Snakelike microstructure capacitive sensor giving consideration to sensitivity and measuring range and preparation method thereof

Abstract

The invention provides a snakelike microstructure capacitive sensor giving consideration to sensitivity and measuring range and a preparation method thereof. The snakelike microstructure capacitive sensor comprises an upper protection layer, an upper electrode layer, a snakelike microstructure layer, a lower electrode layer and a lower protection layer which are sequentially stacked from top to bottom. The snakelike microstructure layer comprises a plurality of periodically bent insulating elastomer units. According to the snakelike microstructure capacitive sensor, high sensitivity can be achieved in a low-voltage stage through the unique deformation characteristic of the snakelike structure, the bearing capacity is further increased through contact of the snakelike structure in a high-voltage stage, and therefore the measuring range of the sensor is remarkably widened, and meanwhile an adjustable mathematical model is provided; the performance can be customized and expanded according to application scenes, and the precision requirements in different application scenes can be fully met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible capacitive sensors, in particular to a serpentine microstructure capacitive sensor and method considering sensitivity and range. BACKGROUND

[0002] Flexible capacitive sensors have a wide range of applications in wearable devices, human-computer interaction, and medical monitoring due to their high sensitivity, fast response, and good flexibility. Traditional flexible capacitive sensors usually use planar electrodes or simple microstructure designs to detect capacitive signals by changing the electrode spacing. However, this design has a contradiction between sensitivity and range: high sensitivity requires a small initial spacing, while a large range requires a large compressible range.

[0003] In the prior art, some sensors introduce microstructures (such as pyramids, columnar structures) to improve sensitivity, but these structures are prone to saturation under high pressure, resulting in limited range. In addition, although porous structures can provide a certain degree of flexibility, uneven pore distribution can affect the consistency of the sensor. Therefore, there is an urgent need for a new structural design that can balance high sensitivity and a large range. SUMMARY

[0004] The present application aims to provide a serpentine microstructure capacitive sensor and its preparation method, which can balance sensitivity and range to solve the above-mentioned problems of the prior art.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A serpentine microstructure capacitive sensor considering sensitivity and range, comprising an upper protective layer, an upper electrode layer, a serpentine microstructure layer, a lower electrode layer and a lower protective layer stacked in order from top to bottom; the serpentine microstructure layer comprises a plurality of periodically curved insulating elastomer units, and the geometric parameters thereof satisfy the following relationship:

[0007]

[0008] In formula (1), C represents the capacitance value; C0 represents the initial capacitance value; F represents the external force; F c represents the critical contact force; H, w, and t represent the height, width, and thickness of the serpentine microstructure, respectively; n represents the number of bending periods; E represents the Young's modulus; d0 represents the initial electrode spacing; A represents the effective electrode area; when F≤F c , the serpentine microstructure undergoes elastic deformation, and the electrode spacing decreases; when F>F c , the adjacent parts of the serpentine microstructure are in contact to form parallel supports.

[0009] Further, the geometric parameters of the serpentine microstructure layer satisfy the performance regulation relationship:

[0010] The sensitivity is improved by reducing the thickness t, lowering the height H or increasing the number of bends n:

[0011]

[0012] The range is expanded by increasing the thickness t, the number of bends n or the modulus E:

[0013]

[0014] In formulas (2)-(3): S1 represents the sensitivity; FS represents the range; H, w, t represent the height, width and thickness of the serpentine microstructure respectively; n represents the number of bending periods; E represents the Young's modulus; d0 represents the initial electrode spacing; A represents the effective electrode area.

[0015] Further, the upper electrode layer and the lower electrode layer are a polyimide flexible substrate with a sputtered copper film, and the thickness of the copper film is 50-200 nm.

[0016] Further, the upper protective layer and the lower protective layer are a polyurethane or epoxy resin packaging film, with a thickness of 30-100 μm and a moisture-proof and impact-resistant coating on the surface.

