Strain-temperature-pressure multi-mode flexible sensing device and preparation method thereof

Abstract

The invention provides a strain-temperature-pressure multi-mode flexible sensing device and a preparation method thereof. The flexible sensing device comprises a soft substrate, a strain layer, a pressure-sensitive layer, a temperature-sensitive layer and a base, the strain layer is a cobweb-shaped electric conductor, can be used for strain sensing and can also be used as a lower electrode of the pressure sensing structure; the pressure-sensitive layer is a sponge which has good conductivity in a pressed state and is loaded with carbon nanotubes and thermoplastic polyurethane, and the sponge is compact in structure and small in pore diameter, so that the pressure-sensitive layer has excellent elastic modulus and a wide pressure detection range; the temperature-sensitive layer is an ink layer with a positive conductivity coefficient characteristic, and can be used as a lower electrode of a temperature sensing structure and a pressure sensing structure; according to the device, monitoring of three physical parameters including strain, temperature and pressure can be achieved, the multi-parameter sensing capacity is successfully fused into a single device, the interaction capacity and the detection dimension of the device are improved, and the applicability of the device in the fields of health monitoring, intelligent wearing and the like is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensing devices, and in particular to a strain-temperature-pressure multimodal flexible sensor device and a preparation method thereof. Background Art

[0002] At present, most traditional flexible sensing devices only have a single sensing function. However, in some practical scenarios, multiple physical quantities often need to be monitored collaboratively. Therefore, researchers focus on integrating multiple physical sensing capabilities into a single device, thereby giving the single device excellent intelligence and interactive characteristics. Because flexible sensors are often used as wearable electronic devices and need to be in contact with the human body for a long time, the development of flexible sensing devices has gradually tended towards green, non-toxic, environmentally friendly, biocompatible, and even biodegradable materials in the past decade. At the same time, organisms in nature often provide important inspiration to scientists. After millions of years of evolution and testing, biological structures and materials such as spider webs, lotus leaf surfaces, and lobster cuticles have provided directions for people to innovatively and rationally design new structures and prepare new materials in flexible sensing devices.

[0003] The current flexible pressure sensing devices can only sense pressure and have a single function; based on this, it is necessary to improve the existing flexible pressure sensing devices. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a strain-temperature-pressure multimodal flexible sensor device and a preparation method thereof.

[0005] The present invention provides the following technical solutions:

[0006] The present invention provides a strain-temperature-pressure multimodal flexible sensor device, comprising:

[0007] soft substrate;

[0008] a strain layer, located on the surface of the soft substrate, wherein the strain layer is a spider-web-shaped conductor;

[0009] a pressure-sensitive layer, located on a surface of the strain layer away from the soft substrate, wherein the pressure-sensitive layer is a sponge loaded with carbon nanotubes and thermoplastic polyurethane;

[0010] a temperature-sensitive layer, which is located on a surface of the pressure-sensitive layer away from the flexible substrate, and is an ink layer having a positive conductivity characteristic;

[0011] A base, whose surface close to the soft substrate is in contact with the temperature-sensitive layer.

[0012] Preferably, the spider-web-shaped conductor comprises a plurality of concentric annular conductive layers and a plurality of radial connecting layers;

[0013] The radial connection layer is arranged along the diameter direction of the annular conductive layer, and its two ends are connected to the annular conductive layer with the largest diameter;

[0014] The width of the quasi-annular conductive layer is 0.5-0.6 mm, the width of the radial connection layer is 0.5-0.6 mm, and the distance between two adjacent concentric annular conductive layers is 1.3-1.5 mm.

[0015] Preferably, the substrate is folded on both sides of the temperature-sensitive layer to form folded portions, wherein the number of folds is 3 to 10 times, and the fold spacing between adjacent folded portions is 3 to 4 mm.

[0016] Preferably, the material of the soft substrate is thermoplastic polyurethane;

[0017] The thickness of the soft substrate is 0.1 to 0.2 mm;

[0018] The thickness of the substrate is 0.1 to 0.2 mm.

[0019] Preferably, the diameter of the annular conductive layer with the largest diameter is 11 to 13 mm.

