Preparation method of graphene-elastomer composite pressure sensor

Abstract

The invention discloses a preparation method of a graphene-elastomer composite pressure sensor. The preparation method comprises the step of generating a polyimide insulating layer on a substrate. And performing laser processing on the polyimide insulating layer to form a porous graphene structure. And introducing an elastomer prepolymer solution into pores of the porous graphene structure and curing to form the pressure sensing element with the graphene-elastomer composite structure. The pressure sensing element on the insulating layer is prepared in situ, so that the problems that the pressure sensing element is easy to fall off and interface gaps exist in a traditional pressure sensing layer attaching mode can be avoided, and the stability and the long-term reliability of the pressure sensor are remarkably improved. According to the invention, the PDMS elastomer is infiltrated into the pores of the porous graphene and cured to form an embedded structure of the elastomer and the graphene, so that the overall supporting performance of the graphene structure is enhanced, and the sensing element is endowed with good elastic recovery capability. After the external force is removed, the elastic network can quickly drive the graphene structure to reset.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of in-situ generation of pressure sensing elements, and particularly relates to a preparation method of a graphene-elastic body composite pressure sensor. BACKGROUND

[0002] With the rapid development of flexible electronics, intelligent robots, wearable devices, underwater vehicles and other fields, flexible pressure sensors capable of achieving high sensitivity, stability and long-term operation on complex curved surfaces have become an important research direction. Current pressure sensors are usually composed of a sensitive layer and a flexible substrate layer, and pressure detection is achieved by resistance changes of the sensitive material under external force. However, the existing technology still has significant deficiencies in material composition, preparation method, and bonding stability with the substrate, which cannot meet the application requirements of new scenarios such as curved structure and high-resolution distributed sensing.

[0003] Firstly, traditional pressure sensitive layers mostly use graphene films, carbon nanotube films, metal nanowire networks and other materials, and are fixed on the surface of the insulating substrate by pasting or transferring. On the planar substrate, a certain adhesion can be maintained, but on the curved shell or large curvature structure, bubbles, wrinkles or local peeling often occur; the interfacial bonding force between the sensitive layer and the insulating substrate is insufficient, and peeling easily occurs under long-term cyclic strain or external impact, significantly reducing signal stability and device life. In addition, the pasting process itself relies on additional processes such as lamination, transfer printing or adhesive fixation, which is not conducive to the integrated preparation of the sensor.

[0004] Secondly, traditional pressure sensitive materials are mostly pure graphene or carbon material accumulation structures, which lack mechanical toughness and do not have an elastic support network that can be self-recovered. After external force loading, the microstructure is easily irreversibly collapsed, leading to problems such as drift, hysteresis, poor cycle stability and other problems in the pressure-resistance response. Such structures will gradually destroy the conductive channels under long-term periodic compression, further weakening the sensing performance.

[0005] Thirdly, in the existing technology, to realize array-type pressure distribution detection, multiple sensitive units are usually pasted on a flexible film and then patterned. However, since the sensitive layer and the substrate are not formed in-situ, stable insulation isolation between units is often difficult to achieve, and signal crosstalk is easily generated. At the same time, the pasted array structure is difficult to maintain layout stability on the curved surface, and local warping, wrinkling or stress concentration will lead to a decrease in array accuracy.

[0006] Finally, the traditional single sensitive layer structure has limitations in high-resolution pressure imaging array applications. To improve the resolution, multiple closely arranged sensitive units are needed; but the attached process is difficult to ensure the consistency of the interface between each unit and the insulating layer, and the stability is poor, and it is difficult to realize the micro-scale isolation structure. In underwater vehicles, wearable tactile systems and other applications, the sensitive element is required to have good protection capability, and the traditional sensitive membrane usually lacks water resistance and corrosion resistance.

[0007] It can be seen that the current technology is still difficult to simultaneously have in-situ preparation, surface adaptability, structural stability, high-resolution array configuration and long-term environmental reliability, so there is an urgent need for a composite pressure sensor preparation method that can construct a sensing unit in the insulating layer and adapt to the curved surface substrate. SUMMARY

[0008] The purpose of the present application is to provide a graphene- elastomer composite pressure sensor preparation method.

[0009] In a first aspect, the present application provides a graphene- elastomer composite pressure sensor preparation method, which comprises:

[0010] Step one, generating a polyimide insulating layer on the substrate.

[0011] Step two, laser processing the polyimide insulating layer to form a porous graphene structure by carbonizing the polyimide irradiated by laser.

[0012] Step three, introducing an elastomer prepolymer solution into the pores of the porous graphene structure.

[0013] Step four, the elastomer prepolymer solution is solidified in the pores of the porous graphene structure to form a pressure sensing element of the graphene-elastomer composite structure.

