Method for preparing multi-scale porous wrinkled dielectric layer and capacitive pressure sensor

Abstract

The application discloses a preparation method of a multi-scale porous wrinkled dielectric layer and a capacitive pressure sensor, and the method comprises the following steps: S1, adding single-layer reduced graphene oxide, polydimethylsiloxane and isopropyl alcohol into a beaker according to the mass ratio of (0.025-0.035):1:(10-15); S2, placing the mixed solution into a magnetic stirring device to continuously stir for 1h at 85 DEG C, and then placing the mixed solution into an oven at 85 DEG C for 12-16h, monitoring the mass change of isopropyl alcohol until the mass fraction of isopropyl alcohol is 10%-15%, and then adding a PDMS curing agent into the beaker; S3, pouring the mixed solution into a mold, and after the surface is leveled, placing the mold into an oven to cure for 1h, and the curing temperature needs to be greater than the boiling point of isopropyl alcohol, and a pore structure and a wrinkled structure are spontaneously formed. The method can spontaneously form a multi-scale pore structure in the dielectric layer and a wrinkled structure on the surface by strictly controlling the addition amount of isopropyl alcohol and reduced graphene oxide and reasonably controlling the curing temperature, and the method has the advantages of low preparation cost, high forming rate, stable sensing effect and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flexible capacitive sensing, and particularly relates to a preparation method of a multi-scale porous wrinkled dielectric layer and a capacitive pressure sensor. BACKGROUND

[0002] Compared with piezoresistive or piezoelectric sensors, the existing capacitive pressure sensor is more sensitive to the small changes of the medium layer or the electrode spacing (such as pressure, strain, etc.), has strong anti-environmental interference ability, and does not need complex external signals, so it has been widely concerned by existing researchers. In recent years, researchers have constructed capacitive sensing structures on flexible substrates, especially by introducing a biomimetic design with multi-scale microstructure into the electrode or the medium layer to realize the coexistence of high sensitivity and wide range of the sensor.

[0003] With the continuous development of micro-nano manufacturing technology and new flexible materials, how to obtain multi-scale structures while simplifying the process has become a key issue for preparing high-performance biomimetic flexible capacitive pressure sensors. For capacitive sensors, the main methods for obtaining surface wrinkled structures and internal hole structures are photolithography template method and solid template sacrifice method; however, both methods require high cost and expensive precision machining instruments, which is not conducive to the preparation and development of flexible capacitive pressure sensors.

[0004] In recent years, researchers generally choose water-soluble solids such as NaCl and NaHCO3 with higher mesh number as the sacrificial template material for preparing porous dielectric layers, but a large number of research results show that its range for improving the sensitivity of the sensor is limited. Liquid sacrificial templates such as isopropyl alcohol can quickly evaporate to trigger phase separation when the substrate is solidified, and then realize uniform hole structure, but its forming rate is poor and the sensing effect is unstable. At the same time, existing research generally uses one-dimensional materials (such as multi-walled carbon nanotubes (MWCNTs) and the like) to improve the dielectric constant, but one-dimensional carbon materials have high aspect ratio and are easy to agglomerate in the matrix, and the effect needs to be considered. Compared with one-dimensional materials, two-dimensional carbon materials (such as reduced graphene oxide) have a two-dimensional sheet structure, and the layers are easy to stack and can tightly fit with the matrix and form a polarization effect of multiple interfaces, which is a more suitable conductive filler for improving the dielectric constant. Therefore, if two-dimensional carbon materials and liquid sacrificial templates can be integrated in the preparation of capacitive sensor devices, a forming method of multi-scale microstructure of dielectric layer with high forming rate and easy preparation can provide new possibilities for improving the sensitivity of existing flexible pressure sensors. SUMMARY

[0005] In view of the shortcomings and deficiencies of the prior art, the purpose of the present application is to provide a preparation method of a multi-scale porous wrinkled dielectric layer which can be spontaneously formed, so as to solve the technical problems of high preparation cost, poor forming rate and unstable sensing effect of the existing dielectric layer with microstructure.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] A preparation method of a multi-scale porous wrinkled dielectric layer, comprising the following steps:

[0008] S1. Add single-layer reduced graphene oxide, polydimethylsiloxane and isopropyl alcohol into a beaker according to a mass ratio of (0.025-0.035):1:(10-15), and record the mass of the added single-layer reduced graphene oxide, polydimethylsiloxane and isopropyl alcohol, respectively;

