A self-supporting wrinkled flexible piezoresistive film, an ultrathin flexible pressure sensor array, and their wearable applications

Abstract

This invention belongs to the field of flexible pressure sensor technology, and discloses a self-supporting wrinkled flexible piezoresistive film, an ultra-thin flexible pressure sensor array, and their wearable applications. The preparation of the self-supporting wrinkled flexible piezoresistive film includes: mixing a CNTs dispersion and a PVA aqueous solution in a volume ratio to form a CNTs / PVA blend; preparing a microstructure template; drop-coating the CNTs / PVA blend onto the microstructure template; and peeling off the dried material to obtain the self-supporting wrinkled flexible piezoresistive film. Then, through screen-printed electrodes, insulating layer bonding, film stacking, and encapsulation processes, an ultra-thin flexible pressure sensor array with a maximum thickness of approximately 110 μm is fabricated. Finally, the array is arranged according to specific sections of the foot, combined with an information acquisition module and a wireless communication module, to form a smart sock with pressure sensing function. The sensor array of this invention is thin, flexible, and can accurately monitor foot pressure, providing a feasible path for the precision and thinness of smart wearable devices.

Description

Technical Field

[0001] This invention belongs to the field of flexible pressure sensor technology, and specifically relates to a self-supporting wrinkled flexible piezoresistive film, an ultra-thin flexible pressure sensor array, and their wearable applications. Background Technology

[0002] With the development of science and technology and social life, the world will inevitably approach a state of high interaction between humans and technology. As a key component of flexible electronics, flexible pressure sensors of various shapes and structures have been invented and successfully applied to fields such as health monitoring, human-computer interaction, and wearable devices, which have had a significant impact on human life, medical education, and industrial development.

[0003] Piezoresistive pressure sensors are relatively simple in structure and principle, characterized by low energy consumption, large sensing range, excellent linearity, low manufacturing cost, and simple readout mechanism. The choice of piezoresistive material is crucial to the performance of flexible sensors. Incorporating conductive materials into a polymer matrix to prepare composite conductive materials can produce high-performance flexible piezoresistive materials. However, conductive materials are difficult to disperse in general polymer matrices, requiring sophisticated processing techniques. For example, low-dimensional carbon materials and polymer PDMS have significantly different surface characteristics, mismatched chemical bond polarities, and poor interfacial compatibility, necessitating complex processes such as co-melting and shearing to form composite conductive materials. For instance, CN120740816A proposes a PDMS / MWCNTs composite conductive material, but the filler-matrix interfacial bonding is poor, the filler content is severely limited, and the conductivity is low and highly volatile. Furthermore, the process requires large amounts of solvent; solvent removal is energy-intensive and causes environmental pollution, and the risk of solvent residue is significantly increased. CN115612167A fills a porous PDMS matrix with carbon nanotubes by mechanical extrusion, and additional conductive polymers are also required. Essentially, it only achieves physical adsorption between carbon nanotubes and the PDMS matrix, which is not conducive to the electrical stability of the composite material and limits the intrinsic piezoresistive properties of carbon-based materials. Summary of the Invention

[0004] In view of the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a self-supporting wrinkled flexible piezoresistive film.

[0005] Another object of the present invention is to provide a self-supporting wrinkled flexible piezoresistive film.

[0006] Another object of the present invention is to provide an ultrathin flexible pressure sensor array.

[0007] Another object of the present invention is to provide an application of the above-mentioned ultrathin flexible pressure sensor array.

[0008] Another object of the present invention is to provide a smart sock with pressure sensing function.

[0009] This provides a feasible path for making smart wearable electronic products more precise and thinner.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for preparing a self-supporting wrinkled flexible piezoresistive film includes the following steps:

[0012] A CNTs dispersion and a PVA aqueous solution were prepared and mixed at a volume ratio to form a CNTs / PVA blend.

[0013] Preparation of microstructure templates;

[0014] The CNTs / PVA blend liquid is drop-coated onto the microstructure template, dried, and then peeled off to obtain a CNTs / PVA composite film, namely a self-supporting wrinkled flexible piezoresistive film.

[0015] Preferably, the CNTs dispersion is obtained by adding hydroxylated CNTs to a solvent and dispersing them ultrasonically to obtain a CNTs dispersion with a concentration of 0.1~10 mg / mL, wherein the solvent is anhydrous ethanol;

[0016] The PVA aqueous solution has a mass concentration of 1~10wt%;

[0017] The volume ratio of the CNTs dispersion to the PVA aqueous solution is 1:2 to 2:1.

[0018] Preferably, the mass percentage of CNTs in the CNTs / PVA blend is 8.7-27.5%.