[0014] As a preferred, the process of introducing the elastomer prepolymer solution into the pores of the porous graphene structure is: using the elastomer prepolymer solution to drop coat a film on the porous graphene structure, so that the elastomer prepolymer solution penetrates into the pores of the porous graphene structure.

[0015] As a preferred, the elastomer prepolymer solution includes mixed PDMS precursors and cross-linking agents. The elastomer prepolymer solution is cross-linked and solidified by heating.

[0016] As a preferred, before generating the polyimide insulating layer on the substrate, an electrically conductive layer for leading out the electric signal of the pressure sensing element is installed or generated on the substrate.

[0017] As preferred, the conductive layer is provided with independent sensing connection sites. Each sensing connection site comprises two electrodes arranged at intervals. A porous graphene structure is laser processed on each sensing connection site, and an elastomer is introduced to form a pressure sensing element unit. Different pressure sensing element units are separated by a polyimide insulation structure to form a pressure sensing array.

[0018] As preferred, after the pressure sensing element is formed, a non-conductive coating is applied on the pressure sensing element to form an encapsulation layer.

[0019] As preferred, the process of forming the polyimide insulation layer is as follows: a polyamide acid solution is sprayed on the substrate to form a polyamide acid film layer. After drying and desolventizing, heat treatment is performed to cause imidization of the polyamide acid to form the polyimide insulation layer. The thickness of the polyimide insulation layer is 5-15 μm.

[0020] As preferred, the area of the polyimide insulation layer that is not irradiated by the laser remains in an insulating state to form a polyimide insulation structure surrounding the porous graphene structure.

[0021] As preferred, the power density of the laser processing is 5×10 4 W / cm 2 ~ 1 ×10 6 W / cm 2 .

[0022] The side of the substrate forming the pressure sensing element is a curved surface structure.

[0023] In a second aspect, the present application provides a graphene-elastomer composite pressure sensor prepared by the above preparation method.

[0024] The present application has the following advantages.

[0025] 1. The present application first constructs a porous graphene structure in a polyimide insulation layer by laser in-situ and forms an elastomer in the pores thereof to obtain a sensing element having both conductive properties and elasticity, realizes in-situ preparation of a pressure sensing element on an insulation layer, avoids the problems of easy falling off and existing interface gap in the traditional pressure sensitive layer attachment mode, and significantly improves the stability and long-term reliability of the pressure sensor.

[0026] 2. The present application forms an interpenetrating structure of elastomer and graphene by infiltrating a PDMS elastomer into the pores of the porous graphene and solidifying, which not only enhances the overall supportability of the graphene structure, but also endows the sensing element with good elastic recovery capability. After the external force is removed, the elastic network can quickly drive the graphene structure to reset, thereby ensuring the repeatability and long-term cyclic stability of the pressure signal.

[0027] 3. The present application forms a polyimide insulating layer closely adhered to the curved surface by spray curing, and the graphene-elastic body composite structure is reliably formed on the curved surface, without the need for a lamination process to obtain a pressure sensing element with stable adhesion, solving the problem of wrinkles or peeling of traditional flexible diaphragms on curved surfaces. At the same time, the polyimide insulating structure not carbonized around the pressure sensing element plays a protective role, further improving the reliability of the graphene-elastic body composite pressure sensor of the present application when subjected to external impact.

[0028] 4. The present application forms a dense array of porous graphene structures on the polyimide insulating layer by laser processing, and the non-carbonized area forms an insulating isolation structure to avoid signal crosstalk, thereby realizing high-resolution real-time acquisition of surface pressure distribution, suitable for applications such as robot touch, wearable devices, and surface pressure imaging of intelligent aircraft. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The flowchart of the preparation method provided for Example 1 of the present application.

[0030] Figure 2 The flowchart of the pressure sensor prepared by the preparation method provided for Example 1 of the present application.

[0031] Figure 3 The sensor resistance-pressure relationship curve graph of Example 1 of the present application

[0032] Figure 4 The sensor sensitivity-pressure change curve graph of Example 1 of the present application

[0033] Figure 5 The linear regression results and sensitivity change trend graph of five different pressure ranges in Example 1 of the present application

[0034] Figure 6 The sensor resistance reciprocal-pressure relationship linear fitting graph in Example 1 of the present application

[0035] Figure 7 The measured pressure versus calculated pressure comparison curve graph in Example 1 of the present application

[0036] Figure 8 The sensor output voltage-temperature change curve graph under different cavity pressures in Example 1 of the present application

[0037] Figure 9 is a comparison curve graph of the electrical properties of the sensor before and after immersion in Example 1 of the present application

[0038] Figure 10 The flowchart of the pressure sensor prepared by the preparation method provided for Example 2 of the present application.

[0039] Figure 11A flow chart of a pressure sensor prepared by the method provided in Embodiment 3 of the present application.

