Laser-induced graphene omnidirectional flexible strain sensor

Abstract

The invention relates to the technical field of flexible strain sensors, in particular to a laser-induced graphene omnidirectional flexible strain sensor. Comprising a flexible substrate, a flexible sensitive layer and a flexible upper cover, both the flexible substrate and the flexible upper cover are made of a polydimethylsiloxane (PDMS) material, the flexible sensitive layer is generated on a mixed substrate of polyimide (PI) and multi-walled carbon nanotubes (MWCNTs) through a laser ablation process, and then the sensitive layer is transferred to the PDMS substrate through a substrate transfer process. The two ends of the flexible sensitive layer are coated with electrode layer external wires, and finally a PDMS solution is poured to wait for curing for packaging. The method can be applied to the fields of wearable electronic equipment and medical monitoring. Through the spiral pattern structure, the stress in each direction can be dispersed more uniformly, and the precision and reliability of the sensor can be improved. The preparation method disclosed by the invention is simple and efficient, does not need a special gas environment, can complete patterning manufacturing of graphene by only one step, and reduces the production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible strain sensors, and in particular to a laser-induced graphene omnidirectional flexible strain sensor. Background Art

[0002] A flexible strain sensor is a sensing element made of flexible materials (such as polymers, nanocomposites, or laser-induced graphene, etc.). When it deforms under an external force, it can detect strain in real time through changes in resistance, capacitance, or optical signals. Laser-induced graphene in-situ generates a three-dimensional porous graphene structure on a flexible substrate through laser direct writing technology. Its high defect density and abundant edge active sites significantly enhance the piezoresistive effect, achieving a highly sensitive response to strain. This material has excellent flexibility, and the porous network structure can adapt to the stress distribution. By adjusting the laser parameters, the porosity, conductivity, and microstructure morphology can be precisely controlled to achieve directional optimization of the sensing performance. In addition, the laser direct writing process supports maskless patterning design and can be directly integrated into flexible devices, providing an efficient and customizable material solution for high-precision strain sensing.

[0003] Traditional commercial flexible strain sensors only show high sensitivity in the main strain direction and have poor response in the non-strain direction. When used, the placement direction of the sensor must be determined first. In practical applications, such as monitoring the movement states of human joints and muscles, the strain conditions in all directions are required. At the same time, as the flexible substrate is the core for conducting strain, its flexibility and extensibility are crucial. The present invention uses a substrate transfer process to attach LIG to the PDMS substrate, significantly improving the strain detection range. In the Chinese patent application: A flexible strain sensor with a highly stretchable and high-precision serpentine electrode structure (Patent Application No.: CN202322812048.X), although LIG can measure the strain in the lateral direction, its strain detection ability in the longitudinal direction is far inferior to that in the main strain direction. Therefore, how to prepare a flexible strain sensor with high stability and omnidirectional detection without reducing the sensitivity is one of the problems that urgently need to be solved at present. Summary of the Invention

[0004] To solve the above problems, the present invention provides a strain sensor that is sensitive to laser-induced graphene omnidirectionally.

[0005] The technical solution adopted by the present invention is: a full-direction flexible strain sensor based on laser-induced graphene. It has a flexible substrate, a flexible sensitive layer, and a flexible upper cover. Both the flexible substrate and the flexible upper cover are made of polydimethylsiloxane (PDMS) material. The flexible sensitive layer is generated on a PI substrate doped with multi-walled carbon nanotubes (MWCNTs) by a laser ablation process, and then the sensitive layer is transferred to the PDMS substrate through a substrate transfer process. Electrode layers are coated at both ends of the flexible sensitive layer and connected to external wires, and finally, a PDMS solution is poured and waited to cure for encapsulation.

[0006] As a further supplementary description of the above technical solution, the substrate of the laser ablation process is a PI substrate doped with MWCNTs, which is formed by mixing MWCNTs surface-functionalized with concentrated sulfuric acid and a PAA solution of PI precursor, and uniformly mixing and curing by ultrasonic waves.

[0007] As a further supplementary description of the above technical solution, for the laser ablation process, the parameter selection is 90 mm / s ± 10 mm / s, and the power is 14% ± 2%. The process parameters within this range can accurately engrave the LIG structure.

[0008] As a further supplementary description of the above technical solution, the flexible sensitive layer is a MWCNTs / LIG composite electrode. The combination of the two materials can significantly improve the conductivity and mechanical properties of the sensor.

[0009] As a further supplementary description of the above technical solution, the flexible sensitive layer is a MWCNTs / LIG composite electrode. The high mechanical strength, excellent conductivity, and one-dimensional nanostructure of MWCNTs can make up for the possible lack of mechanical properties of LIG, and at the same time enhance the conductive network of the composite material; while the porous three-dimensional structure of LIG provides a uniformly dispersed carrier for MWCNTs, further expanding the specific surface area and promoting electron / ion transport. This composite system can significantly improve the mechanical stability and functionality of the material.

