Single-fiber vector stress-strain sensor based on process of coating solid and liquid double metal layers on surface of spandex fiber and preparation method of single-fiber vector stress-strain sensor

Abstract

The invention discloses a single-fiber vector stress-strain sensor based on a process of coating and plating a solid and liquid double-metal layer on the surface of a spandex fiber, which comprises the spandex fiber as a matrix, a lower electrode layer deposited on the surface of the matrix, an upper electrode layer deposited on the lower electrode layer, and the matrix, the lower electrode layer and the lower electrode layer are packaged through a flexible packaging layer; the lower electrode layer is gold nanoparticles attached to the substrate, the upper electrode layer comprises a metal nickel-plated layer on the lower electrode layer and a liquid metal layer coated on the metal nickel-plated layer, and the flexible packaging layer is made of chitosan. According to the invention, the problem of irreversible conductivity degradation caused by repeated stretching of the existing sensor is solved. The invention further discloses a preparation method of the single-fiber vector stress-strain sensor based on the process of coating the surface of the spandex fiber with the solid and liquid double metal layers.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and flexible sensor technology, and relates to a single-fiber vector stress-strain sensor based on a process of coating a solid-liquid bimetallic layer on the surface of spandex fiber. This invention also relates to a method for preparing a single-fiber vector stress-strain sensor based on a process of coating a solid-liquid bimetallic layer on the surface of spandex fiber. Background Technology

[0002] With the rapid development of wearable electronic devices and soft robots, the demand for flexible sensors is increasing. Traditional rigid sensors struggle to adapt to dynamic deformations such as bending and stretching, limiting their application in fields such as human health monitoring and electronic skin. Flexible single-fiber tensile sensors, as core components, need to possess excellent flexibility, high sensitivity, vector monitoring capabilities, and operational stability. Existing single-fiber sensors primarily utilize conductive layers consisting of metallic and non-metallic coatings. However, these layers are prone to fracture under repeated deformation, leading to performance degradation. Summary of the Invention

[0003] The purpose of this invention is to provide a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic coating process on the surface of spandex fibers, which solves the problem of irreversible conductivity degradation caused by repeated stretching of existing sensors.

[0004] Another objective of this invention is to provide a method for fabricating a single-fiber vector stress-strain sensor based on a process of coating a solid-liquid bimetallic layer onto the surface of spandex fibers.

[0005] The technical solution adopted in this invention is a single-fiber vector stress-strain sensor based on a process of coating a solid and liquid bimetallic layer on the surface of spandex fiber. It includes spandex fiber as a substrate, a lower electrode layer deposited on the surface of the substrate, an upper electrode layer deposited on the lower electrode layer, and the substrate, the lower electrode layer, and the lower electrode layer are encapsulated by a flexible encapsulation layer. The lower electrode layer is gold nanoparticles attached to the substrate, and the upper electrode layer includes a nickel plating layer on the lower electrode layer and a liquid metal layer coated on the nickel plating layer. The flexible encapsulation layer is made of chitosan.

[0006] The second technical solution adopted in this invention is a method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fibers, which is implemented according to the following steps: Step 1: Sensitize the spandex fiber; Step 2: Using the spandex fiber treated in Step 1 as a substrate, gold nanoparticles are grown on its surface as the lower electrode layer. Step 3: Place the spandex fiber treated in Step 2 into the nickel plating solution for plating, and plate a metal nickel layer on the lower electrode layer. After plating, rinse with deionized water and dry. Step 4: Place the spandex fibers dried in Step 3 into liquid metal to coat them with a liquid metal layer. Step 5: Immerse the nickel-plated spandex fiber coated with liquid metal in step 4 in a chitosan solution to prepare the encapsulation layer.

[0007] Furthermore, the sensitization treatment in step 1 specifically involves immersing the spandex fiber in ethanol for 10-20 minutes, then rinsing it with deionized water and drying it.

