Flexible capacitive pressure sensor structure and motion detection application method thereof

Abstract

The invention discloses a flexible capacitive pressure sensor structure and a motion detection application method thereof. The flexible capacitive pressure sensor structure comprises an upper waterproof layer, an upper electrode layer, a dielectric layer, a lower electrode layer and a lower waterproof layer which are stacked. Wherein the electrode layer comprises a polydimethylsiloxane thin film substrate, a polyimide thin film and laser-induced graphene, and the dielectric layer comprises a polydimethylsiloxane thin film and a micro-conical array structure which is subjected to laser orthogonal processing. The method has the advantages of high sensitivity, high consistency, high stability, high reliability and high repeatability.

Description

Technical Field

[0001] The present invention relates to the fields of wearable motion detection and underwater detection, and in particular to a flexible capacitive pressure sensor structure and a motion detection application method thereof. Background Art

[0002] As a pressure sensor, flexible electronic skin has found widespread application in healthcare, pressure sensing, human-computer interaction, robotics, and other fields due to its inherent flexibility, portability, and versatility. As a skin-like material, the development of flexible electronic skin not only offers greater functional diversity than other non-flexible materials but also offers greater convenience. This material can adhere to surfaces, such as objects or the human body, to detect a range of stimuli, including pressure, strain, temperature, and gas.

[0003] As one of the fundamental physical quantities in nature, pressure is crucial in many fields. For example, in engineering, pressure detection is a key tool to ensure the safe operation of structures and equipment. Underwater exploration is an important means of marine scientific research, resource development, and environmental protection. Traditional underwater detection equipment is usually bulky, expensive, and difficult to operate. The rise of flexible devices has brought new opportunities for underwater exploration. With the development of the times, when wearable flexible electronic skin is stimulated by external stimuli, it can convert the stimulus into different physical quantities for classification through triboelectricity, piezoelectricity, piezoresistance, piezocalyst, etc.

[0004] Capacitive pressure sensors are a very common type of pressure sensor, primarily consisting of upper and lower electrodes and a dielectric layer. Fabrication involves a variety of methods, including chemical methods, inkjet printing, 3D printing, and laser fabrication. The capacitance of a capacitor is determined by two key parameters: the relative dielectric constant and the distance between the plates. Therefore, variations in the plate distance and the relative dielectric constant under pressure are crucial for optimizing the sensor's response. By adjusting these parameters, including the mechanical properties, material composition, and structural characteristics of the dielectric layer, the sensor's response can be optimized.

[0005] When it comes to underwater detection, not only must packaging be addressed, but the sensor must also meet sensitive detection standards. The introduction of micro- and nanostructures offers a new approach to enhancing sensor performance. Laser processing technology, with its maskless nature and simple steps, can induce or construct micro- and nanostructures on a variety of flexible materials, which is of great significance for the fabrication of micro- and nano-dielectric layers and electrodes. Summary of the Invention

[0006] In order to improve the detection sensitivity, repeatability and long-term response consistency of existing underwater pressure sensors, the present invention provides a flexible capacitive pressure sensor structure and a motion detection application method thereof.

[0007] The first aspect of the present invention discloses a flexible capacitive pressure sensor structure, comprising upper and lower waterproof layers and a strain detection layer stacked together, wherein the strain detection layer comprises laser-induced graphene with a porous structure as upper and lower electrode layers and a polydimethylsiloxane dielectric layer with a micro-conical structure.

[0008] A second aspect of the present invention discloses a motion detection application method, comprising the following steps:

[0009] Acquire a capacitance change signal of the flexible capacitive pressure sensor structure described in the first aspect attached to a motion detection position;

[0010] The motion posture result of the operation detection position is judged according to the capacitance change signal.

[0011] Compared with the prior art, the beneficial effects of the present invention are: the flexible capacitive pressure sensor structure of the present invention is based on laser-induced graphene and laser-orthogonally processed micro-conical structured polydimethylsiloxane material, which has high sensitivity, high consistency, high stability, reliability and repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the structure of the flexible capacitive pressure sensor of the present invention.