[0019] Preferably, the concentration of the CNTs dispersion is 10 mg / mL; the mass concentration of the PVA aqueous solution is 5%; and the volume ratio of the CNTs dispersion to the PVA aqueous solution is 2:3 to 2:1.

[0020] Preferably, the material of the microstructure template is selected from polydimethylsiloxane; the microstructure template is obtained by coating the liquid polymer material of the template onto the rough surface of sandpaper, letting it stand, heating it, and then peeling it off.

[0021] The sandpaper has a mesh size of 600-800; the heating is performed at 80-100℃ for 10-40 minutes.

[0022] A self-supporting wrinkled flexible piezoresistive film is prepared by the above method;

[0023] The thickness of the self-supporting pleated flexible piezoresistive film is 20~40μm, the average undulation height of the pleated structure is 20~30μm, and the surface resistance is 5~192 Ω·cm.

[0024] An ultrathin flexible pressure sensor array is fabricated by the following method:

[0025] Silver paste interdigitated electrode array screen-printed on a single-sided adhesive PET film;

[0026] A double-sided adhesive PET insulating layer is attached to the electrode on side A;

[0027] Two of the above-mentioned self-supporting pleated flexible piezoresistive films are stacked on the electrode unit on side A;

[0028] Cover the B-side electrode with a PET film to complete the encapsulation and obtain an ultra-thin flexible pressure sensor array.

[0029] Preferably, the interdigitated electrode array is 4×4 pixels, the sensor unit size is 3mm×3mm, and the electrode array is composed of A-side electrode and B-side electrode. After packaging, the sensor array thickness is 100~120μm and the area is 16±1mm×18±1mm.

[0030] Application of the aforementioned ultrathin flexible pressure sensor array in wearable devices.

[0031] A smart sock with pressure sensing function, comprising:

[0032] The flexible sensing system consists of two or more ultra-thin flexible pressure sensor arrays arranged together.

[0033] The signal acquisition system includes a flexible bridging circuit, an analog multiplexer switch, a multi-channel synchronous analog-to-digital converter, and a microcontroller, which are used to receive and process pressure signals acquired by the flexible pressure sensor and array, and convert analog signals into digital signals.

[0034] The wireless communication module includes a wireless transceiver unit, which is communicatively connected to the signal acquisition module. The wireless transceiver unit is used to upload the data to an external terminal device and receive instructions from the external terminal device to configure the system operating mode or initiate real-time pressure feedback.

[0035] Preferably, the number and arrangement of the flexible pressure sensor array in each zone are as follows: 3 panels in the toe zone of the foot, located between the 1st metatarsal bone, the 2nd and 3rd metatarsal bones, and the 4th and 5th metatarsal bones, respectively; 3 panels in the anterior metatarsal zone of the foot, located between the 1st metatarsal bone, the 2nd and 3rd metatarsal bones, and the 4th and 5th metatarsal bones, respectively; 3 panels in the lateral zone of the foot, distributed from front to back; 3 panels in the heel zone, distributed in a triangular shape; 2 panels in the plantar arch zone, distributed from front to back; 3 panels in the Achilles tendon zone, distributed in a triangular shape from top to bottom; 1 panel each in the anterior ankle zone, lateral malleolus, medial malleolus, and tarsometatarsal joint zone; and 3 panels in the metatarsophalangeal joint zone, located between the 1st metatarsal bone, the 2nd and 3rd metatarsal bones, and the 4th and 5th metatarsal bones, respectively, on the dorsum of the foot.

[0036] The smart sock's base is a thermoplastic polyurethane (TPU) film, with a flexible pressure sensor array fixed between two TPU films; the information acquisition and wireless communication module is installed above the front ankle area of ​​the sock.

[0037] The signal acquisition module includes an analog multiplexer, a multi-channel synchronous analog-to-digital converter, and a microcontroller, used to synchronously acquire data from multiple sensor arrays.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] (1) The self-supporting wrinkled piezoresistive film preparation process proposed in this invention is simple and efficient, and has the advantage of mass production.

[0040] (2) The self-supporting piezoresistive thin film proposed in this invention has high electrical stability and combines the advantages of thinness and stable pleated structure, thus ensuring the stability of the sensor.