[0017] A preparation method of a serpentine microstructure capacitive sensor that balances sensitivity and range, for making the above-mentioned capacitive sensor, comprising the following steps:

[0018] (a) Serpentine mold making:

[0019] A serpentine microstructure mold is made using photosensitive resin through 3D printing technology, with a printing accuracy of ≤0.1 mm, a smooth mold surface and periodic curved grooves;

[0020] (b) Serpentine microstructure forming:

[0021] Polydimethylsiloxane (PDMS) is mixed with a crosslinking agent at a ratio of 10:1 and stirred;

[0022] PDMS mixture is injected into the inner wall of the mold after applying a release agent;

[0023] Vacuum degassing for 20 minutes and curing at 80°C for 2 hours, then demolding to obtain a serpentine microstructure;

[0024] (c) Electrode layer preparation:

[0025] A copper film is sputtered on a polyimide substrate, with a sputtering power of 200 W and a sputtering time of 5 minutes, to form an electrode with a thickness of 100 nm, serving as the upper electrode and the lower electrode;

[0026] (d) Sensor assembly:

[0027] The serpentine microstructure is sandwiched between the upper electrode and the lower electrode, the two ends of the serpentine microstructure are in close contact with the surface of the electrode, and a flexible adhesive is used for fixation, forming an assembly;

[0028] (e) encapsulation protection:

[0029] A polyurethane or epoxy resin is coated on the surface of the assembly to form a protective layer with a thickness of 30-100 μm.

[0030] According to the above technical solution, compared with the prior art, the serpentine structure elastic deformation and the dual-state deformation characteristics of contact support are used to realize the unification of high sensitivity and wide range; meanwhile, a controllable mathematical model is proposed, including a segmented force and capacitance control model, a sensitivity and range control model, the performance of which can be customized and expanded according to the application scene, and the precision requirements in different application scenes can be fully met. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a sectional view of the overall structure of the serpentine microstructure capacitive sensor of the application;

[0032] Figure 2 is a structural schematic diagram of the serpentine microstructure layer of the application;

[0033] Figure 3 is a test curve of the serpentine microstructure capacitive sensor of the application;

[0034] Figure 4 is a mold schematic diagram for manufacturing the serpentine structure of the application;

[0035] In the figure: 1, upper protective layer; 2, upper electrode layer; 3, serpentine microstructure layer; 4, lower electrode layer; 5, lower protective layer. DETAILED DESCRIPTION

[0036] The preferred embodiments of the application will be described in detail below with reference to the accompanying drawings.

[0037] As shown in Figures 1-2 the serpentine microstructure capacitive sensor considering sensitivity and range, includes upper protective layer 1, upper electrode layer 2, serpentine microstructure layer 3, lower electrode layer 4 and lower protective layer 5 which are stacked from top to bottom; the serpentine microstructure layer 3 includes a plurality of periodic bending insulating elastomer units, and the geometric parameters satisfy the following relationship:

[0038]

[0039] In formula (1), C represents the capacitance value; C0 represents the initial capacitance value; F represents the external force; F crepresents the critical contact force; H, w, t represent the height, width and thickness of the serpentine microstructure, respectively; n represents the number of bending periods; E represents the Young's modulus; d0 represents the initial electrode spacing; A represents the effective electrode area.

[0040] As shown in Figure 3 , when subjected to pressure, F≤F c , the serpentine structure first undergoes elastic deformation, reducing the upper and lower electrode spacing and rapidly changing the capacitance value, achieving high sensitivity detection; as the pressure increases, until F>F c , the adjacent parts of the serpentine structure are in contact with each other, forming a mechanical support, which significantly improves the range of the sensor while maintaining the capacitance response; this phased response mechanism enables the sensor to have both high sensitivity and wide range.

[0041] The preparation of the serpentine microstructure capacitance sensor that takes into account sensitivity and range includes the following steps:

[0042] (a) Serpentine mold making: using high-precision photosensitive resin, a 3D printing technology is used to make a mold for the serpentine microstructure, with a printing accuracy of 0.1 mm. As shown in Figure 4 , the size of the mold is a 2cm×2cm planar area, containing a groove with 4 periodic bends; the inner surface of the mold is smooth to ensure the surface quality of the subsequent injected material. After printing, the mold needs to be cleaned and dried to ensure no impurities and residues.

[0043] (b) Serpentine microstructure forming: an insulating elastomer material is used to prepare the serpentine microstructure layer. Specifically, polydimethylsiloxane (PDMS) is used as the base material, and silica gel crosslinking agent and solvent are added to the PDMS based on the ratio of 10:1; at the same time, the inner wall of the mold is smeared with vaseline for easy demolding; after preparing the mold, the mixed PDMS material is injected into the mold to ensure that it covers all the serpentine structures; then, the mold is placed in a vacuum box for vacuum treatment to remove air bubbles and ensure uniform distribution of the material in the mold; the vacuum treatment time is 20 minutes, and then the mold is placed in an oven at 80℃ for 2 hours until the material is completely cured; finally, the serpentine microstructure is obtained after demolding.

