Capacitive pressure sensor based on laser direct writing, bimodal pressure sensor and preparation method and application thereof

Abstract

The invention belongs to the technical field of flexible sensors, and particularly relates to a capacitive pressure sensor based on laser direct writing, a bimodal pressure sensor and a preparation method and application thereof. The capacitive pressure sensor is composed of two same composite electrodes. The composite electrode is prepared by performing secondary laser direct writing on a PDMS layer through a resistive pressure sensor, and the resistive pressure sensor comprises a Kevlar / graphene base material layer and a PDMS layer; the graphene surface of the Kevlar / graphene base material layer is coated with the PDMS layer; the Kevlar / graphene base material layer is formed by directly writing laser on the surface of the Kevlar fabric. The bimodal pressure sensor comprises the capacitive pressure sensor and a resistive pressure sensor.

Description

Technical Field

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

[0002] In recent years, with the development of flexible electronic devices, great attention has been paid to fields such as flexible displays, flexible photovoltaics, chemical and biosensors, and flexible sensors. As an important part of the electronic field, flexible sensors play a crucial 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 human wearable devices due to their breathability and conformability to the human body. Another example is in practical life such as bundling and packaging goods in logistics transportation, where certain fabrics are adopted due to their softness, high strength, and ability to wrap irregular objects. Among various types of flexible fabric sensors, flexible fabric pressure sensors are widely used in fields such as medical health monitoring, intelligent wearables, and human-computer interaction due to their high sensitivity, biocompatibility, and durability.

[0003] Laser direct writing technology (DLW) is a way of patterning by directly focusing a laser beam on the surface or inside of a material, and has characteristics such as high precision, high resolution, no need for a mask, and dynamic adjustability, and is widely used in fields such as materials science, micro-nano structure manufacturing, and sensor manufacturing. The interaction between laser and matter generates new functional substances, endowing the raw materials with new functions.

[0004] Graphene is a very good material with excellent properties, and due to its mechanical properties and excellent electrical conductivity, it is often used in flexible pressure sensors. Compared with graphene prepared by CVD growth and reduction-oxidation methods, the preparation process of laser-induced graphene (LIG) is the simplest. The preparation process based on laser-induced graphene as a pressure sensor can greatly reduce the preparation process and cost. The range of precursors that can be selected is wider, etc. In fabric-based LIG flexible electronic devices, Kevlar is often used as a precursor material for LIG preparation due to its unique chemical structure.

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

[0006] The technical problem to be solved by the present invention is to provide, in view of the deficiencies of the prior art, an effective simplification of the preparation process of a bimodal pressure sensor using direct laser writing technology (DLW), and to use DLW to prepare a capacitive pressure sensor and a bimodal pressure sensor based on two materials, Kevlar and PDMS, respectively.

[0007] To solve the above technical problem, the present invention discloses a capacitive pressure sensor based on direct laser writing. The capacitive pressure sensor is composed of two identical composite electrodes; the composite electrodes are obtained by subjecting a resistive pressure sensor to secondary laser writing of a PDMS layer.

[0008] Among them, 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 direct laser writing on the surface of a Kevlar fabric.

[0009] Further, the preparation method of the above capacitive pressure sensor is also within the protection scope of the present invention. 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, that is, 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] Among them, for the laser, its laser parameters are: line spacing 0.45 mm, laser speed 50 mm / s, and laser power 3.2 W.

[0011] Specifically, the preparation method of 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 conductive silver paste on the edge of the graphene surface and connecting a copper wire, and then coating a PDMS mixture on the graphene surface, and curing it to obtain the resistive pressure sensor.

[0012] Among them, for the laser, its laser parameters are: line spacing 0.05 - 0.08 mm, laser speed 75 - 80 mm / s, and laser power 4.8 - 7.2 W.

[0013] Among them, 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] Among them, the coating is completed by spin coating, and the specific process parameters are: spin coating speed 300 - 500 rpm, acceleration 300 - 500 rpm / s, and spin coating time 10 - 50 s.

[0015] Among them, for the curing, the process parameters are: maintaining at 80°C for 2 h.

[0016] In some embodiments of the present invention, the resistive pressure sensor for preparing the capacitive pressure sensor is prepared by using the above-mentioned preparation method of the resistive pressure sensor. Among them, in the process of preparing the resistive pressure sensor, the parameters of the laser are: line spacing 0.05 mm, laser speed 75 mm / s, and 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 applications of the above-mentioned capacitive pressure sensor or dual-mode pressure sensor in the packaging of goods in logistics transportation and real-time monitoring are also within the protection scope of the present invention.

