Preparation method and application of a double-layer conical array flexible pressure sensor

Abstract

This invention discloses a method for fabricating a double-layer conical array flexible pressure sensor: First, a 3D model of the required mold is created using SolidWorks modeling software, and then the model is printed using photopolymerization 3D printing technology. Next, a flexible organic material is prepared, added to the mold, and placed in a vacuum chamber to eliminate air bubbles. A pre-fabricated surface perforated mold is then placed on top of the original mold, followed by curing in an oven for several hours. After curing, the sample is demolded and cut into rectangular pieces. Finally, the sample is immersed in a carbon nanotube (CNT) solution, and after stirring, a double-layer conical array flexible pressure sensor with uniformly coated CNTs and surface wrinkled microstructures is obtained. This invention utilizes photopolymerization 3D printing to realize a double-layer conical array flexible pressure sensor with micron-level wrinkled microstructures. This fabrication method is simple, has a high repeatability, short cycle time, and is easy to control.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic component production, in particular to a preparation method and application of a double-layer conical array flexible pressure sensor. BACKGROUND

[0002] As a new type of sensor technology, flexible pressure sensors are mainly applied in the fields of biomedicine, robots, smart homes, etc. Compared with traditional silicon-based pressure sensors, flexible pressure sensors have the characteristics of flexibility, lightness, low cost, and easy molding. In smart homes, flexible pressure sensors can be used in furniture such as mattresses and sofas to achieve intelligent detection and adjustment; in human-computer interaction technology, flexible sensors can improve the flexibility and comfort of wearable devices; in the medical field, the application of flexible pressure sensors in surgical instruments can not only improve the treatment effect but also reduce the risk of medical treatment.

[0003] The parameters for evaluating the performance of pressure sensors include sensitivity, pressure range, response time, and repeatability. Since the principle of piezoresistive pressure sensors is based on the change of the contact surface resistance when pressure is applied, in order to improve the overall performance of flexible sensors, the surface geometry and hierarchy of flexible pressure sensors can be changed to reduce the internal resistance of the sensor and increase the compressibility. Many researchers have tried pyramid, dome or cylinder microstructures and replicated the microstructure by polydimethylsiloxane (PDMS), but the introduction method of such microstructures requires complex process, long cycle time and high cost, and it is difficult to have a wide pressure sensing range and high sensitivity.

[0004] Therefore, there is currently a need for a low-cost and simple process to create surface microstructures for high sensitivity of flexible pressure sensors. In order to achieve this purpose, some researchers have turned their attention to 3D printing technology, which has low technical cost, simple operation and low cost. Some people have tried to use fused deposition type (FDM) or ink writing type (DIW) 3D printing technology to make microstructures, but these 3D printing technologies have low precision. To create more complex and higher precision microstructures, and to achieve high sensitivity and wide pressure range sensing of microstructure pressure sensors with simple preparation process is one of the research difficulties in the field of flexible pressure sensors, and is also an important basis for the industrialization of flexible pressure sensors. SUMMARY

[0005] The present application is directed to the deficiencies of the prior art, based on the conical array flexible pressure sensor, a double-layer structure conical array flexible pressure sensor based on 3D printing is proposed, and a preparation method is provided. The high sensitivity of force signal to electrical signal is realized in a wide pressure range, the response speed is fast, and the response signal repeatability is good. Under the 3D modeling mold, the repeatability is high and the preparation cost is low.

[0006] Technical solution

[0007] The application aims to provide a preparation method of a double-layer conical array flexible pressure sensor, which is prepared based on 3D printing and comprises the following steps:

[0008] S1, designing a 3D model of a bottom and a top cover conical hole array mold

[0009] A groove mold model is designed using modeling software, and a dense array of conical small holes is designed in the groove mold; then a cover mold model is designed, and a dense array of conical protrusions is designed on the surface of the cover mold;

[0010] Based on the designed groove mold model and cover mold model, a printing platform of a light curing printer is fixed at a preset angle, and layer-by-layer printing is performed on the printing platform to obtain a groove mold and a cover mold;

