Capacitive pressure sensor based on laser direct writing, dual-mode pressure sensor, and preparation method and application thereof

Abstract

The present invention belongs to the field of flexible sensor technology, specifically relating to a capacitive pressure sensor and a dual-mode pressure sensor based on laser direct writing, as well as their preparation methods and applications. The capacitive pressure sensor comprises two identical composite electrodes; the composite electrodes are produced by secondary laser direct writing onto a PDMS layer in a resistive pressure sensor. The resistive pressure sensor comprises a Kevlar / graphene substrate layer and a PDMS layer; the PDMS layer is coated on the graphene surface of the Kevlar / graphene substrate layer; the Kevlar / graphene substrate layer is formed by laser direct writing onto the surface of a Kevlar fabric. The dual-mode pressure sensor comprises the capacitive pressure sensor and the resistive pressure sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and in particular relates to a capacitive pressure sensor based on laser direct writing, a dual-mode pressure sensor, and a preparation method and application thereof. Background Art

[0002] In recent years, with the development of flexible electronic devices, fields such as flexible displays, flexible photovoltaics, chemical and biological sensors, and flexible sensors have received great attention. As an important component of the electronics field, flexible sensors play a vital role in flexible electronics. However, in some application scenarios, there is an urgent need for flexible, tough, comfortable and breathable fabric substrates. For example, they are widely used in wearable devices due to their breathability and body fit. For example, in real life such as bundling and packaging goods in logistics and transportation, certain fabrics are used due to their softness, high strength and ability to wrap irregular objects. Among the various categories of flexible fabric sensors, flexible fabric pressure sensors are widely used in medical health monitoring, smart wearables, and human-computer interaction due to their high sensitivity, biocompatibility and durability.

[0003] Laser direct writing (DLW) is a method of patterning a material by directly applying a focused laser beam to its surface or interior. Its high precision and resolution, mask-free operation, and dynamic adjustability have led to its widespread application in materials science, micro-nanostructure fabrication, and sensor manufacturing. The interaction between laser and matter creates new functional materials, imbuing the raw material with new capabilities.

[0004] Graphene is a highly desirable material with excellent properties. Due to its mechanical strength and exceptional conductivity, it is often used in flexible pressure sensors. Compared to graphene grown using CVD or redox methods, the preparation process for laser-induced graphene (LIG) is the simplest. The preparation of pressure sensors based on LIG can significantly reduce the number of steps and costs. This also allows for a wider range of precursors to be selected. In fabric-based LIG flexible electronics, Kevlar is often used as a precursor material due to its unique chemical structure.

[0005] Therefore, it is of great significance to develop a new capacitive pressure sensor and dual-modal pressure sensor based on DLW technology and combining the advantages of Kevlar material and LIG material. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a method for effectively simplifying the preparation process of a dual-modal pressure sensor using laser direct writing technology (DLW). DLW is used to prepare a capacitive pressure sensor and a dual-modal pressure sensor based on Kevlar and PDMS materials respectively.

[0007] In order to solve the above technical problems, the present invention discloses a capacitive pressure sensor based on laser direct writing. The capacitive pressure sensor consists of two identical composite electrodes; the composite electrode is made by secondary laser direct writing of PDMS layer through a resistive pressure sensor.

[0008] The resistive pressure sensor includes a Kevlar / graphene substrate layer and a PDMS layer; the PDMS layer is covered on the graphene surface of the Kevlar / graphene substrate layer; and the Kevlar / graphene substrate layer is formed by laser direct writing on the surface of the Kevlar fabric.

[0009] Furthermore, the preparation method of the above-mentioned capacitive pressure sensor is also within the protection scope of the present invention, and the preparation method includes the following steps: using a laser to perform secondary processing on the PDMS layer of the resistive pressure sensor to form a periodic ridge-like microstructure on the PDMS layer, thereby obtaining a composite electrode, placing the PDMS layers of the two composite electrodes face to face, with the ridge structures arranged vertically, and fixing them to obtain the capacitive pressure sensor.

[0010] The laser parameters of the laser are: line spacing 0.45 mm, laser speed 50 mm / s, and laser power 3.2 W.