[0040] Reference numerals: 1, substrate; 2, conductive layer; 3, porous graphene structure; 4, polyimide insulating structure 4; 5, encapsulation layer. DETAILED DESCRIPTION

[0041] The present application is further described below in conjunction with the accompanying drawings.

[0042] Embodiment 1

[0043] As shown in FIG. 1, a method for preparing a graphene- elastomer composite pressure sensor includes the following steps: Figure 1

[0044] Step 1: Prepare a conductive layer 2 on the front side of the substrate 1. The conductive layer 2 includes a signal transmission structure and two electrodes (only the electrodes are shown in the figure, and the signal transmission structure is not shown) arranged at intervals. The two electrodes are led out to the external interface through the signal transmission structure.

[0045] In this embodiment, the conductive layer 2 is prepared in the following manner:

[0046] Step 1: After the substrate 1 is cleaned with ethanol or isopropanol, dried with nitrogen, and subjected to plasma surface activation treatment, a silver nanometer conductive ink with a solid content of 20-40 wt% is deposited on the target area according to the preset electrode pattern using an inkjet printing device or a fine screen printing process; after deposition, pre-baking is performed at 40-80 °C to remove the solvent and stabilize the pattern. Subsequently, optical sintering is performed using a pulsed xenon lamp or a flash light source, and the light pulse energy density is about 2-8 J / cm 2 , so that the silver nanoparticles are instantaneously sintered and form a continuous metal conductive network. If necessary, thin layer electroplating (such as copper plating or nickel-gold plating, with a thickness of 1-10 μm) can be performed on the sintered metal pattern to improve corrosion resistance and underwater stability, thereby obtaining the conductive layer 2. The finally formed conductive layer 2 has good continuity, adhesion, and conductivity, and can serve as a carrier for the subsequent graphene-elastomer composite sensitive layer.

[0047] Step 2: Mix a polyamic acid resin with a solid content of 15 wt% and N-methyl pyrrolidone (NMP) solvent at a mass ratio of 4:1, thoroughly stir and ultrasonically degas, and then filter to obtain a polyamic acid (PAA) solution. Spray the polyamic acid solution on the substrate 1 with the conductive layer 2 in a pneumatic atomization manner to form a uniform polyamic acid film layer. In the pneumatic atomization spraying, the nozzle diameter is 0.3 mm, the spraying distance is 100 mm, the rate is 0.5 mL / min, and the uniform polyamic acid film layer is formed after reciprocating spraying 3-5 times at 25 °C and a humidity of 50%. The polyamic acid serves as a prepolymer of polyimide.

[0048] ​Step three, place the shell substrate with the polyamide acid film layer into an oven, first dry at 80°C for 30 min to remove the solvent, then cure at 300°C for 1 h to complete the imidization, forming a polyimide (PI) insulation layer with a thickness of 10 μm. In some other embodiments, the thickness of the polyimide insulation layer can also take other values between 5 μm and 15 μm, such as 5 μm, 15 μm.

[0049] Step four, place the substrate 1 with the polyimide insulation layer into an infrared pulsed laser processing device. Set the infrared pulsed laser processing parameters: wavelength 1064 nm, spot size 50 μm, frequency 30 kHz, power density 1.5 ×10 4 W / cm 2 Laser scanning processing is performed on the polyimide insulation layer. The range and path of laser scanning processing are adjusted according to the pre-set sensing structure size. In the laser processing, the polyimide insulation layer is instantaneously pyrolyzed by laser irradiation to form a conductive porous graphene structure 3, while the area not irradiated by the laser remains insulating, forming a polyimide insulation structure 4 surrounding the porous graphene structure 3. The porous graphene structure 3 formed by carbonization is electrically connected to the two electrodes of the corresponding external interface on the conductive layer 2. The resistance of the porous graphene structure 3 can be measured through the two electrodes.

[0050] In this step, since the porous graphene structure 3 is formed in situ on the polyimide insulation layer by pyrolysis, the porous graphene structure 3 and the polyimide structure are integrated structures within the same height range. The polyimide structure surrounds the porous graphene structure 3, providing insulation protection around the porous graphene structure 3 while also providing protection for the porous graphene structure 3.

[0051] In this embodiment, only one independent porous graphene structure 3 is formed in the polyimide insulation layer.

[0052] Step five, mix PDMS (polydimethylsiloxane) precursor, hydrogen-containing silicon crosslinking agent and Pt catalyst to obtain elastomer prepolymer solution. The mass ratio of PDMS precursor and hydrogen-containing silicon crosslinking agent is 10:1. After degassing the elastomer prepolymer solution, the elastomer prepolymer solution is drop-coated on the surface of the porous graphene structure 3 to form a film, so that the elastomer prepolymer solution penetrates into the pores of the porous graphene structure 3. Then, after curing at 80 °C for 2 h, the elastomer prepolymer solution in the pores of the porous graphene structure 3 forms an elastic filling structure. The elastic filling structure and the porous graphene structure 3 are embedded in the same space and form a pressure sensing element of the graphene-elastomer composite structure. The thickness of the pressure sensing element is 30 μm. In the pressure sensing element, the lower 15 μm is the porous graphene structure filled with PDMS elastomer, and the upper 15 μm is the PDMS elastomer layer covering the outer surface of the porous graphene structure. Therefore, the finally formed graphene-elastomer composite layer will be thicker than the porous graphene structure 3.