[0009] S2. Put the mixed solution into a magnetic stirrer for continuous stirring at 85℃ for 1h, and then place it in an oven at 85℃ for 12-16h to evaporate the excess isopropyl alcohol, monitor the mass change of the isopropyl alcohol, and when the mass fraction of the isopropyl alcohol is 10%-15%, add a PDMS curing agent into the beaker and stir at room temperature by magnetic force;

[0010] S3. Pour the mixed solution into a 20mm*20mm*(0.3-0.7)mm thick mold, and after the surface is leveled, place the mold in an oven for curing for 1h, and the curing temperature needs to be higher than the boiling point of isopropyl alcohol to ensure that the isopropyl alcohol is completely boiled and evaporated, so that the hole structure is spontaneously formed in the dielectric layer, and the wrinkle structure is spontaneously formed on the surface.

[0011] As a preferred embodiment of the present application, the mass ratio of polydimethylsiloxane to PDMS curing agent in step S2 is 10:1, and the curing temperature in step S3 is controlled between 85℃ and 95℃.

[0012] As a preferred embodiment of the present application, before adding the PDMS curing agent in step S2, the mass fraction of the single-layer reduced graphene oxide is controlled to be 3%, the mass fraction of the isopropyl alcohol is controlled to be 10%, and the mass fraction of the polydimethylsiloxane is controlled to be 87%.

[0013] The present application also provides a capacitive pressure sensor, which comprises a silica gel damping layer, an upper bionic microstructure conductive electrode plate, a lower bionic microstructure conductive electrode plate, a multi-scale porous wrinkled dielectric layer and a lead wire; wherein the upper bionic microstructure conductive electrode plate and the lower bionic microstructure conductive electrode plate are made of polyethylene terephthalate or polyimide film, the surface of the side of the upper bionic microstructure conductive electrode plate and the lower bionic microstructure conductive electrode plate in contact with the multi-scale porous wrinkled dielectric layer is distributed with bionic spine-like microstructures, and a conductive contact layer is arranged by spraying, the sheet resistance of the contact layer is 3.0-5.0Ω / m2; the surface of the multi-scale porous wrinkled dielectric layer is distributed with wrinkle structures, and the inside is distributed with hole structures.

[0014] As a preferred embodiment of the present application, the thickness of the silica gel damping layer is 0.5 mm, the thickness of the biomimetic upper microstructure conductive electrode plate and the biomimetic lower microstructure conductive electrode plate is 0.125-0.15 mm, and the thickness of the multi-scale porous wrinkled dielectric layer is controlled to be 0.3-0.7 mm.

[0015] As a preferred embodiment of the present application, the biomimetic spine-like microstructure distributed on the surface of the biomimetic upper microstructure conductive electrode plate and the biomimetic lower microstructure conductive electrode plate is a spine-like microstructure mimicking the spider leg tactile hair receptor, and the height of the spine-like microstructure is 100-150 μm, which is connected by two fitting curves, and the formulas of the two fitting curves are as follows:

[0016] f 1( x )=[-3.784* e ^( -x 2 )-1.392* x 2 -3.152] / 1000, wherein: -1 x <0;

[0017] f 2( x )=[3.784* e ^( x 2 )+1.392* x 2 -3.152] / 1000, wherein: 0 x <1.

[0018] As a preferred embodiment of the present application, the spraying method of the contact layer is that a mixed solution of 10 mg / mL silver nanowire solution and 20% mass fraction of nano-indium tin metal oxide solution is sprayed on the contact surface of the biomimetic upper microstructure conductive electrode plate, the biomimetic lower microstructure conductive electrode plate and the multi-scale porous wrinkled dielectric layer, the mass ratio of the two is 1:1, 1.5 mL is sprayed each time, and the sprayed layer is dried at 60°C for 30 min, the spraying is repeated for 5-10 times, until the square resistance of the contact layer reaches 3.0-5.0 Ω / m2.

[0019] As a preferred embodiment of the present application, the multi-scale porous wrinkled dielectric layer is prepared by the preparation method of the multi-scale porous wrinkled dielectric layer described above.

[0020] As a preferred embodiment of the present application, the surface of the multi-scale porous wrinkled dielectric layer is distributed with wrinkled structures with a height of 100-200 nm and a diameter of 70-150 nm, and the inner portion is distributed with hole structures with a diameter of 200-400 nm.