[0013] Figure 2 This is a flow chart of the preparation method of the flexible capacitive pressure sensor of the present invention.

[0014] Figure 3 Scanning electron microscope images of a micro-conical dielectric layer prepared using different laser powers during the preparation process of the flexible capacitive pressure sensor fabricated using the method of the present invention.

[0015] Figure 4 This is a graph showing the capacitance change of the micro-cone structure of the flexible capacitive pressure sensor of the present invention under different loads.

[0016] Figure 5 The capacitance response characteristic diagram of the flexible capacitive pressure sensor of the present invention is shown in FIG.

[0017] (a) Load-dependent responses under different pressure ranges (10–500 g).

[0018] (b) Frequency response analysis when the load is 50g;

[0019] (c) Dynamic performance of response and recovery time under 50 g load;

[0020] (d) Long-term cycling stability test (1000 cycles) under a 20 g load.

[0021] (e) Zoomed-in view highlighting the consistency of response during long-term cycling testing.

[0022] Figure 6 This is a graph showing the capacitance change caused by the flexible capacitive pressure sensor of the present invention being attached to various parts of the human body.

[0023] (a) Arterial pulse test;

[0024] (b) Human wrist flexion test;

[0025] (c) finger flexion test;

[0026] (d) Finger press sensor test.

[0027] Figure 7 This is the capacitance change of the flexible capacitive pressure sensor of the present invention when it is installed on the inner wall of a container under the water surface and the water pressure continues to increase and change.

[0028] Figure 8 The flexible capacitive pressure sensor of the present invention is installed at the tail of the remote-controlled electric fish, and the signal detected by the sensor when the electric fish swims from the bottom of the water to the surface of the water when the electric fish is fully immersed in water.

[0029] In the figure: 1 upper waterproof layer, 2 upper electrode layer, 21 upper polydimethylsiloxane film substrate, 22 upper polyimide film, 23 upper laser-induced graphene, 3 dielectric layer, 31 polydimethylsiloxane film, 32 laser-processed micro-cone array structure, 4 lower electrode layer, 41 lower polydimethylsiloxane film substrate, 42 lower polyimide film, 43 lower laser-induced graphene, 5 lower waterproof layer. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0032] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0033] like Figure 1 As shown, the flexible capacitive pressure sensor structure includes a stacked upper waterproof layer 1, an upper electrode layer 2, a dielectric layer 3, a lower electrode layer 4, and a lower waterproof layer 5. Among them, the upper electrode layer 2 includes an upper polydimethylsiloxane film substrate 21, an upper polyimide film 22, and an upper laser-induced graphene 23, the dielectric layer 3 includes a polydimethylsiloxane film 31 and a laser-processed micro-cone array structure 32, and the lower electrode layer 4 includes a lower polydimethylsiloxane film substrate 41, a lower polyimide film 42, and a lower laser-induced graphene 43. It should be noted that Figure 1 The unfolding of the layers is for illustration purposes only. In practice, the layers should fit tightly together.

[0034] Specifically, the preparation method of the flexible capacitive pressure sensor is as follows: Figure 2 The method includes steps S01-S07:

[0035] Step S01: Figure 2 (a) A polyimide film is adhered to a polydimethylsiloxane (PDMS) film substrate.

[0036] Step S02: Figure 2 (b) A carbon dioxide laser with a central wavelength of 10.6 μm is used to perform line scanning processing on a certain area of the polyimide film. The surface of the polyimide film in this area is induced by the laser into a three-dimensional porous structure of graphene, i.e. Figure 2 Laser-induced graphene (LIG) in (c).

[0037] Step S03: Figure 2 (d) Using a femtosecond laser with a central wavelength of 800 nm, the same area of the polydimethylsiloxane film was orthogonally scanned. Figure 2 (e) The flat surface morphology of the polydimethylsiloxane film in this area is processed into a micro-cone array structure.

[0038] Reference Figure 3 , Figure 3 The scanning electron microscope images of the micro-cone-shaped dielectric layer prepared by this scheme at different laser powers are shown. Figure 3 (d)-(f) are 5 mW laser power; Figure 3 (g)-(i) are 7 mW laser power.