[0044] (c) Electrode layer preparation: The upper and lower electrodes are made by metal plating film using sputtering process. In this step, copper is selected as the electrode material because of its good electrical conductivity and low cost. First, the electrode material to be plated polyimide (PI) film is used as the substrate, the size of the PI film is 3 cm x 3 cm, and the thickness is 25 μm; a 100 nm thick copper layer is uniformly plated on the surface of the PI film by sputtering deposition process, which is used as the base layer of the upper and lower electrodes; during sputtering, the control parameters are sputtering power of 200 W and sputtering time of 5 minutes, to ensure uniform and good adhesion of the copper layer.

[0045] (d) Sensor assembly: The prepared serpentine microstructure layer is accurately attached to the designated position between the lower electrode layer to form a 3*3 serpentine microstructure array, and finally a sandwich structure of the sensor is formed. First, the bottom electrode layer (copper plated PI film) is connected to the serpentine microstructure layer to ensure that the top end of the serpentine structure is in close contact with the lower electrode; then, the top electrode is attached to the top surface of the serpentine structure; to ensure the stability of the entire structure, double-sided tape or flexible adhesive (such as PDMS) can be used to slightly coat the contact position between the serpentine structure and the electrode to make it solidify, forming an assembly.

[0046] (e) Packaging protection: In order to improve the stability and protection ability of the sensor, the entire sensor will be sealed by packaging process finally. Transparent polyurethane (PU) or epoxy resin is used as the packaging material, and a thin film is coated on the surface of the entire sensor to ensure its moisture-proof, dust-proof and anti-impact ability; the thickness of the packaging layer is controlled at about 50 μm to ensure that it will not affect the elasticity and capacitance response characteristics of the sensor.

[0047] Further, the geometric parameters of the serpentine microstructure layer in the preferred embodiment satisfy the following performance regulation relationship:

[0048] The sensitivity is improved by reducing the thickness t, reducing the height H or increasing the number of bends n:

[0049]

[0050] The range is expanded by increasing the thickness t, the number of bends n or the modulus E:

[0051]

[0052] In formulas (2)-(3): S1 represents the sensitivity; FS represents the range; H, w, t represent the height, width and thickness of the serpentine microstructure respectively; n represents the number of bending periods; E represents the Young's modulus; d0 represents the initial plate spacing; A represents the effective area of the electrode.

[0053] In specific applications, by adjusting the thickness, width, and period of the serpentine microstructure, the sensor performance (sensitivity, range) can be controlled, enabling sensor applications in various environments, such as the following applications in robot tactile scenarios and soil blasting monitoring scenarios in hypergravity environments.

[0054] Application Example One: Application of Serpentine Microstructure Sensor in Robot Tactile Scene

[0055] 1. Sensor installation and debugging

[0056] Install the serpentine microstructure sensor on the robot hand or tactile probe. The size of the sensor is adjusted according to the robot structure design, and the general sensor area is 3cm x 3cm. The width of each unit of the serpentine microstructure is 0.5mm, and the pitch is 1mm, which is suitable for different sizes of tactile demand. The installation position of the sensor should ensure that its surface can contact with external objects and accurately respond to the changes of the objects.

[0057] At the same time, on the back of the sensor, use silicone rubber (such as medical silicone or soft PU material) to firmly paste it on the contact area of the robot hand. The thickness of the silicone rubber is 0.3mm to ensure sufficient elasticity and signal transmission stability. During installation, about 0.2ml of silicone rubber is evenly applied, and gently pressed for 10 seconds to ensure good adhesion.

[0058] 2. Data acquisition and processing

[0059] Connect the serpentine microstructure sensor to the data acquisition module in the robot control system. Use the internal software platform of the robot (such as the ROS system) or data processing software (such as MATLAB, LabVIEW) for real-time data acquisition. Set the sampling frequency to 1000Hz or higher to ensure that the rapidly changing tactile signals can be captured.

[0060] In the process of tactile signal processing, use a high-pass filter to remove low-frequency noise and a low-pass filter to remove high-frequency interference to ensure that the acquired tactile signals are accurate and error-free. In addition, use a dynamic threshold detection algorithm to identify the hardness or softness of different touch objects in real time. By writing appropriate programs, real-time feedback can be achieved to guide the robot to classify and respond to different objects based on touch.