[0008] Further, step 2 specifically involves: preparing a chloroauric acid solution with a concentration of 20-30 mol / L and a sodium borohydride solution with a concentration of 0.01-0.03 g / L; then stretching and winding spandex fibers onto a glass slide; immersing the slide in the chloroauric acid solution for 1-3 minutes, then rinsing it with water 3-5 times; immersing it in the sodium borohydride solution for 1-3 minutes, then rinsing it with water 3-5 times; repeating this process of immersion in chloroauric acid solution - rinsing with water - immersion in sodium borohydride solution - rinsing with water 8 times; and finally drying the slide.

[0009] Further, step 3 specifically involves: stretching and winding the spandex fibers with surface-grown gold nanoparticles obtained in step 2 onto a glass slide, immersing them in a nickel plating solution for 20-30 minutes, washing them with deionized water after plating, and then drying them to obtain spandex fibers with a nickel plating layer.

[0010] Furthermore, the nickel plating solution is prepared as follows: using deionized water as a solvent, NiSO4·6H2O, NaH2PO2·H2O, and lactic acid are dissolved in the solvent to obtain a chemical nickel plating solution. Then, NaOH solution is used to adjust the pH of the chemical nickel plating solution to 4-6 to obtain the final nickel plating solution. The concentrations of solutes in the electroless nickel plating solution are as follows: 20-30 g / L NiSO4·6H2O, 20-30 g / L NaH2PO2·H2O, and 20-30 mL / L lactic acid.

[0011] Furthermore, during the plating process in step 3, the electroplating conditions are as follows: the distance between the cathode and anode is 2-4 cm, and the current density is 800-1200 mA / dm². 2 The electroplating time is 20-40 minutes, the electroplating temperature is 40-60℃, and the pH value is 8-10.

[0012] Further, step 4 specifically involves immersing the spandex fibers dried in step 3 in an indium tin alloy for 20-40 minutes to coat them with a liquid metal layer.

[0013] Further, step 5 specifically involves immersing the spandex fiber obtained in step 4 in a chitosan solution for 1-2 hours to form a film, and then drying it to obtain a single-fiber vector stress-strain sensor.

[0014] Furthermore, the chitosan solution was prepared according to the following method: Dissolve 2-4g of chitosan in 80-100mL of 1%-3% acetic acid solution, heat in a water bath at 50-70℃ for 10-30min and stir at 800-1000r / min to obtain chitosan solution.

[0015] The beneficial effects of this invention are: Traditional "core-shell" structure composite conductive fiber conductive layers are usually rigid coatings such as metal or non-metallic materials. After long-term stretching cycles, "cracks" will appear, resulting in irreversible degradation of conductivity. The liquid metal dynamic compensation strategy adopted in this invention effectively improves the problem of conductivity decay caused by long-term and multiple stretching cycles. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope image of the original spandex fiber used in the embodiments of the present invention; Figure 2 This is a scanning electron microscope image of the spandex fiber with gold seeds attached in Embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of spandex fibers after chemical nickel plating in Example 1 of the present invention; Figure 4 This is a scanning electron microscope image of spandex fibers coated with liquid metal in Example 1 of the present invention; Figure 5 This is a scanning electron microscope image of spandex fibers coated with chitosan in Example 1 of the present invention; Figure 6 This is a resistivity data graph showing the tensile response time of the spandex fiber with a nickel / liquid metal coating that has high sensitivity and high stability, prepared in Example 1 of this invention. Figure 7 This is a resistance data graph of a tensile cyclic test of a single-fiber vector stress-strain sensor prepared in Example 1 of the present invention, based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber. Figure 8 This is a graph showing the change in tensile resistance of different original lengths of a single-fiber vector stress-strain sensor prepared based on a solid-liquid bimetallic coating process on the surface of spandex fiber, as described in Example 1 of this invention. Figure 9 This is a graph showing the resistance change of the sensor prepared in Embodiment 1 of the present invention when it is attached to the neck and the head is nodding. Figure 10 This is a graph showing the resistance change of the sensor prepared in Embodiment 1 of the present invention when it is attached to the elbow and the elbow is bent. Figure 11This is a graph showing the resistance change of the sensor prepared in Embodiment 1 of the present invention when it is attached to the wrist and the wrist is flexed. Figure 12 This is a graph showing the resistance change of the sensor prepared in Embodiment 1 of the present invention when it is attached to the knee and the knee is bent. Detailed Implementation

[0017] The following detailed description is provided in conjunction with specific implementation methods.