[0041] (3) The flexible pressure sensor proposed in this invention has excellent linearity (R0). 2 With a wide pressure range (< 1000 kPa) response of 0.99, it has a significant advantage in simplifying data processing and is suitable for multi-point precision monitoring. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the fabrication process of the CNTs / PVA composite film and the ultrathin flexible pressure sensor array of the present invention;

[0043] Figure 2 This is a curve showing the relationship between the mass fraction of CNTs and the surface resistance of the CNTs / PVA composite film in this invention;

[0044] Figure 3 This is a morphological image of the wrinkled microstructure on the surface of the CNTs / PVA composite film of the present invention;

[0045] Figure 4 This is a schematic diagram of the electrodes of the pressure sensor array of the present invention;

[0046] Figure 5 This is the pressure sensitivity curve of the pressure sensor array sensing unit of the present invention;

[0047] Figure 6 This is a diagram showing the partitioned structure of the pressure-sensitive socks of the present invention. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. However, the implementation of the present invention is not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0049] Example 1

[0050] Weigh 150 mg of hydroxylated carbon nanotubes (hydroxylated CNTs) powder, add it to 15 mL of anhydrous ethanol to prepare a 10 mg / mL CNTs ethanol dispersion, and sonicate for 2 hours while keeping the temperature below 25 °C.

[0051] Add 5g of polyvinyl alcohol (PVA) powder (PVA1788) and 95g of deionized water to a 200mL beaker. Add a magnetic stir bar, wrap the mouth of the beaker with aluminum foil, place the beaker in a water bath heating device, and stir magnetically at 90℃ for 3 hours to fully dissolve the PVA powder. Then cool and let stand until the bubbles are eliminated to obtain a 5wt% PVA aqueous solution.

[0052] CNTs ethanol dispersion and PVA aqueous solution were mixed at volume ratios of 2:1, 3:2, 1:1, 2:3, and 1:2, respectively. The CNTs / PVA water-ethanol mixtures were then magnetically stirred for 30 minutes, sonicated for 2 hours, and the temperature was controlled below 25°C. The mass percentages of CNTs in the resulting CNTs / PVA water-ethanol mixtures were 27.5%, 22.2%, 16.0%, 11.2%, and 8.7%, respectively.

[0053] To select the optimal concentration ratio for piezoresistive performance, the present invention simultaneously implemented the following scheme for five CNTs / PVA water-ethanol blend solutions: 30 μL of the blend solution was drop-coated onto a 1 cm × 1 cm smooth PDMS film, heated at 60 °C for 12 minutes, dried to form a CNTs / PVA composite film, peeled off, and adhered to a glass plate with double-sided tape. The thickness and sheet resistance of the composite film were measured using a profilometer and a four-probe instrument, respectively, and the surface resistance was calculated.

[0054] Please see Figure 2When the volume ratio of the mixed liquid is 2:3, i.e., the mass percentage of CNTs is 11.2%, the surface resistivity of the CNTs / PVA composite film drops sharply, indicating that this concentration ratio is within the percolation range of CNTs / PVA. The percolation range refers to the phenomenon in polymer-based composite materials where the material properties undergo a fundamental change when the volume fraction of conductive filler reaches a certain value. Before this critical value, filler particles are relatively dispersed in the matrix material and do not form effective interconnected pathways. When the filler content exceeds the percolation range, a continuous conductive network is formed, and the material resistance tends to stabilize. When the concentration of the CNTs / PVA composite material is within the percolation range, pressure can increase the physical contact between CNT molecules, exhibiting higher sensitivity.

[0055] Example 2

[0056] Weigh 1.2g of PDMS liquid polymer matrix and 0.12g of crosslinking agent into a small beaker, mix them thoroughly with a syringe, and place them in a 3℃ refrigerator to stand and remove bubbles.

[0057] Use 3M 9495LE double-sided tape to attach a 3cm x 3cm 800-grit square piece of sandpaper to a 3cm x 3cm polystyrene (PS) flat plate, and then place it on a horizontal heating table.

[0058] Pour the PDMS mixture into a PS flat-bottomed pan with sandpaper attached, let it stand for 30 minutes to allow the PDMS to spread evenly on the sandpaper, then heat it at 90℃ for 30 minutes to cure, and peel it off to obtain a microstructured PDMS film with a thickness of about 1 mm.

[0059] The microstructured PDMS film was placed on a glass plate, and 270 μL of a CNTs / PVA water-ethanol blend solution with a preferred CNTs mass fraction of 11.2 wt% was dropped onto it. The mixture was then dried on a heating table at 60 °C for 25 minutes. The resulting wrinkled CNTs / PVA composite film was peeled off and cut into several 3 mm × 3 mm squares.

[0060] Please see Figure 3 The average undulation height of the CNTs / PVA composite film wrinkled structure is 20~30μm.

[0061] Example 3

[0062] A method for fabricating an ultrathin flexible pressure sensor array, comprising:

[0063] Please see Figure 4 The electrode array has 4×4 pixels, the sensing unit size is 3mm×3mm, and the electrode arrays on the A side and the B side form a set of electrode arrays.

