Waterproof sensor with fine and large strain detection capability and preparation method thereof

Abstract

The invention discloses a waterproof sensor with fine and large strain detection capability. The waterproof sensor sequentially comprises a protective layer, a silver film, a graphene film and a flexible base material from top to bottom, a micro-column structure is arranged on the flexible base material; the graphene film is sprayed on the flexible base material to cover the micro-column structure; the silver film is arranged on the surface of the graphene film in a magnetron sputtering mode to form a conducting layer, and the two sides of the silver film are connected with wires. And the protective layer is poured on the silver film. The sensor prepared by the invention has waterproof capability and fine and large strain detection capability, and can be better applied to human body vital sign monitoring.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a waterproof sensor with the ability to detect both fine and large strain, and its preparation method. Background Technology

[0002] Flexible strain sensors have attracted widespread attention due to their promising applications in wearable devices, artificial electronic skin, health monitoring, and motion detection. These applications place high demands on flexible sensors, as people inevitably come into contact with humid air and water in daily life. Therefore, waterproof strain sensors have received extensive research and attention. Furthermore, the sensors need to simultaneously possess the ability to detect both minute and large strains during use to accommodate subtle physiological signals and large-amplitude joint movements. However, traditional metal- or semiconductor-based strain sensors, due to their inherently brittle structure, often exhibit high rigidity and a limited sensing range (less than 5%). This limitation significantly restricts their use in flexible, wearable applications and those requiring high tensile strain sensing. Therefore, developing highly sensitive waterproof sensors with both minute and large strain detection capabilities for human vital sign monitoring is crucial. Microcrack strain sensors are renowned for their excellent measurement sensitivity, but fabricating waterproof sensors with both minute and large strain detection capabilities remains a significant challenge. Summary of the Invention

[0003] The purpose of this invention is to provide a waterproof sensor with both fine and large strain detection capabilities and a method for its fabrication. The sensor fabricated by this invention is waterproof and possesses both fine and large strain detection capabilities, making it better suited for monitoring human vital signs.

[0004] The technical solution of the present invention is as follows: A waterproof sensor with fine and large strain detection capabilities, comprising, from top to bottom, a protective layer, a silver film, a graphene film, and a flexible substrate; a micropillar structure is disposed on the flexible substrate; the graphene film is sprayed onto the flexible substrate to cover the micropillar structure; the silver film is magnetron sputtered onto the surface of the graphene film to form a conductive layer, and wires are connected to both sides of the silver film; the protective layer is cast onto the silver film.

[0005] The aforementioned waterproof sensor, which possesses both fine and large strain detection capabilities, uses a silicone film as the material for its protective layer and flexible substrate.

[0006] The aforementioned waterproof sensor with the ability to detect both fine and large strain has a graphene film thickness of 0.5-1.5 micrometers.

[0007] The aforementioned waterproof sensor with the ability to detect both fine and large strain has a graphene film with a thickness of 1 micrometer.

[0008] The aforementioned waterproof sensor with the ability to detect both fine and large strains has a silver film thickness of 200-400 nanometers.

[0009] The aforementioned waterproof sensor with the ability to detect both fine and large strains has a silver film thickness of 300 nanometers.

[0010] The aforementioned waterproof sensor with the ability to detect both fine and large strains has a micropillar structure formed by an array of multiple cylinders, with the cylinders having a height of 100-300 micrometers and a diameter of 500-700 micrometers.

[0011] The aforementioned waterproof sensor with the capability to detect both fine and large strain has a microstructure with a height of 200 micrometers and a diameter of 600 micrometers.

[0012] The aforementioned method for fabricating a waterproof sensor capable of detecting both fine and large strain includes the following steps:

[0013] Step 1: Mix silicone adhesive A and silicone adhesive B at a mass ratio of 1:1 and then cure to obtain a flexible substrate and micropillar structure;

[0014] Step 2: Spray the graphene film evenly onto the flexible substrate;

[0015] Step 3: Magnetron sputter the silver thin film onto the graphene thin film;

[0016] Step 4: Fix a pair of wires to both ends of the silver film and cure.

[0017] Step 5: Mix silicone A and silicone B in a 1:1 mass ratio and pour the mixture onto the silver film. After curing, the finished product is obtained.

