyclic stability of the sensor.

[0029] The ion gel electrolyte membrane has a second microstructure array on the lower surface of the zinc electrode. The second microstructure array is a microgroove array or a micropit array, which is used to store electrolyte to maintain the interfacial ion concentration and form a physical interlock with the zinc electrode to prevent lateral slippage during compression cycling.

[0030] This embodiment uses a microgroove array as an example. The trenches are 50 micrometers deep and 100 micrometers wide, and are distributed in a grid pattern. The second microstructure array has two functions: First, the trenches or pits can serve as electrolyte storage pools, maintaining a constant ion concentration at the electrode interface during compression cycling and preventing an increase in interfacial impedance due to electrolyte extrusion. Second, the uneven structure of the microgrooves or pits forms a physical interlock with the zinc electrode surface, effectively preventing lateral slippage during compression cycling, thereby improving the stability of the sensor during long-term cycling.

[0031] An encapsulation layer with venting gaps encapsulates the stacked structure, allowing the zinc electrode, ion gel electrolyte membrane, and copper electrode to fit tightly together, and allowing hydrogen gas generated by the electrochemical reaction to be discharged through the venting gaps.

[0032] In this embodiment, the encapsulation layer with venting gaps is a polyimide tape. The polyimide tape is wrapped around the laminated structure. During the wrapping process, a gap is reserved between two adjacent turns of tape along the wrapping direction to form venting gaps. Metal wires are led out from the zinc electrode surface and the copper electrode surface respectively for outputting electrical signals.

[0033] The power generation principle of the sensor in this embodiment is as follows: Figure 2 As shown in Figure a, in the ionogel electrolyte membrane, phosphate dissociates into hydrogen ions and dihydrogen phosphate ions. The zinc electrode, being chemically reactive, loses electrons to become zinc ions and enters the electrolyte, leaving a large number of electrons on its surface. These electrons then move directionally to the copper electrode surface due to the potential difference, where hydrogen ions gain electrons and become hydrogen gas. The reaction occurring at the zinc electrode is Zn → Zn2. 2+ +2e - The reaction that occurs at the copper electrode is 2H. + +2e - →H2↑. The generated hydrogen gas is discharged through the venting gaps in the encapsulation layer, maintaining the internal pressure balance of the sensor and ensuring continuous close contact between the electrodes and the electrolyte membrane.

[0034] Figure 2Figure b illustrates the specific fabrication process of the sensor. A certain amount of multi-walled carbon nanotubes (MWCNTs) and cellulose nanofibers (CNFs) were added to 10 ml of deionized water. The mixture was ultrasonically dispersed and stirred for 1 hour at room temperature to obtain a homogeneous suspension. Subsequently, 1 g of polyvinyl alcohol (PVA) powder was added, and the mixture was heated in a 90°C water bath and continuously stirred for 2 hours to obtain a homogeneous solution. After the solution cooled to room temperature, a certain amount of phosphoric acid solution was added and stirred until homogeneous. The mixture was then poured into a 3D-printed polytetrafluoroethylene (PTFE) mold and stored in a -20°C freezer for 12 hours. The mold was thawed at room temperature for 3 hours, and this freeze-thaw process was repeated for 3 cycles to finally form a tough PVA / CNFs / MWCNTs / H3PO4 conductive hydrogel. By preparing hydrogels with different mass fractions of MWCNTs, CNFs, and H3PO4, as well as hydrogels with different microstructure sizes, their mechanical and electrical properties were compared, and the electrochemical pressure sensor with the best performance was selected. A sandwich structure was used to combine copper and zinc plates as positive and negative electrodes with the gel electrolyte. Copper foil is used for the wires connecting the two metal electrodes, and the assembly is encapsulated with PI tape. The dimensions of the self-powered pressure sensor are approximately 2cm × 2cm × 0.7cm (length × width × height).