[0053] In some embodiments, the elastomer prepolymer solution is only drop-coated on the porous graphene structure 3. In some other embodiments, the elastomer prepolymer solution is drop-coated to cover the entire front surface of the substrate 1.

[0054] Step six, encapsulate the pressure sensing element and the conductive layer 2.

[0055] 6-1. Clean and dry the substrate 1 on which the pressure sensing element and the conductive layer 2 are formed, so as to improve the adhesion and uniformity of the subsequent coating layer.

[0056] 6-2. Spray polyurethane-siloxane type coating on the entire front surface of the substrate 1 on which the pressure sensing element and the conductive layer 2 are arranged. Use 365 nm ultraviolet light to irradiate for 10 min, so that the coating is cured to form an encapsulation layer 5 with a thickness of 5 μm. The encapsulation layer 5 has the characteristics of softness, transparency and water and corrosion resistance, which can effectively prevent ion penetration and mechanical wear and ensure the long-term stable output of the pressure sensing element.

[0057] In some embodiments, the polyurethane-siloxane type coating includes a main agent, a diluent and a photoinitiator. The mass ratio of the main agent, the diluent and the photoinitiator is 10:3:1.

[0058] The substrate 1, the conductive layer 2, the pressure sensing element and the encapsulation layer 5 prepared in this embodiment constitute a composite pressure sensor. When the composite pressure sensor is subjected to extrusion pressure, the pressure sensing element of the graphene-elastic body composite structure will be deformed, thereby changing the electrical properties of the porous graphene structure 3, so that the resistance of the pressure sensing element changes. When the extrusion pressure is removed, the presence of the elastic body allows the pressure sensing element to return to its original state. It can be seen that the pressure sensing element formed in situ in the polyimide insulating layer in this embodiment has piezoresistive properties and can be used for accurate detection.

[0059] In this embodiment, the front surface of the substrate 1 is a planar structure, and the structure of the graphene-elastic body composite pressure sensor prepared is as shown in Figure 2

[0060] The composite pressure sensor prepared in this embodiment was tested for performance, including absolute accuracy test, response time test, working temperature range test and waterproof performance test, as follows:

[0061] 1. Absolute accuracy test

[0062] 1.1 Test principle

[0063] This test aims to verify the electrical response characteristics of the composite pressure sensor and establish a resistance-pressure relationship model to realize the quantitative conversion of the sensing signal to pressure value. The output signal data of the sensor is converted to digital quantity by a voltage dividing circuit, with a range of output signal data = 0-4095, and the corresponding output voltage V is:

[0064] V = data / 4095 x 3.3 (1)

[0065] According to the voltage dividing characteristics, the resistance value R of the sensor can be obtained:

[0066] R = data / (4096-data) x 180kΩ (2)

[0067] The force response of the sensor can be approximated as an inverse relationship model:

[0068] F = K / R (3)

[0069] Wherein: F is the pressure (Pa), specifically the pressure generated by the external force on the sensor; R is the resistance of the sensor (Ω), obtained by converting the output data; K is the proportionality constant (Pa·Ω), obtained by calibration.

[0070] By fitting and analyzing the measured pressure and resistance data, the sensitivity and linearity characteristics of the sensor in different pressure intervals can be obtained to complete the calibration of electrical performance and sensitivity evaluation.

[0071] 1.2 Test device and method​

[0072] To comprehensively evaluate the static electrical properties and force response characteristics of graphene-elastomer composite pressure sensors, a controllable and highly accurate pressure loading and signal acquisition system with strong repeatability was built. The system includes a graphene-elastomer composite pressure sensor, a rigid fixture, a hot press, a precision digital pressure gauge, a pressure regulating valve, and a two-way valve. The graphene-elastomer composite pressure sensor is fixed in the groove at the bottom of the rigid fixture and is stably and uniformly loaded by the hot press down pressure device. The host computer control end records the sensor output data in real time and synchronously collects the pressure signal with the precision digital pressure gauge. The system adjusts the gas pressure through the pressure regulating valve and controls the gas in and out of the cavity through the two-way valve to accurately control the pressure loading rate and constant pressure time. During the test, a constant temperature environment (25±1℃) is maintained to eliminate the influence of temperature drift, and each level of loading is maintained for 10s to ensure stability.