[0011] The conical holes and protrusion surfaces on the groove mold and the cover mold both have wrinkle microstructures formed by layer-by-layer printing of the light curing printer;

[0012] S2, preparation of a double-layer structure conical array PDMS

[0013] After the PDMS main agent and the curing agent are mixed, they are poured into the groove mold, and then the cover mold is covered, so that the conical array protrusions on the cover mold are embedded in the mixture of the PDMS main agent and the curing agent. After the mixture of the PDMS main agent and the curing agent is cured, the mold is removed to obtain a double-layer structure conical array PDMS;

[0014] S3, conductive integration of the surface of the double-layer structure conical array PDMS

[0015] A CNT and deionized water mixture solution is configured, the double-layer structure conical array PDMS is immersed in the mixture solution, and then it is taken out and dried to obtain a CNT uniformly coated double-layer structure conical array CNT / PDMS conductive functional layer;

[0016] S4, parallel placement of conductive copper foils on the upper and lower sides of the double-layer structure conical array CNT / PDMS conductive functional layer to form upper and lower electrodes, thereby obtaining a double-layer structure conical array microstructure flexible pressure sensor.

[0017] As a preferred, in the step S1,

[0018] The design using modeling software includes setting the interval between two cones to be 0.1-0.3 mm;

[0019] The layer-by-layer printing comprises: setting the printing precision as 0.1-0.2 mm according to the interval of 0.1-0.3 mm between the cones two by two during printing;

[0020] The light-curing printer uses high-temperature-resistant photosensitive resin;

[0021] The preset angle is a, and the range of a is as follows:

[0022] The optimal printing angle of the printing platform of the light-curing printer is b, and 0.99b

[0023] The optimal printing angle b is calculated according to the following formula:

[0024] b = arctan (c / d)

[0025] Wherein c is the layer height parameter set on the light-curing printer, and d is the pixel width parameter set on the light-curing printer h;

[0026] The wrinkle microstructure refers to: due to the principle of light-curing layer-by-layer printing, the model to be printed will be first divided into a layer-by-layer structure, and the light-curing printer will project the shape of the previous layer of the model on the photosensitive resin for light-curing forming, and after the previous layer is formed, the model will be slightly raised, and then the shape of the next layer of the model is printed, and the required mold is printed in this way. After printing, a wrinkle structure is left on the surface of the entire mold; the wrinkle microstructure on the conical surface of the conical part of the mold is arranged in a thread-like manner from top to bottom, and the wrinkle microstructure of the flat part of the mold is arranged in a stripe-like parallel manner; the pitch of the stripe in the wrinkle microstructure is 50-100 microns; the pitch of the thread in the wrinkle microstructure is 50-100 microns.

[0027] Preferably, in the step S2, the prepared double-layer structure of the conical array PDMS comprises: a PDMS block, a conical protrusion on the upper surface of the PDMS block, and a conical hole on the lower surface of the PDMS block, wherein the bottom surface of the conical protrusion has a circular diameter of 1-3 mm, a conical height of 0.5-3 mm, and a PDMS block thickness of 1-2 mm; the bottom surface of the bottom surface conical hole has a circular diameter of 0.1-0.3 mm, and the conical hole depth is 0.1-0.3 mm.

[0028] Preferably, in the step S2, the main agent is polydimethyl-methylvinylsiloxane, and the curing agent is polydimethyl-methylhydrogen siloxane;

[0029] The PDMS main agent and the curing agent are mixed and poured into the groove mold, including: the PDMS main agent and the curing agent are uniformly mixed in a mass ratio of 10:1, vacuumized in a vacuum box to eliminate bubbles, and then poured into the 3D printed groove mold;

[0030] The mixture of the PDMS main agent and the curing agent is cured and demolded, including: after curing on a glue baking machine at 70-90 DEG C, the top cover mold is removed, and the PDMS is demolded from the mold.

[0031] As preferred, in the step S3, the mass ratio of the CNT and the deionized water in the mixed solution is 1:10; the double-layer structure cone array PDMS is immersed in the mixed solution, including: after being immersed in the mixed solution, magnetic stirring is used; and the drying includes: drying in an oven.