[0035] Nanocomposites have excellent flexibility and biocompatibility. Cellulose is an abundant natural renewable material on Earth, and cellulose nanofibers (CNFs) extracted from it are ideal materials for making flexible electronic devices. Figure 2 Figure c illustrates the crosslinking mechanism of the hydrogel. The carboxyl groups on CNFs can form hydrogen bonds with the hydroxyl groups on the PVA molecular chains, and hydrogen bonds can also be formed between the carboxyl groups of CNF molecular chains. Introducing CNFs into the PVA hydrogel system significantly improves the mechanical properties of the hydrogel. For conductive materials, MWCNTs are added to improve the conductivity of the hydrogel. During the mixing process of the composite, the carboxyl groups of MWCNTs form hydrogen bonds with the hydroxyl groups on the PVA molecular chains, and internal hydrogen bonds can also be formed between the PVA molecular chains. A simple freeze-thaw method allows microcrystalline crosslinking points to form between the PVA molecular chains, resulting in a double crosslinking network of PVA-PVA and PVA-CNFs, further improving the mechanical properties of the hydrogel. The addition of phosphoric acid provides a large number of conductive ions to the hydrogel, providing raw materials for electrochemical reactions while also greatly improving the conductivity of the hydrogel. The overall composite hydrogel materials play their respective roles and are well-integrated. Using this hydrogel with excellent mechanical strength as the dielectric layer of a sensor can significantly improve the durability of the sensor.

[0036] Specifically, the ionogel electrolyte membrane is formed by cross-linking raw materials containing the following mass fractions through freeze-thaw cycles: 8%-12% polyvinyl alcohol, 0.4%-0.8% cellulose nanofibers, 0.3%-0.9% multi-walled carbon nanotubes, 0.5%-1% phosphoric acid, and 90.8%-85.3% deionized water.

[0037] In this embodiment, the composition is 10 wt% polyvinyl alcohol, 0.8 wt% cellulose nanofibers, 0.6 wt% multi-walled carbon nanotubes, 0.8 wt% phosphoric acid, and 87.8 wt% deionized water.

[0038] Specifically, the roles of each component are as follows: polyvinyl alcohol serves as the hydrogel matrix, providing a moist microenvironment, promoting the dissociation of phosphate and enhancing ionic conductivity; cellulose nanofibers are used to enhance the mechanical strength of the hydrogel and ensure stability during long-term compression cycles; multi-walled carbon nanotubes are used to reduce the internal impedance of the hydrogel and increase the output current; phosphate provides a large number of conductive ions, providing raw materials for electrochemical reactions while also greatly improving the conductivity of the hydrogel.

[0039] Figure 3 Images a, b, and c in the figure show SEM images of the hydrogel's microstructure. In the hydrogel system, the interactions between various materials form a three-dimensional porous network structure. This uniform and dense porous structure provides more channels for ion migration, thereby enhancing electrical conductivity and also contributing to improved mechanical properties of the hydrogel. Figure 3 Figure 'a' shows a SEM image of a hydrogel without CNFs, which has low crosslinking density, incomplete pore structure, and is prone to collapse. Figure 3 b in the image shows a hydrogel with a uniformly distributed pore structure and robust pore walls, while Figure 3 The 'c' in the figure reveals the additional cross-linking network at the edge of the pore wall, which is the result of CNFs strengthening the cross-linking network. Figure 3 Images d and e show SEM images and polarized light microscopy photographs, respectively, of the agglomerates formed inside the gel due to excessive addition of H3PO4 and CNFs. Large fiber bundles are clearly visible. This is because as the added acid concentration increases, the pH value decreases, reducing the number of charged carboxyl groups, which in turn reduces the counterion entropy and the electrostatic repulsion between fibers, leading to a tendency for the average hydrodynamic particle size to increase. Therefore, further investigation is needed to explore the effect of the concentration of added substances on the hydrogel properties. Figure 3 f in the figure shows the EDS elemental distribution of the composite hydrogel, indicating that each component is uniformly dispersed inside the hydrogel.