[0039] By comparison, it can be found that the micro-cone structure produced by 7mW laser power is taller, the radius of the top structure is narrower, and the micro-cone structure is clearer. This high-roughness dielectric layer can significantly improve the response performance of the flexible capacitive pressure sensor.

[0040] Step S04: Figure 2 (f) The processed polydimethylsiloxane film is placed between two processed polyimide films to form a laminate. It is important to note that the processed region (laser-induced graphene) of the polyimide film should be adjacent to the surface of the polydimethylsiloxane film. The laser-induced graphene region should overlap with the micro-cone array structure region.

[0041] Step S05: Use epoxy resin to coat and seal along the edges of the stack to ensure a sealed package.

[0042] Step S06: placing the stacked structure in a room temperature environment for a curing process for 24 hours.

[0043] Step S07: Wrap an additional layer of waterproof tape on the sensor to ensure its stability and reliability in underwater working scenarios.

[0044] The flexible capacitive pressure sensor fabricated using the above method has enhanced sensing performance due to the presence of a micro-cone array structure in its dielectric layer. Analysis suggests that this may be due to the following reasons:

[0045] Using a digital bridge, the flexible capacitive pressure sensors with different dielectric layers prepared by the method of this scheme under laser power parameters of 0mW (Sensor-0), 5mW (Sensor-5), and 7mW (Sensor-7) were tested for pressure response ability. The test results are shown in the figure. Figure 4 shown.

[0046] The results show that sensors with a micro-conical dielectric layer exhibit superior responsiveness. For example, under a load of 200g, the responsiveness of Sensor-7 increased by approximately 2.5 times compared to Sensor-0. This is primarily attributed to the presence of the island microstructures, which increase the deformation range of the dielectric layer and the fluctuation in the dielectric constant between air and the polydimethylsiloxane film. In the absence of pressure, air exists within the micro-conical structures decorated with nanoclusters on the dielectric layer's surface. When pressure is applied, the air is relatively compressed, causing the dielectric constant of the entire sensor to become that of the polydimethylsiloxane film itself. Because the dielectric constant of the polydimethylsiloxane film (ε≈2.7) is greater than that of air (ε≈1), the change in the effective dielectric constant is more pronounced. Therefore, sensors with micro-conical structures exhibit higher responsiveness, or higher sensitivity, than sensors without them.

[0047] Through long-term cyclic loading, the flexible capacitive pressure sensor prepared by the method of this scheme under 7mW laser power was explored and the long-term stability test was carried out. The test results are as follows Figure 5 As shown in (a)-(e).

[0048] like Figure 5 As shown in (a), 5 cycles of load tests were performed on Sensor-7, ranging from 10g to 500g, showing stable response characteristics and closely overlapping cycle curves. It is able to show highly repeatable responses to pressure changes in a relatively wide range, confirming the reliability of its dynamic response test.

[0049] Figure 5 Further analysis in (b) shows that changing the frequency of pressure applied by the test platform has a negligible effect on the peak amplitude of the sensor response waveform, and only affects the waveform density corresponding to different pressure frequencies. This indicates that the sensor has stable performance at different frequencies and ensures that the sensor has good adaptability in various working environments.

[0050] Figure 5 (c) further demonstrates the dynamic process of the sensor's time response under a 50g pressure load, with a response time of 126ms and a recovery time of 155ms. This is because the device itself is mainly made of polydimethylsiloxane film and has slight hysteresis, but it also meets the needs of the device itself.

[0051] Figure 5 In (d), to evaluate long-term stability, Sensor-7 was cycled under a 20g load. The response curve exhibited only minor fluctuations, demonstrating consistent performance even under long-term testing.

[0052] Figure 5 The magnified image in (e) further confirms the sensor's ability to maintain excellent response after long-term cycling, highlighting its robustness and long-term durability. With its good sensitivity and excellent stability, the sensor shows its potential for application in the field of biological signal detection.

[0053] The sensor prepared based on the above steps has high sensitivity, high consistency, high stability, reliability and repeatability. Therefore, it can be used not only in motion detection with small amplitude, but also in detection of repetitive movements.

