Serpentine microstructure capacitance sensor with sensitivity and range and preparation method thereof

Abstract

The application provides a serpentine microstructure capacitor sensor and a preparation method thereof, which take into account sensitivity and range, and comprise, from top to bottom, an upper protective layer, an upper electrode layer, a serpentine microstructure layer, a lower electrode layer and a lower protective layer; the serpentine microstructure layer comprises a plurality of periodically curved insulating elastomer units. The serpentine microstructure capacitor sensor can realize high sensitivity in a low pressure stage through the unique deformation characteristics of the serpentine structure, and further increase the bearing capacity through the contact of the serpentine structure in a high pressure stage, so as to significantly widen the range of the sensor, and a controllable mathematical model is proposed, so that the performance can be customized and expanded according to the application scene, and the precision requirement in different application scenes can be fully met.

Description

Technical Field

[0001] This invention relates to the field of flexible capacitive sensor technology, specifically to a serpentine microstructure capacitive sensor and method that balances sensitivity and measurement range. Background Technology

[0002] Flexible capacitive sensors are widely used in wearable devices, human-computer interaction, and medical monitoring due to their high sensitivity, fast response, and good flexibility. Traditional flexible capacitive sensors typically employ planar electrodes or simple microstructure designs, detecting capacitance signals by varying the electrode spacing. However, this design presents a trade-off between sensitivity and range: high sensitivity requires a small initial spacing, while a large range necessitates a large compressibility range.

[0003] In existing technologies, some sensors improve sensitivity by introducing microstructures (such as pyramidal or columnar structures), but these structures are prone to saturation under high pressure, leading to limited measurement range. Furthermore, while porous structures offer some flexibility, uneven pore distribution can affect sensor consistency. Therefore, a novel structural design is urgently needed to achieve a balance between high sensitivity and a large measurement range. Summary of the Invention

[0004] The purpose of this invention is to provide a serpentine microstructure capacitive sensor that balances sensitivity and measurement range, and its fabrication method, in order to overcome the shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A serpentine microstructure capacitive sensor that balances sensitivity and measurement range includes, from top to bottom, an upper protective layer, an upper electrode layer, a serpentine microstructure layer, a lower electrode layer, and a lower protective layer; the serpentine microstructure layer comprises several periodically bent insulating elastomer units, the geometric parameters of which 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 The critical contact force is represented by H, w, and t, which represent the height, width, and thickness of the serpentine microstructure, respectively; n represents the number of bending cycles; E represents Young's modulus; d0 represents the initial electrode spacing; A represents the effective electrode area; when F ≤ F c When F > F, the serpentine microstructure undergoes elastic deformation, and the electrode spacing decreases; c At that time, adjacent parts of the serpentine microstructure come into contact to form parallel supports.

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

[0010] Sensitivity can be improved by reducing the thickness t, decreasing the height H, or increasing the number of bends n:

[0011]

[0012] The measurement range can be extended by increasing the thickness t, the number of bends n, or the modulus E:

[0013]

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

[0015] Furthermore, the upper electrode layer and the lower electrode layer are flexible polyimide substrates sputtered with copper films, and the thickness of the copper films is 50-200 nm.

[0016] Furthermore, the upper and lower protective layers are polyurethane or epoxy resin encapsulation films with a thickness of 30-100μm and a moisture-proof and impact-resistant coating on the surface.

[0017] A method for fabricating a serpentine microstructure capacitive sensor that balances sensitivity and measurement range, comprising the following steps:

[0018] (a) Making a snake-shaped mold:

[0019] A serpentine microstructure mold was manufactured using photosensitive resin and 3D printing technology, with a printing accuracy of ≤0.1mm. The mold surface was smooth and contained periodically curved grooves.

[0020] (b) Serpentine microstructure forming:

[0021] Polydimethylsiloxane (PDMS) and crosslinking agent were mixed at a ratio of 10:1 and stirred.

[0022] After applying a release agent to the inner wall of the mold, inject the PDMS mixture.