[0040] exist Figure 3 As shown in the infrared spectrum of g, the PVA sample appears to be at 3438 cm⁻¹. -1A strong absorption peak was formed at this point, corresponding to the stretching vibration absorption peak of -OH. In the infrared spectrum of cellulose nanofibers, the wavenumber is 831 cm⁻¹. -1 The characteristic signal peaks corresponding to the β-1,4-glycosidic bonds between cellulose glucose units are 1058 and 2904 cm⁻¹. -1 These peaks correspond to the stretching vibrations of the CO and CH bonds in carbon nanofibers, respectively, with a wavenumber of 3422 cm⁻¹. -1 The absorption peak corresponds to the stretching vibration of -OH. MWCNTs powder at 3440 cm⁻¹ -1 A strong absorption peak was formed at 1643 cm⁻¹, which proves the presence of -OH. -1 The absorption peak at 1633 cm⁻¹ can be attributed to the stretching vibration of -COOH. This indicates that the surface of multi-walled carbon nanotubes contains oxygen-containing groups (-OH and -COOH). In the infrared spectrum of the PVA / CNF / MWCNT composite hydrogel, the peak at 1633 cm⁻¹ is [missing information]. -1 The broad peak corresponding to the carboxyl stretching vibration of carbon nanofibers, and the presence of -OH indicates the formation of more hydrogen bonds between PVA and CNF, with the hydrogel showing a peak at 3238 cm⁻¹. -1 The stretching vibration of the hydroxyl group occurs at this location. Figure 3 In the X-ray diffraction pattern shown by h, the original polyvinyl alcohol exhibits a strong peak at the 2θ = 19.4 Å (101) plane and a weak peak at the 2θ = 22.4 Å (200) plane. The typical peak of CNF is located at 2θ = 32 Å, representing the (100) plane. In the X-ray diffraction pattern of the hydrogel sample, the above peaks appear simultaneously without significant deviation, indicating that the materials are tightly bonded to form a hydrogel. Figure 3 In the Raman spectrum shown by i, MWCNTs are at 1327 cm⁻¹ -1 There is a D peak at 1589cm. -1 There is a G peak at 2651cm. -1 The second harmonic of the D peak is present, i.e., a two-dimensional (2D) peak. The D, G, and 2D peaks of the hydrogel are all in the same position, indicating that no byproducts are generated in the hydrogel. Figure 3 g, h, and i in the figure represent the Fourier transform infrared spectrum, X-ray diffraction spectrum, and Raman spectrum of the ion gel electrolyte membrane, respectively, which confirm the uniform dispersion of each component in the hydrogel and the complete formation of the cross-linked network.

[0041] To optimize sensor performance, the effects of the addition ratios of various materials and the microstructure of the hydrogel surface on its performance parameters were further investigated. The mechanical and electrical properties of the hydrogel were primarily tested. The content of CNFs mainly affects the mechanical strength of the hydrogel. After optimizing the optimal CNF ratio, MWCNTs and H3PO4 were added to measure their conductivity, thereby optimizing the best material ratio. Finally, the sensitivity of sensors fabricated with hydrogels of different microstructure sizes was tested to screen for the optimal microstructure size.

[0042] Figure 4 Figure 'a' shows the stress-strain curves of hydrogels with different CNFs contents. By comparison, it can be found that the hydrogel containing 0.8 wt% CNFs has the best mechanical properties, with a tensile strain of up to 360% and a tensile stress of up to 0.65 MPa. Figure 4 Figure b illustrates the effect of different MWCNT contents on its electrical properties. Hydrogels exhibit two conductivity mechanisms: contact conductivity and tunneling conductivity. With increasing MWCNT content, the MWCNT contacts become denser, leading to a continuous increase in the hydrogel's conductivity. However, since MWCNTs are hydrophobic, increasing their content reduces the hydrogel's water content, lowering the internal ion concentration and thus reducing its conductivity. Based on test data, a concentration of 0.6 wt% was selected. At this level, the added MWCNTs increased the hydrogel's conductivity to a relatively saturated value, and the decrease in water content was less compared to the hydrogel without added MWCNTs. Figure 4 As shown in Figure c, hydrogels with different phosphate contents were assembled into sensors to measure the initial current. A higher initial current means higher output power, but it also means increased static power consumption, which reduces the sensor's lifespan. Furthermore, it was found that excessive phosphate addition produced many particulate substances within the hydrogel, which were aggregates of CNF and MWCNT. This is because the average hydrodynamic particle size tends to increase as the pH decreases. Therefore, considering multiple factors, 0.8 mL of phosphate was added to achieve a concentration of 1 mol / L within the hydrogel. At this concentration, the initial current remained relatively high, and large-scale aggregation did not occur within the hydrogel. After studying the material ratio, the influence of the hydrogel surface microstructure on the sensor sensitivity was investigated. Figure 3 As shown in d), it was found that the sensor exhibits the highest overall sensitivity and best contact characteristics across the entire sensing range when the radius of the microhemispherical is 2.0 mm. This led to the investigation of the optimal material ratio and microstructure dimensions for the sensor.