[0010] As a further supplementary description of the above technical solution, the overall radius of the flexible sensitive layer is 10 mm ± 2 mm, the thickness is about 15 μm, and the width of each LIG is 120 μm ± 20 μm.

[0011] As a further supplementary description of the above technical solution, the flexible sensitive layer is prepared in one stroke by a laser ablation process, and can be regarded as five connected concentric rings as a whole, and the radii of each ring increase in turn.

[0012] As a further supplementary description of the above technical solution, the flexible sensitive layer is generated on a PI substrate by a laser ablation process, and then the sensitive layer is transferred to the PDMS substrate through a substrate transfer process.

[0013] As a further supplementary description of the above technical solution, the substrate transfer process is to pour a liquid PDMS solution onto the PI substrate after laser ablation, wait for the PDMS to cure, and then tear it off to obtain a PDMS substrate with a sensitive layer.

[0014] As a further supplementary description of the above technical solution, the electrode layer material is conductive silver paste. There are four electrode layers of the same size located at the four corners of the flexible sensitive layer respectively, each with a side length of 0.5 cm and a thickness of 100 mm.

[0015] As a further supplementary description of the above technical solution, the thickness of the flexible substrate and the flexible upper cover is 500 μm - 2000 μm. Within this range, good resilience and tensile resistance of the sensor can be ensured. At the same time, within this thickness range, with the increase of the thickness, a part of the strain performance will be lost and the pressure sensing performance will be improved.

[0016] Adopting the above technical solution, the present invention has the following beneficial effects: Optimize stress distribution: Through the spiral pattern structure, the present invention can more evenly disperse the stress in all directions, which helps to improve the accuracy and reliability of the sensor.

[0017] Improve strain performance: By combining the PDMS flexible substrate with the unique LIG structure, the strain sensing sensitivity and strain detection range are improved.

[0018] Simplify the manufacturing process: The preparation method of the present invention is simple and efficient, without the need for a special gas environment. The patterning manufacturing of graphene can be completed in only one step, reducing the production cost.

[0019] Optimize the application scenario: The omnidirectional detection ability and the large detection range are beneficial to the application of the sensor in different human behavior scenarios, promoting the application and development of flexible strain sensors in the fields of remote medical treatment and human-computer interaction. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the split structure of a laser-induced graphene omnidirectional flexible strain sensor provided by an embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of the overall structure of a laser-induced graphene omnidirectional flexible strain sensor provided by an embodiment of the present invention.

[0022] Figure 3 It is a schematic diagram of the patterning LIG laser path of a laser-induced graphene omnidirectional flexible strain sensor provided by an embodiment of the present invention.

[0023] Figure 4Schematic diagram of a flexible substrate and a flexible upper cover of a laser-induced graphene omnidirectional flexible strain sensor provided by an embodiment of the present invention.

[0024] Figure 5 Schematic diagram of a process flow of a laser-induced graphene omnidirectional flexible strain sensor provided by an embodiment of the present invention.

[0025] Figure 6 Schematic diagram of a Wheatstone bridge of a laser-induced graphene omnidirectional flexible strain sensor provided by an embodiment of the present invention. Detailed implementation manners

[0026] The present invention provides a laser-induced graphene omnidirectional flexible strain sensor, and its structural schematic diagram is as shown in Figure 1 、 Figure 2 and Figure 4 shown, wherein Figure 1 is a schematic diagram of an overall split structure, including a flexible substrate 1, a flexible upper cover 2, a laser-induced graphene layer 3, and a conductive silver paste electrode 4.

[0027] The LIG patterning structure is as shown in Figure 3 shown, and this structure is prepared with an infrared laser in one stroke. Lead electrodes 5 are arranged around it, and the surfaces of the lead electrodes are coated with conductive silver paste.

[0028] The sensitive layer described in the present invention is an MWCNTs-LIG composite material. Through the combination of their good mechanical properties and electrical properties, its tensile limit length and sensitivity coefficient are respectively increased by about 10% and 30% compared with the single LIG sensitive layer.

[0029] The MWCNTs-doped PI substrate described in the present invention is formed by uniformly mixing and curing PAA and MWCNTs powder. Preferably, the mass ratio of the two is selected as 200:1 for mixing, which can not only ensure a sufficient concentration of MWCNTs, but also ensure a good dispersion effect of MWCNTs.

[0030] The laser-induced graphene layer described in the present invention is located on the surface of the flexible substrate. Preferably, the thickness of the flexible substrate is 500 μm to 2000 μm.