[0021] The capacitive pressure sensor has good stability, durability and repeatability, high sensitivity, suitable sensing range and can meet the requirements of the corn high-speed precision sowing monitoring field, and can be applied to a sowing monitoring system.

[0022] Advantages and beneficial effects of the present application:

[0023] (1) The present application provides a preparation method for spontaneously forming two kinds of microstructure dielectric layers, which introduces isopropyl alcohol and single-layer reduced graphene oxide as a sacrificial template and dielectric filler in the PDMS main agent, and by strictly controlling the addition amount of isopropyl alcohol and reduced graphene oxide and reasonably controlling the curing temperature, a multi-scale pore structure can be spontaneously formed in the dielectric layer, and a wrinkle structure is formed on the surface. Compared with other existing preparation methods, this method has low preparation cost, does not need to use other microstructure templates, has high forming rate, stable sensing effect and good reliability (the capacitance change rate curve is relatively stable in 60000 excitation cycles, and the baseline drift degree is 1.35% after 30000 cycles).

[0024] (2) The scientific mechanism of the dielectric layer forming two kinds of microstructures provided by the present application is as follows: the added single-layer rGo carbon material has a large specific surface area and a certain sheet rigidity. In the rGO / PDMS system, when the PDMS is cured in the mold, the surface of the PDMS is cured first, and the lower layer is cured later, which makes the difference between the elastic modulus of the upper and lower layers large, and the surface instability phenomenon is easily generated, and then the wrinkle phenomenon is generated on the curing surface. In the IPA / rGO / PDMS ternary system, since the oven curing temperature is between 85-95℃, which is much higher than the boiling point of IPA, the rapid evaporation of IPA makes the system concentration increase significantly, triggering the solvent-induced phase separation phenomenon. This phenomenon can make the IPA phase present in the form of droplets and evaporate outward, and then form a larger pore structure in the system. At the same time, the rGO particles will play the role of "anchor point" when evaporating, that is, the Pickering emulsion stabilization phenomenon occurs, and then the evaporation rate of IPA is slowed down, so that the stable pore structure is generated. Therefore, the IPA / rGO / PDMS three work together, and finally the dielectric layer spontaneously forms two kinds of microstructures.

[0025] (3) The dielectric layer in the capacitive pressure sensor provided by the present application is a multi-scale porous wrinkle structure. The dielectric layer introduces two kinds of microstructures, further improves the difference of stress unevenness and local elastic modulus, and then ensures the sensitivity and response time of the sensor. In addition, the bionic sharp spike microstructure existing on the surface of the upper and lower electrode plates can significantly reduce the lower limit of the sensor for detecting weak pressure, further improve the sensitivity of the sensor, and the silver nanowire (AgNWs) solution used in the upper and lower electrode plates has very high conductivity, so the response time is fast.

[0026] (4) The pressure sensing device provided by the application has high sensitivity, a suitable sensing range, good stability, durability and repeatability, and can meet the requirements of the corn high-speed precision sowing monitoring field, and is the most suitable choice for realizing high-speed precision sowing signal monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The figures are electron micrographs of the surface morphology of the dielectric layer obtained by different test combinations, wherein (a) is 1% rGO+10% IPA; (b) is 1% rGO+15% IPA; (c) is 1% rGO+20% IPA; (d) is 2% rGO+10% IPA; (e) is 2% rGO+15% IPA; (f) is 2% rGO+20% IPA; (g) is 3% rGO+10% IPA; (h) is 3% rGO+15% IPA; and (i) is 3% rGO+20% IPA;

[0028] Figure 2 The figures are electron micrographs of the cross-sectional morphology of the dielectric layer obtained by different test combinations, wherein (a) is 1% rGO+10% IPA; (b) is 1% rGO+15% IPA; (c) is 1% rGO+20% IPA; (d) is 2% rGO+10% IPA; (e) is 2% rGO+15% IPA; (f) is 2% rGO+20% IPA; (g) is 3% rGO+10% IPA; (h) is 3% rGO+15% IPA; and (i) is 3% rGO+20% IPA;

[0029] Figure 3 The figures are sensitivity characterization curves of the pressure sensing device under different test combinations;