[0018] Compared with existing technologies, this invention uniformly sprays a graphene film onto a flexible substrate and then uses magnetron sputtering to deposit a silver film on the graphene surface to form a conductive layer. When subjected to strain, the upper silver film separates to form microcracks. The graphene film fills these microcracks, and the micropillar structure promotes the propagation of the microcracks, breaking the conductive path and resulting in a significant change in resistance. This gives the strain sensor a larger range and sensitivity, effectively improving the problems of low sensitivity and poor repeatability of crack-effect-based sensors. It can be better applied to monitoring human vital signs, such as subtle physiological signals and large-amplitude joint movements. Simultaneously, this invention uses a protective encapsulation layer to encapsulate the entire sensor in a waterproof film, preventing the penetration of aqueous solutions, ensuring normal sensor operation, and restricting the upward degree of freedom of the crack islands. This interaction facilitates effective separation and reconnection between crack islands, further improving the overall performance of the sensor. The sensor prepared by this invention is suitable for detecting subtle and large strains, including arterial pulse signals, vibrations, and large-amplitude joint bending movements. This sensor has broad application prospects as a next-generation underwater flexible strain sensor. Attached Figure Description

[0019] Figure 1 This is an exploded view of the structure of the present invention;

[0020] Figure 2 This is a schematic diagram of the structure of the present invention;

[0021] Figure 3 This is a schematic diagram of the waterproof sensor surface before stretching.

[0022] Figure 4 This is a schematic diagram of the surface of the waterproof sensor after stretching.

[0023] Figure 5 This is a schematic diagram of the segmented sensitivity of the waterproof sensor provided in the embodiments of this application;

[0024] Figure 6 Results of the waterproof sensor provided in the embodiments of this application under strains of 0.2%, 0.3%, 0.4%, 0.5%, and 0.6%;

[0025] Figure 7 Optical microscope images of the waterproof sensor provided in the embodiments of this application at 0-50% stretching degree;

[0026] Figure 8 The results of uniaxial cyclic tensile testing of the waterproof sensor provided in the embodiments of this application.

[0027] Figure Labels

[0028] 1. Protective layer; 2. Conductor; 3. Silver film; 4. Graphene film; 5. Micropillar structure; 6. Flexible substrate; Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0030] Example: A waterproof sensor with the ability to detect both fine and large strain, such as... Figure 1 and Figure 2 As shown, from top to bottom, the structure includes a protective layer 1, a silver film 3, a graphene film 4, and a flexible substrate 6. A micropillar structure 5 is disposed on the flexible substrate 6. The graphene film 4 is sprayed onto the flexible substrate 6 and covers the micropillar structure 5. The silver film 3 is magnetron sputtered onto the surface of the graphene film 4 to form a conductive layer, and wires 2 are connected to both sides of the silver film 3. The protective layer 1 is cast onto the silver film 3. The protective layer 1, silver film 3, graphene film 4, and flexible substrate 6 form a sandwich structure. In this example, the wires 2 are connected to both ends of the silver film 3 via conductive silver paste. Both the flexible substrate 6 and the protective layer 1 are silicone films. The silicone film is obtained by mixing and curing adhesives a and b in a 1:1 mass ratio, where adhesive a is silicone adhesive a and adhesive b is silicone adhesive b. The thickness of the graphene film 4 is 1 micrometer. The silver film 3 has a thickness of 300 nanometers; the micropillar structure 5 is formed by an array of multiple cylinders, with a height of 100-300 micrometers and a diameter of 500-700 micrometers.

[0031] The steps for manufacturing a waterproof sensor in this example are as follows:

[0032] Step 1: First, pour the A and B components of the silicone into a beaker at a mass ratio of 1:1 and stir thoroughly for 1 minute. Then, place the beaker containing the mixed silicone into a vacuum chamber and let it stand to eliminate the air bubbles generated by stirring. After the air bubbles are completely eliminated, pour it into a polytetrafluoroethylene mold with a micro-pillar structure 5 and cure it at room temperature for 4 hours to obtain a flexible substrate 6 with a micro-pillar structure 5.

[0033] Step 2: Weigh 0.02g of single-layer graphene powder and mix it with 50ml of anhydrous ethanol. Stir the mixture with ultrasonication and disperse it for 3 minutes to obtain a dispersion with a concentration of 0.4mg / ml. The instrument power is 800w and the oscillation frequency is 20KHZ.

[0034] Step 3: Using a 0.3mm nozzle spray gun, spray the monolayer graphene dispersion onto the flexible substrate 6 as evenly as possible at a spray pressure of 150Kpa from a distance of about 30cm from the surface of the flexible substrate 6. The spraying time is about 15 minutes. Place the flexible substrate 6 sprayed with monolayer graphene into a vacuum chamber and allow it to dry completely at room temperature.

[0035] Step 4: Use an ultra-vacuum magnetron sputtering coating machine (power 70W, 45 minutes) to sputter a silver film 3 on the surface of single-layer graphene (power 65W, 30 minutes), with a sputtering pressure of 2.5pa;

[0036] Step 5: Immerse the flexible wire 2 in deionized water and ultrasonically clean for 15 minutes to remove surface contaminants. Then place the wire 2 in a vacuum until completely dry. Adhere the flexible wire 2 with conductive silver paste to both ends of the silver film 3. Pour a 1:1 mass ratio of silicone A and silicone B (a bubble-removing silicone mixture) onto the surface of the wire 2 and the substrate as a waterproof layer. Finally, allow it to cure naturally at room temperature to reduce the generation of internal stress.

