Flexible capacitive sensor based on gradient interlocking microstructure

Abstract

The invention relates to the field of capacitance type sensor structures based on bionics, and discloses a flexible capacitance type sensor based on a gradient interlocking microstructure, the flexible capacitance type sensor is composed of an upper electrode layer, a lower electrode layer and a functional layer, the upper electrode layer and the lower electrode layer are of a one-to-four array type pole plate structure, an upper pole plate is a main pole plate, and a lower pole plate is four branch pole plates; the functional layer is divided into three layers, the top of the functional layer is a PDMS / CNTs layer containing a rectangular pyramid array microstructure, a TPU film is arranged close to the bottom of the functional layer, the bottom of the functional layer is a PDMS / CNTs layer containing a gradient dome array microstructure, and the three functional layers are vertically stacked to form stable gradient interlocking. The capacitive sensor refers to the structure of a human skin dermis-epidermis interface, and the special shape of the dielectric layer enables the capacitive sensor to have higher sensitivity, larger measuring range and more stable data output compared with a common capacitive sensor. According to the invention, a larger stress area is realized on a limited area, the stress is dispersed, the single-point overload pressure is effectively reduced, and the measurement range is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of bionics-based capacitive sensor structures, and in particular to a flexible capacitive sensor based on a gradient interlocking microstructure. Background Art

[0002] In recent years, sensors, as core sensing devices of modern industry and intelligent systems, have shown significant development trends in terms of technological innovation, application expansion and market scale. The sensor industry is undergoing a leap from single perception to systematic intelligence. Driven by both technological innovation and industrial upgrading, its cornerstone role in the digital economy will be further highlighted.

[0003] Among them, the research on capacitive sensors has made significant progress in technological innovation and application expansion, and its core development direction focuses on high precision, flexibility, integration and intelligence. At present, the research direction of capacitive sensors is mostly focused on the miniaturization and multifunctional integration of sensors and the optimization of signal processing, while ignoring the influence of dielectric layer materials and their structural design on sensor output results. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a flexible capacitive sensor based on a gradient interlocking microstructure, which expands the traditional sandwich stacking structure by imitating the three-dimensional interlocking structure of the dermis-epidermis interface in human skin. Two microstructure layers are introduced in the middle layer, and a thin film dielectric layer is embedded between them to ensure the electrical insulation performance of the capacitor. The top layer adopts a tetrahedral grid design, while the bottom layer is a dome structure array. Compared with a single microstructure, this interlocking structure can distinguish stress concentration areas, broaden the dynamic response range, and has the characteristics of high sensitivity and large range.

[0005] To achieve the above objectives, the present invention is implemented by the following technical solutions: A flexible capacitive sensor based on a gradient interlocking microstructure includes five parts: an upper electrode, a top layer of a dielectric layer, a middle layer of a dielectric layer, a bottom layer of a dielectric layer, and a lower electrode;

[0006] The top layer of the dielectric layer is a polydimethylsiloxane (PDMS) film doped with carbon nanotubes (CNTs), and the lower surface thereof has a 15×15 tetrahedral pyramidal microstructure, the ratio of the side length to the height of a single micro-cone is 3:4, and the ratio of the center distance between two micro-cones to the height is 2:5;

[0007] The bottom layer of the dielectric layer is the same piece of polydimethylsiloxane (PDMS) film doped with carbon nanotubes (CNTs). Its upper surface has a microstructure composed of 5×5 hemispheres. The hemispherical microstructures in different regions are increased in height respectively. The ratio of the increased height to the radius of the central hemisphere and the four hemispheres at the corners is 8:3 to 3:1. The ratio of the increased height to the radius of the eight hemispheres surrounding the central hemisphere is 4:1 to 9:2. The ratio of the increased height to the radius of the remaining hemispheres is 8:1 to 9:1. The ratio of the center distance between two hemispheres to the radius is 115:300.