[0030] Figure 4 The figures are test results of the 3% rGO+10% IPA pressure sensing device, wherein (a) is a sensitivity fitting curve; (b) is a micro-pressure sensing test; (c) is a dynamic response test; and (d) is a step test;

[0031] Figure 5 The figures are durability test results of the pressure sensing device under the optimal sensitivity (3% rGO+10% IPA);

[0032] Figure 6 The figures are optimal selection test results of the sensor device, wherein (a) is the monitoring error of the sensor device using different test combinations; and (b) is a bench sowing signal image of different devices under 10km / h and 20cm plant spacing. DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0034] The present application provides a capacitive pressure sensor, which comprises a silica gel damping layer, a biomimetic upper microstructure conductive electrode plate I, a biomimetic lower microstructure conductive electrode plate II, a multi-scale porous wrinkled dielectric layer III and a lead wire; wherein the thickness of the silica gel damping layer is 0.5 mm, which is used to improve the durability of the pressure sensor; the biomimetic upper microstructure conductive electrode plate I and the biomimetic lower microstructure conductive electrode plate II are PET (polyethylene terephthalate) or PI (polyimide) films with a thickness of 0.125-0.15 mm, the surface of the side of the biomimetic upper microstructure conductive electrode plate I and the biomimetic lower microstructure conductive electrode plate II in contact with the multi-scale porous wrinkled dielectric layer III is distributed with biomimetic spine-like microstructures, and a conductive contact layer is arranged by spraying, the sheet resistance (Rs) of the contact layer is 3.0-5.0 Ω / m2; the surface of the multi-scale porous wrinkled dielectric layer III is distributed with a wrinkled structure, and the inside is distributed with a hole structure, and the thickness is controlled to be 0.3-0.7 mm.

[0035] Further, in the embodiment, the biomimetic spine-like microstructures distributed on the surface of the biomimetic upper microstructure conductive electrode plate I and the biomimetic lower microstructure conductive electrode plate II are spine-like microstructures mimicking the spider leg tactile hair receptors, the height of the spine-like microstructures is 100-150 μm, which is connected by two fitting curves, and the formulas of the two fitting curves are as follows:

[0036] f 1( x )=[-3.784* e ^( -x 2 )-1.392* x 2 -3.152] / 1000, wherein: -1 x <0;

[0037] f 2( x )=[3.784* e ^( x 2 )+1.392* x 2 -3.152] / 1000, wherein: 0 x <1;

[0038] The bionic sharp spike microstructure is arranged to reduce the contact area of the upper and lower electrode plates, and can amplify the input signal, thereby significantly improving the sensitivity of the sensor. Specifically, the processing method of the conductive electrode plate with the bionic sharp spike microstructure on the surface is as follows: the A-PET sheet (amorphous PET) is heated to 95-120°, and then poured into a mold with the bionic sharp spike microstructure; then cooled, and the PET film can be taken out after solidification.

[0039] Further, in the embodiment, the spraying method of the contact layer is as follows: a mixed solution (mass ratio 1:1) of a 10 mg / mL silver nanowire (AgNWs) solution and a 20% mass fraction of a nanometer indium tin metal oxide (ITO) solution is sprayed on the contact surface of the bionic upper microstructure conductive electrode plate I, the bionic lower microstructure conductive electrode plate II and the multi-scale porous wrinkled dielectric layer III, 1.5 mL is sprayed each time, and the contact layer is dried at 60°C for 30 min after spraying, and the spraying is repeated 5-10 times until the square resistance of the contact layer reaches 3.0-5.0 Ω / square meter.

[0040] Further, in the embodiment, the multi-scale porous wrinkled dielectric layer III has a wrinkled structure with a height of 100-200 nm and a diameter of 70-150 nm, and an internal hole structure with a diameter of 200-400 nm. The wrinkled structure and the hole structure of the multi-scale porous wrinkled dielectric layer III are spontaneously formed by strictly controlling the addition amount of isopropyl alcohol (IPA), reduced graphene oxide and PDMS main agent during preparation, and the two microstructures (internal hole structure and surface wrinkled structure) can be obtained simultaneously without using other microstructure templates, and the preparation method is simple, low in cost and high in forming rate. Specifically, the preparation method comprises the following steps:

[0041] S1. Select a 50 mL empty beaker and a 10 cm long glass rod, and record the total mass m1 at this time;

