Double-sensing-mechanism flexible sensor and preparation method and application thereof

Abstract

The invention relates to the technical field of flexible sensors, in particular to a dual-sensing-mechanism flexible sensor and a preparation method and application thereof.According to the dual-sensing-mechanism flexible sensor, a green and environment-friendly high-molecular polymer serves as a main body material, and the conductivity of hydrogel is achieved through interaction of an ionized ion solution or conductive particles and the hydrogel. Conductive hydrogel is used as an electrode material, non-conductive hydrogel is used as a friction layer and matched with an elastomer material to serve as a packaging layer, and a friction layer hydrogel-electrode layer hydrogel-friction layer hydrogel and elastomer packaging edge sandwich structure is prepared; the preparation method is simple, the wearable sensing function is achieved based on the coupling effect of two different sensing mechanisms of piezoresistive sensing and triboelectric sensing, and compared with a traditional hydrogel sensor, the hydrogel sensor has more sensing functions, sensing signals are more stable and accurate, and the anti-interference effect of the whole sensing system is better.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and particularly relates to a flexible sensor with a dual sensing mechanism, a preparation method thereof, and an application thereof. Background Art

[0002] A sensor can convert external physical, chemical and other signals into electrical signals. Most traditional sensors are made of rigid materials, which are difficult to meet the needs of some special occasions, and the convenience of use is greatly limited. Flexible sensors have good application prospects in the fields of human-computer interaction, soft robots, motion detection, wearable devices, electronic skin, etc. due to their good toughness and wide response range.

[0003] Some methods for preparing sensors using flexible materials have been reported in the existing literature. For example, materials such as polymer polymers, papers, and textiles are used as substrate materials to make the sensors have excellent stretchability. For example, PDMS and graphite are used, and a piezoresistive sensor is prepared with graphite as the middle interlayer. However, PDMS is difficult to degrade, and the preparation process is relatively complex and costly. A pressure sensor is prepared using graphene, silver nanosheets and polymer materials, making the sensor have characteristics such as small size, high resolution, fast response and high sensitivity. Since this method uses silver nanosheets, the manufacturing cost of the sensor is relatively high; some also use other metal materials to increase the conductivity of the sensor, but the chemical activity of the metal is relatively high and it is easy to be oxidized. When the sensor is used for a long time, the sensing effect will decline.

[0004] Hydrogels have good toughness, ductility, stretchability, and adhesiveness, and can adhere well to other objects. Due to the high water content and stable three-dimensional network structure of hydrogels, hydrogels are good substrate materials for making electronic skin, wearable devices, and flexible sensors.

[0005] However, most of the existing flexible sensors prepared from hydrogels are piezoresistive sensing, triboelectric sensing, and piezoelectric sensing, but the sensing systems are mostly single-signal sensing, and the accuracy of the obtained information needs to be improved, and they are prone to failure after being interfered by the external environment.

[0006] The existing flexible sensors have a single sensing mechanism, mostly one of triboelectric sensing, piezoelectric sensing, and piezoresistive sensing. This will lead to a lack of reliability in the signals output by the flexible sensors, and there is a lack of reliable verification means to verify the accuracy of the signals. In order to improve the accuracy of the signals output by single-signal flexible sensors, the current practice is to add materials that are difficult to degrade or more expensive materials during the preparation; this causes greater pressure on the preparation cost of the sensors and the subsequent treatment after use, and the prepared sensors still need to rely on the access of an external power source to output signals. Summary of the Invention

[0007] The present invention aims to solve the problems of a single sensing mechanism of flexible sensors, low signal credibility, and the need for an external power source for existing sensors to output signals.

[0008] To solve the above problems, the present invention is realized through the following technical solutions.

[0009] A dual-sensing mechanism flexible sensor includes a packaging layer, and the inner side wall of the packaging layer is fixedly connected to the side walls of the first friction layer, the electrode layer, and the second friction layer in a ring shape. The side walls on both sides of the electrode layer are respectively adhered and fixedly connected to the side walls of the first friction layer and the second friction layer. The other two sides of the electrode layer are respectively connected to two wires, and the wires penetrate through the side wall of the packaging layer.

[0010] The first friction layer is a non-conductive layer with a thickness of 5-8 mm. The materials of the first friction layer and the second friction layer are chitosan-polyvinyl alcohol hydrogel.

[0011] The electrode layer is a conductive layer with a thickness of 5-8 mm. The material of the electrode layer is phosphoric acid-chitosan-glycerol-polyvinyl alcohol hydrogel.

[0012] The packaging layer is a non-conductive elastic layer with a thickness of 0.5-2 mm. The material of the packaging layer is AB-phase silica gel.