[0020] In a second aspect, the present invention further provides a method for preparing the strain-temperature-pressure multimodal flexible sensor device, comprising the following steps:

[0021] The conductive carbon paste is mixed with ink having positive conductivity coefficient characteristics to obtain PTC ink; the PTC ink is printed on a substrate and dried to obtain an ink layer having positive conductivity coefficient characteristics, which is the temperature-sensitive layer;

[0022] Folding the substrate on both sides of the temperature-sensitive layer to form a folded portion;

[0023] The conductive carbon paste is printed on a soft substrate and dried to form a spider-web-like conductor, which is the strain layer;

[0024] Adding carbon nanotubes and thermoplastic polyurethane into anhydrous ethanol and dispersing them to obtain a suspension;

[0025] The melamine sponge is immersed in the suspension and dried to melt the thermoplastic polyurethane to obtain a sponge loaded with carbon nanotubes and thermoplastic polyurethane, which is the pressure-sensitive layer;

[0026] The temperature-sensitive layer, the pressure-sensitive layer and the strain layer are laminated in sequence to obtain a strain-temperature-pressure multimodal flexible sensor device.

[0027] Preferably, in the step of mixing the conductive carbon paste with the ink having positive conductivity coefficient characteristics, the mass ratio of the conductive carbon paste to the ink having positive conductivity coefficient characteristics is (1-3):(1-3).

[0028] Preferably, in the step of adding carbon nanotubes and thermoplastic polyurethane to anhydrous ethanol, the mass ratio of the carbon nanotubes, thermoplastic polyurethane and anhydrous ethanol is (0.05-0.1):(0.25-0.3):(25-30).

[0029] Preferably, the melamine sponge is soaked in the suspension and then dried at 150-160° C. for 1-2 hours to melt the thermoplastic polyurethane.

[0030] Preferably, the PTC ink is printed on the substrate, and in the drying step, the drying temperature is 60-70°C;

[0031] The conductive carbon paste is printed on a soft substrate, and in the drying step, the drying temperature is 60-70°C.

[0032] The strain-temperature-pressure multimodal flexible sensor device and its preparation method of the present invention have the following advantages compared with the prior art:

[0033] 1. The strain-temperature-pressure multimodal flexible sensor device of the present invention has a strain layer that is a spider-web-shaped conductor, which can be used for strain sensing and as the lower electrode of a pressure sensing structure; the pressure-sensitive layer is a sponge loaded with carbon nanotubes and thermoplastic polyurethane, which has good conductivity under pressure. The sponge has a dense structure and a small pore size, so it has an excellent elastic modulus and thus has a wide pressure detection range; the temperature-sensitive layer is an ink layer with a positive conductivity coefficient, which can be used for temperature sensing and as the lower electrode of a pressure sensing structure; the sensor of the present invention can monitor three physical parameters: strain, temperature and pressure, and successfully integrates multi-parameter sensing capabilities into a single device to improve the device's interactive capabilities and detection dimensions, and enhance its applicability in fields such as health monitoring and smart wearables. When the strain-temperature-pressure multimodal flexible sensor device of the present invention performs strain sensing, it is necessary to detect changes in the resistance value at both ends of the spider-web-shaped conductor. External stress will cause it to generate strain, thereby changing its own resistance value. When the strain-temperature-pressure multimodal flexible sensor device of the present invention performs temperature sensing, it is necessary to detect changes in the resistance value at both ends of the temperature-sensitive layer. Since a PTC ink layer (an ink layer with a positive temperature coefficient characteristic) is used, its resistance value will change with the ambient temperature. When the strain-temperature-pressure multimodal flexible sensor device of the present invention performs pressure sensing, the temperature-sensitive layer and the spider-web-shaped conductor can serve as upper and lower electrodes to detect changes in the resistance value of the pressure-sensitive layer (a sponge loaded with carbon nanotubes and thermoplastic polyurethane). As the pressure changes, the resistance value of the pressure-sensitive layer changes.

[0034] 2. The strain-temperature-pressure multimodal flexible sensor device of the present invention folds the substrate on both sides of the temperature-sensitive layer to form folded portions, thereby reducing the mechanical loss of the entire sensor during stretching and the impact of the sensor's tensile strain on the temperature sensing function.

[0035] 3. The preparation method of the strain-temperature-pressure multimodal flexible sensor device of the present invention selects a printing (i.e., screen printing) process in the process of patterning the electrode plate of the sensor. The printing process has low cost, simple operation, and wide material compatibility, and the same pattern can be mass-produced at one time; in addition, the combined immersion-high-temperature drying process also has the characteristics of low cost and environmental friendliness, and the main materials used to prepare the sensor have the advantages of low cost and green and non-toxic, making the entire sensor preparation process economical, efficient and more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0037] Figure 1 Schematic diagram of the structure of the strain-temperature-pressure multimodal flexible sensor device of the present invention;

[0038] Figure 2 Schematic diagram of the structure of the spider web-shaped conductor of the present invention;

[0039] Figure 3 A physical picture of the strain-temperature-pressure multimodal flexible sensor device prepared by the present invention;

[0040] Figure 4 This is a flow chart of a method for preparing a strain-temperature-pressure multimodal flexible sensor device according to the present invention;