[0008] Preferably, the upper electrode plate is a flexible material carrying a square copper metal electrode plate, serving as the upper electrode plate of the capacitor.

[0009] Preferably, the middle layer of the dielectric layer is a layer of tpu film.

[0010] Preferably, the lower electrode plate is a flexible material carrying four square copper electrode plates of the same size, which is exactly covered by the upper electrode plate.

[0011] Preferably, the preparation process of the polydimethylsiloxane and carbon nanotube composite film includes the following steps:

[0012] S1. Preparation of CNTs dispersion liquid: In the material preparation and initial mixing stage, CNTs are uniformly dispersed in an organic solvent through ultrasonic oscillation. The organic solvent includes ethanol or toluene.

[0013] S2. Co-blending treatment of CNTs and PDMS: Next, enter the uniform mixing stage of CNTs and PDMS. Mix the above CNTs dispersion liquid with PDMS, and again use ultrasonic treatment technology to promote the uniform dispersion of CNTs in the PDMS matrix.

[0014] S3. Removal of organic solvent: Subsequently, remove the organic solvent at a suitable temperature, and the specific suitable temperature is 90 - 95 °C.

[0015] S4. Preparation and mixing of curing agent: Then, mix strictly according to the mass ratio of PDMS:curing agent of 10:1 to ensure the uniformity of the PDMS matrix and the integrity of the subsequent cross-linking reaction.

[0016] S5. Defoaming treatment of composite material: After stirring the curing agent evenly, thoroughly remove the bubbles in the mixture through vacuum drying technology to obtain a uniform PDMS-CNTs composite material.

[0017] S6. Mold Filling and Secondary Defoaming: Enter the forming and curing stage. Pour the above-mentioned uniform PDMS-CNTs mixture into the pre-prepared pyramid mold and gradient dome structure mold made of polyurethane, and perform vacuum drying again to remove the existing bubbles, ensuring uniform performance after film formation.

[0018] S7. Film Curing and Demolding: Subsequently, place the mold at a specific temperature for curing. The specific temperature is 50 - 60 °C, and the curing time is 1 - 2 hours. After curing, carefully remove the film from the mold.

[0019] S8. Sensor Assembly and Forming: Perform the assembly step. Assemble the formed PDMS-CNTs film and tpu film with the upper and lower electrode plates in a laminated manner to obtain a flexible capacitive sensor.

[0020] The present invention provides a flexible capacitive sensor based on a gradient interlocking microstructure, having the following beneficial effects:

[0021] 1. The present invention realizes a larger force-bearing area on a limited area, disperses stress, effectively reduces the single-point overload pressure, and expands the measurement range. Inspired by the octopus tentacle, different from the method of adjusting the dome radius in the multi-level dome structure, under the premise of keeping the dome radius constant in the interlocking structure, a gradient design strategy of arranging an array of constant dome radii is adopted to indirectly construct a significant height gradient difference, thereby realizing a remarkable expansion of the linear range. In this design, it is ensured that the number of contacts between each dome and the pyramid microstructure remains consistent, guaranteeing the gradual activation of the stress area. Compared with the non-uniform dome structure design, the number of micro-cones in the pyramid microstructure layer is fully utilized, thereby increasing the stress concentration area and improving the sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the preparation process of the present invention;

[0023] Figure 2 It is a schematic diagram of the pyramid microstructure on the top layer of the dielectric layer of the present invention;

[0024] Figure 3 It is a schematic diagram of the specific dimension information of the pyramid of the present invention;

[0025] Figure 4 It is a schematic diagram of the hemispherical microstructure on the bottom layer of the dielectric layer of the present invention;

[0026] Figure 5 It is a schematic diagram of the specific dimension information of the hemispherical structure of the present invention;

[0027] Figure 6 It is a schematic side view of the sensor dielectric layer of the present invention;

[0028] Figure 7 Schematic diagram of the hemispherical structure heightening of the present invention;