[0018] Example 1 This invention relates to a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic coating process for spandex fiber. The sensor comprises spandex fiber as a substrate, a lower electrode layer deposited on the substrate surface, and an upper electrode layer deposited on the lower electrode layer. The substrate, the lower electrode layer, and the upper electrode layer are encapsulated by a flexible encapsulation layer. The lower electrode layer consists of gold nanoparticles attached to the substrate. The upper electrode layer includes a nickel plating layer on the lower electrode layer and a liquid metal layer coated on the nickel plating layer. The flexible encapsulation layer is made of chitosan.

[0019] Example 2 Based on Example 1, the present invention provides a method for fabricating a single-fiber vector stress-strain sensor using a solid-liquid bimetallic coating process on the surface of spandex fibers, which is implemented according to the following steps: Step 1: Soak the spandex fiber in ethanol for 10-20 minutes, then rinse with deionized water and dry. Step 2: Prepare a chloroauric acid solution with a concentration of 20-30 mol / L and a sodium borohydride solution with a concentration of 0.01-0.03 g / L. Then, stretch and wind the spandex fibers treated in Step 1 onto a glass slide. Immerse the slide in the chloroauric acid solution for 1-3 minutes, then rinse it with water 3-5 times. Next, immerse it in the sodium borohydride solution for 1-3 minutes, then rinse it with water 3-5 times. Repeat this process of immersion in chloroauric acid solution, rinsing with water, immersion in sodium borohydride solution, and rinsing with water 8 times. Finally, dry the slide. Step 3: Stretch and wind the spandex fiber with gold nanoparticles grown on the surface obtained in Step 2 onto a glass slide, immerse it in the nickel plating solution for 20-30 minutes, wash it with deionized water after plating and dry it to obtain the spandex fiber with a metal nickel plating layer. The nickel plating solution is prepared as follows: using deionized water as a solvent, NiSO4·6H2O, NaH2PO2·H2O, and lactic acid are dissolved in the solvent to obtain a chemical nickel plating solution. Then, NaOH solution is used to adjust the pH of the chemical nickel plating solution to 4-6 to obtain the final nickel plating solution. The concentrations of solutes in the electroless nickel plating solution are as follows: 20-30 g / L NiSO4·6H2O, 20-30 g / L NaH2PO2·H2O, and 20-30 mL / L lactic acid. The electroplating process conditions are as follows: the distance between the cathode and anode is 2-4 cm, and the current density is 800-1200 mA / dm². 2 The electroplating time is 20-40 minutes, the electroplating temperature is 40-60℃, and the pH value is 8-10. Step 4: Immerse the spandex fibers dried in Step 3 in indium tin alloy for 20-40 minutes to coat them with a liquid metal layer. Step 5: The nickel-plated spandex fiber coated with liquid metal in step 4 is immersed in chitosan solution to prepare the encapsulation layer. Specifically, the spandex fiber obtained in step 4 is immersed in chitosan solution for 1-2 hours to form a film, and then dried to obtain a single-fiber vector stress-strain sensor.

[0020] Example 3 Based on Example 2, the chitosan solution was prepared according to the following method: Dissolve 2-4g of chitosan in 80-100mL of 1%-3% acetic acid solution, heat in a water bath at 50-70℃ for 10-30min and stir at 800-1000r / min to obtain chitosan solution.

[0021] The principle of the single-fiber vector stress-strain sensor based on the solid-liquid bimetallic layer coating process of spandex fiber is as follows: Spandex fiber: As an elastic substrate for sensors, it provides tensile strength and flexibility. Its polymer structure allows for large deformation and works in conjunction with the coating to transfer strain to the conductive layer. Gold nanoparticles, also known as gold seed layers, act as a catalyst layer, lowering the energy barrier in the nickel plating process and promoting uniform nickel deposition. They connect with spandex fibers through adsorption, ensuring a strong subsequent plating layer.