[0013] Preferably, the wire is a copper wire.

[0014] Preferably, the packaging layer is a dumbbell-shaped shell, and both sides of the shell are open. The open ends on both sides are respectively adhered to the edges of the side walls of the first friction layer and the second friction layer.

[0015] Preferably, the first friction layer, the electrode layer, and the second friction layer are all dumbbell-shaped cylinders.

[0016] Preferably, the dual-sensing mechanism flexible sensor is dumbbell-shaped, and in the dual-sensing mechanism flexible sensor, the electrode layer is respectively connected to the first friction layer and the second friction layer to form a sandwich structure.

[0017] Preferably, the first friction layer and the second friction layer are exactly the same.

[0018] A preparation method of a dual-sensing mechanism flexible sensor includes the following steps: S1. Mix and heat and stir an aqueous chitosan solution and an aqueous polyvinyl alcohol solution to obtain a friction layer hydrogel solution; S2. Mix and heat and stir an aqueous phosphoric acid-chitosan solution and an aqueous phosphoric acid-glycerol-polyvinyl alcohol solution to obtain an electrode layer hydrogel solution; S3. After placing wires at both ends of the friction layer hydrogel solution in step S1 and the electrode layer hydrogel solution in step S2, freeze-thaw cycles are performed multiple times to obtain the friction layer hydrogel and the electrode layer hydrogel; S4. Place the friction layer hydrogel in step S3 on the upper and lower sides of the electrode layer hydrogel in step S3, and perform freeze-thaw cycles multiple times to obtain a hydrogel sensor; S5. Package, heat, and dry the hydrogel sensor in step S4 to obtain a dual-sensing mechanism flexible sensor.

[0019] In step S1, by volume ratio, chitosan aqueous solution: polyvinyl alcohol aqueous solution = 1: 0.8 - 4, the heating temperature is 35 - 45 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 40 rpm.

[0020] Preferably, in step S1, by mass ratio, chitosan in the chitosan aqueous solution: water = 1: 10 - 20. When preparing the chitosan aqueous solution, the heating temperature is 35 - 45 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 40 rpm.

[0021] Preferably, in step S1, by mass ratio, polyvinyl alcohol in the polyvinyl alcohol aqueous solution: water = 1: 10 - 20. When preparing the polyvinyl alcohol aqueous solution, the heating temperature is 90 - 95 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 30 rpm.

[0022] In step S2, by volume ratio, phosphoric acid-chitosan aqueous solution: phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1: 0.8 - 4, the heating temperature is 90 - 95 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 30 rpm.

[0023] Preferably, in step S2, by mass ratio, in the phosphoric acid-chitosan aqueous solution, phosphoric acid: chitosan: water = 1: 1 - 2: 10 - 20. When preparing the phosphoric acid-chitosan aqueous solution, the heating temperature is 35 - 45 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 30 rpm.

[0024] Preferably, in step S2, by mass ratio, in the phosphoric acid-glycerol-polyvinyl alcohol aqueous solution, phosphoric acid: glycerol: polyvinyl alcohol: water = 1: 1 - 2: 1 - 2: 10 - 20. When preparing the phosphoric acid-glycerol-polyvinyl alcohol aqueous solution, the heating temperature is 90 - 95 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 30 rpm.

[0025] In step S3, by volume ratio, friction layer hydrogel solution: electrode layer hydrogel solution = 1: 1 - 1.6.

[0026] In step S3, it is frozen in an environment of -20°C to -15°C for 10 to 12 hours, and thawed in an environment of 25 - 30°C for 1.5 to 2 hours; in step S3, cycling multiple times means cycling 4 to 6 times.

[0027] In step S4, the freeze-thaw cycle is 1 to 2 times, and the freeze-thaw operation in step S4 is the same as that in step S3.

[0028] Preferably, the encapsulating material in step S5 is AB-phase silica gel.

[0029] Preferably, the drying temperature in step S5 is 45°C to 60°C, and it is dried for 2 to 3 hours.

[0030] A dual-sensing mechanism flexible sensor, and the application of the dual-sensing mechanism flexible sensor in motion detection, wearable devices, and electronic skin.

[0031] Using chitosan-polyvinyl alcohol hydrogel as the friction layer, and chitosan-polyvinyl alcohol-phosphoric acid-glycerol hydrogel as the electrode layer, and placing it in the middle, a dual-sensing mechanism hydrogel sensor in the shape of a "sandwich structure" of chitosan-polyvinyl alcohol - chitosan-polyvinyl alcohol-phosphoric acid-glycerol - chitosan-polyvinyl alcohol is obtained.