[0019] Specifically, in some embodiments of the present invention, the surface of the simulated goods is wrapped with Kevlar fabric, and four capacitive pressure sensors are respectively prepared on the surface of the Kevlar fabric, and the real-time collision situation of the goods during transportation is reflected by the capacitance change. The sensor provided by the present invention realizes the integration of the packaging function and the monitoring function at the same time, and realizes the function integration and synchronous remote wireless data transmission of goods packaging and monitoring pressure signals on the same fabric by integrating a Bluetooth module. The expansion of this application is expected to reduce costs and simplify the process for the monitoring and warning equipment in logistics transportation.

[0020] Furthermore, the applications of the above-mentioned capacitive pressure sensor or dual-mode pressure sensor in the preparation of intelligent driving helmets are 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 strap in the helmet, and a dual-mode sensor of resistive and capacitive types is simultaneously prepared on the surface of the strap. An integrated monitoring driving helmet is prepared by using the characteristics of a low detection limit threshold and a high pressure-bearing range, and the micro-expression changes of the driver and the occurrence of accidental impacts are monitored simultaneously.

[0022] Beneficial effects: 1. Using the laser direct writing technology to prepare the dual-mode pressure sensor can effectively simplify the preparation process.

[0023] 2. The capacitive pressure sensor can be realized by laser processing on the basis of the resistive sensor.

[0024] 3. The advantage of preparing sensors with flexible Kevlar fabrics is that, compared with rigid packaging, they can wrap different regular items, integrating the functions of item packaging and pressure monitoring into one.

[0025] 4. The smart helmet prepared with flexible Kevlar fabrics can monitor both resistive and capacitive sensors simultaneously. Brief Description of the Drawings

[0026] The following further specifically describes the present invention in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0027] Figure 1 It is a flowchart for preparing resistive and capacitive pressure sensors provided by the present invention and a schematic cross-sectional view of Kevlar fabric after laser induction.

[0028] Figure 2 It is an SEM diagram of the original Kevlar in the embodiment of the present invention, the LIG obtained by S1 in Embodiment 1, and the LIG obtained by S1 in Embodiment 2.

[0029] Figure 3 It is a cross-sectional SEM diagram of the composite electrode obtained after secondary processing in S3 of Embodiment 2 of the present invention.

[0030] Figure 4 It is a switching characteristic diagram of the Kevlar / LIG substrate without the PDMS layer as a pressure sensor under different presses in Embodiment 1 of the present invention.

[0031] Figure 5 It is a performance exploration diagram of the resistive pressure sensor prepared in Embodiment 1 of the present invention.

[0032] Figure 6 It is a performance exploration diagram of the capacitive pressure sensor prepared in Embodiment 2 of the present invention.

[0033] Figure 7 It is a schematic diagram of the application of the capacitive pressure sensor in logistics transportation in the embodiment of the present invention.

[0034] Figure 8 It is an application effect diagram of the capacitive pressure sensor in logistics transportation in the embodiment of the present invention.

[0035] Figure 9 It is a schematic diagram of the application of the resistive-capacitive dual-mode pressure sensor in a smart helmet in the embodiment of the present invention.

[0036] Figure 10 It is a capacitance change diagram of the smart helmet when the tester repeatedly wears the smart helmet and is subjected to external impacts in the embodiment of the present invention.

[0037] Figure 11 This is the resistance change diagram under different micro - expressions when the tester wears the intelligent helmet in the embodiment of the present invention. Detailed implementation manners

[0038] In the following embodiments, the experimental methods are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0039] 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 It is the preparation flow chart of the resistive and capacitive pressure sensors and the schematic cross - section diagram of the Kevlar fabric after laser induction. As Figure 1 shown in a of, by using the laser direct writing technology (DLW) to prepare laser - induced graphene (LIG) on the Kevlar fabric, and then spin - coating a PDMS layer on the LIG, a resistive pressure sensor can be prepared; further, by performing secondary laser processing on the PDMS layer of the resistive pressure sensor to form a composite electrode with a periodic ridge - like microstructure, and integrating two pieces of the composite electrodes, a capacitive pressure sensor can be obtained. Figure 1 b in is the schematic cross - section diagram of the Kevlar fabric after laser induction. It can be seen from the figure that the original Kevlar fabric is divided into two layers: the upper layer facing the laser is LIG. By controlling the laser parameters, the laser only interacts with a part of the Kevlar fabric, so as to retain the original fabric at the end far from the laser. In practical applications, the original fabric will be in direct contact with the skin, having better skin - friendliness and breathability.