[0073] The test procedure is as follows:

[0074] 1. Place the graphene-elastomer composite pressure sensor on the test platform and fix it with the rigid fixture;

[0075] 2. Start the hot press down pressure mechanism to ensure uniform force;

[0076] 3. Close the two-way valve and gradually increase the gas pressure in the cavity through the pressure regulating valve;

[0077] 4. Read the pressure signal in real time through the digital pressure gauge and synchronously collect the resistance output;

[0078] 5. Establish the pressure-resistance correspondence curve;

[0079] 6. Perform nonlinear fitting and sensitivity segmentation calculation on the experimental data.

[0080] The hot press can achieve continuous adjustable loading in the range of 0-200kPa, with a resolution better than 10Pa and an absolute accuracy >10hPa, meeting the electrical performance calibration requirements of graphene-elastomer composite pressure sensors.

[0081] 1.3 Test results and analysis

[0082] (1) Fitting curve and sensitivity characteristics

[0083] Based on the collected experimental data, nonlinear fitting analysis was performed on the sensor resistance output, and the results are shown in Figure 3 It can be seen that the sensor output resistance decreases monotonically with the increase of external loading pressure. In the low pressure region (0-20kPa), the curve slope is larger and the sensitivity is higher; in the high pressure region (>80kPa), the curve gradually tends to be flat and the sensitivity decreases, which reflects the typical flexible resistance pressure sensitive response characteristics.

[0084] Figure 3 The blue dots are experimental data, and the red curve is the optimal fitting result. The two are highly consistent, with a best linear fit goodness of R2=0.998, indicating that the model can accurately reflect the force-electric response relationship of the sensor. Further calculation of the sensitivity curve with pressure change ( Figure 4 ) shows that the sensitivity rises rapidly in the low pressure zone, and then gradually decreases with increasing pressure. This indicates that the graphene-elastic body composite pressure sensor has higher resolution in small pressure detection scenarios (such as touch sensing or flow field disturbance monitoring), and shows stable response output in high pressure zone.

[0085] The overall sensitivity curve shows an exponential decay trend, which is consistent with the compression saturation and interface contact characteristics of the graphene-elastic body composite pressure sensor.

[0086] (2) Piecewise linearity and K value solving

[0087] To further analyze the linearity characteristics in different pressure intervals, the test interval is divided into five segments according to the change trend of the fitting curve. Linear regression analysis is performed on each interval to obtain the sensitivity constant K and the determination coefficient R2, and the results are shown in Table 1.

[0088] Table 1 Sensitivity constant and fitting goodness of different pressure intervals

[0089] Interval number Pressure range (Pa) Number of samples K (Pa·Ω) R2 1 [100,12000] 18 2.62 x 10 7 ]] 0.987 2 [12000,20000] 18 7.45 x 10 7 ]] 0.972 3 [20000,37000] 18 1.04 x 10 8 ]] 0.954 4 [37000,80000] 18 1.58 x 10 8 ]] 0.989 5 [80000,200000] 18 3.21 x 10 8 ]] 0.946

[0090] As can be seen from the table, the fitting goodness of the five intervals is more than 0.94, indicating that the piecewise linear model can effectively describe the response law of the sensor in different pressure ranges. With the increase of pressure, the K value gradually increases, reflecting the decreasing trend of the equivalent sensitivity in high pressure zone. This phenomenon is mainly due to the compression saturation of the sensing unit and the weakening effect of the interface contact resistance.

[0091] Figure 5 In the middle, different color straight lines correspond to five linear intervals, and the slope change reflects the decreasing trend of sensitivity. The linear slope is the largest in the low pressure zone, and the response is the most sensitive; in the high pressure zone, the curve is slow, and the linear range is narrow.

[0092] In addition, Figure 6 shows the linear fitting result of the reciprocal of resistance and pressure, and its high correlation further verifies the correctness of the F=K / R model.

[0093] (3) Back calculation verification and model reliability analysis

[0094] Based on the Ki value of each interval, the pressure is calculated by the inverse calculation model , and compared with the measured pressure by double Y-axis analysis, as shown in Figure 7 .

[0095] The results show that the two curves have consistent trends and high coincidence in the full range, and the overall fitting goodness reaches R2=0.99. In the whole range, the maximum pressure error

[0096] Conclusion: The composite pressure sensor shows stable and repeatable electrical response characteristics in the range of 0-200 kPa, with a maximum absolute accuracy error of 780.6 Pa, less than 10 hPa (i.e. 1000 Pa). The resistance decreases significantly with increasing pressure, and the overall change rule is clear. The linear fitting determination coefficient of each pressure segment is higher than R2=0.94, and the correlation coefficient of the inverse calculated pressure and the measured pressure is about R=0.99, indicating that the established F=K / R force-electricity model can accurately describe the nonlinear response rule of the sensor. The test system runs stably and the data is consistent, and the model accuracy meets the performance calibration and batch consistency verification requirements of the graphene-elastic body composite pressure sensor.