[0011] Specifically, the method for preparing the resistive pressure sensor includes the following steps: using a laser to prepare laser-induced graphene on the surface of Kevlar fabric to obtain a Kevlar / graphene substrate layer, coating the edge of the graphene surface with conductive silver paste and connecting copper wire, then coating the PDMS mixture on the graphene surface, and obtaining the resistive pressure sensor after curing.

[0012] The laser parameters of the laser are: line spacing 0.05~0.08mm, laser speed 75~80mm / s, and laser power 4.8~7.2W.

[0013] The PDMS mixture includes a PDMS prepolymer and a curing agent; the mass ratio of the PDMS prepolymer to the curing agent is 10:1.

[0014] The coating is completed by spin coating, and the specific process parameters are: spin coating speed 300~500rpm, acceleration 300~500rpm / s, and spin coating time 10~50s.

[0015] The curing process parameters are as follows: maintaining at 80° C. for 2 hours.

[0016] In some embodiments of the present invention, a resistive pressure sensor used to prepare a capacitive pressure sensor is prepared using the above-mentioned method for preparing a resistive pressure sensor, wherein, during the preparation of the resistive pressure sensor, the laser parameters are: line spacing 0.05 mm, laser speed 75 mm / s, laser power 7.2 W; the coating is completed by spin coating, and the specific process parameters are: spin coating speed 500 rpm, acceleration 500 rpm / s, and spin coating time 10 s.

[0017] The present invention also provides a dual-mode pressure sensor, characterized in that the dual-mode pressure sensor includes the above-mentioned capacitive pressure sensor and resistive pressure sensor.

[0018] Furthermore, the application of the above-mentioned capacitive pressure sensor or dual-mode pressure sensor in the packaging and real-time monitoring of goods in logistics transportation also falls within the protection scope of the present invention.

[0019] Specifically, in some embodiments of the present invention, a simulated cargo surface is wrapped with Kevlar fabric, and four capacitive pressure sensors are placed on each surface. These sensors use capacitance changes to reflect the real-time collision conditions of the cargo during transportation. The sensor provided by this invention integrates both packaging and monitoring functions. By integrating a Bluetooth module into the same fabric, the packaging and pressure signal monitoring functions are integrated and simultaneously transmitted wirelessly over long distances. This expanded application is expected to reduce costs and simplify processes for monitoring and early warning equipment in logistics and transportation.

[0020] Furthermore, the application of the above-mentioned capacitive pressure sensor or dual-mode pressure sensor in the preparation of an intelligent driving helmet is also within the protection scope of the present invention.

[0021] Specifically, in some embodiments of the present invention, Kevlar fabric is used to replace the traditional straps in the helmet, and resistive and capacitive dual-modal sensors are simultaneously prepared on the surface of the straps. The characteristics of low detection limit threshold and high pressure range are utilized to prepare an integrated monitoring driving helmet, while monitoring the driver's micro-expression changes and the occurrence of accidental collisions.

[0022] Beneficial effects:

[0023] 1. Using laser direct writing technology to prepare dual-modal pressure sensors can effectively simplify the preparation process.

[0024] 2. Capacitive pressure sensors can be realized through laser processing based on resistive sensors.

[0025] 3. The advantage of using flexible Kevlar fabric to make sensors is that compared to rigid packaging, it can wrap items of different shapes and integrate item packaging functions and pressure monitoring functions.

[0026] 4. A smart helmet made of flexible Kevlar fabric can monitor both resistive and capacitive sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0028] Figure 1 This is a flow chart for the preparation of resistive and capacitive pressure sensors provided by the present invention and a schematic diagram of the cross-section of Kevlar fabric after laser induction.

[0029] Figure 2 These are SEM images of the original Kevlar in the examples of the present invention, the LIG prepared by S1 in Example 1, and the LIG prepared by S1 in Example 2.

[0030] Figure 3 This is a cross-sectional SEM image of the composite electrode obtained after secondary processing in S3 in Example 2 of the present invention.

[0031] Figure 4 Graph showing the switching characteristics of a Kevlar / LIG substrate not covered with a PDMS layer as a pressure sensor under different pressures in Example 1 of the present invention.

[0032] Figure 5 This is a performance exploration diagram of the resistive pressure sensor prepared in Example 1 of the present invention.