[0040] Example 1: Preparation of the resistive pressure sensor S1. Preparation of laser - induced graphene (LIG): First, take a piece of Kevlar fabric that has been ultrasonically cleaned with ethanol and deionized water in sequence, and adjust the parameters of the carbon dioxide laser to prepare LIG on the surface of the Kevlar fabric to obtain a Kevlar / LIG substrate layer. Among them, the parameters of the carbon dioxide laser are: line spacing 0.08 mm, laser speed 80 mm / s, and laser power 4.8 W.

[0041] S2. Preparation of the resistive pressure sensor: Apply conductive silver paste at the edge joints of the LIG, and then attach conductive copper wires. After that, place the Kevlar / LIG substrate layer on the knob of a spin coater, and coat 2 ml of the PDMS mixture on the LIG surface with an area of 1 cm × 1 cm. Spin coat for 50 s under the parameters of a spin coating speed of 300 rpm and an acceleration of 300 rpm / s to obtain Kevlar / LIG / PDMS. Remove the spin-coated substrate from the spin coater and place it in an oven at 80 °C for 2 h to cure the PDMS, thus obtaining the resistive pressure sensor; among them, the PDMS mixture contains a PDMS prepolymer and a curing agent with a mass ratio of 10:1.

[0042] Example 2: Preparation of the capacitive pressure sensor S1. Preparation of laser-induced graphene (LIG): First, take a piece of Kevlar fabric that has been ultrasonically cleaned successively with ethanol and deionized water, and adjust the parameters of a carbon dioxide laser to prepare LIG on the surface of the Kevlar fabric to obtain the Kevlar / LIG substrate layer. Among them, the parameters of the carbon dioxide laser are: line spacing 0.05 mm, laser speed 75 mm / s, and laser power 7.2 W.

[0043] S2. Preparation of the resistive pressure sensor: Apply conductive silver paste at the edge joints of the LIG, and then attach conductive copper wires. After that, place the Kevlar / LIG substrate layer on the knob of a spin coater, and coat 2 ml of the PDMS mixture on the LIG surface with an area of 1 cm × 1 cm. Spin coat for 10 s under the parameters of a spin coating speed of 500 rpm and an acceleration of 500 rpm / s to obtain the Kevlar / LIG / PDMS substrate. Remove the spin-coated substrate from the spin coater and place it in an oven at 80 °C for 2 h to cure the PDMS, thus obtaining the resistive pressure sensor; among them, the PDMS mixture contains a PDMS prepolymer and a curing agent with a mass ratio of 10:1.

[0044] S3. Preparation of the capacitive pressure sensor: Use a carbon dioxide laser to perform secondary processing on the PDMS layer of the resistive pressure sensor obtained in S2 to generate periodic ridge-shaped microstructures on the surface of the PDMS layer to obtain a composite electrode; place the PDMS layers of the two composite electrodes face to face, and form a capacitive pressure sensor after the ridge structures are vertically arranged and fixed; among them, the parameters of the carbon dioxide laser in the secondary processing are: line spacing 0.45 mm, laser speed 50 mm / s, and laser power 3.2 W.

[0045] Example 3: Performance characterization of the resistive pressure sensor and the capacitive pressure sensor The micro-morphologies of the original Kevlar, the LIG prepared from S1 in Example 1, and the LIG prepared from S1 in Example 2 were characterized by a scanning electron microscope. Figure 2 are the SEM images of the original Kevlar, the LIG prepared from S1 in Example 1, and the LIG prepared from S1 in Example 2. Among them, Figure 2 a in Figure 2 and b in Figure 2 are the SEM images of the surface of the original Kevlar fabric. Figure 2 c in Figure 2 and d in Figure 2 are the high-resolution SEM images of the LIG prepared from S1 in Example 1. Figure 2 It can be seen that after the original smooth and cross-arranged Kevlar is laser processed, the smooth surface structure is damaged, and a porous microstructure is generated. Since Kevlar is a potential fabric substrate material, as an aramid fiber, due to its special molecular structure, some of its elements will generate gases through pyrolysis under the action of laser, such as generating gases such as CO, CO2, and NO, and finally volatilize from the fabric surface, leaving a carbon-rich skeleton.