[0043] The hydrogel in the medium layer was simulated using the finite element analysis software COMSOL. Figure 5Figure 'a' shows the stress distribution of different microstructures under applied pressure, with the microstructure shapes being a microhemispherical structure, a pyramidal structure, and a microconical structure. The results show that, compared to the pyramidal and microconical structures, the microhemispherical structure exhibits a more uniform stress distribution, with stress not concentrated at the tips. This avoids excessive localized stress during compression, thus preventing microstructure damage and ensuring the cyclic stability of the sensor. Therefore, the microhemispherical structure was chosen for the preparation of the hydrogel surface.

[0044] Figure 5 Figure 'b' illustrates the sensor's sensing principle. First, the output voltage is determined by the nature of the electrochemical reaction and the contact area. The applied pressure does not change the nature of the electrochemical reaction. Due to the presence of microstructures, the contact area between the electrode plates and the electrolyte increases with increasing pressure, resulting in more positive and negative charges accumulating at the two electrode plates, thus increasing the output voltage. Simultaneously, when the hydrogel electrolyte is compressed, the internal ionic conduction pathways become denser, and the conductive carbon nanotubes make more complete contact, increasing the conductivity and thus reducing the internal resistance of the hydrogel. According to Ohm's law I=U / R, as the applied pressure increases, the output voltage increases while the internal resistance decreases, resulting in a continuous increase in the output current. The applied pressure can be determined by measuring the corresponding current signal.

[0045] For the sensor performance testing, the sensor's sensing performance was tested first. Figure 6 The expression 'a' in the figure illustrates the relationship between the output current and the applied pressure, and the sensitivity formula is defined as follows: S =Δ I / Δ P ,in S To express sensitivity, the current response of the sensor is defined as Δ. I Δ I Right now II 0, where I 0 represents the output current without pressure. I It is the output current under load pressure, representing the relative change in output current when there is pressure and no pressure, Δ. PThe pressure change applied to the sensor is the sensitivity. The sensor has a linear detection range of three segments: 1.126 mA / kPa in the first segment (0-5 kPa), 0.186 mA / kPa in the second segment (5-20 kPa), and 0.027 mA / kPa in the third segment (20-100 kPa). Compared with previous studies, the designed pressure sensor exhibits relatively higher sensitivity across the stress range. The reason for the multi-segment sensitivity can be reasonably explained: under low pressure, the microstructure of the compressed hydrogel surface expands the contact area between the electrode and the hydrogel, rapidly increasing the output voltage. Simultaneously, the internal conductive pathways open, and the internal resistance decreases significantly. Their synergistic effect leads to a sharp increase in current, defining the first sensitive stage. As compression increases, the microspheres gradually flatten, slowing the changes in output voltage and current, corresponding to the second stage. Further pressure increases stabilize the interfacial contact and output voltage, and saturate the internal conductive network. The rate of change then drops to a minimum, representing the third sensitive stage.

[0046] The hysteresis characteristics of the sensor were tested through repeated pressure tests. The results show that the maximum hysteresis error of the sensor is as low as 2.43% within the pressure range of 0-100 kPa. Figure 6 As shown in b. This is because the hydrogel electrolyte layer has excellent compression properties, able to return to the same position after repeated compression, exhibiting both the inherent properties of carbon-based nanomaterials and the softness similar to textile fibers. Figure 6 As shown in c, when the applied pressure increases from 0 to 100 kPa, the correspondence between the pressure and resistance signals can be observed, which demonstrates the pressure-sensitive performance of the sensor. Figure 6 Figure d shows the cyclic test under five different loading pressures (2, 10, 40, 80, 100 kPa). The current signal in the experiment changes under the same pressure and remains basically constant. Figure 6 The 'e' in the figure illustrates the change in output current at different frequencies (10, 30, 50, 100, 200 mm / min) under the same pressure. It can be found that the change in output current changes with the increase of the applied frequency, which also indicates that the sensor has the function of detecting dynamic pressure. Figure 6 The f in the figure shows that the response time and recovery time are 0.22s and 0.41s, respectively, which are longer than those of sensors reported in relevant literature. This may be due to the high cross-linking density of the hydrogel, which increases the time for plastic deformation while increasing the mechanical strength. Figure 6 The 'g' indicates that the sensor's lowest detection limit is 75 Pa. The addition of microstructures on the hydrogel surface enables the sensor to detect minute pressures. Figure 6 The 'h' in the figure indicates that the output signal remains constant when pressure is applied to the sensor for a period of time, demonstrating that it has the function of detecting static pressure. Figure 6 The 'i' in the figure illustrates the effect of temperature on the sensor response. The relative change in output current increases with increasing temperature, reaching approximately 7% at 60°C. This is because the increased temperature leads to increased ion mobility within the hydrogel, altering the initial current. Furthermore, when the temperature rises above 60°C, the hydrogel's cross-linking network is disrupted, and the hydrogel begins to dissolve. Figure 6 The value j in the figure shows that the sensor has undergone 9,000 cycles at low (3 kPa), medium (40 kPa), and high (100 kPa) pressures, and the output current remains stable during these multiple compression cycles.