[0022] Nickel plating layer: As a rigid conductive layer, formed by electroless nickel plating, it provides a stable resistance path. When the fiber is stretched, the nickel layer responds first to deformation, and the resistance changes; it interacts with the liquid metal layer, enhancing conductivity through interfacial effects. Liquid metal layer: Composed of an indium-tin alloy, it serves as a dynamic compensation layer. Its fluidity fills microcracks in the nickel layer during stretching, preventing interruptions in the conductive path. It forms a solid-liquid interface with the nickel layer, bonding through capillary action to enhance the sensor's durability. Flexible encapsulation layer: Using chitosan as a protective layer, made of biopolymer material, its function is to isolate environmental interference (such as moisture or friction), improve the chemical stability of the sensor and wearability. It is connected to the liquid metal layer through hydrogen bonding to ensure the integrity of the overall structure. In terms of interaction: each layer forms a functional gradient structure—the spandex fiber bears mechanical strain, the gold seed layer guides the nickel plating, the nickel plating layer and the liquid metal layer work together to achieve conductivity and self-repair, and the chitosan layer protects the internal structure. The design of this invention enables the conductive layer to maintain continuity when the sensor is stretched, thereby solving the problem of conductivity degradation in traditional sensors.

[0023] Example 4 This invention discloses a method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fibers. The method is implemented according to the following steps: Step 1: Sensitize the spandex fiber in ethanol for 10 minutes, then rinse with deionized water and dry. Step 2, Gold Seed Attachment: Prepare a 20 mol / L chloroauric acid solution and a 0.01 g / L sodium borohydride solution. Pour 100 mL of each solution into a petri dish. Immerse the soaked spandex yarn in the chloroauric acid solution for 1 minute, then rinse 2-3 times with water. Next, immerse it in the sodium borohydride solution for 1 minute, and rinse 3-5 times with water. Repeat this cycle 8 times.

[0024] Step 3, Electroplating: The spandex yarn obtained in Step 1 is stretched and wound onto a glass slide, and then immersed in a nickel plating solution for 20 minutes. The composition of the electroless nickel plating solution is: NiSO4·6H2O 20g / L, NaH2PO2·H2O 20g / L, lactic acid 20mL / L, and deionized water as the solvent. After the electroless nickel plating solution is prepared, the pH of the solution is adjusted to 4 using NaOH solution to obtain the final electroless nickel plating solution. After plating, the solution is washed with deionized water and dried to obtain nickel-plated spandex fibers.

[0025] The electroplating process conditions are: a distance of 2 cm between the cathode and anode, and a current density of 800 mA / dm². 2 The electroplating time was 20 minutes, the electroplating temperature was 40℃, and the pH value was 8.

[0026] Step 4: Immerse the nickel-plated spandex fiber obtained in Step 2 in liquid metal for 20 minutes, wherein the liquid metal is an indium-tin alloy.

[0027] Step 5: Immerse the spandex fiber obtained in Step 3 in a chitosan solution for 1 hour, form a film, and then dry it to obtain a spandex nickel / liquid metal coated fiber with high stability and high sensitivity. The chitosan solution is prepared by dissolving 2g of chitosan in 80mL of a 1% acetic acid solution and heating it in a 50℃ water bath for 10 minutes with a stirring rate of 800r / min.

[0028] The substrate of the sensor in this invention is spandex fiber, a highly elastic polymer material that provides flexibility and stretchability to the sensor. Figure 1 As shown, the original spandex fiber has a smooth cylindrical structure with a uniform diameter, providing a foundation for subsequent coating adhesion. A layer of gold nanoparticles is formed on the surface of spandex fibers through sensitization treatment and gold seed attachment steps, such as... Figure 2 As shown, gold seeds are evenly distributed on the fiber surface, serving as catalytic sites to promote the growth of subsequent metal coatings. This layer is connected to the fiber core through physical adsorption, ensuring a strong bond.