[0032] As preferred, the upper electrode and the lower electrode are both conductive copper foils.

[0033] The application also provides an application of the double-layer structure cone array flexible pressure sensor, including the following steps: fixing the upper electrode on an electrically controlled displacement platform of vertical displacement,

[0034] placing the lower electrode on the surface of a precision balance, and connecting the upper electrode and the lower electrode with a digital source table through copper foils,

[0035] the electrically controlled displacement platform is driven by a stepping motor to apply pressure to the upper electrode of the cone array flexible pressure sensor; and the current signal is measured by the digital source table with different pressures;

[0036] the response and recovery time of the cone array microstructure flexible pressure sensor are 10 ms and 7 ms respectively;

[0037] the sensitivity of the cone array flexible pressure sensor reaches 118.5 kPa in the range of 0-0.22 kPa -1 .

[0038] The application has the following characteristics and beneficial effects:

[0039] By adopting the technical scheme, polydimethylsiloxane (PDMS) is used as a flexible substrate, light curing 3D printing technology is used to construct a dense cone array and a small conical protrusion on the surface of a mold, and 50-100 microns of wrinkle microstructures are uniformly distributed on each cone structure and the substrate. After demolding, carbon nanotubes are immersed on the surface of the microstructure PDMS to serve as a microstructure conductive functional layer. The 3D modeling mold used introduces a microstructure method, which is low in price and can be repeatedly used, can artificially control structure parameters, has high reusability, and ensures the production efficiency of the flexible sensor.

[0040] The microstructure conductive functional layer and two copper foil electrodes are arranged in a "sandwich" structure to form a flexible piezoresistive pressure sensor, which realizes high-sensitivity sensing of force signal to electric signal in a wide pressure range, fast response speed and good repeatability of response signal.

[0041] In addition, the preparation process is simple and low-cost, the mold can be repeatedly used, the mold parameters can be artificially controlled, and the preparation cost is greatly reduced. The mold raw material is low in price, non-toxic and non-polluting, green and environmentally friendly, and suitable for batch production.

[0042] The whole structure is light, thin and soft, and can be used in new wearable devices, and has high market value and industrialization potential. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0044] Figure 1 The photo and structural schematic diagram of the conical array CNT / PDMS conductive functional layer in the embodiment of the present application are shown, and the conical array PDMS of the double-layer structure prepared in step S2 is shown in the structural schematic diagram, which includes a PDMS block, a conical protrusion on the upper surface of the PDMS block and a conical hole on the lower surface of the PDMS block, wherein d is the pitch of the conical protrusion, h1 is the conical height, and h2 is the thickness of the PDMS block.

[0045] Figure 2 The performance test schematic diagram of the sensor prepared in the embodiment of the present application is composed of a stepping motor, a controller, a precision balance computer and a digital source instrument.

[0046] Figure 3 The pressure-current step response curve of the sensor in the embodiment of the present application is shown, which records the current feedback of the sensor under four different pressures.

[0047] Figure 4 The pressure-current response / recovery time curve of the sensor in the embodiment of the present application is shown, the left side is the response time after applying pressure, and the right side is the recovery time after releasing pressure.

[0048] Figure 5 The pressure-current change relationship diagram of the sensor prepared by the conical array CNT / PDMS conductive functional layer in the embodiment of the present application is shown, wherein the sensor shows good sensitivity (the sensitivity is the slope of the current-pressure curve in the figure) in the low pressure part. DETAILED DESCRIPTION

[0049] This invention provides a method for fabricating a flexible pressure sensor with a double-layer conical array based on 3D printing, the steps of which are as follows:

[0050] S1. 3D model of the mold for the tapered hole array of the bottom and top caps.

[0051] A groove mold was designed using modeling software, and a dense array of conical holes was designed inside the groove. Then, a raised cap mold with a surface conical array was designed, and the conical surface was printed layer by layer using a photopolymer printer to obtain the wrinkled microstructure of the conical surface.