[0047] Figure 7 The power generation characteristics of the self-powered pressure sensor were demonstrated. Figure 7 The 'a' in the figure indicates that the internal impedance of the hydrogel gradually decreases as the applied pressure increases, verifying the piezoresistive characteristics described above. For example... Figure 7 As shown in b, the shape of the curve is similar to that of the sensitivity curve, further confirming that the sensor regulates its output current by changing its internal conductive path through pressure. Figure 7 Figure 'c' shows the impedance spectrum of the sensor's two plates immersed in a phosphoric acid solution of the same concentration, compared with that of the sensor's impedance spectrum. The similarity in impedance profiles indicates that the solid electrolyte exhibits conductivity similar to that of a liquid environment. Furthermore, an equivalent circuit diagram of the impedance was obtained through fitting, and the conductivity under different pressures can be calculated using specific circuit component parameter values. Figure 7 The curve 'd' in the figure shows the relationship between the output current and the number of sensors connected in parallel. When only six sensors are connected in parallel, the output current can reach 24.6 mA under no pressure. Compared with reported self-powered sensors, the number of sensors required to achieve the same current is reduced, which is beneficial for the miniaturization of sensor array integration. Furthermore, the linear relationship shown in the figure also indicates that the internal resistance of the sensors is low, resulting in less internal energy loss when used as power supply elements. Figure 7 The value 'e' in the figure shows the change in the sensor's output voltage after 48 hours. The output voltage only decreased by 0.04V after 48 hours, indicating that the sensor has the ability to be used for a relatively long time. Figure 7 The value 'f' in the figure shows the voltage curves of commercial capacitors with different capacitance values ​​during the charging process, indicating that they can be used to charge capacitors and achieve energy storage. Furthermore, Figure 6 The graph 'g' shows the output voltage and current curves of sensors with different load resistances at 100 kPa. As the resistance increases, the voltage across the load resistance increases, while the current decreases. Figure 7 The value of 'h' in the figure indicates that the sensor's output power reaches a maximum of 3.96mW when the load resistance is 70Ω, exceeding that of many reported self-powered pressure sensors, such as... Figure 7As shown in f, the sensor's output voltage and current at 100 kPa are compared with those of other reported sensors. The sensor has a large open-circuit voltage (1.1 V) and short-circuit current (16.1 mA).

[0048] The present invention proposes a method for fabricating a self-powered pressure sensor, applicable to any of the self-powered pressure sensors described above. The method includes the following steps: S1. Add multi-walled carbon nanotubes and cellulose nanofibers to deionized water, ultrasonically disperse and stir for 1 hour at room temperature to obtain a uniform suspension.

[0049] The amount of multi-walled carbon nanotubes added was 0.6 wt%, and the amount of cellulose nanofibers added was 0.8 wt%.

[0050] S2. Add polyvinyl alcohol powder to a uniform suspension and stir continuously in a water bath at 90℃-100℃ for 2-3 hours. After cooling to room temperature, add phosphoric acid and stir to mix evenly to obtain an ion gel precursor solution.

[0051] In this embodiment, polyvinyl alcohol powder was added to a uniform suspension and stirred continuously in a 90°C water bath for 2 hours. After cooling to room temperature, phosphoric acid was added and stirred until uniformly mixed to obtain an ion gel precursor solution. The amount of polyvinyl alcohol added was 10 wt%, and the amount of phosphoric acid added was 0.8 wt%.

[0052] S3. Pour the ion gel precursor solution into a polytetrafluoroethylene mold. The top of the polytetrafluoroethylene mold has an array of pits that complement the hemispherical microstructure, and the bottom has an array of raised patterns that complement the microgroove array or micropit array.

[0053] In this embodiment, the radius of the top recess is 2.0 mm, and the bottom raised pattern is a grid-like raised strip that complements the microgroove. The raised strip has a height of 50 micrometers and a width of 100 micrometers.