[0097] 2 Response time test

[0098] 2.1 Test purpose

[0099] To evaluate the response speed and real-time performance of the composite pressure sensor under dynamic load, and verify its adaptability in fast pressure change conditions, the response time of the sensor is tested and analyzed to determine whether it can meet the real-time demand of monitoring the flow field disturbance and pulsating pressure of underwater vehicles.

[0100] 2.2 Test device and method

[0101] To accurately determine the response time of the sensor, a test platform composed of Raspberry Pi, power amplifier, piezoelectric actuator (PZT) and high-precision signal acquisition system is built. Raspberry Pi controls the piezoelectric actuator to generate mechanical displacement, and records the trigger timestamp of the driving signal at the same time; the computer side synchronously acquires the sensor output signal and records the response timestamp, and the response time can be obtained by calculating the time difference between the two. This method can effectively reduce system delay and sampling error.

[0102] The test process is as follows:

[0103] 1. Fix the sensor on the test platform and connect it to the PZT actuator controlled by Raspberry Pi;

[0104] 2. Record the initial output of the sensor in the unloaded state (about 500); ​

[0105] 3. Control the power amplifier output drive voltage through Raspberry Pi, trigger PZT to produce instantaneous displacement, and record the trigger time t1 at the same time;

[0106] 4. When the sensor detects a sudden change in pressure, the system automatically records the response time t2 ;

[0107] 5. Response time Δt = t2 - t1 ;

[0108] 6. Repeat the experiment several times and eliminate abnormal data to calculate the average response time.

[0109] 2.3 Test results and analysis

[0110] According to the force action start time t1 recorded by the program and the response time t2 of the sensor detecting the pressure change, the difference between the two is the response time of the sensor. Some raw data is listed in Table 2. After multiple tests and elimination of abnormal values, the average of the remaining valid data is taken, and the average response time of the graphene-elastomer composite pressure sensor is finally measured to be about 25.514 ms.

[0111] Table 2 Sensor response time test data

[0112] Serial number Response time t2 (s) Start time t1 (s) Time difference Δt (s) 1 1760502126.526810 1760502126.498762 0.028048 2 1760502245.862843 1760502245.837491 0.025352 3 1760502366.493117 1760502366.473926 0.019191 4 1760502487.411837 1760502487.382045 0.029792 5 1760502605.949328 1760502605.926574 0.022754 6 1760502726.067831 1760502726.038492 0.029339 7 1760502845.692574 1760502845.672943 0.019631 8 1760502966.412038 1760502966.384726 0.027312 9 1760503085.941873 1760503085.917462 0.024411 10 1760503206.577638 1760503206.549327 0.028311

[0113] After repeated testing and elimination of abnormal values, the average response time of the graphene-elastomer composite pressure sensor is calculated to be about 25.5 ms. The results show that the sensor has a fast response to external load changes, with smooth signal rising edge and no significant oscillation, indicating rapid internal electrical conductance channel change and stable electrode contact. Compared with traditional polymer-based resistive sensors, it has faster response speed and higher signal consistency.

[0114] 2.4 Conclusion

[0115] The experimental results show that the average response time of the composite pressure sensor is about 25.5 ms, with rapid response and good repeatability, which can meet the real-time requirements of underwater vehicle surface transient pressure disturbance monitoring. The results verify the excellent time response performance of the sensor in dynamic pressure environment, providing data support for its application in high-speed flow field measurement and tactile recognition scenarios.

[0116] 3. Test of working temperature range

[0117] 3.1 Purpose of the test

[0118] To verify the output stability and temperature drift performance of the composite pressure sensor under different temperature conditions, and evaluate its reliability in underwater environment, the response characteristics of the sensor output with temperature change were tested under multiple constant cavity pressures to analyze the temperature drift law and determine the effectiveness of the temperature compensation design.

[0119] 3.2 Test method

[0120] In the experiment, the sensor was fixed and installed on a loading platform with temperature control function, and a constant pressure gas loading method was used. The cavity pressure was set to 1-10 kPa, divided into ten pressure intervals. The temperature control range was -25-70°C, and the output signal was collected after each temperature point was kept stable for 5 min.

[0121] The signal acquisition was performed using a high-precision voltage acquisition module, and each group of data was recorded 10 times and averaged to reduce random noise. The criteria are as follows: if the output signal fluctuates less than ±1% with temperature change under the same cavity pressure, and no obvious monotonic change trend is shown, the sensor is considered to have no significant temperature drift in this temperature range.

[0122] The structure of the experimental device is as follows: the sensor body is installed above the fixture, and the temperature sensing wire is built in the cavity. The system is composed of multiple temperature inspection instruments, precision pressure gauges, pressure regulating valves and two-way valves to realize synchronous temperature and pressure control and real-time monitoring

[0123] 3.3 Test results and analysis

[0124] Figure 8 The curves of the average output voltage of the sensor with temperature change under different cavity pressures (1-10 kPa) are shown. The data of each group is basically parallelly distributed, and no obvious rising or falling trend is shown, indicating that the output of the sensor is not sensitive to temperature change.