[0032] Placing the sensor with the sandwich structure on an acrylic board, applying AB-phase silica gel on the side of the hydrogel, placing the hydrogel of the sensor with the applied AB-phase silica gel in a blast drying oven, heating and standing still to wait for the silica gel to solidify, and the flexible sensor with the dual-sensing mechanism is prepared.

[0033] The flexible sensor integrates piezoresistive sensing and triboelectric sensing on one sensor. The whole sensor has a "sandwich" structure, and the conductive hydrogel in the middle serves as both the electrode layer of the piezoresistive sensor and the triboelectric sensor.

[0034] The sensor uses hydrogel as the main body, and ionic solution and elastic encapsulating material as auxiliary materials. The hydrogel is prepared by the freeze cycling method.

[0035] If the proportion of polyvinyl alcohol solution in the hydrogel of the electrode layer is too large, it is likely to cause the sensing signal of the hydrogel to weaken, and at the same time, the tensile strength increases, reducing the overall flexibility of the sensor.

[0036] The application of the dual-sensing mechanism flexible sensor in the present invention in stress, strain sensing, and flexible wearable devices.

[0037] Compared with the prior art, the beneficial effects of the present invention: 1. The preparation method of the present invention is simple and convenient, can be mass-produced in the actual production process, and the prepared flexible sensor has a wide application prospect in the fields of flexible sensing and wearable devices, etc.

[0038] 2. The main materials of the present invention are chitosan and polyvinyl alcohol. The purchase costs of the two materials are relatively low, and both have good water solubility and degradability, enabling green and harmless treatment to be well achieved after the sensor reaches the end of its service life.

[0039] 3. The sensing signal of the present invention can output one more signal compared with traditional flexible sensors, realizing the coupling of piezoresistive signals and triboelectric signals, making the sensing system more stable. The two signals can also be verified with each other. The sensing layer is the electrode layer and the tribo layers on both sides of the electrode layer. When one of the sensing layers of the present invention fails, other sensing layers can continue to support the operation of the sensing system, and the service life of the entire sensor can also be extended.

[0040] 4. In the present invention, the electrode layer of the sensor can be used as both a stress and strain sensor and as the electrode layer of a tribo sensor to collect charges.

[0041] 5. Phosphoric acid is used in the present invention to adjust the conductivity of the hydrogel of the electrode layer, making it easier to obtain conductivity for the hydrogel of the electrode layer. The dropped conductive ion solution is a low-concentration and weakly acidic inorganic acid. In an acidic environment, the solubility of chitosan increases, making it easier to form a double-network crosslinked hydrogel with polyvinyl alcohol, giving the sensor good toughness.

[0042] When preparing the hydrogel of the electrode layer, a high-concentration conductive ion solution cannot be used. The hydrogel of the electrode layer contains more moisture at room temperature. When the two hydrogels are adhered, the conductive ions phosphate and hydrogen ions inside the electrode layer will penetrate into the tribo layer hydrogel on the contact surface, resulting in a weakened triboelectric effect of the sensor. Nor can an acid with strong oxidizing property be used, which will cause the polymer molecular chain to depolymerize, reducing the performance of the hydrogel of the electrode layer.

[0043] The encapsulation layer material in the present invention is an elastic insulating material AB-phase silica gel, which not only plays a role in fixing the two hydrogels, preventing the sensor from falling apart during repeated bending deformation, but also plays a role in fixing the led-out wires, preventing the wires from falling off during use. At the same time, the elastic material can also better fix the components inside the flexible sensor and make the sensor better adhere to the human skin. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 a is the resistance test diagram of the hydrogel of the electrode layer in the initial state of Example 1, Figure 1 b is the resistance test diagram of the hydrogel of the electrode layer in the stretched state of Example 1.

[0045] Figure 2 is the schematic diagram of the change rate of the resistance after the hydrogel of the electrode layer in Example 1 is reciprocally stretched by 2.5 cm.

[0046] Figure 3 a is a physical diagram and schematic diagram of Example 1, where the electrode layer hydrogel is attached to the finger as a piezoresistive sensor to detect the change rate of resistance during the movement of the finger joint; Figure 3 b is a physical diagram and schematic diagram of Example 1, where the electrode layer hydrogel is attached to the wrist as a piezoresistive sensor to detect the change rate of resistance during the movement of the wrist joint.

[0047] Figure 4 It is a test diagram of the triboelectrically lit LED lamp of the dual-sensing mechanism flexible sensor in Example 1.