[0054] S4. Transfer the polytetrafluoroethylene mold containing the ionogel precursor solution to an environment of -30°C to -20°C and freeze for 12-18 hours. Then thaw at room temperature for 2-3 hours and repeat this freeze-thaw cycle 2-3 times to allow the ionogel precursor solution to crosslink and solidify in situ, forming an ionogel electrolyte membrane with a hemispherical microstructure array on the upper surface and a microgroove array or micropit array on the lower surface.

[0055] In this embodiment, a polytetrafluoroethylene mold containing an ion gel precursor solution is transferred to a -20°C environment and frozen for 12 hours, then thawed at room temperature for 3 hours, and this freeze-thaw cycle is repeated 3 times to allow the ion gel precursor solution to crosslink and solidify in situ, forming an ion gel electrolyte membrane with a hemispherical microstructure array on the upper surface and a microgroove array or micropit array on the lower surface.

[0056] Specifically, during freezing, ice crystals form inside the hydrogel, which acts as a pore-forming agent; during thawing, the polyvinyl alcohol molecular chains are re-crosslinked through hydrogen bonds and microcrystalline regions, causing the ion gel precursor solution to crosslink and solidify in situ, forming an ion gel electrolyte membrane with a hemispherical microstructure array on the upper surface and a microgroove array or micropit array on the lower surface.

[0057] S5. Remove the ion gel electrolyte membrane from the polytetrafluoroethylene mold, attach its lower surface to the zinc electrode that has been treated with phosphoric acid solution to remove the oxide layer, and attach its upper surface to the copper electrode that has been treated with phosphoric acid solution to remove the oxide layer, forming a stacked structure.

[0058] Specifically, the microgroove array on the lower surface forms a physical interlock with the zinc electrode, and the hemispherical microstructure array on the upper surface forms a modulated contact interface with the copper electrode.

[0059] S6. A polyimide tape is used to wrap a multilayer structure. During the wrapping process, a gap is reserved between two adjacent turns of polyimide tape along the wrapping direction to form an air venting gap, ultimately resulting in a self-powered pressure sensor.

[0060] Specifically, the size of the reserved gap ensures that hydrogen can be smoothly discharged when the sensor is under pressure, while maintaining a tight fit between the zinc electrode, the ion gel electrolyte membrane, and the copper electrode.

[0061] Reference Figure 8 The present invention proposes a self-powered pressure monitoring system, applied to any of the self-powered pressure sensors described above, the system comprising: A self-powered pressure sensor serves as both the system power source and the pressure-sensitive element, with its output providing both electrical energy and a current signal carrying pressure information. The voltage conditioning circuit has its input terminal electrically connected to the output terminal of the self-powered pressure sensor. It is used to convert the current signal carrying pressure information into a voltage signal and filter and amplify it to generate a conditioned voltage signal. The microcontroller has an analog-to-digital converter interface that is electrically connected to the output of the voltage conditioning circuit to convert the conditioned voltage signal into digital pressure data. The wireless transmission module is electrically connected to the communication interface of the microcontroller and is used to transmit digital pressure data to the host computer wirelessly. The voltage conditioning circuit, microcontroller, and wireless transmission module are all powered independently by the self-powered pressure sensor.

[0062] In this embodiment, both the microcontroller and the wireless transmission module are configured with a low-power operating mode. When the current signal output by the self-powered pressure sensor is lower than a preset threshold, the microcontroller controls the wireless transmission module to enter a sleep state to reduce the system's static power consumption.

[0063] Specifically, such as Figure 8 As shown in Figure a, the sensor can act as a pressure-regulated voltage source to light multiple LEDs connected in series. When no pressure is applied to the sensor, the bulbs are off. As the pressure applied to the sensor increases, the brightness of the bulbs also increases. When the sensor applies a pressure of 100 kPa, the brightness of the bulbs reaches its maximum, indicating that the sensor has a visual pressure monitoring function. On the other hand, the output power of the sensor can drive other circuit units, thus enabling the creation of a self-powered pressure detection system (such as...). Figure 8 (As shown in b and c in the diagram). Specifically, the system uses a pressure sensor as its power source, providing a pressure detection signal. This signal is then processed by an operational amplifier and a voltage regulator to obtain a stable output signal. The processed signal is transmitted to a microcontroller (MCU) for analog-to-digital conversion, and finally transmitted to the host computer software via a Bluetooth wireless module (BLE). Both the MCU and BLE are configured for low power consumption. This sensor exhibits high sensitivity and good stability, allowing the self-powered pressure detection system to be used as a wearable device to detect human activity. Figure 8 (as shown in di).