[0125] The quantitative analysis results show that the output fluctuation amplitude of each pressure group in the whole temperature range is less than ±0.8%, and the linear fitting slope is close to 0, indicating that the temperature change has little effect on the output. The small deviation between different pressure groups is mainly due to the gas pressure disturbance, and the contribution of temperature factor can be ignored.

[0126] The results show that the sensor has excellent temperature stability in the range of -25-70°C, the performance of the sensitive layer and electrode interface is stable in this range, and the thermal expansion coefficients of the flexible substrate PDMS and the graphene / silver nanowire composite sensitive layer are well matched, effectively suppressing the thermal strain coupling effect.

[0127] 3.4 Conclusion

[0128] The experimental results show that the output signal of the composite pressure sensor is stable and has no obvious drift in the temperature range of-25~70°C. The voltage-temperature curve is smooth and the fluctuation range is less than ±1%, which verifies the effectiveness of the temperature compensation design of the device. Due to the use of flexible composite film structure and metal / polymer conductor optimization, the temperature response of the sensor mainly shows random noise fluctuation rather than systematic drift, and the overall thermal stability is good, which can meet the temperature adaptability requirements of underwater vehicles in long-term operation environment.

[0129] 4. Waterproof performance test

[0130] 4.1 Purpose of test

[0131] To evaluate the reliability and sealing performance of graphene-elastomer composite pressure sensor in long-term underwater environment, this experiment aims to verify its waterproof ability and the stability of electrical performance after immersion, to ensure that the sensor has good service life and data stability under the target working condition.

[0132] 4.2 Test method and process

[0133] To test the resistance and stability of graphene-elastomer composite pressure sensor under water, the sample is completely immersed in clean water for 24 hours. After taking it out, wipe the surface water with absorbent paper, and repeat the measurement under the same loading conditions as the "basic electrical performance test". By comparing the electrical response curves before and after immersion, the performance change after long-term work under water is quantitatively analyzed.

[0134] The test process is as follows:

[0135] 1. The graphene-elastomer composite pressure sensor sample is completely immersed in water and kept stationary for 24 hours;

[0136] 2. After taking it out and wiping the surface water, install it on the test platform;

[0137] 3. Repeat the test under the same environmental and loading conditions as Experiment 1 (basic electrical performance test);

[0138] 4. Fit and compare the two sets of test data to evaluate the change in electrical performance;

[0139] 5. According to the change rate and the difference of the fitting curve, judge its waterproof and stability performance.

[0140] 4.3 Test results and analysis

[0141] Figure 9The performance comparison results of the graphene-elastomer composite pressure sensor before and after immersion treatment are shown. Among them, the red curve represents the test data before immersion, and the orange curve represents the test data after immersion. It can be seen that the two curves are highly coincident in the full range, the response trend of the sensor output resistance with pressure change remains consistent, and only a slight fluctuation exists in the low pressure segment, with a change amplitude less than 1%.

[0142] It is shown that after 24 h of immersion, the electrical performance of the sensor does not show significant drift or degradation, indicating that the sensitive layer, electrode layer and packaging layer structure remain stable under long-term immersion conditions. The interface between the PET waterproof film and the PDMS elastic layer is well combined, effectively preventing electrode corrosion or resistance mutation caused by water penetration.

[0143] 4.4 Test Conclusion

[0144] The comprehensive analysis results show that the graphene-elastomer composite pressure sensor maintains stable performance after 24 h of underwater immersion, and its resistance-pressure response curve is almost identical to the initial state, indicating that the device has good waterproof sealing and environmental stability. The sensor as a whole meets the IP67 level requirement and is suitable for long-term underwater use or monitoring application in humid environments.

[0145] Example 2

[0146] A graphene-elastomer composite pressure sensor preparation method, the difference between this embodiment and example 1 is that the front surface of the substrate 1 is a curved surface structure, and each step is the same as example 1. The structure of the graphene-elastomer composite pressure sensor prepared is as shown in Figure 10 The curved surface structure of the substrate 1 does not affect the formation and adhesion of the pressure sensing element, because the polyimide insulating layer is formed by spraying a polyamide acid solution on the substrate 1 and then curing.

[0147] Example 3

[0148] An array type graphene-elastomer composite pressure sensor preparation method, the difference between this embodiment and example 1 is that:

[0149] In step one, the conductive layer 2 prepared on the front surface of the substrate 1 includes a plurality of sensing connection sites. Each sensing connection site includes two electrodes arranged at intervals. The electrodes are led out to the external interface through a signal transmission structure. At least one electrode in each sensing connection site is led out through an independent signal transmission structure, so that each can independently detect the electrical signal.