[0052] S2, Preparation of a double-layered conical array of PDMS (polydimethylsiloxane)

[0053] Mix the main agent and curing agent in a petri dish at a mass ratio of 10:1 until homogeneous. Place the dish in a vacuum chamber to remove air bubbles, then pour the mixture into a 3D-printed groove mold. Place the raised conical array cap on the groove mold and press it until fully embedded. Next, place the dish on a 70-90℃ baking machine. After curing, remove the top cap mold and demold the PDMS from the mold. Cut the cured PDMS block into small rectangular pieces.

[0054] S3, Conductive Integration on the Surface of a Dual-Layer Conical Array PDMS

[0055] A CNT and deionized water mixture was prepared at a mass ratio of 1:10. The double-layer conical array PDMS was immersed in the mixture and magnetically stirred. After being removed, it was dried in an oven at 70-90°C to obtain a CNT / PDMS conductive functional layer with uniform CNT coating.

[0056] S4. Fabrication of a flexible pressure sensor with a double-layer conical array microstructure.

[0057] Conductive copper foils are placed parallel to each other on the upper and lower sides of the double-layer conical array CNT / PDMS conductive functional layer to form the upper and lower electrodes, and wires are led out from the upper and lower electrodes.

[0058] In step S1, the conical holes of the bottom groove mold in the mold design are arranged in a close array in the template, with the interval being the minimum precision of the printer; the cones of the top cover protrusion mold in the mold design are distributed on the mold in a close array, with the interval being the minimum precision of the printer.

[0059] In step S2, the diameter of the bottom circle of each cone of the prepared double-layer structured conical array PDMS is about 1-3 mm, the height of the cone is about 0.5-3 mm, and the thickness of the PDMS block is about 1-2 mm; the diameter of the bottom cone hole is about 0.1-0.3 mm, the height of the cone is 0.1-0.3 mm, and the fold spacing is 50-100 micrometers.

[0060] In step S2, the main agent is polydimethyl-methylvinylsiloxane.

[0061] In step S2, the curing agent is polydimethyl-methylhydrosiloxane.

[0062] The upper electrode, lower electrode, and electrode wire are all made of conductive copper foil.

[0063] This invention provides a flexible pressure sensor with a double-layer conical array fabricated by 3D printing and its fabrication method, comprising the following steps:

[0064] S1. Design a 3D model of the mold with a bottom grooved conical hole and a top protruding conical array.

[0065] A 3×3cm groove mold was designed using modeling software, and a dense array of conical holes was designed inside the groove. Then, a 3×3cm raised cap mold with a surface conical array was designed, and the conical surface wrinkled microstructure was obtained by printing layer by layer using a photopolymer printer.

[0066] Unlike common fused deposition modeling (FDM) printing, S1 uses stereolithography (SLA) to construct 3D solids by irradiating photosensitive resin with ultraviolet light. First, a 3D structural design model to be printed is created using Solidworks modeling software. The photosensitive resin is then introduced into the printer's print chamber, and the printing platform is fixed using positioning jigs, adjusting its position and angle. Because stereolithography printing has extremely high precision, a suitable angle results in a smooth, wrinkle-free print surface. The printing angle arctan(layer height / pixel width) needs to be controlled within 1% of 45°, excluding deviations from the optimal 45° printing angle. At this angle, the printed model will have a jagged structure. In S2, this jagged structure is molded using PDMS, and only then does the mold achieve a wrinkle-like texture.

[0067] Once everything is set up, start the printer and focus the ultraviolet light on the designated area. When the ultraviolet light shines on the surface of the photosensitive resin, it causes a polymerization reaction, curing each cross-section of the printed object layer by layer. As printing progresses, the printer will gradually raise the printing platform from the slot to continue printing the next layer of structure until the entire model is printed.

[0068] S2, Preparation of a double-layered conical array of PDMS (polydimethylsiloxane)

[0069] Mix the main agent and curing agent in a petri dish at a mass ratio of 10:1 until homogeneous. Place the dish in a vacuum chamber to remove air bubbles, then pour the mixture into a 3D-printed groove mold. Place the raised conical array cap on the groove mold and press it until fully embedded. Next, place the dish on a 70-100℃ baking machine. After curing, remove the top cap mold and demold the PDMS from the mold. Cut the cured PDMS block into small rectangular pieces.