[0033] Figure 6 This is a performance exploration diagram of the capacitive pressure sensor prepared in Example 2 of the present invention.

[0034] Figure 7 Schematic diagram of the application of a capacitive pressure sensor in logistics transportation according to an embodiment of the present invention.

[0035] Figure 8 This is a diagram showing the application effect of a capacitive pressure sensor in logistics transportation according to an embodiment of the present invention.

[0036] Figure 9 Schematic diagram of the application of a resistive-capacitive dual-mode pressure sensor in a smart helmet according to an embodiment of the present invention.

[0037] Figure 10 This is a graph showing the capacitance changes of the smart helmet when a tester repeatedly wears the smart helmet and is subjected to external impact in an embodiment of the present invention.

[0038] Figure 11 This is a graph showing resistance changes under different micro-expressions when a tester wears a smart helmet according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0040] The present invention provides a capacitive pressure sensor based on laser direct writing, a dual-mode pressure sensor and a preparation method thereof. Figure 1 The preparation flow chart of resistive and capacitive pressure sensors and the cross-section diagram of Kevlar fabric after laser induction are shown in the figure. Figure 1 As can be seen from a in the figure, a resistive pressure sensor can be prepared by preparing laser-induced graphene (LIG) on Kevlar fabric through laser direct writing technology (DLW), and then spin-coating a PDMS layer on the LIG. Furthermore, the PDMS layer of the resistive pressure sensor is subjected to secondary laser processing to form a composite electrode with a periodic ridge-like microstructure. After integrating the two composite electrodes, a capacitive pressure sensor is obtained. Figure 1 Figure b is a schematic diagram of the cross-section of Kevlar fabric after laser induction. It can be seen from the figure that the original Kevlar fabric is layered into two layers: the upper layer facing the laser is LIG. The laser parameters are controlled so that the laser only interacts with a part of the Kevlar fabric, thereby retaining the original fabric away from the laser end. In actual application, the original fabric will be in direct contact with the skin, with better skin-friendliness and breathability.

[0041] Example 1: Preparation of a resistive pressure sensor

[0042] S1. Preparation of Laser-Induced Graphene (LIG): First, a piece of Kevlar fabric was ultrasonically cleaned in ethanol and then in deionized water. LIG was then prepared on the surface of the Kevlar fabric using the following parameters: line spacing of 0.08 mm, laser speed of 80 mm / s, and laser power of 4.8 W.

[0043] S2. Fabrication of a resistive pressure sensor: Conductive silver paste was applied to the LIG edge joints, followed by conductive copper wire. The Kevlar / LIG substrate layer was then placed on the knob of a spin coater. A 1 cm × 1 cm LIG surface area was coated with 2 ml of the PDMS mixture at a spin coating speed of 300 rpm and an acceleration of 300 rpm / s for 50 seconds to obtain the Kevlar / LIG / PDMS. The coated substrate was removed from the spin coater and cured in an oven at 80°C for 2 hours to obtain the resistive pressure sensor. The PDMS mixture contained a 10:1 mass ratio of PDMS prepolymer to curing agent.

[0044] Example 2: Preparation of a capacitive pressure sensor

[0045] S1. Preparation of Laser-Induced Graphene (LIG): First, a piece of Kevlar fabric was ultrasonically cleaned in ethanol and then in deionized water. LIG was then deposited on the surface of the Kevlar fabric using the following parameters: line spacing of 0.05 mm, laser speed of 75 mm / s, and laser power of 7.2 W.

[0046] S2. Fabrication of a resistive pressure sensor: Conductive silver paste was applied to the LIG edge joints, followed by conductive copper wire. The Kevlar / LIG substrate layer was then placed on the knob of a spin coater. A 1 cm × 1 cm LIG surface area was coated with 2 ml of the PDMS mixture at a spin coating speed of 500 rpm and an acceleration of 500 rpm / s for 10 seconds to obtain a Kevlar / LIG / PDMS substrate. The coated substrate was removed from the spin coater and cured in an oven at 80°C for 2 hours to obtain the resistive pressure sensor. The PDMS mixture contained a 10:1 mass ratio of PDMS prepolymer to curing agent.