[0042] S2. Add single-layer reduced graphene oxide (rGo), polydimethylsiloxane (PDMS main agent) and isopropyl alcohol (IPA) into the 50 mL beaker according to the mass ratio of (0.025-0.035):1:(10-15), and record the mass of the added single-layer reduced graphene oxide m2, the mass of the added polydimethylsiloxane (PDMS main agent) m3 and the mass of the added isopropyl alcohol (IPA) m4, respectively;

[0043] S3. Put the mixed solution into a magnetic stirrer and continuously stir at 85°C for 1 h, and then place it in an 85°C oven for 12-16 h to evaporate the excess isopropyl alcohol. The mass change of isopropyl alcohol is closely monitored until the mass fraction of isopropyl alcohol is 10%-15%. At this time, the PDMS curing agent (the mass ratio of PDMS main agent to PDMS curing agent is 10:1) is added to the beaker, and the magnetic stirring is carried out at room temperature for 15 min.

[0044] S4. Pour the mixed solution into a 20mm*20mm*(0.3-0.7, preferably 0.5) mm thick polytetrafluoroethylene mold, and after the surface is leveled, place the mold in an oven for curing for 1h, the curing temperature needs to be greater than the boiling point of IPA (82.5℃), to ensure that the IPA is completely boiled and evaporated, and the internal hole structure and surface wrinkle structure are spontaneously formed, at this time the preparation of the multi-scale porous wrinkle dielectric layer III is completed.

[0045] In this embodiment, the curing process is simultaneously affected by two factors, one is the phase separation of the system caused by the volatilization of IPA, and the other is the difference in the coefficient of thermal expansion caused by the inconsistency between the surface curing and the internal curing speed, under the joint influence of the two, the hole structure and the wrinkle structure are spontaneously formed. To ensure that the wrinkle structure is formed on the surface of the dielectric layer and the hole structure is formed inside, the amount of isopropyl alcohol added should ensure that the viscosity of the solution is between 15000-25000 mPa·s, and the curing temperature is preferably controlled between 85℃-95℃.

[0046] In the preparation of the dielectric layer, various different proportions of rGO and IPA were tried, and it was found that the mass fraction of rGO and IPA directly affects the surface and internal structure of the dielectric layer, and there is no obvious rule for this influence, but a group of schemes that can produce both microstructures with high sensitivity was accidentally discovered during the test. The test schemes provided in Table 1 are described in detail below.

[0047] Table 1 Test combination of flexible capacitive pressure sensor

[0048] Test scheme rGO mass fraction (%) IPA mass fraction (%) 1 1 10 2 1 15 3 1 20 4 2 10 5 2 15 6 2 20 7 3 10 8 3 15 9 3 20

[0049] The surface morphology and cross-sectional morphology of the dielectric layer obtained by the above-mentioned 9 test schemes were analyzed, and the results are shown in Figure 1 and Figure 2 As can be seen from Figure 1 and 2 When the mass fraction of rGO is 1%, increasing the mass fraction of IPA cannot change the surface morphology and internal structure of the dielectric layer, the surface has no wrinkle structure and the inside has no hole structure; when the mass fraction of rGO is 2%, the elastic instability of the film cannot be induced, and no wrinkles are produced, and as the mass fraction of IPA increases, the hole distribution and diameter become smaller until they disappear; when the mass fraction of rGO is 3%, as the mass fraction of IPA increases, the surface wrinkle structure and hole structure significantly decrease with the increase of the mass fraction of IPA.

[0050] The dielectric layer obtained by the above-mentioned 9 test schemes is used in a pressure sensor, and the capacitance change rate, sensing range and sensitivity of the pressure sensor are obtained by testing, and the results are shown in Table 2,Figure 3 、 Figure 4 (a) shown.