[0070] S3, Conductive Integration on the Surface of a Dual-Layer Conical Array PDMS

[0071] A CNT and deionized water mixture was prepared at a mass ratio of 1:10. The double-layer conical array PDMS was immersed in the mixture and magnetically stirred. After being removed, it was placed in an oven at 70-90°C to dry, thus obtaining a CNT uniformly coated double-layer conical array CNT / PDMS conductive functional layer.

[0072] S4. Fabrication of a flexible pressure sensor with a double-layer conical array microstructure.

[0073] Conductive copper foils are placed parallel to each other on the upper and lower sides of the double-layer conical array CNT / PDMS conductive functional layer to form the upper and lower electrodes, and wires are led out from the upper and lower electrodes.

[0074] This invention also discloses a flexible pressure sensor with a double-layer conical array structure based on 3D printing, such as... Figure 1 As shown, the double-layer conical array flexible pressure sensor was fabricated using the 3D printing-based fabrication method provided in the above embodiments.

[0075] This embodiment tests the performance of the fabricated pressure sensor, and the test data is used to further illustrate its performance:

[0076] During testing, such as Figure 2 As shown, the upper electrode is fixed on a vertically displaced electrically controlled displacement platform, and the lower electrode is placed on the surface of a precision balance. The upper and lower electrodes are led out with copper foil and connected to a digital source meter to measure the change curve of the current signal with different pressures.

[0077] Based on the test results, such as Figure 3 As shown, the double-layer conical array microstructure flexible pressure sensor prepared by this invention can respond quickly to different pressures and has good repeatability of the response signal. Figure 4 This indicates that the flexible pressure sensor with a conical array microstructure prepared in this invention has rapid response and recovery capabilities to pressure, with response and recovery times of 10 ms and 7 ms, respectively. Furthermore, as... Figure 5As shown, the honeycomb microstructure flexible pressure sensor prepared by this invention can achieve highly sensitive sensing of force signals to electrical signals over a wide pressure range, with a sensitivity as high as 118.5 kPa. -1 .

[0078] In summary, the test results show that the technical solution provided by the embodiments of the present invention not only simplifies the process and reduces costs, but also significantly improves the performance of the resulting flexible pressure sensor.

[0079] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments, including components, without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for fabricating a double-layer conical array flexible pressure sensor, wherein the double-layer conical array flexible pressure sensor is fabricated based on 3D printing, characterized in that, Includes the following steps: S1. 3D model of the mold for the tapered hole array of the bottom and top caps. A groove mold model is designed using modeling software, with a closely spaced array of conical holes inside the groove mold; then a cap mold model is designed, with a closely spaced array of conical protrusions on the surface of the cap mold. Based on the designed groove mold model and cap mold model, a UV curing printer is used to fix the printing platform of the UV curing printer at a preset angle, and the printing is performed layer by layer on the printing platform to obtain the groove mold and cap mold. The conical holes and raised surfaces on the groove mold and the cap mold all have folded microstructures formed by layer-by-layer printing by the photopolymer printer; S2, Fabrication of a double-layer conical array PDMS After mixing the PDMS base agent and curing agent, pour the mixture into the groove mold, and then cover it with the cap mold, so that the conical array on the cap mold protrudes and embeds the mixture of PDMS base agent and curing agent. After the mixture of PDMS base agent and curing agent is cured, demold to obtain a double-layer structure conical array PDMS. S3, Conductive Integration on the Surface of a Dual-Layer Conical Array PDMS A mixture of CNTs and deionized water was prepared, and the double-layer conical array PDMS was immersed in the mixture. After that, it was taken out and dried to obtain a double-layer conical array CNT / PDMS conductive functional layer uniformly coated with CNTs. S4. Place conductive copper foils parallel to each other on the upper and lower sides of the double-layer conical array CNT / PDMS conductive functional layer to form the upper electrode and the lower electrode, thus obtaining a flexible pressure sensor with a double-layer conical array microstructure. In step S1, the design using modeling software includes: setting the interval between any two cones to 0.1~0.3mm; The layer-by-layer printing includes: setting the printing accuracy to 0.1~0.2mm based on the interval between each pair of cones being 0.1~0.3mm during printing; The photopolymer printer uses a high-temperature resistant photosensitive resin. Let the preset angle be 'a', and the range of 'a' is as follows: Let the optimal printing angle of the printing platform of the aforementioned photopolymer printer be b, where 0.99b < a < b, or b < a < 1.01b. The optimal printing angle b is calculated as follows: b = arctan(c / d) Where c is the layer height parameter set on the photopolymer printer, and d is the pixel width parameter set on the photopolymer printer; The aforementioned wrinkled microstructure refers to the following: Due to the principle of photopolymerization layer-by-layer printing, the model to be printed is first divided into horizontal layers. The photopolymerization printer projects the shape of the previous layer onto the photosensitive resin for photopolymerization. After the previous layer is formed, the model rises slightly, and then the shape of the next layer is printed. This process is repeated to create the required mold. After printing, a wrinkled structure is left on the entire surface of the mold. On the conical surface of the conical part of the mold, the wrinkled microstructure is arranged in a spiral pattern from top to bottom, while the wrinkled microstructure on the planar part of the mold is arranged in a parallel stripe pattern. The spacing between the stripes in the wrinkled microstructure is 50-100 micrometers; the spacing between the threads in the wrinkled microstructure is 50-100 micrometers.