[0064] Please see Figure 1Silver paste was screen-printed onto the A and B sides of the interdigitated electrode array on a single-sided adhesive PET film, and then heat-treated at 90°C for 40 minutes. A custom double-sided adhesive PET insulating layer was then attached to the A-side electrode array. Two 3mm×3mm CNTs / PVA composite films were stacked and laid flat on the A-side electrode array unit. The B-side electrode array PET film was then covered, and custom flexible cables were soldered to complete the array encapsulation.

[0065] Please see Figure 5 The flexible pressure sensing unit exhibits near linearity (R0) over a relatively large pressure range (< 1000 kPa). 2 The pressure response is 0.99 kPa, and the pressure response sensitivity is 0.15 kPa. -1 .

[0066] Example 4

[0067] Please see Figure 6 The thermoplastic polyurethane (TPU) film, softened by heating, is tightly covered onto the resin foot model. A small hot press is then used to heat and pressurize the TPU film, allowing it to complete the three-dimensional molding of the sock.

[0068] Customized flexible cables are installed onto TPU socks using a hot-pressing method to form a flexible bridging circuit framework. The ends of the flexible cables have exposed ports for connection to a flexible pressure sensor array.

[0069] The core component of pressure-sensitive socks is a flexible pressure sensor and its array. Based on the foot's skeletal structure and stress patterns, the flexible pressure sensor array is arranged in the following specific zones: toe zone, forefoot zone, lateral plantar zone, heel zone, plantar arch zone, Achilles tendon zone, anterior ankle zone, lateral malleolus, medial malleolus, tarsometatarsal joint zone, and metatarsophalangeal joint zone. Among these:

[0070] The toe area of ​​the foot uses a three-piece flexible pressure sensor array, located between the first metatarsal bone, the second and third metatarsal bones, and the fourth and fifth metatarsal bones, respectively;

[0071] Three flexible pressure sensor arrays are used in the forefoot region, located between the 1st metatarsal bone, between the 2nd and 3rd metatarsal bones, and between the 4th and 5th metatarsal bones, respectively;

[0072] Three flexible pressure sensor arrays are distributed from front to back on the lateral side of the sole;

[0073] Three flexible pressure sensor arrays are distributed in a triangular shape in the heel area;

[0074] Two flexible pressure sensor arrays are distributed from front to back in the plantar arch area;

[0075] Three flexible pressure sensor arrays are distributed in a triangular shape from top to bottom in the Achilles tendon area;

[0076] A flexible pressure sensor array is used in the anterior ankle region, lateral malleolus, medial malleolus, and tarsometatarsal joint region.

[0077] The metatarsophalangeal joint area uses a three-piece flexible pressure sensor array, located on the dorsum of the foot between the first metatarsal bone, between the second and third metatarsal bones, and between the fourth and fifth metatarsal bones.

[0078] When installing a flexible pressure sensor array on a sock, first connect a flexible cable to a layer of TPU film, then cover it with another layer of TPU film, and use a hot-pressing method to fix the array between the two TPU layers.

[0079] The signal acquisition module performs pixel scanning using an analog multiplexer and batch sampling using an ADS1298 multi-channel synchronous analog-to-digital converter. The microcontroller controls the multiplexer to cyclically select each sensing unit and synchronously reads multiple signals in each selected state, enabling the simultaneous acquisition of pressure data from multiple arrays.

[0080] The wireless communication module includes a wireless transceiver unit, which is communicatively connected to the signal acquisition module. The wireless transceiver unit is used to upload the data to an external terminal device and receive instructions from the external terminal device to configure the system operating mode or initiate real-time pressure feedback.

[0081] The signal acquisition and wireless communication module is installed above the front ankle area of ​​the sock, without obstructing or affecting foot movement.

[0082] The pressure-sensitive socks prepared based on the above method can assist in the diagnosis, prevention and rehabilitation of foot diseases in medical scenarios through precise monitoring and analysis of foot pressure, help optimize sports posture and avoid sports injuries in sports scenarios, and can also serve as an intelligent interactive medium to achieve natural control of external devices, demonstrating outstanding application value and innovative benefits in multiple fields.

[0083] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method of making a self-supporting, crumpled, flexible piezoresistive membrane, characterized in that, Includes the following steps: A CNTs dispersion and a PVA aqueous solution were prepared and mixed at a volume ratio to form a CNTs / PVA blend. Preparation of microstructure templates; The CNTs / PVA blend liquid is drop-coated onto the microstructure template, dried, and then peeled off to obtain a CNTs / PVA composite film, namely a self-supporting wrinkled flexible piezoresistive film.