[0051] Table 2 Sensitivity and sensing range of pressure sensor device obtained under different test combinations

[0052] Test combination Capacitance change rate Perception range / (kPa) Sensitivity / (kPa -1 ) 1% rGO + 10% IPA 1.82 0-65 [S1: 0.023] 1% rGO + 15% IPA 1.99 0-65 [S1 : 0.15 (0-15 kPa) S2: 0.012 (15-65 kPa)] 1% rGO + 20% IPA 2.23 0-65 [S1 : 0.34 (0-3 kPa) S2: 0.010 (3-65 kPa)] 2% rGO + 10% IPA 5.95 0-77 [S1 : 0.924 (0-5 kPa) S2: 0.024 (5-77 kPa)] 2% rGO + 15% IPA 4.67 0-75 [S1 : 0.76 (0-3 kPa) S2: 0.03 (3-65 kPa)] 2% rGO + 20% IPA 3.01 0-84 [S1 : 0.156 (0-10 kPa) S2: 0.017 (10-84 kPa)] 3% rGO + 10% IPA 37.40 0-102 S1 : 3.5526 (0-2.2 kPa) S2: 0.4026 (2.2-67 kPa) S3: 0.1661 (67-102 kPa) 3% rGO + 15% IPA 18.09 0-100 [<S1: 1.780 (0-1.5 kPa) S2: 0.173 (1.5-66 kPa) S3: 0.05 (66-100 kPa)>] 3% rGO + 20% IPA 10.63 0-78 [<S1: 0.501 (0-6.6 kPa) S2: 0.089 (6.6-78 kPa)>]

[0053] From the above results, it can be seen that when the mass fraction of rGO is 3% and the mass fraction of IPA is 10%, the pressure sensor device obtains the highest capacitance change of 37.40 and the highest sensing range of 102.2kPa, and the sensitivity in 0-2.2kPa reaches 3.553kPa -1 ; when the mass fraction of rGO is 3% and the mass fraction of IPA is 15%, a larger wrinkle structure is generated on the surface of the pressure sensor device, and a high sensitivity of 1.780kPa -1 in 0-1.5kPa can also be obtained. The above results show that the introduction of two microstructures at the same time can significantly improve the sensitivity of the pressure sensor device.

[0054] Since the pressure sensor device prepared by 3% rGO+10% IPA has the highest sensitivity, it is the most suitable choice for realizing sowing signal monitoring, therefore, the device is further tested; specifically, the pressure sensor device is subjected to micro-pressure sensing, dynamic response and step test, respectively, and the results are shown in Figure 4 (b) to (d). From the micro-pressure sensing test results, it can be seen that the minimum resolution of the sensor device is 6.9Pa, corresponding to a 0.1g weight, at this time the capacitance change is 3.40%. For a single corn seed (350mg), the resolution of the sensor device is 32Pa, and the capacitance change rate reaches 17.90%, at this time the signal-to-noise ratio SNR of the sensor device is 21.6dB>20dB, which can effectively meet the related needs in the field of sowing monitoring.

[0055] The present application uses a vibration exciter and a frequency generator to test the dynamic response of the sensor device, which is limited by the collection frequency of the bridge (80Hz, 12.5ms), so the present application only tests the sensor device in the range of 0.5Hz-6Hz. When the frequency of the frequency generator is 6Hz and the amplitude voltage is 20Vpp (the maximum amplitude that DG1022Z can output), the peak value of the change rate of the sensor device is 1.88, and when the frequency of the frequency generator is 0.5Hz, the peak value of the change rate of the sensor device is 1.97, and the dynamic sensitivity decay is 4.78%, the above results reflect that the sensor device has good tracking ability and low distortion degree for dynamic signals.

[0056] The dynamic step test can evaluate the response ability of the flexible sensor device to sudden loads in actual application. As Figure 4(d) As shown, no significant hysteresis occurred as the force loading instrument continuously pressed against the sensor surface, indicating that the sensor exhibited a good abrupt response capability.

[0057] In the embodiment, for the pressure sensor prepared in different test combinations, when the mass fraction of rGO is 3wt% and the mass fraction of IPA is 10%, the sensor obtains the highest sensitivity, and at the same time, the surface of the sensor appears a wrinkle structure and a hole structure in the interior, and is more prone to damage compared with other test combinations. Therefore, the sensor is selected as the stability test sensor, and the result is shown in Figure 5 Figure 5 As can be seen, in the 60000 excitation cycles, the capacitance change rate curve is relatively stable, and no baseline shift occurs. The initial value of the capacitance after the first cycle is 19.0911pF, and the initial value of the capacitance after the 30000th cycle is 19.3496pF, and the baseline drift degree is 1.35%, which meets the use requirement. In addition, the capacitance change rate curves during the 4020-4027, 29000-29008 and 50000-50010 cycles are selected respectively, and the result is that the capacitance change rate is relatively stable, indicating that the pressure sensor has good reliability.