[0048] Figure 5 a is a schematic diagram of the resistance change rate when the chitosan to polyvinyl alcohol ratio is 1:0.8 in Example 1; Figure 5 b is a schematic diagram of the change rate of resistance of different ratios of chitosan to polyvinyl alcohol in Example 1.

[0049] Figure 6 a is a physical diagram of the dual-sensing flexible sensor in the knee joint leg-lifting test in Example 1; Figure 6 b is a physical diagram of the dual-sensing flexible sensor in the knee joint walking test in Example 1; Figure 6 c is a physical diagram of the dual-sensing flexible sensor in the knee joint squatting test in Example 1.

[0050] Figure 7 It is a schematic diagram of the test results of the dual-sensing mechanism flexible sensor in Example 1 under different knee joint movements; Figure 7 a is the voltage signal diagram of the leg-lifting test, Figure 7 b is the resistance change rate diagram of the leg-lifting test, Figure 7 c is the voltage signal diagram of the walking test, Figure 7 d is the resistance change rate diagram of the walking test, Figure 7 e is the voltage signal diagram of the squatting test, Figure 7 f is the resistance change rate diagram of the squatting test.

[0051] Figure 8 It is a schematic diagram of the test results of the dual-sensing mechanism flexible sensor in Example 2 under different knee joint movements; Figure 8 a is the voltage signal diagram of the leg-lifting test, Figure 8 b is the resistance change rate diagram of the leg-lifting test, Figure 8 c is the voltage signal diagram of the walking test, Figure 8 d is the resistance change rate diagram of the walking test, Figure 8 e is the voltage signal diagram for the squatting test, Figure 8 and f is the diagram of the resistance change rate for the squatting test.

[0052] Figure 9 a is the schematic diagram of the overall structure of the dual-sensing mechanism flexible sensor in Embodiment 1 of the present application.

[0053] Figure 9 b is the schematic top view of the sandwich structure after horizontal sectioning of the dual-sensing mechanism flexible sensor in Embodiment 1.

[0054] Figure 9 c is the schematic diagram of the arrangement structure of the electrode layer and the friction layer sensors at both ends of the dual-sensing mechanism flexible sensor in Embodiment 1.

[0055] Figure 10 is the schematic diagram of the triboelectric sensing measurement of the dual-sensing mechanism flexible sensor in Comparative Example 5.

[0056] Figure 9 The reference numerals in the figures: the first friction layer 1, the electrode layer 2, the second friction layer 3, the wire 4, and the encapsulation layer 5. Detailed implementation manners

[0057] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0058] Chitosan (CS) was purchased from Tianjin Zhonglian Chemical Reagent Co., Ltd., model: the deacetylation degree of the CS sample was 95%.

[0059] Polyvinyl alcohol (PVA) was purchased from Tianjin Huasheng Chemical Reagent Co., Ltd., the model of PVA was 1799, and the alcoholysis degree was 98%.

[0060] AB-phase silica gel was purchased from Beijing Sanjing Xinde Technology Co., Ltd., model: SJ3220.

[0061] In the following embodiments, unless otherwise specified, in the prepared dumbbell-shaped dual-sensing mechanism flexible sensor, the initial length of each layer of the electrode layer and the friction layer was fixed at 6.8 cm, and the initial width was fixed at 7 mm; the thickness of the electrode layer and the friction layer was subject to the data recorded in the embodiments.

[0062] Preferably, the AB-phase silica gel is the encapsulation layer with a thickness of 0.5 - 2 mm.

[0063] In the following embodiments, unless otherwise specified, thawing is carried out at room temperature of 25~30 °C, and the room temperature in the following embodiments is 25 °C.

[0064] Unless otherwise specified in the following examples, the AB-phase silica gel has a packaging layer thickness of 1 mm.

[0065] In the following examples, the data was tested using conventional methods with the corresponding instruments. The LED lamp was purchased from Guangzhou Haoyun Security Technology Co., Ltd., model LED12612. The resistance change rate tester was purchased from Shenzhen Yisheng Shengli Technology Co., Ltd., model 4091A. The voltage signal tester was purchased from St. Louis Company, model c-DAQ-9171.

[0066] Example 1 Chitosan, polyvinyl alcohol, glycerol, and phosphoric acid were selected to prepare a dual-sensing mechanism flexible sensor.

[0067] A preparation method for a dual-sensing mechanism flexible sensor includes the following steps: Step S1: Chitosan and water were mixed at a mass ratio of 1:10 and stirred at 10 rpm for 40 min in a 35°C water bath environment to obtain a chitosan aqueous solution. Polyvinyl alcohol and water were mixed at a mass ratio of 1:10 and stirred at 10 rpm for 40 min in a 95°C water bath environment until completely dissolved to obtain a polyvinyl alcohol aqueous solution. The chitosan aqueous solution and the polyvinyl alcohol aqueous solution were mixed at a volume ratio of 1:1 and stirred at 30 rpm in a 95°C water bath for 40 min to obtain a friction layer hydrogel solution.