[0029] Next, a nickel layer is deposited on the fiber surface using an electroplating process to form a solid-phase metal coating, such as... Figure 3 As shown, the nickel-plated metal layer completely covers the fiber, exhibiting a continuous metallic luster. It is chemically bonded to the gold seed layer, forming the rigid conductive part of the sensor. This layer provides the main conductive path and has a certain degree of mechanical strength.

[0030] A liquid metal (such as an indium-tin alloy) is coated on top of the nickel plating layer as a dynamic compensation layer, such as... Figure 4 As shown, the liquid metal layer fills the microscopic defects in the nickel layer, forming a solid-liquid bimetallic interface. This interface bonds with the nickel layer through wetting, enhancing the ductility of the conductive layer. This layer, acting as a flowable conductive medium, can compensate for cracks during tensile testing.

[0031] The flexible encapsulation layer is a chitosan coating layer, which serves a protective function, as shown in the attached image. Figure 5 As shown, the chitosan membrane uniformly coats the entire fiber and is connected to the liquid metal layer through physical cross-linking, preventing coating detachment and improving the sensor's biocompatibility. Thus, the sensor forms a multi-layered structure with spandex fiber as the core, consisting of a gold seed layer, a nickel plating layer, a liquid metal layer, and a chitosan layer from the inside out. Each layer is tightly connected through chemical or physical means to ensure overall consistency.

[0032] As a single-fiber device, the sensor can be directly woven into textiles. Its electrical connection is achieved through electrodes at both ends of the fiber (such as by connecting to the measurement circuit through silver paste or wires). It has a simple and compact structure and is suitable for wearable applications.

[0033] The sensor fabricated in this invention operates based on the piezoresistive effect: when a fiber is subjected to tensile stress, the geometry of the conductive layer (nickel plating and liquid metal) changes, leading to a change in resistance. By monitoring the resistance value, the magnitude and direction of the strain (vector information) can be deduced. The working process is as follows: Strain application: The sensor is attached to the monitored area (such as a human joint). When the area moves and is stretched, the spandex fiber deforms and transmits the strain to the conductive layer. Resistance response: In the conductive layer, the nickel plating layer serves as the main conductive path, and its resistance increases with stretching; the liquid metal layer flows dynamically, compensating for any cracks that may appear in the nickel layer and maintaining conductive continuity. For example... Figure 6 As shown, the sensor prepared in this embodiment exhibits a rapid increase in resistance and a short response time when stretched, indicating that its working principle is highly efficient. Signal monitoring: The resistance change at both ends of the fiber is measured using an external circuit (such as a simple bridge or ohmmeter), and the data can be converted into strain values, such as... Figure 7 Cyclic tests showed that the sensor prepared in this embodiment exhibited stable resistance changes under repeated stretching, proving the effectiveness of the liquid metal compensation mechanism. Vector monitoring: Due to the one-dimensional structure of fibers, the tensile direction is related to the change in resistance, thus enabling the differentiation of strain directions (e.g., transverse or longitudinal) and achieving vector monitoring. Figure 8-12 As shown, an application example is presented: Figure 8 The graphs showing the change in resistance under tension at different original lengths of the sensors demonstrate that the change in sensor resistance is only related to the tension length and is independent of the original length of the sensors, thus verifying the universality of the working principle. Figures 9 to 12 The graphs show the resistance changes when the sensor is attached to the neck, elbow, wrist, and knee, corresponding to nodding, elbow flexion, wrist flexion, and knee flexion movements. The resistance signal changes with the amplitude of the movement, proving that the sensor can monitor human movement in real time.