[0029] Figure 8 Schematic diagram of some performance data during the experiment of the present invention;

[0030] Figure 9 Schematic diagram of the flexible capacitive sensor structure of the present invention;

[0031] Figure 10 Schematic diagram of four different gradient interlocking microstructures conceived in the present invention. Detailed implementation manners

[0032] Next, in conjunction with the accompanying drawings of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Embodiment:

[0034] Please refer to the attached Figure 1 - attached Figure 10 , the embodiment of the present invention provides a flexible capacitive sensor based on a gradient interlocking microstructure, including an upper plate, a top dielectric layer, a middle dielectric layer, a bottom dielectric layer, and a lower plate;

[0035] The upper plate is a flexible material carrying a square metal copper plate and serves as the upper plate of the capacitor.

[0036] The top dielectric layer is a polydimethylsiloxane (PDMS) film doped with carbon nanotubes (CNTs). Its lower surface has a 15×15 pyramid-shaped microstructure, and the ratio of the side length to the height of a single micro-pyramid is 3:4. The center distance between two micro-pyramids and the height ratio is 2:5.

[0037] The middle dielectric layer is a layer of tpu film.

[0038] The bottom dielectric layer is the same polydimethylsiloxane (PDMS) film doped with carbon nanotubes (CNTs). Its upper surface has a microstructure composed of 5×5 hemispheres. The hemispheres in different regions are heightened respectively. The heightening height of the central hemisphere and the four corner hemispheres and the hemisphere radius ratio is 8:3 to 3:1. The heightening height of the eight hemispheres surrounding the central hemisphere and the hemisphere radius ratio is 4:1 to 9:2. The heightening height of the remaining hemispheres and the hemisphere radius ratio is 8:1 to 9:1. The center distance between two hemispheres and the radius ratio is 115:300.

[0039] The lower electrode plate is a flexible material carrying four square copper electrode plates of the same size, which is exactly covered by the upper electrode plate.

[0040] The material selection of the dielectric layer film needs to have excellent mechanical properties, electrical properties, processing technology and compatibility with other materials. The combination of polydimethylsiloxane (PDMS) and carbon nanotubes (CNTs) stands out in this context. PDMS is known for its excellent flexibility and biocompatibility, suitable for flexible electronic devices and adaptable to complex surfaces and dynamic deformations. CNTs provide high electrical conductivity, thermal conductivity and mechanical strength, and the large specific surface area also improves the sensitivity of the sensor. When combined, PDMS imparts flexibility and biocompatibility to the material, while CNTs contribute electrical conductivity and mechanical strength. By adjusting the content of CNTs, the electrical conductivity of the composite material can be precisely controlled to meet different application requirements. In addition, this composite material is easy to prepare by methods such as solution processing or mold forming, with good processability and cost-effectiveness.

[0041] The preparation process of the composite film of polydimethylsiloxane (PDMS) and carbon nanotubes (CNTs) includes the following steps:

[0042] S1. Preparation of CNTs dispersion: In the material preparation and initial mixing stage, CNTs are uniformly dispersed in an organic solvent through ultrasonic oscillation. The organic solvent includes ethanol or toluene;

[0043] S2. Blending treatment of CNTs and PDMS: Next, enter the uniform mixing stage of CNTs and PDMS. Mix the above CNTs dispersion with PDMS, and again use ultrasonic treatment technology to promote the uniform dispersion of CNTs in the PDMS matrix;

[0044] S3. Removal of organic solvent: Subsequently, the organic solvent is removed at a suitable temperature, and the suitable temperature is specifically 90 - 95 °C;

[0045] S4. Preparation and mixing of curing agent: Then, strictly mix according to the mass ratio of PDMS:curing agent of 10:1 to ensure the uniformity of the PDMS matrix and the integrity of the subsequent cross-linking reaction;

[0046] S5. Defoaming treatment of composite material: After stirring the curing agent evenly, through vacuum drying technology, the bubbles in the mixture are completely removed to obtain a uniform PDMS-CNTs composite material;