[0068] Step S2: Phosphoric acid, chitosan, and water were mixed at a mass ratio of 1:2:20 and stirred at 30 rpm for 40 min in a 3'5°C water bath environment to obtain a phosphoric acid-chitosan aqueous solution. Phosphoric acid, glycerol, polyvinyl alcohol, and water were mixed at a mass ratio of 1:2:2:20 and stirred at 30 rpm in a 95°C water bath environment until completely dissolved to obtain a phosphoric acid-glycerol-polyvinyl alcohol aqueous solution. The phosphoric acid-chitosan aqueous solution and the phosphoric acid-glycerol-polyvinyl alcohol aqueous solution were mixed at a volume ratio of 1:1 and stirred at 30 rpm in a 95°C water bath for 40 min to obtain an electrode layer hydrogel solution.

[0069] Step S3: The two hydrogel solutions were spread flat in a mold, frozen at -20°C for 10 h, taken out, and thawed at room temperature (25°C) for 2 h. The freeze-thaw cycle was repeated 4 times. When the electrode layer hydrogel solution was first poured into the mold, copper wires should be led out at both ends of the electrode layer hydrogel solution. The copper wires should be in sufficient contact with the hydrogel solution, that is, the copper wires should be inserted 3 mm into the hydrogel solution to facilitate connection to the instrument when measuring signals later.

[0070] The volume of the hydrogel solution required for each layer is 12 ml. The triboelectric layer hydrogel and the electrode layer hydrogel are prepared respectively. Among them, To prepare the first triboelectric layer 1 and the second triboelectric layer 3, 2 portions of the same 12 ml triboelectric layer hydrogel solution in step S1 are prepared. To prepare the electrode layer hydrogel 2, 1 portion of the 12 ml electrode layer hydrogel solution in step S2 is prepared.

[0071] The triboelectric layer hydrogel is also Figure 9 a~ Figure 9 The first triboelectric layer 1 in c, and the material is chitosan-polyvinyl alcohol hydrogel.

[0072] The electrode layer hydrogel is also Figure 9 a~ Figure 9 The electrode layer 2 in c, and the material is phosphoric acid-chitosan-glycerol-polyvinyl alcohol hydrogel.

[0073] Step S4: Place the electrode layer hydrogel in the middle, and place the triboelectric layer hydrogels on the upper and lower sides of the electrode layer hydrogel respectively to form a sandwich structure. After continuing the freeze-thaw cycle 2 times, the preparation of the sensor hydrogel is completed.

[0074] In this embodiment, the thickness of each of the electrode layer and the triboelectric layer is 5 mm.

[0075] Step S5: After the hydrogel completes the freeze-thaw cycle, apply liquid silicone at the edges, and let it stand in a 45 °C air dryer for 2 - 3 h. After the silicone is completely solidified, a dual-sensing mechanism flexible sensor is obtained. The structural schematic diagram is as Figure 9 shown.

[0076] Conductivity test of the electrode layer Take the phosphoric acid-glycerol-chitosan-polyvinyl alcohol hydrogel as one section of the wire and connect it to the circuit. When a 5 V DC power supply is turned on, the LED light is lit. When the hydrogel is stretched, the brightness of the LED light decreases. The hydrogel has certain conductivity, and at the same time, the resistance changes during stretching. As Figure 1 a~ Figure 1 shown in b, it can be observed that the resistance increases from 1.0319 KΩ to 2.4725 KΩ, indicating that the electrode layer hydrogel has conductivity.

[0077] Electrode layer tensile resistance change Prepare the electrode layer hydrogel into a dumbbell shape, and connect wires to both ends of the hydrogel. Continuously stretch the hydrogel reciprocally to obtain the change rate of the resistance of the hydrogel during stretching. When stretching a length of 2.5 cm reciprocally, it can be observed that the change rate of the resistance of the hydrogel is stable at around 90% and remains constant. The tensile resistance change rate is as Figure 2 shown.

[0078] Electrode layer motion sensing test Attach the dumbbell-shaped hydrogel to the finger joints and wrist joints. When the finger joints and wrist joints bend, the hydrogel undergoes strain, causing the internal conductive ions to rearrange, resulting in a change in the resistance of the hydrogel. Based on the resistance change of the hydrogel, the motion of some joint parts can be sensed. The test results are as Figure 3 a~ Figure 3 shown in b. When the finger bends about 45 degrees, the resistance change rate is 30%. When the finger bends about 90 degrees, the resistance change rate is 35%. When the finger is fully bent, the resistance change rate reaches 45%. When the finger is fully extended, the resistance change rate returns to 0. When the wrist bends back and forth, the resistance change rate continuously changes and remains near 90%, and there are no large data fluctuations.