[0061] 3. Response mechanism of soft object touch

[0062] When the serpentine microstructure sensor contacts a soft object (such as food, clothing), due to the elasticity of the serpentine structure, the microstructure on the surface of the sensor will be slightly compressed or deformed, causing the capacitance value to change. The capacitance change of the sensor is closely related to the size of the contact force and the softness of the object. In specific applications, the response of the sensor to soft objects can be tested by the following steps: gently touching or pressing the soft object (soft clothing, fabric or fruit), monitoring the output signal of the sensor; observe how the serpentine structure gradually compresses or deforms during the touching process, and the change in capacitance value; by comparing with standard objects of known hardness, confirm whether the sensor can accurately detect the contact force and surface characteristics of soft objects; for example, when the sensor contacts an apple, the signal output by the sensor will show a clear low-amplitude fluctuation with a long duration, indicating that the object is relatively soft and requires a small force to deform the sensor.

[0063] 4. Response mechanism for hard object contact

[0064] When the serpentine microstructure sensor contacts a hard object (wall, tool, hard metal object), the serpentine structure of the sensor will undergo a large instantaneous compression, and the change in capacitance value will significantly increase. The contact of a hard object will cause a deeper compression of the microstructure on the surface of the sensor, rapidly changing the capacitance. The sensor response at this time is as follows: when the sensor contacts a hard object, the output signal presents a high-amplitude instantaneous peak, and the signal duration is short, indicating that the object is relatively hard; the response of the sensor to hard objects is relatively rapid, with a short rise time of the waveform, suitable for identifying the collision or contact of high-hardness objects.

[0065] 5. Practical application of robot tactile feedback

[0066] Through real-time tactile signal feedback, the robot can respond differently according to the properties of the touched object (such as hardness, softness). For example: when touching food or clothing, the sensor can help the robot judge the softness of the object and avoid damaging the object by excessive pressure; when contacting a hard object, the sensor can quickly detect the collision and adjust the robot's movement path or force through algorithms to avoid damaging the object or causing harm to the robot; in addition, the sensor shows high sensitivity in grasping operations. The robot can adjust the grasping force in real time according to the tactile signal, so that the grasping process can accurately perceive the object without damaging soft objects.

[0067] Application Example Two, Super-Gravity Blasting Application

[0068] In soil blasting engineering, monitoring the changes in vibration, pressure wave, and strain caused by blasting is crucial for ensuring project safety and optimizing blasting schemes. In hypergravity environments, the response of soil to blasting is more complex, often accompanied by stronger shock waves and pressure waves. Therefore, it is particularly important to use high-precision sensors to monitor these changes in real time. Serpentine microstructure capacitive sensors, with their excellent sensitivity, flexibility, and ability to adapt to extreme environments, are ideal choices for such applications.

[0069] To adapt to soil blasting in hypergravity environments, serpentine microstructure capacitive sensors need to be designed with high flexibility, high pressure resistance, and the ability to respond stably to small changes. The sensor body is composed of polydimethylsiloxane (PDMS) and carbon nanotubes (CNT). PDMS provides good flexibility, while CNT enhances its electrical conductivity and fatigue resistance. The serpentine microstructure design allows the sensor to accurately sense pressure and strain changes. The width of the microstructure unit is 0.5 mm, and the spacing is 1 mm. To increase the durability and stability of the sensor, the surface is coated with polyurethane or epoxy resin to prevent the effects of high temperature, corrosion, and other external environments on the sensor.

[0070] In soil blasting engineering, the installation and testing environment of serpentine microstructure capacitive sensors are particularly critical. In practical applications, the sensor needs to be embedded in the soil near the blasting point or in the crack area, and through contact with the soil, it can monitor the small changes produced during blasting in real time. In hypergravity simulation experiments, the sensor can be embedded in soil samples, and different gravity environments (2-100 times gravity) can be simulated through a centrifuge or hypergravity equipment to simulate the actual situation after soil blasting. The sensitivity and accuracy of this sensor allow it to work stably in complex blasting environments and capture all the small changes from the soil.

[0071] The working principle of the serpentine microstructure capacitive sensor is based on capacitance changes. During blasting, the soil will produce instantaneous pressure waves and strain changes, which will cause deformation of the sensor microstructure, thereby causing changes in capacitance. By measuring these changes with a capacitance meter, the sensor can accurately record the vibration and pressure changes experienced by the soil during blasting. Engineers can analyze the dynamic response of the soil through data processing software to help optimize the blasting scheme.