[0064] Reference Figure 9 The present invention proposes a method for monitoring human movement rehabilitation, which is applied to a self-powered pressure monitoring system as described above. The method includes the following steps: A1. Attach the self-powered pressure sensor to the joint area of ​​the human body to be monitored.

[0065] Specifically, such as Figure 8 As shown in d, the sensor can be attached to multiple joints such as fingers, wrists, elbows, and knees to detect limb movements in different parts of the body.

[0066] A2. The self-powered pressure sensor generates a current signal in response to preset rehabilitation training movements. The current signal serves as both the power source for the system and the sensing signal source carrying joint movement pressure information. A3. The voltage conditioning circuit converts the current signal into a conditioning voltage signal and filters and amplifies it to generate a conditioning voltage signal that is proportional to the joint movement pressure. A4. The microcontroller acquires the conditioning voltage signal at a preset sampling frequency, quantizes the analog voltage value into a digital pressure data sequence, and sends it through the wireless transmission module. A5. The host computer inputs the received digital stress data sequence into the pre-trained convolutional neural network model, extracts the spatiotemporal features of the digital stress data sequence, identifies the corresponding rehabilitation action category, and obtains the motion posture recognition result.

[0067] Sensors were used to monitor human rehabilitation training movements. Each movement was tested using five sensors placed on different parts of the body, thus establishing five signal channels. Figure 9 (a) uses convolutional neural networks to process and analyze data. Figure 9 (b) Each different training movement involves different postures and limb flexion, thus generating a unique electrical signal waveform. Figure 9 (c) Principal component analysis (PCA) is used to reduce the dimensionality of the data, visually demonstrating the similarities and differences between the variables. Figure 9 The diagram shows five regions, each represented by a different color, indicating different postures. PCA reveals the differences between various movement postures. Figure 9 As shown in 'e', ​​the CNN model exhibits a steady decrease in training loss and a gradual increase in training accuracy as the number of epochs increases, until it reaches final convergence. After nearly 100 epochs of testing, the model achieved a 100% recognition rate. Figure 9 The expression 'f' in the figure shows the training confusion matrix obtained using the CNN algorithm, with an accuracy of 100%. Furthermore, Figure 9 The prediction confusion matrix of the CNN algorithm proposed in g shows an accuracy of 97%. These results clearly validate the reliability and accuracy of the pose recognition system and demonstrate the potential of the sensor in wearable devices.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A self-powered pressure sensor, characterized by, include: A zinc electrode is used as the negative electrode; A copper electrode, serving as the positive electrode, is positioned opposite the zinc electrode; An ion gel electrolyte membrane is disposed between a zinc electrode and a copper electrode. The zinc electrode, the ion gel electrolyte membrane, and the copper electrode together form a stacked structure. The ion gel electrolyte membrane has a first microstructure array transferred by a 3D printing template on the upper surface facing the copper electrode. The first microstructure array is a uniformly arranged hemispherical microstructure. The ion gel electrolyte membrane has a second microstructure array on the lower surface of the zinc electrode. The second microstructure array is a microgroove array or a micropit array, which is used to store electrolyte to maintain the interfacial ion concentration and form a physical interlock with the zinc electrode to prevent lateral slippage during compression cycling. An encapsulation layer with venting gaps encapsulates the stacked structure, allowing the zinc electrode, ion gel electrolyte membrane, and copper electrode to fit tightly together, and allowing hydrogen gas generated by the electrochemical reaction to be discharged through the venting gaps. The radius of a single hemispherical microstructure ranges from 1 mm to 2.5 mm; the ionogel electrolyte membrane is formed by freeze-thaw crosslinking of raw materials comprising the following mass fractions: 8%-12% polyvinyl alcohol, 0.4%-0.8% cellulose nanofibers, 0.3%-0.9% multi-walled carbon nanotubes, 0.5%-1% phosphoric acid, and 90.8%-85.3% deionized water.

2. The self-powered pressure sensor of claim 1, wherein, Both the zinc and copper electrodes are metal sheets with a thickness of 0.3 mm to 0.6 mm and a purity of over 98%, and their surfaces are treated with phosphoric acid solution to remove the oxide layer.

3. The self-powered pressure sensor according to claim 1, characterized in that, The encapsulation layer with venting gaps is a polyimide tape. The polyimide tape is wrapped around the laminated structure. During the wrapping process, a gap is reserved between two adjacent turns of tape along the wrapping direction to form venting gaps.