[0079] Triboelectric performance test Figure 4 In, the LED lights are connected in series and soldered on the circuit board. One end of the series-connected LED lights is grounded, and the other end is connected to the copper wire of the dual-sensing mechanism flexible sensor. Use a polytetrafluoroethylene film to vertically contact the friction layer 1 or friction layer 3 of the dual-sensing mechanism flexible sensor, and the LED lights will light up, as shown in Figure 4 . When contacting back and forth, the LED lights alternate between on and off.

[0080] Place the prepared dual-sensing mechanism flexible sensor on a vertical reciprocating contact test bench, select a polytetrafluoroethylene film as the other friction layer, and test the power supply ability at a contact frequency of 2 Hz. The results are as Figure 4 shown; connect the LED lights in series in the circuit, and 11 LED bulbs can be lit after contact.

[0081] Dual-sensing test Fix the dual-signal sensor on the knee and test the electrical signals generated during leg lifting, walking, and squatting respectively. The measurements are as Figure 6 a~ Figure 6 c shown, and the measurement results are as Figure 7 a~ Figure 7 f shown; the voltage signal during leg lifting is -1V~0.75V, and the resistance change rate is 25%. The voltage signal during walking is -3V~2V, and the resistance change rate is 32%. The voltage signal during squatting is -2.5V~2V, and the resistance change rate is 32%. Therefore, when the resistance change rate is close, the voltage signal can be used for differentiation.

[0082] Example 2 Compared with Example 1, the difference is that the thickness of both the friction layer and the electrode layer is 8 mm, and the amount of hydrogel solution required for each layer in step S3 is 16 ml. Other conditions are exactly the same as those in Example 1.

[0083] When the thicknesses of both the electrode layer and the friction layer become 8 mm, the triboelectric and piezoresistive change data obtained are as Figure 8 shown. The measured triboelectric data during squatting is -4 V to 4 V, the voltage magnitude during 90-degree leg raising is -3 V to 3 V, and the voltage during walking is -0.75 V to 0.5 V. The piezoresistive sensing signal is that the resistance change rate during squatting is 40%, the resistance change rate during leg raising is 25%, and the resistance change rate during walking is 15%.

[0084] The voltage signal increases during squatting, decreases during walking, and remains unchanged during leg raising. In terms of the resistance change rate, the resistance change rate values generated by the three motions have a large difference and are more distinguishable. Example 3 Compared with Example 1, the difference is that in step S2, the phosphoric acid-chitosan aqueous solution and the phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1:0.8, and the others are exactly the same as in Example 1.

[0085] The maximum resistance change rate measured by reciprocating stretching of 2.5 cm is 150.26%, and the measurement results are as Figure 5 shown in a.

[0086] Analysis of various data: The measured voltage signal during leg raising is -3.5 V to 4 V, and the resistance change rate is 5.5%. The voltage signal during walking is -0.4 V to 0.5 V, and the resistance change rate is approximately 7.1%. The voltage signal during squatting is -9.5 V to 10 V, and the resistance change rate is 10.33%.

[0087] The magnitude of the voltage signal during squatting is twice that during leg raising, and the voltage signal during walking is within -0.5 V to 0.5 V. When the resistance change rates are close, it is distinguished according to the magnitude of the voltage value. At the same time, during leg raising and squatting, the knee bending amplitudes are close, but the voltage signals are quite different, and the actions causing the signals can be better distinguished according to the voltage signals.

[0088] Example 4 Compared with Example 1, the difference is that in step S2, in terms of volume ratio, when the phosphoric acid-chitosan aqueous solution: phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1:4, the others are exactly the same as in Example 1.

[0089] The resistance change rate is 115.7%.

[0090] Data analysis of each item: The measured voltage signal during leg raising is -3V to 4.2V, and the resistance change rate is 24.3%. The voltage signal during walking is -1.5V to 1V, and the resistance change rate is 22.13%. The voltage signal during squatting is -5V to 4.5V, and the resistance change rate is 33.8%. When the resistance change rates during leg raising and walking are close, the action that forms the signal can be judged according to the voltage signal.