[0031] The laser-induced graphene layer described in the present invention is a spiral patterning structure. Preferably, the number of spiral rings of the patterning structure is 4 to 6, and the width of the LIG line is 120 μm ± 10 μm.

[0032] The Wheatstone bridge described in the present invention is as shown in Figure 6 shown, R x is a strain resistor, and its resistance value increases with the increase of the external strain. R refis a reference resistor, whose function is to ensure that the output of the bridge is 0 under the condition of zero external strain. R0 is a fixed voltage-dividing resistor, and two arms of the bridge select R0 and R with the same equal resistance value x、 R ref together constitute a semi-equal-arm Wheatstone bridge V cc is a constant voltage input, amplified by the circuit and output by V out wherein V out the output quantity is proportional to the sensor resistance R x input quantity

[0033] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments and drawings of the present invention. Obviously, the described embodiments are not limitations of the present invention. Based on the embodiments in this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by this disclosure

[0034] As Figure 5 shown, this embodiment also provides a preparation method for a laser-induced graphene omnidirectional flexible strain sensor, including the following steps Step 1): Prepare MWCNTs by chemical vapor deposition method, and perform surface functionalization through concentrated sulfuric acid treatment. Select a PAA solution with a mass ratio of 200:1 and mix it with the above-functionalized MWCNTs, ultrasonically disperse for 30 min, and cure at 170 °C for 2 hours to obtain a MWCNTs / PI film

[0035] Step 2): Generate and pattern LIG on the MWCNTs / PI substrate to obtain a LIG-MWCNTs (LM) composite sensitive material

[0036] Step 3): Uniformly coat the pre-prepared PDMS solution on the PI substrate, and then cure it. Obtain a PI-LM-PDMS composite structure

[0037] Step 4): Manually peel off the PI in the composite structure to obtain an LM-PDMS composite structure

[0038] Step 5): Brush conductive silver paste at both ends of the LM region in the LM-PDMS composite structure obtained above, place it in a 70 °C constant temperature environment and dry it for 40 min to ensure sufficient curing

[0039] Step 6): Manufacture a flexible upper cover on the structure obtained above according to the method mentioned in Step 2. Obtain a patterned strain sensor

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser-induced graphene omnidirectional flexible strain sensor, characterized in that: It includes a flexible substrate, a flexible sensitive layer, and a flexible upper cover. Both the flexible substrate and the flexible upper cover are made of polydimethylsiloxane - PDMS material. The flexible sensitive layer is formed by laser - induced LIG on polyimide - PI and then adhered to the flexible substrate through a transfer process. Conductive silver paste electrodes are provided at both ends of the flexible sensitive layer and are externally connected to wires.

2. The biaxial flexible strain sensor of laser-induced graphene according to claim 1, characterized in that: The flexible sensitive layer is a MWCNTs - LIG composite material, and their properties are complementary, significantly improving the force and electrical properties of the sensor.

3. The all-directional flexible strain sensor made of laser-induced graphene according to claim 1, characterized in that: The flexible sensitive layer is prepared in one stroke by a laser ablation process and is regarded as five connected concentric rings as a whole.

4. The all-directional flexible strain sensor based on laser-induced graphene according to claim 3, characterized in that: The laser ablation process is completed by a CO2 laser engraving machine, with parameters selected as 90mm / s ± 10mm / s and a power of 14% ± 2%.

5. The all-directional flexible strain sensor of laser-induced graphene according to claim 1, characterized in that: The flexible sensitive layer is generated on a MWCNTs / PI substrate by a laser ablation process, and then the sensitive layer is transferred to a PDMS substrate through a substrate transfer process.

6. The all-directional flexible strain sensor based on laser-induced graphene according to claim 5, wherein: The MWCNTs / PI substrate is formed by ultrasonically and uniformly mixing and curing MWCNTs surface - functionalized with concentrated sulfuric acid and PI precursor PAA solution.

7. The all-directional flexible strain sensor based on laser-induced graphene according to claim 5, wherein: The substrate transfer process is to pour a liquid PDMS solution onto the PI substrate after laser ablation, and after waiting for the PDMS to cure, tear it off to obtain a PDMS substrate containing the sensitive layer.

8. The all-directional flexible strain sensor made of laser-induced graphene according to claim 1, wherein: There are four conductive silver paste electrodes of the same size, which are respectively located at the four corners of the flexible sensitive layer, and each side length is 40mm.

9. The all-directional flexible strain sensor based on laser-induced graphene according to claim 8, wherein: The conductive silver paste electrodes are dried in an environment of 70°C for 40min to ensure the full curing of the silver paste.

10. A laser-induced graphene omnidirectional flexible strain sensor according to claim 1, characterized in that: The thickness of the flexible substrate and the flexible upper cover is 500μm - 2000μm.

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