4. The self-powered pressure sensor according to claim 1, characterized in that, The sensitivity S of the sensor is defined as S=ΔI / ΔP; where ΔI is the difference between the output current with and without a pressure load; and ΔP is the pressure change applied to the sensor.

5. A method for fabricating a self-powered pressure sensor, characterized in that, Applied to the self-powered pressure sensor as described in any one of claims 1-4, the method comprises the following steps: S1. Add multi-walled carbon nanotubes and cellulose nanofibers to deionized water, disperse them ultrasonically at room temperature and stir for 1 hour to obtain a uniform suspension. S2. Add polyvinyl alcohol powder to a uniform suspension, stir continuously in a water bath at 90℃-100℃ for 2-3 hours, cool to room temperature, add phosphoric acid and stir to mix evenly to obtain an ion gel precursor solution. S3. Pour the ion gel precursor solution into a polytetrafluoroethylene mold. The top of the polytetrafluoroethylene mold has an array of pits that complements the hemispherical microstructure, and the bottom has an array of raised patterns that complement the microgroove array or micropit array. S4. Transfer the polytetrafluoroethylene mold containing the ion gel precursor solution to an environment of -30°C to -20°C and freeze for 12-18 hours. Then thaw at room temperature for 2-3 hours and repeat this freeze-thaw cycle 2-3 times to allow the ion gel precursor solution to crosslink and solidify in situ, forming an ion gel electrolyte membrane with a hemispherical microstructure array on the upper surface and a microgroove array or micropit array on the lower surface. S5. Take the ion gel electrolyte membrane out of the polytetrafluoroethylene mold, attach its lower surface to the zinc electrode which has been treated with phosphoric acid solution to remove the oxide layer, and attach its upper surface to the copper electrode which has been treated with phosphoric acid solution to remove the oxide layer, to form a stacked structure. S6. A polyimide tape is used to wrap a multilayer structure. During the wrapping process, a gap is reserved between two adjacent turns of polyimide tape along the wrapping direction to form an air venting gap, ultimately resulting in a self-powered pressure sensor.

6. A self-powered pressure monitoring system, characterized in that, The system, applied to the self-powered pressure sensor as described in any one of claims 1-4, comprises: A self-powered pressure sensor serves as both the system power source and the pressure-sensitive element, with its output providing both electrical energy and a current signal carrying pressure information. The voltage conditioning circuit has its input terminal electrically connected to the output terminal of the self-powered pressure sensor. It is used to convert the current signal carrying pressure information into a voltage signal and filter and amplify it to generate a conditioned voltage signal. The microcontroller has an analog-to-digital converter interface that is electrically connected to the output of the voltage conditioning circuit to convert the conditioned voltage signal into digital pressure data. The wireless transmission module is electrically connected to the communication interface of the microcontroller and is used to transmit digital pressure data to the host computer wirelessly. The voltage conditioning circuit, microcontroller, and wireless transmission module are all powered independently by the self-powered pressure sensor.

7. The self-powered pressure monitoring system according to claim 6, characterized in that, Both the microcontroller and the wireless transmission module are configured with a low-power operating mode. When the current signal output by the self-powered pressure sensor is lower than a preset threshold, the microcontroller controls the wireless transmission module to enter a sleep state to reduce the system's static power consumption.

8. A method for monitoring human movement rehabilitation, characterized in that, Applied to the self-powered pressure monitoring system as described in any one of claims 6-7, the method comprises the following steps: A1. Attach the self-powered pressure sensor to the joint area of ​​the human body to be monitored; A2. The self-powered pressure sensor generates a current signal in response to preset rehabilitation training movements. The current signal serves as both the power source for the system and the sensing signal source carrying joint movement pressure information. A3. The voltage conditioning circuit converts the current signal into a conditioning voltage signal and filters and amplifies it to generate a conditioning voltage signal that is proportional to the joint movement pressure. A4. The microcontroller acquires the conditioning voltage signal at a preset sampling frequency, quantizes the analog voltage value into a digital pressure data sequence, and sends it through the wireless transmission module. A5. The host computer inputs the received digital stress data sequence into the pre-trained convolutional neural network model, extracts the spatiotemporal features of the digital stress data sequence, identifies the corresponding rehabilitation action category, and obtains the motion posture recognition result.

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