[0047] S3. Preparation of a capacitive pressure sensor: A carbon dioxide laser is used to perform secondary processing on the PDMS layer of the resistive pressure sensor obtained in S2 to produce a periodic ridge-like microstructure on the surface of the PDMS layer, thereby obtaining a composite electrode. The PDMS layers of the two composite electrodes are placed face to face, and the ridge structures are arranged vertically and fixed to form a capacitive pressure sensor. The parameters of the carbon dioxide laser used in the secondary processing are: line spacing 0.45 mm, laser speed 50 mm / s, and laser power 3.2 W.

[0048] Example 3: Performance Characterization of Resistive and Capacitive Pressure Sensors

[0049] Scanning electron microscopy was used to characterize the micromorphology of the original Kevlar, the LIG prepared by S1 in Example 1, and the LIG prepared by S1 in Example 2. Figure 2 The SEM images of the original Kevlar, the LIG prepared by S1 in Example 1, and the LIG prepared by S1 in Example 2 are shown, wherein: Figure 2 a and Figure 2 b is the SEM image of the original Kevlar fabric surface. Figure 2 c and Figure 2 d in the figure is a high-resolution SEM image of LIG prepared by S1 in Example 1. Figure 2 Zhongehe Figure 2 f is the high-resolution SEM image of LIG prepared by S1 in Example 2. Figure 2 It can be seen that the original Kevlar with a smooth surface and cross-arranged structure has its smooth surface structure destroyed after laser processing, resulting in a porous microstructure. Since Kevlar is a potential fabric base material, as an aramid fiber, due to its special molecular structure, some of its elements will produce gases through pyrolysis under the action of laser, such as CO, CO2 and NO, which will eventually evaporate from the fabric surface, leaving a carbon-rich skeleton.

[0050] The cross-section of the composite electrode obtained after the secondary processing in S3 in Example 2 was characterized by scanning electron microscopy. Figure 3 is a cross-sectional SEM image of the composite electrode obtained after secondary processing in S3 in Example 2. Figure 3 It can be seen that the composite electrode consists of three layers: the top layer is the PDMS layer with a ridge-like microstructure, the middle layer is the porous LIG layer, and the bottom layer is the Kevlar substrate that remains unprocessed by the laser.

[0051] The Kevlar / LIG substrate prepared in S1 of Example 1 was used as a pressure sensor. A Mark-10 force gauge was used to apply force to the sensor surface. An LCR source meter was connected to the sensor and a computer was connected to the source meter to measure the resistance change of the sensor in real time. The switching characteristics of the Kevlar / LIG pressure sensor under different pressures were measured. Figure 4 The switching characteristics of Kevlar / LIG substrate as a pressure sensor under different pressures are shown in the figure. Figure 4It can be seen that when using uncoated PDMS LIG as a sensor, after multiple presses at the falling edge, it can be found that the greater the pressure used, the higher the resistance (the vertical axis is the resistance change rate). This is because when the pressure is too high, the internal conductive path of the LIG is broken, causing the LIG resistance to increase. Therefore, when not coated with PDMS, the Kevlar / LIG-based pressure sensor does not have cyclic stability and repeatability.

[0052] While applying force on the sensor surface through a Mark-10 force gauge, an LCR source meter is connected to the sensor, and a computer is connected to the source meter to obtain the resistance change of the sensor in real time. The performance of the resistive pressure sensor prepared in Example 1 is investigated through the resistance change. Figure 5 This is a performance exploration diagram of the resistive pressure sensor prepared in Example 1, wherein: Figure 5 a in the equation is the repeatability of the resistive pressure sensor under different pressures. Figure 5 b in the figure is the resistance response of the resistive sensor under the loading-unloading condition of 5 kPa. Figure 5 Where c is the response time of the resistive pressure sensor at 5kPa, Figure 5 Where d is the recovery time of the resistive pressure sensor at 5kPa, which is given by Figure 5 The resistive pressure sensor exhibits good cyclic stability and repeatability across different pressure ranges during three consecutive dynamic loading and unloading pressure cycles, as shown by its response curves within different pressure ranges. This demonstrates its ability to stably and repeatably detect pressures of varying magnitudes. The sensor's response time and recovery time are shown. The response time is defined as the time required for the output signal to reach 90% of its final steady-state value after a step change in the input occurs. The recovery time is defined as the time required for the output signal to return to 10% of its initial steady-state value after a step change in the input returns to its initial value. Under an external pressure of 5 kPa, the sensor exhibits a fast response time of approximately 60.49 ms and a fast recovery time of 51.74 ms.