[0037] To further illustrate the ability of the waterproof sensor described in this embodiment to detect both fine and large strains, Figure 2 This is a schematic diagram of the waterproof sensor surface film before stretching. Figure 4 This is a schematic diagram showing the stretched surface film of the waterproof sensor. From... Figure 3 and Figure 4 As can be seen, when the stretching degree increases further, the silver cracks become larger near micropillar structure 5. These cracks require the lower monolayer graphene to bridge and form new conductive bridges, ensuring that the sensor still has a certain number of conductive pathways under high strain. After the strain is released, the upper and lower silicone layers help to tightly connect the cracks, and the composite film returns to its initial resistance value. Figure 4 In the middle, R Ag0 R is the initial resistance of silver film 3. C R is the resistance of each crack island. b This is the contact resistance between the crack islands via monolayer graphene. Compared to the resistance of the monolayer graphene network connecting each crack island, the resistance of the silver film is negligible. Therefore, the series connection R... Ag0 and R C It can be simplified to R C This simplifies the equivalent circuit. Figure 4 The equivalent resistance R eq It can be represented as:

[0038]

[0039] Furthermore, the waterproof sensor of this embodiment is used to test the strain signal. Figure 5 This is a schematic diagram of the segmented sensitivity of the waterproof sensor provided in the embodiments of this application (GF = 2387.5, 43% < ε < 50%). Figure 6 Results of the waterproof sensor provided in the embodiments of this application under strains of 0.2%, 0.3%, 0.4%, 0.5%, and 0.6%. Figure 7 The optical microscope images of the waterproof sensor provided in this application embodiment at 0-50% stretching show numerous sheet-like crack island structures of varying sizes and irregular shapes on the sensor surface in the initial unstretched state. This is due to graphene agglomeration caused by uneven spraying. When the sensor is stretched further to 30%, narrow seam areas are formed between the cracks. When stretched further, even to 50%, the area of ​​these seam areas also expands accordingly, forming relatively large cracks. The crack area around the micropillar structure 5 is larger than that of other areas. Figure 8 The results of uniaxial cyclic tensile testing of the waterproof sensor provided in this application embodiment are shown. The sensor was subjected to 50 uniaxial cyclic tensile tests within five ranges: 5%, 10%, 15%, 25%, and 35%. Three stable test results were plotted. The graph shows that the waterproof sensor exhibits a large resistance signal change and cyclic stability across different ranges. Therefore, this flexible strain sensor possesses a large range, high sensitivity, and cyclic stability, showing promising application prospects in structural health monitoring.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications assumed above should also be considered within the scope of protection of the present invention.

Claims

1. A waterproof sensor with the ability to detect both fine and large strain, characterized in that: From top to bottom, it includes a protective layer (1), a silver film (3), a graphene film (4), and a flexible substrate (6); a micropillar structure (5) is provided on the flexible substrate (6); the graphene film (4) is sprayed onto the flexible substrate (6) to cover the micropillar structure (5); the silver film (3) is magnetron sputtered onto the surface of the graphene film (4) to form a conductive layer, and wires (2) are connected to both sides of the silver film (3); the protective layer (1) is cast onto the silver film (3).

2. The waterproof sensor with fine and large strain detection capabilities according to claim 1, characterized in that: The protective layer (1) and the flexible substrate (6) are made of silicone film.

3. The waterproof sensor with fine and large strain detection capabilities according to claim 1, characterized in that: The thickness of the graphene film (4) is 0.5-1.5 micrometers.

4. The waterproof sensor with fine and large strain detection capabilities according to claim 3, characterized in that: The thickness of the graphene film (4) is 1 micrometer.

5. The waterproof sensor with fine and large strain detection capabilities according to claim 1, characterized in that: The thickness of the silver film (3) is 200-400 nanometers.

6. The waterproof sensor with fine and large strain detection capabilities according to claim 5, characterized in that: The thickness of the silver film (3) is 300 nanometers.

7. The waterproof sensor with fine and large strain detection capabilities according to claim 1, characterized in that: The micropillar structure is formed by arranging multiple cylindrical arrays, with the height of the cylinders being 100-300 micrometers and the diameter being 500-700 micrometers.

8. The waterproof sensor with fine and large strain detection capabilities according to claim 1, characterized in that: The micropillar structure has a height of 200 micrometers and a diameter of 600 micrometers.

9. The method for preparing a waterproof sensor with fine and large strain detection capabilities according to any one of claims 1-8, characterized in that: Includes the following steps: Step 1: Mix silicone A and silicone B in a 1:1 mass ratio and then cure to obtain a flexible substrate and micropillar structure; Step 2: Spray the graphene film evenly onto the flexible substrate; Step 3: Magnetron sputter the silver thin film onto the graphene thin film; Step 4: Fix a pair of wires to both ends of the silver film and cure. Step 5: Mix silicone A and silicone B in a 1:1 mass ratio and pour the mixture onto the silver film. After curing, the finished product is obtained.

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