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

[0024] (c) Electrode layer fabrication:

[0025] A copper film was sputtered onto a polyimide substrate at a sputtering power of 200W for 5 minutes to form an electrode with a thickness of 100nm, which served as the upper and lower electrodes.

[0026] (d) Sensor assembly:

[0027] A serpentine microstructure is sandwiched between the upper and lower electrodes, so that the two ends of the serpentine microstructure are in close contact with the electrode surface, and a flexible adhesive is used to fix it to form an assembly.

[0028] (e) Encapsulation protection:

[0029] Polyurethane or epoxy resin is coated on the surface of the assembly to form a protective layer 30-100μm thick.

[0030] As can be seen from the above technical solutions, compared with the existing technology, the present invention achieves the unity of high sensitivity and wide range by using the dual-state deformation characteristics of the serpentine structure elastic deformation and contact support; at the same time, it proposes an adjustable mathematical model, including a segmented force and capacitance control model, a sensitivity control model and a range control model, the performance of which can be customized and extended according to the application scenario, and can fully meet the accuracy requirements of different application scenarios. Attached Figure Description

[0031] Figure 1 This is a cross-sectional view of the overall structure of the serpentine microstructure capacitive sensor of the present invention;

[0032] Figure 2 This is a schematic diagram of the serpentine microstructure layer of the present invention;

[0033] Figure 3 The test curves for the serpentine microstructure capacitive sensor of this invention are shown below.

[0034] Figure 4 This is a schematic diagram of the mold used in this invention to manufacture the serpentine structure;

[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 Implementation

[0036] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] like Figure 1-2 The serpentine microstructure capacitive sensor shown, which balances sensitivity and measurement range, comprises, from top to bottom, an upper protective layer 1, an upper electrode layer 2, a serpentine microstructure layer 3, a lower electrode layer 4, and a lower protective layer 5. The serpentine microstructure layer 3 includes several periodically bent insulating elastomer units, the geometric parameters of which 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 cThe critical contact force is represented by H, w, and t, which represent the height, width, and thickness of the serpentine microstructure, respectively; n represents the number of bending cycles; E represents Young's modulus; d0 represents the initial electrode spacing; and A represents the effective electrode area.

[0040] like Figure 3 As shown, when subjected to pressure, F ≤ F c At this time, the serpentine structure first undergoes elastic deformation, reducing the distance between the upper and lower electrodes and causing a rapid change in capacitance, thus achieving high-sensitivity detection; as the pressure increases, until F > F c At this time, adjacent parts of the serpentine structure come into contact with each other, forming mechanical support, which significantly increases the sensor's range while maintaining capacitive response; this staged response mechanism enables the sensor to have both high sensitivity and wide range characteristics.

[0041] The fabrication of the serpentine microstructure capacitive sensor that balances sensitivity and measurement range includes the following steps:

[0042] (a) Serpentine Mold Fabrication: A serpentine microstructure mold is fabricated using high-precision photosensitive resin and 3D printing technology, with a printing accuracy of 0.1 mm. For example... Figure 4 As shown, the mold has a 2cm x 2cm planar area containing four periodically curved grooves; the inner surface of the mold is smooth to ensure the surface quality of the subsequently injected material. After printing, the mold needs to be cleaned and dried to ensure there are no impurities or residues.

[0043] (b) Serpentine Microstructure Molding: The serpentine microstructure layer was prepared using an insulating elastomer material. Specifically, polydimethylsiloxane (PDMS) was used as the base material. A silicone crosslinking agent and solvent were added to the PDMS and stirred evenly according to the specified ratio (PDMS: crosslinking agent = 10:1). Simultaneously, petrolatum was applied to the inner wall of the mold for easy demolding. After preparing the mold, the mixed PDMS material was injected into the mold, ensuring coverage of all serpentine structures. Then, the mold was placed in a vacuum chamber for vacuum treatment to remove air bubbles and ensure uniform material distribution within the mold. The vacuum treatment time was 20 minutes, followed by curing in an oven at 80°C for 2 hours until the material was completely cured. Finally, the serpentine microstructure was demolded.