[0091] Example 5 As Figure 9 a~ Figure 9 c shown, a dual-sensing mechanism flexible sensor includes a packaging layer 5. The inner side wall of the packaging layer 5 is fixedly connected to the side walls of the first friction layer 1, the electrode layer 2, and the circumferential side of the second friction layer 3. The side walls on both sides of the electrode layer 2 are respectively attached to the side walls of the first friction layer 1 and the second friction layer 3. The other two sides of the electrode layer 2 are respectively connected to two wires 4, and the wires 4 penetrate through the side wall of the packaging layer 5.

[0092] The first friction layer 1 is a non-conductive layer with a thickness of 5 to 8 mm. The materials of the first friction layer 1 and the second friction layer 3 are chitosan-polyvinyl alcohol hydrogel.

[0093] The electrode layer 2 is a conductive layer with a thickness of 5 to 8 mm. The material of the electrode layer 2 is phosphoric acid-chitosan-glycerol-polyvinyl alcohol hydrogel.

[0094] The packaging layer 5 is a non-conductive elastic layer with a thickness of 0.5 - 2 mm. The material of the packaging layer 5 is AB-phase silica gel.

[0095] Preferably, the wire 4 is a copper wire.

[0096] Preferably, the packaging layer 5 is a dumbbell-shaped shell with open ends on both sides. The open ends on both sides are respectively attached to the edge of the side wall of the first friction layer 1 and the second friction layer B.

[0097] Preferably, the first friction layer 1, the electrode layer 2, and the second friction layer 3 are all dumbbell-shaped cylinders.

[0098] Preferably, the dual-sensing mechanism flexible sensor is dumbbell-shaped. In the dual-sensing mechanism flexible sensor, the electrode layer 2 is respectively connected to the first friction layer 1 and the second friction layer 3 to form a sandwich structure.

[0099] Preferably, the first friction layer 1 and the second friction layer 3 are exactly the same.

[0100] Comparative Example 1 The difference from Example 1 is that, by volume ratio, phosphoric acid-chitosan aqueous solution: phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1:0.5. Other conditions are the same as those in Example 1. The hydrogel lacks the crosslinking of chitosan molecular chains and polyvinyl alcohol molecular chains inside, and its mechanical properties are poor and it cannot withstand stretching. It will break when stretched by 2.5 cm, and the sensor cannot be successfully prepared.

[0101] Comparative Example 2 The difference from Example 1 is that, by volume ratio, when phosphoric acid-chitosan aqueous solution: phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1:8, the resistance change rate drops to 89%. Other conditions are the same as those in Example 1. When the proportion of the polyvinyl alcohol solution is on the high side, the resistance change rate will decrease when stretching the same length. In the subsequent application of the sensor, it is difficult to have good data on the resistance change rate.

[0102] Comparative Example 3 Compared with Example 1, the difference is that the thickness of each layer is changed to 9 mm, and other conditions remain unchanged. In step S4, after the friction layer and the electrode layer are stacked together, after two freeze-thaw cycles, the friction layer and the electrode layer are separated, making the obtained electrical signal difficult to use and causing large interference by itself; with the increase in thickness, a sandwich-structured sensor cannot be manufactured.

[0103] Comparative Example 4 Compared with Example 1, the difference is that the thickness of each layer is changed to 3 mm, and other conditions remain unchanged. If the thickness of each layer is to be changed, when spreading the hydrogel solution, the liquid level thickness will be lower than that in Example 1, resulting in excessive loss of moisture in the friction layer and the electrode layer after four freeze-thaw cycles in step S3, and the hydrogel shows hardening and warping phenomena, resulting in incomplete fitting of the friction layer and the electrode layer when the friction layer and the electrode layer are stacked in step S4. Finally, a sandwich-structured sensor cannot be manufactured.

[0104] Comparative Example 5 Compared with Example 1, the difference is that in step S2, by volume ratio, when phosphoric acid-chitosan aqueous solution: phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1:6, and other conditions are exactly the same as those in Example 1.

[0105] The resistance change rate is 111.598%.

[0106] Data analysis: Under this ratio, no obvious peak can be seen through the comparison of the voltage signal waveform, and the point at 0V cannot be seen in the measured waveform. No voltage signal change can be seen when the voltage signal is -1V~0.5V, indicating that it is impossible to identify when it is in the walking state and the walking frequency cannot be seen. In addition, the voltage size of the data drops from 2V to 1.75V in the first 4 seconds, and the voltage is not stable enough in the subsequent time. At the same time, it cannot have similar waveforms as Example 1 and Example 2. The peak is wide and there is more noise. Figure 10 .

[0107] When using triboelectric sensing alone, it is obvious that there is a lot of noise in the data. Figure 10 .