[0047] S6. Mold Filling and Secondary Defoaming: Entering the forming and curing stage, pour the above-mentioned uniform PDMS-CNTs mixture into the pre-prepared pyramid mold and gradient dome structure mold made of polyurethane, and vacuum dry again to remove the existing bubbles to ensure uniform performance after film formation;

[0048] S7. Film Curing and Demolding: Subsequently, place the mold at a specific temperature for curing. The specific temperature is 50-60°C, and the curing time is 1-2 hours; after curing is completed, carefully remove the film from the mold;

[0049] S8. Sensor Assembly and Forming: Perform the assembly step, and assemble the formed PDMS-CNTs film and tpu film with the upper and lower electrode plates in a laminated manner to obtain a flexible capacitive sensor, as Figure 9 shown.

[0050] This invention draws on the multi-scale sensing mechanism of insect antennae. By using contact structures of different heights, material type recognition, softness evaluation, and precise quantification of Young's modulus can be achieved. Inspired by the sucker structure of octopus tentacles, research shows that dome structures of different sizes have different sensitivity and linear range characteristics. By optimizing the combination of multi-level dome microstructures with different periods and diameters, the linear range can be significantly improved while maintaining high sensitivity. Based on these innovative ideas, aiming at the technical bottlenecks of film microstructure limitations and the mutual restriction between sensing area and range, on the basis of the pyramid-circular interlocking structure, making full use of the designability of the microstructure stress concentration area and the controllability of the sensor response range, an innovative design scheme of gradient interlocking microstructure is proposed. In this invention, four different gradient interlocking microstructures (as Figure 10 shown) are conceived, namely concentric circle gradient support, concentric circle gradient splitting, triangular wave gradient, and rhombus gradient. These gradient interlocking structures can greatly improve the relaxation time of the sensor, shorten the response time, delay deformation saturation, reduce the initial capacitance, increase the measurement range, enhance the anti-interference ability, and improve the sensor stability.

[0051] The working state of the present invention will be described in detail below:

[0052] The flexible capacitive strain sensor is composed of a multi-channel sensing array and a PDMS / CNTs (polydimethylsiloxane / carbon nanotubes) thin film with a gradient interlocking microstructure, and can efficiently obtain the Young's modulus of the object surface. If the structure of an octopus tentacle is followed, at the existing microcone distribution density, introducing a secondary small dome structure into the large dome gap will not form a new effective stress concentration area. Instead, it will lead to a decrease in the signal-to-noise ratio due to the mismatch between the microcone-dome space. Based on the contact mechanics model (Hertz contact theory) calculation, the hardness (Young's modulus) of the material needs to obtain two parameters: the contact force and the pressing depth simultaneously. After introducing a dome structure with a height gradient distribution, the gradient interlocking structure can synchronously obtain the contact force and pressing depth data, thus having the ability to sense the Young's modulus of the object, better distinguish objects with different hardness levels, and obtain more sensing information. The middle layer of the sensor is the functional layer, which is the core part of the sensor and is responsible for sensing external stimuli (such as pressure, strain, etc.) and converting them into electrical signals. According to the different capacitance change trends of the four-channel arrays of the lower electrode plate, the pressure changes from the X, Y, and Z axes can be detected. The capacitance of the sensor can be described by the following formula:

[0053]

[0054] Among them, ε represents the dielectric constant, A represents the overlapping area between the upper and lower electrode plates, and d represents the distance between the two electrode plates. When the sensor is subjected to stress, the distance d between the two electrode plates and the overlapping area between the upper and lower electrode plates change, resulting in a change in capacitance. According to the change in the relative capacitance of the capacitive sensor, the magnitude and distribution of the external force can be obtained, thereby analyzing external information. Through the improved iTransformer neural network model, the multi-channel electrical signals of the flexible capacitive strain sensor are decoupled, and the magnitude of the contact force is accurately extracted.