[0044] (c) Electrode layer fabrication: The upper and lower electrodes are fabricated using a sputtering process for metal deposition. Copper is chosen as the electrode material due to its good conductivity and low cost. First, a polyimide (PI) film, 3cm × 3cm in size and 25μm in thickness, is used as the substrate. A 100nm thick copper layer is uniformly deposited on the surface of the PI film using a sputtering deposition process, serving as the base layer for both the upper and lower electrodes. During sputtering, the sputtering power is controlled at 200W and the sputtering time at 5 minutes to ensure a uniform and well-adhered copper layer.

[0045] (d) Sensor Assembly: The prepared serpentine microstructure layer is precisely applied to the designated positions between the lower electrode layers to form a 3*3 serpentine microstructure array, ultimately forming the sandwich structure of the sensor. First, the bottom electrode layer (copper-plated PI film) is aligned with the serpentine microstructure layer, ensuring that the top 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 a flexible adhesive (such as PDMS) can be lightly applied to the contact points between the serpentine structure and the electrode to allow it to cure, forming the assembly.

[0046] (e) Encapsulation Protection: To improve the stability and protection of the sensor, the entire sensor will be sealed through an encapsulation process. Transparent polyurethane (PU) or epoxy resin is used as the encapsulation material, and a thin film is coated to protect the entire sensor surface, ensuring its moisture-proof, dust-proof, and impact-resistant capabilities. The thickness of the encapsulation layer is controlled at around 50 μm to ensure that it does not affect the sensor's elasticity and capacitive response characteristics.

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

[0048] Sensitivity can be improved by reducing the thickness t, decreasing the height H, or increasing the number of bends n:

[0049]

[0050] The measurement range can be extended by increasing the thickness t, the number of bends n, or the modulus E:

[0051]

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

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

[0054] Application Example 1: Application of snake-shaped microstructure sensors in robot tactile scenarios:

[0055] 1. Sensor installation and debugging

[0056] The snake-shaped microstructure sensor is mounted on the robot's gripper or tactile probe. The sensor size is adjusted according to the robot's structural design; typically, the sensor area is 3cm × 3cm, each unit of the snake-shaped microstructure is 0.5mm wide, and the spacing is 1mm, suitable for tactile needs of different sizes. The sensor's installation position should ensure that its surface can contact external objects and accurately respond to changes in those objects.

[0057] Meanwhile, on the back of the sensor, it is firmly attached to the contact area of ​​the robot's gripper using silicone rubber (such as medical-grade silicone or soft PU material). The silicone is 0.3mm thick to ensure sufficient elasticity and signal transmission stability. During installation, approximately 0.2 ml of silicone is applied evenly and gently pressed for 10 seconds to ensure good adhesion.

[0058] 2. Data Acquisition and Processing

[0059] Connect the snake-shaped microstructure sensor to the data acquisition module in the robot's control system. Use the robot's internal software platform (such as the ROS system) or data processing software (such as MATLAB or LabVIEW) for real-time data acquisition. Set the sampling frequency to above 1000Hz to ensure the capture of rapidly changing tactile signals.

[0060] In the tactile signal processing, a high-pass filter is used to remove low-frequency noise, and a low-pass filter is used to remove high-frequency interference to ensure the accuracy of the acquired tactile signals. Furthermore, a dynamic threshold detection algorithm is used to identify the hardness or softness of different tactile objects in real time. By writing appropriate programs, real-time feedback can be achieved, guiding the robot to classify and respond to the tactile sensations of different objects.