[0058] In summary, by testing the sensitivity, stability and the like of the sensor with the highest sensitivity, it is shown that the indicators of the sensor can meet the related requirements in the field of seeding monitoring.

[0059] In addition, in order to prove that the sensor prepared in the application has certain advantages in key characterization parameters such as sensitivity, response time and pressure sensing range compared with existing sensor, the sensor with the highest sensitivity (3% rGO+10% IPA) is compared with other pressure sensors reported recently, and the specific conditions are shown in Table 3.

[0060] Table 3 Comparison of capacitive pressure sensor and samples in published literature

[0061] Material Microstructure type Maximum sensitivity / (kPa -1 ​ Perception range / (kPa) Stability (cycle times) Response time / (ms) PDMS (existing) Pyramid 4.25 0-100 1100 100 PDMS / CB (existing) Hollow thorn 2.557 0-500 1000 220 PVA / EmimCl (existing) / 5.55 2.5-16 3000 673 PDMS (existing) Rugosity 0.057 0-100 10000 360 TP / Ni / SL / PAM (existing) / 5.65 0-350 10000 150 PDMS / Au / lonic gel (existing) Pyramid rugosity 33.7 0-3000 4500 17 PDMS (existing) Hole 0.18 0-400 10000 200 PDMS / AgNWs (existing) Hole 0.62 0-1 / / PDMS / CaCu3Ti4O 12 (Existing) Hole 1.66 0-1.4 2000 94 Go / cellulose (existing) Fiber foam 0.63 0-50 500 300 Ecoflex / Ga / In / Sn (existing) Microconvex 1.061 0-50 3000 91 PDMS / Go (existing) Hole 0.627 0-33 2500 540 Conductive carbon ink (existing) Hole 1.47 0-100 4000 780 PDMS (existing) Pyramid hole 14.6 0-35 5000 150 PDMS / CNTs (existing) Bionic 0.81 0-130 5000 90 PDMS / MWCNTs (existing) Rugosity 1.448 0-20 8000 209 PDMS / rGO / IPA (the present invention) Rugosity + hole 3.553 0-102 30000 226

[0062] It can be proved by the above results that the sensor provided by the application has good stability, durability and repeatability, high sensitivity, suitable sensing range, and can meet the related requirements in the field of high-speed precision seeding monitoring of corn.

[0063] The sensor prepared from 3% rGO+10% IPA and 3% rGO+15% IPA is applied in the field of agricultural machinery, and is specifically related to the seeding monitoring of the full-constraint brush belt type seeding device. The sensor can collect the electrical signals of the seed population flowing through the sensor by being installed at the seeding port, and the seeding state can be monitored by identifying the characteristics of the electrical signals. ​

[0064] The present application tests the monitoring error under different working speeds, such as Figure 6 (a) As shown, when the working speed is 10 km / h, the monitoring error is 1.02%, which is 2.46% lower than another level; when the working speed is 12 km / h, the sowing monitoring error is 1.49%, which is reduced by 3.31%; when the working speed is 14 km / h, the sowing monitoring error is 2.16%, which is reduced by 4.08%; it can be seen that when the flexible sensor device of 3% rGO+10% IPA is used, the monitoring error is significantly lower than that of 3% rGO+15% IPA (p<0.01), obviously the test combination of 3% rGO+10% IPA is more suitable for sowing monitoring scene.

[0065] With the increase of working speed, the time of seed flowing through the surface of the sensor device becomes shorter, which causes the decrease of effective signal characteristics, which is the fundamental reason for the increase of sowing monitoring error. Obviously, the higher the sensitivity of the sensor device, the more significant the signal peak value characteristics collected by the PCAP01 capacitance monitoring chip at higher working speed, Figure 6 (b) The sowing signals collected by the above two sensors at 10 km / h can be seen, the higher the sensitivity of the sensor, the higher the capacitance change value, and the more significant the mechanical characteristic signal, which is more suitable for sowing signal peak value identification algorithm for monitoring.

[0066] The sensitivity of the sensor device is a significant factor to determine whether the mechanical sensor can be applied to the sowing monitoring field. The above test results show that using the sensor device to collect mechanical signals may be a new monitoring method suitable for precision sowing monitoring operation, and a stress capacitance type sowing monitoring system can be developed based on the sensor device, PCAP01 capacitance monitoring chip and peak value identification algorithm.