[0053] While applying force on the sensor surface through a Mark-10 force gauge, an LCR source meter is connected to the sensor, and a computer is connected to the source meter to obtain the capacitance change of the sensor in real time. The performance of the capacitive pressure sensor prepared in Example 2 is investigated through the capacitance change. Figure 6 This is a performance exploration diagram of the capacitive pressure sensor prepared in Example 2, wherein: Figure 6 a in the equation is the repeatability of the capacitance sensor under different pressures. Figure 6 b in the figure is the capacitance response under increasing pressure. Figure 6c in the figure is the capacitance response diagram of the capacitive pressure sensor under 1kPa loading-unloading pressure conditions. Figure 6 Where d is the response time of the capacitive pressure sensor at a pressure of 1 kPa, Figure 6 The e in is the recovery time of the capacitive pressure sensor under 1kPa pressure. Figure 6 As can be seen, the capacitive sensor maintains a stable signal output across different pressure ranges after undergoing three loading and unloading cycles with the same pressure load, demonstrating its excellent ability to detect varying pressures. The sensor is also able to detect the capacitive response corresponding to the applied pressure even when subjected to continuous step-change pressure, demonstrating its ability to maintain a stable output signal under dynamic conditions. The sensor's response time and recovery time are shown. The response time is defined as the time required for the output signal to reach 90% of its final steady-state value after a step change in the input occurs. The recovery time is defined as the time required for the output signal to return to 10% of its initial steady-state value after the input returns from a step value to its initial value. The sensor exhibits a fast response time of approximately 139.27ms and a fast recovery time of 89.99ms under loading and unloading pressure conditions of 1kPa.

[0054] Example 4: Application of capacitive pressure sensors in logistics and transportation

[0055] In order to verify the application prospects of capacitive pressure sensors in logistics and transportation, an experiment simulating cargo transportation collision was carried out. Figure 7 This is a schematic diagram of the application of capacitive pressure sensors in logistics and transportation, where: Figure 7 a in the figure is a schematic diagram of the position distribution of the capacitive pressure sensor after the object is wrapped with Kevlar fabric. Figure 7 Figure b shows a real-life cart in logistics transport. The experimental steps are as follows: The surface of simulated cargo is wrapped with Kevlar fabric. Four sensors are fabricated on the Kevlar fabric, positioned in front, behind, left, and right of the simulated cargo, numbered 1, 2, 3, and 4. Finally, the wrapped simulated cargo is placed in the center of a remote-controlled car. A wireless module is mounted on the roof of the car to transmit capacitance data wirelessly in real time.

[0056] Figure 8 This is the effect diagram of the application of capacitive pressure sensor in logistics transportation, among which, Figure 8 a in the figure is the capacitance change of each capacitive pressure sensor after simulating the collision of cargo during the forward movement. Figure 8 b in the figure is the capacitance change of each capacitive pressure sensor after simulating the collision of the cargo during the backward movement. Figure 8 The c in the equation is the capacitance change of each capacitive pressure sensor after simulating the side collision of the cargo. Figure 8As can be seen, when the simulated car is traveling forward and then rear-ending another vehicle, the collision process can be divided into three phases: pre-collision, collision instant, and post-collision. When the vehicle is struck, the simulated cargo encased in the sensor slides in the direction of the vehicle's travel due to inertia, striking the interior wall of the vehicle. Consequently, the capacitance of sensor 1, corresponding to the collision, changes accordingly. The capacitance signals of the other sensors, unaffected by pressure, remain virtually unchanged. Similarly, when the car is struck backward, the collision process also occurs in three phases. At the collision instant, the capacitance response of sensor 2 suddenly increases, indicating the vehicle was struck backward. Furthermore, when the stationary car is struck from the side by another vehicle, the collision process can be divided into four phases: pre-collision, collision instant 1, collision instant 2, and post-collision. After the vehicle is struck, the simulated cargo moves in the opposite direction of the collision due to friction between its bottom and the vehicle's interior, causing the capacitance response of sensor 3 to increase. After the simulated cargo's initial impact, it rebounds, moving in the direction of the vehicle's impact. Upon impact with the right interior wall of the vehicle, the capacitance of sensor 4 changes accordingly, and the simulated cargo eventually comes to a stop due to friction.