[0061] 3. Response mechanism to soft object touch

[0062] When a serpentine microstructure sensor comes into contact with a soft object (such as food or clothing), the elasticity of the serpentine structure causes slight compression or deformation of the microstructure on the sensor surface, resulting in a change in capacitance. The change in capacitance is closely related to the magnitude of the contact force and the softness of the object. In practical applications, the sensor's response to soft objects can be tested through the following steps: lightly touch or press the soft object (soft clothing, fabric, or fruit) and monitor the sensor's output signal; observe how the serpentine structure gradually compresses or deforms during the touch, and the change in capacitance; confirm whether the sensor can accurately detect the contact force and surface characteristics of the soft object by comparing it with a standard object of known hardness. For example, when the sensor comes into contact with an apple, the sensor's output signal will exhibit significant low-amplitude fluctuations with a relatively long duration, indicating that the object is highly soft and requires a small force to deform the sensor.

[0063] 4. Response mechanism to contact with hard objects

[0064] When the serpentine microstructure sensor comes into contact with a hard object (wall, tool, hard metal), the serpentine structure of the sensor undergoes significant instantaneous compression, resulting in a markedly increased change in capacitance. Contact with a hard object causes deep compression of the sensor's surface microstructure, rapidly altering the capacitance. The sensor response at this time is as follows: when the sensor comes into contact with a hard object, the output signal exhibits a high-amplitude instantaneous peak with a short duration, indicating high object hardness; the sensor responds quickly to hard objects, with a short waveform rise time, making it suitable for detecting collisions or touches with high-hardness objects.

[0065] 5. Practical Applications of Robotic Tactile Feedback

[0066] Through real-time tactile signal feedback, the robot can respond differently based on the properties of the object it touches (such as hardness and softness). For example, when touching food or clothing, sensors help the robot determine the object's softness, avoiding excessive pressure that could damage it. When contacting hard objects, sensors can quickly detect collisions and adjust the robot's movement path or force through algorithms to prevent damage to the object or the robot itself. Furthermore, the sensors exhibit high sensitivity during grasping operations. The robot can adjust its grasping force in real time based on tactile signals, ensuring accurate object perception without damaging soft objects.

[0067] Application Example 2: Application of Supergravity Blasting

[0068] In soil blasting engineering, monitoring changes in vibration, pressure waves, and strain caused by blasting is crucial for ensuring project safety and optimizing blasting plans. In hypergravity environments, the soil's response to blasting is more complex, often accompanied by stronger shock and pressure waves. Therefore, employing high-precision sensors to monitor these changes in real time is particularly important. Snake-shaped microstructure capacitive sensors, with their excellent sensitivity, flexibility, and adaptability to extreme environments, are ideal for such applications.

[0069] To withstand soil blasting in hypergravity environments, the serpentine microstructure capacitive sensor needs to be designed with high elasticity, high pressure resistance, and a stable response to minute changes. The sensor body is a composite of polydimethylsiloxane (PDMS) and carbon nanotubes (CNTs). PDMS provides good elasticity, while CNTs enhance conductivity and fatigue resistance. The serpentine microstructure design allows the sensor to accurately sense pressure and strain changes; the microstructure unit width is 0.5 mm, and the spacing is 1 mm. To increase the sensor's durability and stability, the surface is coated with polyurethane or epoxy resin to prevent the sensor from being affected by external environmental factors such as high temperatures and corrosion.

[0070] In soil blasting engineering, the installation and testing environment of the serpentine microstructure capacitive sensor is particularly critical. In practical applications, the sensor needs to be embedded in the soil near the blast point or in crack areas, monitoring minute changes generated during blasting in real time through contact with the soil. In hypergravity simulation experiments, the sensor can be embedded in soil samples, and different gravity environments (2-100 times gravity) can be simulated using centrifuges or hypergravity equipment to simulate the actual situation after soil blasting. The sensitivity and accuracy of this sensor enable it to operate stably in complex blasting environments, capturing all minute changes from the soil.

[0071] The working principle of the serpentine microstructure capacitive sensor is based on capacitance changes. During blasting, the soil generates instantaneous pressure waves and strain changes. These changes cause deformation of the sensor's microstructure, which in turn induces 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 then analyze the dynamic response of the soil using data processing software to help optimize blasting plans.