[0108] Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will appreciate that modifications may be made to the technical solutions described in the embodiments, or that some of the technical parameters may be replaced by equivalents. Those skilled in the art will appreciate that the material required to prepare the hydrogel may also be cellulose, and the ionic solution may be acetic acid, dilute hydrochloric acid, dilute sulfuric acid, or the like. Any modifications, equivalent replacements, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A dual-sensing mechanism flexible sensor, characterized in that, It includes a packaging layer (5), and the inner side wall of the packaging layer (5) is fixedly connected to the side walls of the first friction layer (1), the electrode layer (2), and the circumferential side of the second friction layer (3). The side walls on both sides of the electrode layer (2) are respectively attached to the side walls of the first friction layer (1) and the second friction layer (3). The other two sides of the electrode layer (2) are respectively connected to two wires (4), and the wires (4) penetrate through the side wall of the packaging layer (5).

2. The flexible sensor with a dual-sensing mechanism according to claim 1, characterized in that, The first friction layer (1) is a non-conductive layer with a thickness of 5 - 8 mm, and the materials of the first friction layer (1) and the second friction layer (3) are chitosan-polyvinyl alcohol hydrogel.

3. The flexible sensor with a dual-sensing mechanism according to claim 1, wherein The electrode layer (2) is a conductive layer with a thickness of 5 - 8 mm, and the material of the electrode layer (2) is phosphoric acid-chitosan-glycerol-polyvinyl alcohol hydrogel.

4. The flexible sensor with a dual sensing mechanism according to claim 1, characterized in that, The packaging layer (5) is a non-conductive elastic layer with a thickness of 0.5 - 2 mm, and the material of the packaging layer (5) is AB-phase silica gel.

5. The preparation method of a dual-sensing mechanism flexible sensor according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Mix the chitosan aqueous solution and the polyvinyl alcohol aqueous solution, heat and stir to obtain a friction layer hydrogel solution. S2. Heat and stir the phosphoric acid-chitosan aqueous solution and the phosphoric acid-glycerol-polyvinyl alcohol aqueous solution to obtain an electrode layer hydrogel solution. S3. After placing wires at both ends of the friction layer hydrogel solution in step S1 and the electrode layer hydrogel solution in step S2, freeze and thaw cyclically for multiple times to obtain a friction layer hydrogel and an electrode layer hydrogel. S4. Place the friction layer hydrogel in step S3 on the upper and lower sides of the electrode layer hydrogel in step S3, and freeze and thaw cyclically for multiple times to obtain a hydrogel sensor. S5. Package, heat, and dry the hydrogel sensor in step S4 to obtain a dual-sensing mechanism flexible sensor.

6. The preparation method of a dual-sensing mechanism flexible sensor according to claim 5, characterized in that, In step S1, by volume ratio, chitosan aqueous solution: polyvinyl alcohol aqueous solution = 1:0.8 - 4, the heating temperature is 35 - 45 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 40 rpm. In step S1, by mass ratio, chitosan in the chitosan aqueous solution: water = 1:10 - 20. In step S1, by mass ratio, polyvinyl alcohol in the polyvinyl alcohol aqueous solution: water = 1:10 - 20.

7. The preparation method of a dual-sensing mechanism flexible sensor according to claim 5, characterized in that, In step S2, by volume ratio, phosphoric acid-chitosan aqueous solution: phosphoric acid-glycerol-polyvinyl alcohol aqueous solution = 1:0.8 - 4, the heating temperature is 90 - 95 °C, the stirring time is 40 - 60 min, and the stirring rate is 10 - 30 rpm. In step S2, by mass ratio, in the phosphoric acid-chitosan aqueous solution, phosphoric acid: chitosan: water = 1:1 - 2:10 - 20. In step S2, by mass ratio, in the phosphoric acid-glycerol-polyvinyl alcohol aqueous solution, phosphoric acid: glycerol: polyvinyl alcohol: water = 1:1 - 2:1 - 2:10 - 20.

8. The preparation method of a dual-sensing mechanism flexible sensor according to claim 5, characterized in that, In step S3, by volume ratio, friction layer hydrogel solution: electrode layer hydrogel solution = 1:1 - 1.

6.

9. The preparation method of a dual-sensing mechanism flexible sensor according to claim 5, characterized in that, In step S3, the freezing is carried out in an environment of -20 °C to -15 °C for 10 - 12 h, and the thawing is carried out in an environment of 25 - 30 °C for 1.5 - 2 h; the multiple cycles in step S3 are 4 - 6 cycles.

10. A dual-sensing mechanism flexible sensor according to any one of claims 1 to 4, characterized in that The application of the dual-sensing mechanism flexible sensor in motion detection, wearable devices, and electronic skin.

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