[0046] The cross-section micro-morphology of the composite electrode obtained after secondary processing in S3 of Example 2 was characterized by a scanning electron microscope. Figure 3 is the cross-section SEM image of the composite electrode obtained after secondary processing in S3 of Example 2. Figure 3 It can be seen that the composite electrode is divided into three-layer structure. The top layer is a PDMS layer with a ridge-like microstructure, the middle layer is a porous LIG, and the bottom layer is the Kevlar substrate reserved without laser processing.

[0047] Using the Kevlar / LIG substrate prepared from S1 in Example 1 as a pressure sensor, while applying force on the sensor surface through a Mark-10 dynamometer, an LCR source meter is connected to the sensor, and a computer is connected to the source meter to obtain the resistance change received by the sensor in real time, and the switching characteristics of the Kevlar / LIG substrate pressure sensor under different presses are tested. Figure 4 is the switching characteristic diagram of the Kevlar / LIG substrate as a pressure sensor under different presses. Figure 4It can be seen that when using uncoated PDMS LIG as a sensor and subjecting it to multiple presses at the falling edge, it is found that the greater the pressure applied, the more the resistance shows an upward trend (the ordinate is the resistance change rate). This is because when the pressure is too high, the internal conductive path of the LIG breaks, resulting in an increase in the resistance of the LIG. Therefore, when not coated with PDMS, the Kevlar / LIG substrate pressure sensor does not possess cycling stability and repeatability.

[0048] While applying force to the sensor surface with a Mark-10 dynamometer, 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 It is a performance investigation diagram of the resistive pressure sensor prepared in Example 1, where Figure 5 a in it is the repeatability of the resistive pressure sensor under different pressures, Figure 5 b in it is the resistance response of the resistive sensor under the loading-unloading condition of 5 kPa, Figure 5 c in it is the response time of the resistive pressure sensor at 5 kPa, Figure 5 d in it is the recovery time of the resistive pressure sensor at 5 kPa. It can be seen from Figure 5 that during three consecutive dynamic loading-unloading pressure cycles of the resistive pressure sensor, from the response curves in different pressure ranges, it can be seen that the sensor exhibits good cycling stability and repeatability in different pressure intervals, indicating that it can stably and repeatedly detect pressures of different magnitudes. The response time and recovery time of the sensor are shown. The response time is defined as the time required for the output signal to reach 90% of its final steady-state value starting from the instant when the input quantity undergoes a step change; 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 quantity changes from a certain step value back to the initial value. Under an external pressure of 5 kPa, this sensor exhibits a rapid response time of approximately 60.49 ms and a rapid recovery time of 51.74 ms.

[0049] While applying force to the sensor surface with a Mark-10 dynamometer, 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 It is a performance investigation diagram of the capacitive pressure sensor prepared in Example 2, where Figure 6 a in it is the repeatability of the capacitive sensor under different pressures, Figure 6 b in it is the capacitance response under continuously increasing pressure, Figure 6In it, c is the capacitance response diagram of the capacitive pressure sensor under the condition of 1 kPa loading-unloading pressure, Figure 6 In it, d is the response time of the capacitive pressure sensor under 1 kPa pressure, Figure 6 In it, e is the recovery time of the capacitive pressure sensor under 1 kPa pressure. It can be seen from Figure 6 that the capacitive sensor undergoes three loading-unloading processes of the same pressure load and still maintains a stable signal output under different pressure ranges, indicating its excellent ability to detect different pressure magnitudes. When the sensor is continuously applied with a step-change pressure, it can still detect the capacitance response corresponding to the applied pressure, showing that the sensor can still stably output signals under dynamic response. The response time and recovery time of the sensor are shown. The response time is defined as the time required for the output signal to reach 90% of its final steady-state value starting from the moment when the input quantity undergoes a step change; 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 quantity changes back from a certain step value to the initial value. The sensor has a fast response time of about 139.27 ms and a fast recovery time of 89.99 ms under the conditions of 1 kPa loading and unloading pressure.