[0072] The application of serpentine microstructure capacitive sensors in soil blasting enables precise monitoring of pressure waves, soil crack propagation, and changes in soil compaction during the blasting process. When blasting occurs, the sensor captures the instantaneously generated pressure wave and records its amplitude and propagation speed. By monitoring changes in capacitance during crack propagation after blasting, the speed and direction of crack propagation and its impact on the surrounding environment can be determined. Furthermore, the sensor can monitor changes in soil compaction, assessing the impact of blasting on soil density and porosity. This real-time monitoring data helps engineers assess the effectiveness of blasting and respond quickly to changes in soil structure.

[0073] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A serpentine microstructure capacitive sensor that balances sensitivity and measurement range, characterized in that, include: The layers are stacked from top to bottom: upper protective layer, upper electrode layer, serpentine microstructure layer, lower electrode layer, and lower protective layer. The serpentine microstructure layer comprises several periodically bent insulating elastomer units, whose geometric parameters satisfy the following relationship: In formula (1): C represents the capacitance value; C0 represents the initial capacitance value; F represents the external force; F c The critical contact force is represented by H, w, and t, which represent the height, width, and thickness of the serpentine microstructure, respectively; n represents the number of bending cycles; E represents Young's modulus; d0 represents the initial electrode spacing; and A represents the effective electrode area. When F≤F c At this time, the serpentine microstructure undergoes elastic deformation, and the electrode spacing decreases; When F>F c At that time, adjacent parts of the serpentine microstructure come into contact to form parallel supports.

2. The serpentine microstructure capacitive sensor that balances sensitivity and measurement range according to claim 1, characterized in that, The geometric parameters of the serpentine microstructure layer satisfy the following performance regulation relationship: Sensitivity can be improved by reducing the thickness t, decreasing the height H, or increasing the number of bends n: The measurement range can be extended by increasing the thickness t, the number of bends n, or the modulus E: In formulas (2)-(3): S1 represents sensitivity; FS represents range; H, w, and t represent the height, width, and thickness of the serpentine microstructure, respectively; n represents the number of bending cycles; E represents Young's modulus; d0 represents the initial electrode spacing; and A represents the effective area of ​​the electrode.

3. The serpentine microstructure capacitive sensor that balances sensitivity and measurement range according to claim 1, characterized in that, The upper and lower electrode layers are flexible polyimide substrates sputtered with copper films, the thickness of which is 50-200 nm.

4. The serpentine microstructure capacitive sensor that balances sensitivity and measurement range according to claim 1, characterized in that, The upper and lower protective layers are polyurethane or epoxy resin encapsulation films with a thickness of 30-100μm and a moisture-proof and impact-resistant coating on the surface.

5. A method for fabricating a serpentine microstructure capacitive sensor that balances sensitivity and measurement range, used to manufacture the capacitive sensor according to any one of claims 1-4, characterized in that, Includes the following steps: (a) Making a snake-shaped mold: A serpentine microstructure mold was manufactured using photosensitive resin and 3D printing technology, with a printing accuracy of ≤0.1mm. The mold surface was smooth and contained periodically curved grooves. (b) Serpentine microstructure forming: Polydimethylsiloxane (PDMS) and crosslinking agent were mixed at a ratio of 10:1 and stirred. After applying a release agent to the inner wall of the mold, inject the PDMS mixture. Vacuum degassing for 20 minutes, followed by curing at 80°C for 2 hours, followed by demolding to obtain a serpentine microstructure; (c) Electrode layer fabrication: A copper film was sputtered onto a polyimide substrate at a sputtering power of 200W for 5 minutes to form an electrode with a thickness of 100nm, which served as the upper and lower electrodes. (d) Sensor assembly: A serpentine microstructure is sandwiched between the upper and lower electrodes, so that the two ends of the serpentine microstructure are in close contact with the electrode surface, and a flexible adhesive is used to fix it to form an assembly. (e) Encapsulation protection: Polyurethane or epoxy resin is coated on the surface of the assembly to form a protective layer 30-100μm thick.

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