[0150] In step four, thermal decomposition occurs within the polyimide insulating layer, forming an array of porous graphene structures 3 spaced apart. Each structure is connected to a corresponding sensing connection site. Regions within the polyimide insulating layer that do not undergo thermal decomposition form a mesh-like polyimide insulating structure 4. The different porous graphene structures 3 are separated by the polyimide insulating structure 4.

[0151] In step five, the elastomer prepolymer solution is drop-coated to cover the entire front surface of the substrate 1, allowing the elastomer prepolymer solution to penetrate all the porous graphene structures 3. After the elastomer prepolymer solution cures, the pores of each porous graphene structure 3 are filled with elastomer. Each elastomer-filled porous graphene structure 3 forms a pressure sensing unit. Multiple pressure sensing units form a pressure sensing array.

[0152] In some embodiments, the center-to-center distance between adjacent pressure sensing units is 0.8 mm to 3 mm. The array density of pressure sensing units in the pressure sensing array is 10 to 150 units / cm². 2 Each pressure sensing unit is 0.3mm to 1.5mm long and 0.2mm to 1mm wide.

[0153] In some embodiments, the front surface of the substrate 1 is a curved structure. Based on the fabrication method provided in this embodiment, which enables in-situ fabrication of pressure sensing elements on curved surfaces, the curved shells of various devices can be directly used as the substrate 1, thereby obtaining a shell structure capable of sensing external pressure distribution. This shell structure can serve as the shell of aircraft or underwater vehicles, facilitating the sensing of airflow changes in the air or waterflow changes in the water.

[0154] The structure of the graphene-elastomer composite pressure sensor prepared in this embodiment is as follows: Figure 11 As shown.

Claims

1. A method for preparing a graphene-elastomer composite pressure sensor, characterized in that: include: A polyimide insulating layer is formed on the substrate (1); Laser processing is performed on the polyimide insulating layer to carbonize the polyimide irradiated by the laser, forming a porous graphene structure (3). An elastomer prepolymer solution is introduced into the pores of the porous graphene structure (3); The elastomer prepolymer solution is cured in the pores of the porous graphene structure (3) to form a pressure sensing element with a graphene-elastomer composite structure.

2. The method for preparing a graphene-elastomer composite pressure sensor according to claim 1, characterized in that: The process of introducing an elastomer prepolymer solution into the pores of the porous graphene structure (3) is as follows: the elastomer prepolymer solution is drop-coated onto the porous graphene structure (3) to form a film, so that the elastomer prepolymer solution penetrates into the pores of the porous graphene structure (3).

3. The method for preparing a graphene-elastomer composite pressure sensor according to claim 2, characterized in that: The elastomer prepolymer solution comprises a mixture of PDMS precursor and crosslinking agent; the elastomer prepolymer solution is crosslinked and cured by heating.

4. The method for preparing a graphene-elastomer composite pressure sensor according to claim 1, characterized in that: Before forming a polyimide insulating layer on the substrate (1), a conductive layer (2) for deriving electrical signals from the pressure sensing element is mounted or formed on the substrate (1).

5. The method for preparing a graphene-elastomer composite pressure sensor according to claim 4, characterized in that: The conductive layer (2) is provided with independent sensing connection positions; each sensing connection position includes two electrodes spaced apart; a porous graphene structure (3) is laser-processed on each sensing connection position and an elastomer is introduced to form a pressure sensing element unit. Different pressure sensing element units are separated by a polyimide insulating structure (4) to form a pressure sensing array.

6. The method for preparing a graphene-elastomer composite pressure sensor according to claim 1, characterized in that: After the pressure sensing element is formed, a non-conductive coating is applied to the pressure sensing element. The coating cures to form an encapsulation layer.

7. The method for preparing a graphene-elastomer composite pressure sensor according to claim 1, characterized in that: The process of generating the polyimide insulating layer is as follows: a polyamic acid solution is sprayed onto the substrate (1) to form a polyamic acid film layer; after drying and solvent removal, heat treatment is performed to imidize the polyamic acid and form a polyimide insulating layer; the thickness of the polyimide insulating layer is 5 μm to 15 μm.

8. The method for preparing a graphene-elastomer composite pressure sensor according to claim 1, characterized in that: The power density of the laser processing is 5×10 4 W / cm 2 ~1 ×10 6 W / cm 2 The areas of the polyimide insulating layer that are not irradiated by the laser remain in an insulating state, forming a polyimide insulating structure (4) surrounding the porous graphene structure (3).

9. The method for preparing a graphene-elastomer composite pressure sensor according to claim 1, characterized in that: The substrate forms a curved surface structure on the side of the pressure sensing element.

10. A graphene-elastomer composite pressure sensor, characterized in that: It is prepared by the preparation method described in claim 1.

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