[0055] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A flexible capacitive sensor based on a gradient interlocking microstructure, characterized in that, It includes five parts: the upper electrode plate, the top layer of the dielectric layer, the middle layer of the dielectric layer, the bottom layer of the dielectric layer, and the lower electrode plate. The top layer of the dielectric layer is a polydimethylsiloxane (PDMS) thin film doped with carbon nanotubes (CNTs). Its lower surface has a 15×15 square pyramid microstructure. The ratio of the side length to the height of a single micro-pyramid is 3:4, and the ratio of the center distance between two micro-pyramids to the height is 2:

5. The bottom layer of the dielectric layer is also a polydimethylsiloxane (PDMS) thin film doped with carbon nanotubes (CNTs). Its upper surface has a microstructure composed of 5×5 hemispheres. The heightening of the hemisphere microstructures in different regions is carried out respectively. The ratio of the heightening height of the central hemisphere and the four corner hemispheres to the radius of the hemisphere is 8:3 - 3:

1. The ratio of the heightening height of the eight hemispheres surrounding the central hemisphere to the radius of the hemisphere is 4:1 - 9:

2. The ratio of the heightening height of the remaining hemispheres to the radius of the hemisphere is 8:1 - 9:

1. The ratio of the center distance between two hemispheres to the radius is 115:

300.

2. The flexible capacitive sensor based on a gradient interlocking microstructure according to claim 1, wherein, The upper electrode plate is a flexible material carrying a square copper metal electrode plate, serving as the upper electrode plate of the capacitor.

3. A flexible capacitive sensor based on a gradient interlocking microstructure according to claim 1, wherein, The middle layer of the dielectric layer is a layer of tpu thin film.

4. A flexible capacitive sensor based on a gradient interlocking microstructure according to claim 1, characterized in that, The lower electrode plate is a flexible material carrying four square copper electrode plates of the same size, which is exactly covered by the upper electrode plate.

5. A flexible capacitive sensor based on a gradient interlocking microstructure according to claim 1, characterized in that, It includes: The preparation process of the polydimethylsiloxane and carbon nanotube composite film includes the following steps: S1. Preparation of CNTs dispersion liquid: In the material preparation and initial mixing stage, CNTs are uniformly dispersed in an organic solvent through ultrasonic oscillation. The organic solvent includes ethanol or toluene. S2. Co-blending treatment of CNTs and PDMS: Next, enter the uniform mixing stage of CNTs and PDMS. Mix the above CNTs dispersion liquid with PDMS, and again use ultrasonic treatment technology to promote the uniform dispersion of CNTs in the PDMS matrix. S3. Removal of organic solvent: Subsequently, the organic solvent is removed at a suitable temperature, and the specific suitable temperature is 90 - 95°C. S4. Blending and mixing of curing agent: Then, strictly mix according to the mass ratio of PDMS:curing agent of 10:1 to ensure the uniformity of the PDMS matrix and the integrity of the subsequent cross-linking reaction. S5. Defoaming treatment of the composite material: After stirring the curing agent evenly, through vacuum drying technology, the bubbles in the mixture are completely removed to obtain a uniform PDMS-CNTs composite material. S6. Mold filling and secondary defoaming: Enter the forming and curing stage. Pour the above uniform PDMS-CNTs mixture into a pre-prepared polyurethane square pyramid mold and a gradient dome structure mold, and vacuum dry again to remove the existing bubbles to ensure the uniform performance of the film after forming. S7. Film curing and demolding: Subsequently, place the mold at a specific temperature for curing. The specific specific temperature is 50 - 60°C, and the curing time is 1 - 2 hours. After curing, carefully take out the film from the mold. S8. Sensor assembly and forming: Perform the assembly step, and assemble the formed PDMS-CNTs film and the tpu film with the upper and lower electrode plates in a laminated manner to obtain flexible capacitive sensing.

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