[0034] Example 5 This invention discloses a method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fibers. The method is implemented according to the following steps: Step 1: Sensitize the spandex fiber in ethanol for 15 minutes, then rinse with deionized water and dry. Step 2, Gold Seed Attachment: Prepare a 25 mol / L chloroauric acid solution and a 0.02 g / L sodium borohydride solution. Pour 100 mL of each solution into a petri dish. Immerse the soaked spandex yarn in the chloroauric acid solution for 2 minutes, then rinse 2-3 times with water. Next, immerse the yarn in the sodium borohydride solution for 2 minutes, rinsing 3-5 times with water. Repeat this cycle 8 times.

[0035] Step 3, Electroplating: The spandex yarn obtained in Step 1 is stretched and wound onto a glass slide, and then immersed in a nickel plating solution for 25 minutes. The composition of the electroless nickel plating solution is: NiSO4·6H2O 225g / L, NaH2PO2·H2O 25g / L, lactic acid 25mL / L, and deionized water as the solvent. After the electroless nickel plating solution is prepared, the pH of the solution is adjusted to 5 using NaOH solution to obtain the final electroless nickel plating solution. After plating, the solution is washed with deionized water and dried to obtain nickel-plated spandex fiber.

[0036] The electroplating process conditions are: a distance of 3 cm between the cathode and anode, and a current density of 1000 mA / dm². 2 The electroplating time was 30 minutes, the electroplating temperature was 50℃, and the pH value was 9.

[0037] Step 4: Immerse the nickel-plated spandex fiber obtained in Step 2 in liquid metal for 30 minutes, wherein the liquid metal is an indium-tin alloy.

[0038] Step 5: Immerse the spandex fiber obtained in Step 3 in a chitosan solution for 1.5 hours, form a film, and then dry it to obtain a spandex nickel / liquid metal coated fiber with high stability and high sensitivity. The chitosan solution is prepared by dissolving 3g of chitosan in 80mL of a 2% acetic acid solution and heating it in a 60℃ water bath for 20 minutes with a stirring rate of 900r / min.

[0039] Example 6 This invention discloses a method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fibers. The method is implemented according to the following steps: Step 1: Sensitize the spandex fiber in ethanol for 20 minutes, then rinse with deionized water and dry. Step 2, Gold Seed Attachment: Prepare a 30 mol / L chloroauric acid solution and a 0.03 g / L sodium borohydride solution. Pour 100 mL of each solution into a petri dish. Immerse the soaked spandex yarn in the chloroauric acid solution for 3 minutes, then rinse 2-3 times with water. Next, immerse the yarn in the sodium borohydride solution for 3 minutes, rinsing 3-5 times with water. Repeat this cycle 8 times.

[0040] Step 3, Electroplating: The spandex yarn obtained in Step 1 is stretched and wound onto a glass slide and immersed in a nickel plating solution for 30 minutes. The composition of the electroless nickel plating solution is: NiSO4·6H2O 30g / L, NaH2PO2·H2O 30g / L, lactic acid 30mL / L, and deionized water as the solvent. After the electroless nickel plating solution is prepared, the pH of the solution is adjusted to 6 using NaOH solution to obtain the final electroless nickel plating solution. After plating, the solution is washed with deionized water and dried to obtain nickel-plated spandex fibers.

[0041] The electroplating process conditions are: a distance of 4 cm between the cathode and anode, and a current density of 1200 mA / dm². 2 The electroplating time was 40 minutes, the electroplating temperature was 60℃, and the pH value was 10.

[0042] Step 4: Immerse the nickel-plated spandex fiber obtained in Step 2 in liquid metal for 40 minutes, wherein the liquid metal is an indium-tin alloy.

[0043] Step 5: Immerse the spandex fiber obtained in Step 3 in a chitosan solution for 2 hours, form a film, and then dry it to obtain a spandex nickel / liquid metal coated fiber with high stability and high sensitivity. The chitosan solution is prepared by dissolving 4g of chitosan in 80mL of a 3% acetic acid solution and heating it in a 70℃ water bath for 30min with a stirring rate of 1000r / min.