2. The method for preparing a self-supporting wrinkled flexible piezoresistive film according to claim 1, characterized in that, The CNTs dispersion is obtained by adding hydroxylated CNTs to a solvent and dispersing them ultrasonically to obtain a CNTs dispersion with a concentration of 0.1~10 mg / mL. The PVA aqueous solution has a mass concentration of 1~10wt%; The volume ratio of the CNTs dispersion to the PVA aqueous solution is 1:2 to 2:

1.

3. The method for preparing a self-supporting wrinkled flexible piezoresistive film according to claim 2, characterized in that, The concentration of the CNTs dispersion is 10 mg / mL; the mass concentration of the PVA aqueous solution is 5%; and the volume ratio of the CNTs dispersion to the PVA aqueous solution is 2:3 to 2:

1.

4. The method for preparing a self-supporting wrinkled flexible piezoresistive film according to claim 1, characterized in that, The material of the microstructure template is selected from polydimethylsiloxane; the microstructure template is obtained by coating the liquid polymer material of the template onto the rough surface of sandpaper, letting it stand, heating it, and peeling it off; The sandpaper has a mesh size of 600-800.

5. A self-supporting, wrinkled, flexible piezoresistive film, characterized in that, The self-supporting pleated flexible piezoresistive film is prepared by the method according to any one of claims 1 to 4; the thickness of the film is 20 to 40 μm, the average undulation height of the pleated structure is 20 to 30 μm, and the surface resistance is 5 to 192 Ω·cm.

6. An ultrathin flexible pressure sensor array, characterized in that, It is prepared by the following method: Silver paste interdigitated electrode array screen-printed on a single-sided adhesive PET film; A double-sided adhesive PET insulating layer is attached to the electrode on side A; Two self-supporting pleated flexible piezoresistive films as described in claim 6 are stacked on the electrode unit on side A; Cover the B-side electrode with a PET film to complete the encapsulation and obtain an ultra-thin flexible pressure sensor array.

7. The ultrathin flexible pressure sensor array according to claim 7, characterized in that, The interdigitated electrode array is 4×4 pixels, and the sensor unit size is 3mm×3mm. It consists of an A-side electrode and a B-side electrode to form an electrode array. After packaging, the sensor array thickness is 100~120μm and the area is 16±1mm×18±1mm.

8. The application of the ultrathin flexible pressure sensor array of claim 6 or 7 in wearable devices.

9. A smart sock with pressure sensing function, characterized in that, include: The flexible sensing system is composed of two or more ultrathin flexible pressure sensor array regions as described in claim 8. The signal acquisition system includes a flexible bridging circuit, an analog multiplexer switch, a multi-channel synchronous analog-to-digital converter, and a microcontroller, which are used to receive and process pressure signals acquired by the flexible pressure sensor and array, and convert analog signals into digital signals. The wireless communication module includes a wireless transceiver unit, which is communicatively connected to the signal acquisition module. The wireless transceiver unit is used to upload the data to an external terminal device and receive instructions from the external terminal device to configure the system operating mode or initiate real-time pressure feedback.

10. The smart sock with pressure sensing function according to claim 9, characterized in that, The number and arrangement of the flexible pressure sensor array in each zone are as follows: 3 panels in the toe zone of the foot, located between the 1st metatarsal bone, the 2nd and 3rd metatarsal bones, and the 4th and 5th metatarsal bones, respectively; 3 panels in the anterior metatarsal zone of the foot, located between the 1st metatarsal bone, the 2nd and 3rd metatarsal bones, and the 4th and 5th metatarsal bones, respectively; 3 panels in the lateral zone of the foot, distributed from front to back; 3 panels in the heel zone, distributed in a triangular shape; 2 panels in the plantar arch zone, distributed from front to back; 3 panels in the Achilles tendon zone, distributed in a triangular shape from top to bottom; 1 panel each in the anterior ankle zone, lateral malleolus, medial malleolus, and tarsometatarsal joint zone; and 3 panels in the metatarsophalangeal joint zone, located between the 1st metatarsal bone, the 2nd and 3rd metatarsal bones, and the 4th and 5th metatarsal bones, respectively on the dorsum of the foot. The smart sock's base is a thermoplastic polyurethane film, and a flexible pressure sensor array is fixed between two layers of polyurethane film; the information acquisition and wireless communication module is installed above the front ankle area of ​​the sock. The signal acquisition module includes an analog multiplexer, a multi-channel synchronous analog-to-digital converter, and a microcontroller, used to synchronously acquire data from multiple sensor arrays.

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