2. The method for fabricating a double-layer conical array flexible pressure sensor according to claim 1, characterized in that, In step S2, the prepared double-layer conical array PDMS includes: a PDMS block, a conical protrusion on the upper surface of the PDMS block, and a conical hole on the lower surface of the PDMS block, wherein the bottom circle diameter of the conical protrusion is 1~3mm, the cone height is 0.5~3mm, and the thickness of the PDMS block is 1~2mm. The diameter of the bottom conical hole is 0.1~0.3mm, and the depth of the conical hole is 0.1~0.3mm.

3. The method for fabricating a double-layer conical array flexible pressure sensor according to claim 2, characterized in that, In step S2 The main agent is polydimethyl-methylvinylsiloxane, and the curing agent is polydimethyl-methylhydrosiloxane; The process of mixing the PDMS main agent and curing agent and pouring them into the groove mold includes: mixing the PDMS main agent and curing agent at a mass ratio of 10:1, placing them in a vacuum chamber to remove air bubbles, and then pouring them into the 3D printed groove mold. The curing and demolding of the mixture of PDMS main agent and curing agent includes: after curing on a 70~90℃ baking machine, removing the top cover mold and demolding the PDMS from the mold.

4. The method for fabricating a double-layer conical array flexible pressure sensor according to claim 3, characterized in that, In step S3 In the CNT and deionized water mixture, the mass ratio of CNT to deionized water is 1:10; The step of immersing the double-layered conical array PDMS into the above-mentioned mixture includes: stirring with magnetic force after immersion in the mixture; The drying process includes: drying in an oven.

5. The method for fabricating a double-layer conical array flexible pressure sensor according to claim 4, characterized in that, Both the upper and lower electrodes are conductive copper foils.

6. The application of the flexible pressure sensor with a double-layer conical array microstructure prepared by the method described in claim 5, characterized in that, Includes the following steps: The upper electrode is fixed on a vertically displaced electrically controlled displacement platform. Place the lower electrode on the surface of the precision balance, and connect the upper and lower electrodes to the digital source meter using copper foil, respectively. The electrically controlled displacement platform is driven by a stepper motor to apply pressure to the upper electrode of the conical array flexible pressure sensor; the change of current signal with different pressures is measured by the digital source meter. The response and recovery times of the tapered array microstructure flexible pressure sensor are 10ms and 7ms, respectively. The conical array flexible pressure sensor achieves a sensitivity of 118.5 kPa within the range of 0-0.22 kPa. -1 .

Images