Claims

1. A single-fiber vector stress-strain sensor based on a solid-liquid bimetallic coating process for spandex fiber surface, characterized in that, The invention includes spandex fibers as a matrix, a lower electrode layer is deposited on the surface of the matrix, an upper electrode layer is deposited on the lower electrode layer, and the matrix, the lower electrode layer, and the lower electrode layer are encapsulated by a flexible encapsulation layer. The lower electrode layer consists of gold nanoparticles attached to a substrate, the upper electrode layer includes a nickel-plated metal layer on the lower electrode layer and a liquid metal layer coated on the nickel-plated metal layer, and the flexible encapsulation layer is made of chitosan.

2. A method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fibers, characterized in that, The specific steps are as follows: Step 1: Sensitize the spandex fiber; Step 2: Using the spandex fiber treated in Step 1 as a substrate, gold nanoparticles are grown on its surface as the lower electrode layer. Step 3: Place the spandex fiber treated in Step 2 into the nickel plating solution for plating, and plate a metal nickel layer on the lower electrode layer. After plating, rinse with deionized water and dry. Step 4: Place the spandex fibers dried in Step 3 into liquid metal to coat them with a liquid metal layer. Step 5: Immerse the nickel-plated spandex fiber coated with liquid metal in step 4 in a chitosan solution to prepare the encapsulation layer.

3. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 2, characterized in that, The sensitization treatment in step 1 specifically involves immersing the spandex fiber in ethanol for 10-20 minutes, then rinsing it with deionized water and drying it.

4. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 2, characterized in that, Step 2 specifically involves: preparing a chloroauric acid solution with a concentration of 20-30 mol / L and a sodium borohydride solution with a concentration of 0.01-0.03 g / L; then stretching and winding spandex fibers onto a glass slide; immersing the slide in the chloroauric acid solution for 1-3 minutes, then rinsing it with water 3-5 times; immersing it in the sodium borohydride solution for 1-3 minutes, then rinsing it with water 3-5 times; repeating this process of immersion in chloroauric acid solution, rinsing with water, immersion in sodium borohydride solution, and rinsing with water 8 times; and finally drying the slide.

5. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 4, characterized in that, Step 3 specifically involves stretching and winding the spandex fibers with gold nanoparticles grown on the surface obtained in step 2 onto a glass slide, immersing them in a nickel plating solution for 20-30 minutes, washing them with deionized water after plating, and then drying them to obtain the spandex fibers with a nickel plating layer.

6. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 5, characterized in that, The nickel plating solution is prepared as follows: using deionized water as a solvent, NiSO4·6H2O, NaH2PO2·H2O, and lactic acid are dissolved in the solvent to obtain a chemical nickel plating solution. Then, NaOH solution is used to adjust the pH of the chemical nickel plating solution to 4-6 to obtain the final nickel plating solution. The concentrations of solutes in the electroless nickel plating solution are as follows: 20-30 g / L NiSO4·6H2O, 20-30 g / L NaH2PO2·H2O, and 20-30 mL / L lactic acid.

7. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 6, characterized in that, During the plating process in step 3, the electroplating conditions are as follows: the distance between the cathode and anode is 2-4 cm, and the current density is 800-1200 mA / dm². 2 The electroplating time is 20-40 minutes, the electroplating temperature is 40-60℃, and the pH value is 8-10.

8. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 7, characterized in that, Step 4 specifically involves immersing the spandex fibers dried in step 3 in an indium tin alloy for 20-40 minutes to coat them with a liquid metal layer.

9. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 7, characterized in that, Step 5 specifically involves immersing the spandex fiber obtained in step 4 in a chitosan solution for 1-2 hours to form a film, and then drying it to obtain a single-fiber vector stress-strain sensor.

10. The method for fabricating a single-fiber vector stress-strain sensor based on a solid-liquid bimetallic layer coating process on the surface of spandex fiber according to claim 9, characterized in that, The chitosan solution was prepared according to the following method: Dissolve 2-4g of chitosan in 80-100mL of 1%-3% acetic acid solution, heat in a water bath at 50-70℃ for 10-30min and stir at 800-1000r / min to obtain chitosan solution.

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