[0054] In this regard, the present invention also discloses a motion detection application method for the flexible capacitive pressure sensor, including the following steps: obtaining the output signal of the above-mentioned strain sensor structure or the above-mentioned flexible capacitive pressure sensor attached to the motion detection position; and judging the running posture result of the running detection position based on the output signal.

[0055] like Figure 6 As shown, the flexible capacitive pressure sensor can be attached to different areas of the hand to verify its application potential in the field of biological signal detection.

[0056] exist Figure 6 In (a), to monitor the arterial pulse, the sensor placed on the inner surface of the subject's wrist successfully captured the periodic pulsating waveform. Figure 6 In (b), the sensor also placed on the outside of the wrist can detect the motion signal generated by limb flexion, where the signal amplitude changes. It is directly related to the degree of flexion. Figure 6 In (c), the sensor is wrapped around a finger for joint motion analysis with bending angles ranging from 30° to 90°, producing clear, gradual response curves corresponding to specific flexion angles, demonstrating excellent finger bending angle resolution. Figure 6 In (d), a controlled pressure test was performed on a fixed sensor platform using a finger pressing the sensor surface. It can be seen that the width of the periodic pressure waveform generated by the system is related to the length of time the sensor is pressed, confirming the operational reliability of the sensor and its applicability for dynamic biomotion monitoring applications.

[0057] Of course, the above-mentioned flexible capacitive pressure sensor can not only be used for biological signal detection, but also can realize detection scenarios such as air flow and water flow micro-disturbance monitoring, air pressure and water pressure measurement, etc.

[0058] For example, a flexible capacitive pressure sensor is installed on the inner wall of a container under the water surface, and the signal collected by the sensor under the increasing and changing water pressure is as follows: Figure 7 The test data shows that the capacitance gradually increases as 250ml of water is gradually added, confirming the consistent function of the sensor under different water pressure environments.

[0059] For example, a sensor was securely attached to the tail fin of an electric fish toy using underwater adhesive to explore its potential for underwater activity detection. Since electric fish primarily propel themselves through the side-to-side oscillation of their tail fin, combining the sensor with the electric fish toy in this way allows for real-time monitoring of its movements.

[0060] like Figure 8 As shown, the sensor was placed in different water pressure environments to evaluate its robustness under different fluid dynamic conditions, such as the response characteristics of fish during upstream movement. The resulting waveform showed a significant decrease in total capacitance during the ascent, confirming that the sensor can detect the upward movement of electric fish.

[0061] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A flexible capacitive pressure sensor structure, characterized in that: It comprises an upper waterproof layer (1), an upper electrode layer (2), a dielectric layer (3), a lower electrode layer (4) and a lower waterproof layer (5) which are stacked.

2. The flexible capacitive pressure sensor structure according to claim 1, characterized in that: The upper electrode layer (2) includes an upper polydimethylsiloxane film substrate (21), an upper polyimide film (22), and an upper laser-induced graphene (23); the dielectric layer (3) includes a polydimethylsiloxane film (31) and a laser-processed micro-cone array structure (32); and the lower electrode layer (4) includes a lower polydimethylsiloxane film substrate (41), a lower polyimide film (42), and a lower laser-induced graphene (43).

3. The flexible capacitive pressure sensor structure according to claim 1, characterized in that: The processed area (laser-induced graphene) of the polyimide film should be adjacent to the processed surface of the polydimethylsiloxane film; the laser-induced graphene area should overlap with the micro-cone array structure area in position.

4. The flexible capacitive pressure sensor structure according to claim 1, characterized in that: Laser-induced graphene is prepared in one go using a laser and used as the electrode for the sensor.

5. The flexible capacitive pressure sensor structure according to claim 1, characterized in that: A microcone array structure was prepared on the surface of polydimethylsiloxane film using femtosecond laser orthogonal scanning processing method.

6. A motion detection application method, characterized in that: The following steps are involved: Acquire a capacitance change signal of a flexible capacitive pressure sensor structure according to claims 1 to 5 attached to a motion detection position; and judge the motion posture result of the operation detection position based on the capacitance change signal.

Images