[0050] Example 4: Application of the capacitive pressure sensor in logistics transportation In order to verify the application prospect of the capacitive pressure sensor in logistics transportation, an experiment on simulating the collision of goods during transportation was carried out. Figure 7 is a schematic diagram of the application of the capacitive pressure sensor in logistics transportation. Among them, Figure 7 in a is a schematic diagram of the position distribution of the capacitive pressure sensor after the object is wrapped with Kevlar fabric, Figure 7 in b is a physical picture of the trolley in logistics transportation. The specific experimental steps are as follows: Use Kevlar fabric to wrap the surface of the simulated goods, and prepare four sensors on the surface of the Kevlar fabric respectively, so that the four sensors are located at the front, back, left and right of the simulated goods respectively, numbered 1, 2, 3, and 4. Finally, place the wrapped simulated goods in the center of the carriage of a remote control car, and install and fix the wireless module on the roof of the car to wirelessly transmit capacitance data in real time.

[0051] Figure 8 is the application effect diagram of the capacitive pressure sensor in logistics transportation. Among them, Figure 8 in a is the capacitance change of each capacitive pressure sensor after the simulated goods collide during the forward movement, Figure 8 in b is the capacitance change of each capacitive pressure sensor after the simulated goods collide during the backward movement, Figure 8 in c is the capacitance change of each capacitive pressure sensor after the simulated goods collide on the side. It can be seen from Figure 8It can be seen that when the simulated car moves forward and collides with the vehicle in front, the collision process is divided into three stages, namely, before the collision, at the moment of collision, and after the collision. When the vehicle is impacted, the simulated goods wrapped by the sensor will slide in the direction of the vehicle's travel due to inertia and thus hit the inner wall of the carriage. Therefore, there will be corresponding capacitance changes in the sensor numbered 1 corresponding to the collision. The capacitance signals of other sensors not subjected to pressure hardly change. Similarly, when the car is impacted in reverse, the collision process is also divided into three stages. At the moment of collision, the capacitance response of the sensor numbered 2 will suddenly increase, indicating that the vehicle is impacted while reversing. In addition, when the car at rest is impacted by other vehicles on the side, the collision process can be divided into four stages, namely, before the collision, at the first moment of collision, at the second moment of collision, and after the collision. After the vehicle is impacted, the simulated goods will move in the opposite direction of the impact due to the friction between the bottom and the carriage, and the capacitance response of the sensor numbered 3 will increase. The simulated goods will hit the inner wall for the first time and then rebound, thus moving in the direction of the vehicle impact. When hitting the right inner wall of the vehicle, there will be corresponding capacitance changes in the sensor numbered 4, and finally the simulated goods will stop under the action of friction.

[0052] Embodiment 5: Application of a Dual-Mode Sensor of a Resistive Pressure Sensor and a Capacitive Pressure Sensor in a Smart Helmet Use Kevlar fabric to replace the traditional strap in the helmet, and simultaneously fabricate a dual-mode sensor of a resistive pressure sensor and a capacitive pressure sensor on the surface of the strap. Figure 9 It is a schematic diagram of the application of a resistive-capacitive dual-mode pressure sensor in a smart helmet, where Figure 9 a in it is a physical picture of a tester wearing a smart helmet during cycling. Figure 9 b in it is a schematic diagram, a 3D diagram of the dual-mode sensor integration system, and a physical picture of the smart helmet. It can be seen that Figure 9 in the entire integration system, the five resistive sensors in the middle area of the Kevlar fabric can respectively correspond to the positions of the left cheekbone, right cheekbone, chin, left temple, and right temple of a person, and are used to detect the resistance response when making different facial expressions. The capacitive pressure sensor is composed of composite electrodes prepared at both ends of the strap (the electrode directions at the left end and the right end are opposite), and is used to test the external impact on the helmet. When wearing, the two 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 Figure 9 shown in b in it. The top of the helmet corresponds to the capacitive pressure sensor, and the inner surface of the strap contains five resistive sensors.

[0053] Figure 10 It is a capacitance change diagram of the smart helmet when a tester repeatedly wears the smart helmet and is externally impacted. Figure 10 a in it is the capacitance change diagram when a tester repeatedly wears the smart helmet. It can be seen from Figure 10As can be seen from a in the figure, for the repeated actions of putting on and taking off the helmet, the capacitive pressure sensor can accurately identify the corresponding wearing actions, and the capacitive response presents a clear and repeatable signal, ensuring monitoring during continuous wearing. At the same time, in real life, falling objects from a height is also a very dangerous behavior. In order to detect emergencies during cycling, a simulation of falling objects from a height was carried out on the worn helmet. Free-fall tests were carried out using objects of different weights at the same position above the helmet respectively. Figure 10 Figure b in the figure is the capacitive change diagram of the smart helmet when it is impacted externally. The calculated impact pressures are 1.1 kPa, 74 kPa, 105 kPa, and 140 kPa respectively. The capacitive response of the capacitive pressure sensor also increases with the increase of pressure. By observing the amplitude of the capacitive response, the severity of the impact can be evaluated, providing key information for rescue after an accident.