[0072] The application of serpentine microstructure capacitive sensors in soil blasting can accurately monitor the pressure waves, soil crack propagation, and changes in soil compaction during the blasting process. When blasting occurs, the sensor can capture the instantaneous pressure wave and record the amplitude and propagation speed of the pressure. By monitoring the capacitance changes after the crack propagation, the expansion speed, direction, and impact on the surrounding environment of the soil crack can be determined. In addition, the sensor can also monitor the changes in soil compaction, and evaluate the impact of blasting on soil density and porosity. These real-time monitoring data can help engineers judge the blasting effect and quickly respond to changes in soil structure.

[0073] The above-described embodiments are merely descriptions of the preferred embodiments of the present application and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A serpentine microstructure capacitance sensor that balances sensitivity and range, characterized in that, The application relates to a flexible capacitive sensor, which comprises an upper protective layer, an upper electrode layer, a serpentine microstructure layer, a lower electrode layer and a lower protective layer which are sequentially stacked from top to bottom. The serpentine microstructure layer comprises a plurality of periodically curved insulating elastomer units, and the geometric parameters of the serpentine microstructure layer satisfy the following relationship: The geometric parameters of the serpentine microstructure layer satisfy the following performance regulation relationship: In formula (1), C represents a capacitance value; C0represents an initial capacitance value; F represents an external force; F c represents a critical contact force; H, w, and t represent height, width, and thickness of the serpentine microstructure, respectively; n represents a number of bending periods; E represents a Young's modulus; d0represents an initial electrode gap; and A represents an effective electrode area. When F≤F c The serpentine microstructure is elastically deformed, and the electrode spacing is reduced. When F > F c the adjacent parts of the serpentine microstructure are in contact forming a parallel support.

2. The serpentine microstructure capacitance sensor with sensitivity and range according to claim 1, characterized in that, The sensitivity is improved by reducing the thickness t, reducing the height H or increasing the bending number n: The range is expanded by increasing the thickness t, the bending number n or the modulus E: In the formula (2)-(3), S1 represents the sensitivity, FS represents the range, H, w and t respectively represent the height, width and thickness of the serpentine microstructure, n represents the bending period number, E represents the Young's modulus, d0 represents the initial electrode plate spacing, and A represents the effective electrode area. The upper electrode layer and the lower electrode layer are polyimide flexible substrates with a copper film sputtered thereon, and the thickness of the copper film is 50-200 nm.

3. The serpentine microstructure capacitance sensor with sensitivity and range according to claim 1, characterized in that, The upper protective layer and the lower protective layer are polyurethane or epoxy resin packaging films, and the thickness is 30-100 mu m, and the surface is provided with a moisture-proof and impact-resistant coating.

4. The serpentine microstructure capacitance sensor with sensitivity and range according to claim 1, characterized in that, The application further discloses a manufacturing method of the flexible capacitive sensor.

5. A method for manufacturing a serpentine microstructure capacitance sensor that balances sensitivity and range, for manufacturing the capacitance sensor according to any one of claims 1 to 4, characterized by, (a) Serpentine mold manufacturing: A serpentine microstructure mold is manufactured by adopting photosensitive resin through 3D printing technology, the printing precision is less than or equal to 0.1 mm, the mold surface is smooth and contains periodic curved grooves; (b) Serpentine microstructure forming: Polydimethylsiloxane (PDMS) is mixed with a crosslinking agent at a ratio of 10:1 and stirred; PDMS mixed solution is injected into the inner wall of the mold after the mold release agent is coated on the inner wall of the mold; Vacuum degassing is carried out for 20 minutes, and curing is carried out at 80 DEG C for 2 hours, and the serpentine microstructure is demolded; (c) Electrode layer preparation: A copper film is sputtered on the polyimide substrate, the sputtering power is 200 W, the sputtering time is 5 minutes, the thickness of the electrode is 100 nm, and the electrode is used as the upper electrode and the lower electrode; (d) Sensor assembly: The serpentine microstructure is clamped between the upper electrode and the lower electrode, the two ends of the serpentine microstructure are in close contact with the surface of the electrode, and the flexible adhesive is used for fixing, so that the assembly body is formed; (e) Packaging protection: Polyurethane or epoxy resin is coated on the surface of the assembly body, and the protective layer with a thickness of 30-100 mu m is formed. ​

Images