[0067] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A capacitive pressure sensor, characterized in that, The device includes a silicone damping layer, a biomimetic upper microstructure conductive electrode plate, a biomimetic lower microstructure conductive electrode plate, a multi-scale porous wrinkled dielectric layer, and conductive wires. The upper and lower biomimetic microstructure conductive electrode plates are made of polyethylene terephthalate or polyimide films. The surfaces of the upper and lower biomimetic microstructure conductive electrode plates that contact the multi-scale porous wrinkled dielectric layer have biomimetic spike-like microstructures distributed on them, and a conductive contact layer is formed by spraying. The sheet resistance of the contact layer is 3.0-5.0 Ω / m². The multi-scale porous wrinkled dielectric layer has a wrinkled structure on its surface and a porous structure inside. The method for fabricating a multi-scale porous wrinkled dielectric layer includes the following steps: S1. Add monolayer reduced graphene oxide, polydimethylsiloxane and isopropanol to a beaker in a mass ratio of (0.025-0.035):1:(10-15), and record the mass of monolayer reduced graphene oxide, polydimethylsiloxane and isopropanol added respectively. S2. Place the mixed solution in a magnetic stirrer and stir continuously at 85°C for 1 hour. Then place it in an 85°C oven for 12-16 hours to evaporate excess isopropanol. Monitor the mass change of isopropanol until the mass fraction of isopropanol is 10%-15%. At this point, add PDMS curing agent to the beaker and stir magnetically at room temperature. S3. Pour the mixed solution into a mold with a thickness of 20mm*20mm*(0.3-0.7)mm until the surface is level. Then, put the mold into an oven to cure for 1 hour. The curing temperature must be higher than the boiling point of isopropanol to ensure that the isopropanol is completely boiled and evaporated, so that the dielectric layer spontaneously forms a porous structure and the surface spontaneously forms a wrinkled structure. The biomimetic spike-like microstructures distributed on the surfaces of the biomimetic upper and lower microstructure conductive electrode plates are inspired by the spike-like microstructures of spider leg hair receptors. The height of the spike-like microstructures is 100-150 μm, and they are formed by connecting two fitting curves. The formulas for the two fitting curves are as follows: f 1( x )=[-3.784* e ^( -x 2 -1.392* x 2 -3.152] / 1000, where: -1 < x <0; f 2( x =[3.784* e ^( x 2 )+1.392* x 2 -3.152] / 1000, where: 0 < x <1.

2. A capacitive pressure sensor according to claim 1, characterized in that, In step S2, the mass ratio of polydimethylsiloxane to PDMS curing agent is 10:1, and in step S3, the curing temperature is controlled between 85℃ and 95℃.

3. A capacitive pressure sensor according to claim 1, characterized in that, Before adding PDMS curing agent in step S2, the mass fraction of monolayer reduced graphene oxide is controlled to be 3%, the mass fraction of isopropanol is 10%, and the mass fraction of polydimethylsiloxane is 87%.

4. A capacitive pressure sensor according to claim 1, characterized in that, The thickness of the silicone damping layer is 0.5 mm, the thickness of the biomimetic upper microstructure conductive electrode plate and the biomimetic lower microstructure conductive electrode plate is 0.125 mm-0.15 mm, and the thickness of the multi-scale porous wrinkled dielectric layer is controlled between 0.3 and 0.7 mm.

5. A capacitive pressure sensor according to claim 1, characterized in that, The contact layer is sprayed using the following method: a mixed solution of 10 mg / mL silver nanowire solution and 20% nano-indium tin oxide solution is sprayed onto the contact surface of the biomimetic upper microstructure conductive electrode plate, the biomimetic lower microstructure conductive electrode plate and the multi-scale porous pleated dielectric layer. The mass ratio of the two solutions is 1:

1. 1.5 mL is sprayed each time, and the solution is dried at 60°C for 30 min after spraying. The spraying is repeated 5-10 times until the sheet resistance of the contact layer reaches between 3.0-5.0 Ω / m².

6. A capacitive pressure sensor according to claim 1, characterized in that, The surface of the multi-scale porous wrinkled dielectric layer is distributed with wrinkled structures of 100nm-200nm in height and 70-150nm in diameter, and the interior is distributed with pore structures of 200-400nm in diameter.

7. The application of the capacitive pressure sensor according to any one of claims 1 to 6 in a seed monitoring system.

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