[0054] Figure 11 Figure is the resistance change diagram of the smart helmet worn by the tester under different micro-expressions. Among them, Figure 11 Figure a in the figure is the resistance response switch characteristics of five parts under the surprised micro-expression. Figure 11 Figure b in the figure is the resistance response switch characteristics of five parts under the speaking micro-expression. Figure 11 Figure c in the figure is the resistance response switch characteristics of five parts under the laughing micro-expression. Figure 11 Figure d in the figure is the resistance response switch characteristics of five parts under the daze micro-expression. As Figure 11 can be seen, the resistance switches in the four corresponding expression diagrams show the resistance responses caused by skin stretching of the five position sensors under the corresponding expressions. When the tester is surprised, the resistive sensor located in the chin area shows a maximum switching ratio of 0.211. When the tester is speaking, the resistive sensor located in the chin position also reaches a maximum switching ratio of 0.153. This may be because significant skin stretching occurs in the lower jaw during the surprised and speaking micro-expressions. When the tester is laughing, the signal waveforms of the five resistive sensors are similar. When the tester is in a daze, the resistance responses of the five sensors are almost zero.

[0055] The present invention uses DLW to prepare LIG on Kevlar to develop a new type of resistive-capacitive dual-mode flexible pressure sensor. It is related to physiological health monitoring and plantar pressure. By virtue of the integrated preparation characteristics of the dual-mode flexible pressure sensor, it can also be applied in monitoring driving helmets. The resistive pressure sensor is used to detect the micro-expression changes of the driver, and the capacitive pressure sensor is used to monitor accidental impacts. At the same time, relying on the excellent wide pressure range of the capacitive sensor and the performance of the fabric-based material, the function of the capacitive sensor can be integrated with the fabric packaging function and further applied to logistics transportation. When the vehicle is impacted or its driving trajectory changes, or when the items inside the vehicle are displaced or collided, the pressure sensor can give a real-time alarm.

[0056] The present invention provides an idea and method for a capacitive pressure sensor, a dual-mode pressure sensor and their preparation methods and applications based on direct laser writing. There are many methods and ways to specifically implement this technical solution. The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be realized by the prior art.

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 electrodes are obtained by subjecting a resistive pressure sensor to secondary laser direct writing of a PDMS layer; Among them, 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.

2. The method for preparing the capacitive pressure sensor according to claim 1, characterized in that, It 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 micro-structure on the PDMS layer, that is, obtaining a composite electrode. Place the PDMS layers of the two composite electrodes face to face, with the ridge structures arranged vertically. After fixing, the capacitive pressure sensor is obtained.

3. The preparation method according to claim 2, wherein For the laser, its laser parameters are: line spacing 0.45 mm, laser speed 50 mm / s, laser power 3.2 W.

4. The preparation method according to claim 2, characterized in that, The preparation method of 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 conductive silver paste on the edge of the graphene surface and connecting copper wires, and then coating a PDMS mixture on the graphene surface. After curing, the resistive pressure sensor is obtained.

5. The preparation method according to claim 4, wherein For the laser, its laser parameters are: line spacing 0.05 - 0.08 mm, laser speed 75 - 80 mm / s, laser power 4.8 - 7.2 W.

6. The preparation method according to claim 4, characterized in that, 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.

7. The preparation method according to claim 4, wherein The coating is completed by spin coating, and the specific process parameters are: spin coating speed 300 - 500 rpm, acceleration 300 - 500 rpm / s, spin coating time 10 - 50 s.

8. A dual-mode pressure sensor, characterized in that, The dual-mode pressure sensor includes the capacitive pressure sensor described in claim 1 and a resistive pressure sensor.

9. The application of the capacitive pressure sensor described in claim 1 or the dual-mode pressure sensor described in claim 8 in the packaging and real-time monitoring of logistics transportation goods.

10. The application of the capacitive pressure sensor described in claim 1 or the dual-mode pressure sensor described in claim 8 in the preparation of intelligent cycling helmets.

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