[0057] Example 5: Application of a dual-mode sensor consisting of a resistive pressure sensor and a capacitive pressure sensor in a smart helmet

[0058] Kevlar fabric is used to replace the traditional straps in the helmet, and a dual-mode sensor consisting of a resistive pressure sensor and a capacitive pressure sensor is prepared on the surface of the strap. Figure 9 This is a schematic diagram of the application of resistance-capacitance dual-mode pressure sensor in smart helmets, where: Figure 9 The a in the figure is a real picture of the tester wearing a smart helmet while riding. Figure 9 The diagram b in Figure 1 is a schematic diagram, a 3D diagram, and a physical diagram of the dual-modal sensor integration system. Figure 9 It can be seen that in the entire integrated system, the five resistive sensors in the middle area of ​​the Kevlar fabric can correspond to the left cheekbone, right cheekbone, chin, left sideburn and right sideburn of the human body, respectively, to detect the resistance response of different facial expressions. The capacitive pressure sensor is composed of composite electrodes prepared at both ends of the strap (the left and right electrodes are in opposite directions) and is used to test the external impact of the helmet. When worn, the ends of the strap are folded inward so that the two electrodes face each other to form a complete capacitive sensor. The specific structure of the smart helmet is as follows Figure 9 As shown in b, the top of the helmet corresponds to a capacitive pressure sensor, and the inner surface of the strap contains five resistive sensors.

[0059] Figure 10 This is a graph showing the capacitance changes of the smart helmet when the tester repeatedly wears it and is subjected to external impact. Figure 10 a in the figure is the capacitance change diagram when the tester repeatedly wears the smart helmet. Figure 10As can be seen from a in the figure, the capacitive pressure sensor can accurately identify the repeated wearing actions of the helmet, and the capacitor response presents a clear and repeatable signal to ensure monitoring in the continuous wearing state. At the same time, falling objects from high altitudes is also a very dangerous behavior in real life. In order to be able to detect emergencies during riding, a simulation of falling objects from high altitudes was performed on the helmet being worn. Free fall tests were performed on objects of different weights at the same position above the helmet. Figure 10 Figure b shows the capacitance change of the smart helmet when it is subjected to external impact. The calculated impact pressures are 1.1kPa, 74kPa, 105kPa, and 140kPa, respectively. The capacitance response of the capacitive pressure sensor also increases with the increase of pressure. By observing the capacitance response amplitude, the severity of the impact can be evaluated, providing key information for post-accident rescue.

[0060] Figure 11 The resistance change diagram of the tester under different micro-expressions when wearing a smart helmet, among which, Figure 11 a in the figure represents the resistance response switching characteristics of the five parts under the micro-expression of surprise. Figure 11 b in the figure represents the resistance response switching characteristics of the five parts under the micro-expression of speaking. Figure 11 The c in the figure represents the resistance response switching characteristics of the five parts under the micro-expression of laughing. Figure 11 The d in the equation is the resistance response switching characteristics of the five parts under the micro-expression of daze. Figure 11 As can be seen, the resistance switching in the corresponding graphs for the four facial expressions demonstrates the resistance response of the five sensors in the corresponding expressions due to skin stretching. When the subject is surprised, the resistive sensor located in the chin area exhibits a maximum on-off ratio of 0.211. When the subject speaks, the resistive sensor located in the chin also reaches a maximum on-off ratio of 0.153. This is likely due to the significant skin stretching of the jaw during the micro-expressions of surprise and speaking. When the subject laughs, the signal waveforms of the five resistive sensors are similar. When the subject is in a daze, the resistance response of the five sensors is almost zero.

[0061] The present invention utilizes DLW to prepare LIG on Kevlar to develop a new type of resistance-capacitance dual-modal flexible pressure sensor. This relates to physiological health monitoring and plantar pressure. The integrated preparation characteristics of the dual-modal flexible pressure sensor can also be used to monitor driving helmets, using a resistive pressure sensor to detect and monitor changes in the driver's micro-expressions, while a capacitive pressure sensor is used to monitor unexpected collisions. Furthermore, thanks to the excellent wide pressure range of the capacitive sensor and the performance of the fabric-based material, the capacitive sensor function can be integrated with the fabric packaging function and further applied to logistics and transportation. If a vehicle is hit or its driving trajectory changes, or if objects are displaced or collided inside the vehicle, the pressure sensor can provide a real-time alarm.

[0062] The present invention provides a capacitive pressure sensor and a dual-mode pressure sensor based on laser direct writing, as well as a method for their preparation and application. While there are numerous methods and approaches for implementing this technical solution, the foregoing description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A capacitive pressure sensor based on laser direct writing, characterized in that: The capacitive pressure sensor is composed of two identical composite electrodes; the composite electrode is made by secondary laser direct writing on the PDMS layer of the resistive pressure sensor. The specific process is as follows: the PDMS layer of the resistive pressure sensor is secondary processed using a laser to form a periodic ridge-like microstructure on the PDMS layer, thereby obtaining the composite electrode; The laser parameters of the secondary processing are as follows: line spacing 0.45 mm, laser speed 50 mm / s, laser power 3.2 W; The capacitive pressure sensor is composed of two identical composite electrodes. The specific process is as follows: the PDMS layers of the two composite electrodes are placed face to face with the ridge structures arranged vertically, and the capacitive pressure sensor is obtained after being fixed; The resistive pressure sensor includes a Kevlar / graphene substrate layer and a PDMS layer; the PDMS layer is coated on the graphene surface of the Kevlar / graphene substrate layer; the Kevlar / graphene substrate layer is formed by laser direct writing on the surface of Kevlar fabric, specifically by using a laser to prepare laser-induced graphene on the surface of the Kevlar fabric to obtain the Kevlar / graphene substrate layer; Among them, the laser induction has the following laser parameters: line spacing 0.05~0.08mm, laser speed 75~80mm / s, and laser power 4.8~7.2W.

2. The capacitive pressure sensor according to claim 1, wherein: The method for preparing the resistive pressure sensor includes the following steps: using a laser to prepare laser-induced graphene on the surface of a Kevlar fabric to obtain a Kevlar / graphene substrate layer; coating the edge of the graphene surface with a conductive silver paste and connecting a copper wire; then coating the graphene surface with a PDMS mixture; and curing the mixture to obtain the resistive pressure sensor.

3. The capacitive pressure sensor according to claim 2, wherein: The PDMS mixture includes a PDMS prepolymer and a curing agent; the mass ratio of the PDMS prepolymer to the curing agent is 10:

1.

4. The capacitive pressure sensor according to claim 2, wherein: The coating is completed by spin coating, and the specific process parameters are: spin coating speed 300~500rpm, acceleration 300~500rpm / s, and spin coating time 10~50s.

5. A dual-mode pressure sensor prepared based on the capacitive pressure sensor according to claim 1, characterized in that: The dual-mode pressure sensor includes a capacitive pressure sensor and a resistive pressure sensor; The resistive pressure sensor includes a Kevlar / graphene substrate layer and a PDMS layer; the PDMS layer is coated on the graphene surface of the Kevlar / graphene substrate layer; the Kevlar / graphene substrate layer is formed by laser direct writing on the surface of Kevlar fabric, specifically by using a laser to prepare laser-induced graphene on the surface of the Kevlar fabric to obtain the Kevlar / graphene substrate layer; Among them, the laser induction has the following laser parameters: line spacing 0.05~0.08mm, laser speed 75~80mm / s, and laser power 4.8~7.2W.

6. Application of the capacitive pressure sensor according to claim 1 or the dual-mode pressure sensor according to claim 5 in the packaging and real-time monitoring of goods in logistics transportation.

7. Use of the capacitive pressure sensor according to claim 1 or the dual-mode pressure sensor according to claim 5 in the preparation of an intelligent driving helmet.

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