[0041] Figure 5 The following are SEM images of the melamine sponge before being immersed in the MWCNT / TPU suspension in Example 1 and the SEM image of the melamine sponge after the immersion is completed and dried;

[0042] Figure 6 This is a graph showing the strain sensing performance results of the strain-temperature-pressure multimodal flexible sensor device prepared in Example 1;

[0043] Figure 7 This is a graph showing the temperature sensing performance of the strain-temperature-pressure multimodal flexible sensor device prepared in Example 1;

[0044] Figure 8 This is a graph showing the pressure sensing performance results of the strain-temperature-pressure multimodal flexible sensor device prepared in test example 1. DETAILED DESCRIPTION

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may be in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this article, it is meant to include any cited numbers (fractions or integers) within the indicated range. The application principle of the present invention is described in detail below in conjunction with the accompanying drawings.

[0047] The present invention provides a strain-temperature-pressure multimodal flexible sensor device, such as Figure 1 Shown, including:

[0048] Soft substrate 1;

[0049] The strained layer 2 is located on the surface of the soft substrate 1 and is a spider-web-shaped conductor.

[0050] A pressure-sensitive layer 3 is located on the surface of the strain layer 2 away from the soft substrate 1. The pressure-sensitive layer 3 is a sponge loaded with carbon nanotubes and thermoplastic polyurethane;

[0051] The temperature-sensitive layer 4 is located on the surface of the pressure-sensitive layer 3 away from the flexible substrate 1. The temperature-sensitive layer 4 is an ink layer with positive conductivity.

[0052] The base 5 has a surface close to the flexible substrate 1 in contact with the temperature-sensitive layer 4 .

[0053] The strain-temperature-pressure multimodal flexible sensor device of the present invention comprises: a flexible substrate 1, a strain layer 2, a pressure-sensitive layer 3, a temperature-sensitive layer 4, and a base 5. The strain layer is located on the surface of the flexible substrate 1. The strain layer 2 is a spiderweb-shaped conductor that can be used for both strain sensing and as the lower electrode of a pressure sensing structure. The pressure-sensitive layer 3 is located on the surface of the strain layer 2 away from the flexible substrate 1. The pressure-sensitive layer 3 is a sponge loaded with carbon nanotubes and thermoplastic polyurethane, which has good conductivity when pressed. The sponge has a dense structure and small pore size, resulting in an excellent elastic modulus and a wide pressure detection range. The temperature-sensitive layer 4 is laminated on one side to the surface of the pressure-sensitive layer 3 away from the flexible substrate 1 and on the other side to the base 5. The temperature-sensitive layer 4 is an ink layer with positive conductivity and can be used for both temperature sensing and as the lower electrode of a pressure sensing structure. The sensor of the present invention can monitor three physical parameters: strain, temperature, and pressure, successfully integrating multi-parameter sensing capabilities into a single device, thereby improving the device's interactive capabilities and detection dimensionality, and enhancing its applicability in fields such as health monitoring and smart wearables. When the strain-temperature-pressure multimodal flexible sensor device of the present invention performs strain sensing, it is necessary to detect the change in resistance value at both ends of the spider-web-shaped conductor. External stress will cause it to generate strain, thereby changing its own resistance value; when the strain-temperature-pressure multimodal flexible sensor device of the present invention performs temperature sensing, it is necessary to detect the change in resistance value at both ends of the temperature-sensitive layer. Since a PTC ink layer (an ink layer with a positive temperature coefficient characteristic) is used, its resistance value will change with the ambient temperature; when the strain-temperature-pressure multimodal flexible sensor device of the present invention performs pressure sensing, the temperature-sensitive layer and the spider-web-shaped conductor can be used as upper and lower electrodes to detect the change in resistance value of the pressure-sensitive layer (sponge loaded with carbon nanotubes and thermoplastic polyurethane). As the pressure changes, the resistance value of the pressure-sensitive layer changes.

[0054] In some embodiments, as Figure 2 As shown, the spider-web-shaped conductor 2 includes a plurality of concentric annular conductive layers 21 and a plurality of radial connection layers 22;

[0055] The radial connection layer 22 is arranged along the diameter direction of the annular conductive layer 21, and its two ends are connected to the annular conductive layer with the largest diameter;

[0056] The width of the quasi-annular conductive layer is 0.5-0.6 mm, the width of the radial connection layer is 0.5-0.6 mm, and the distance between two adjacent concentric annular conductive layers is 1.3-1.5 mm.

[0057] The spider-web-shaped conductor 2 of the present invention includes a plurality of concentric annular conductive layers 21 and a plurality of radial connection layers 22. Specifically, the plurality of annular conductive layers 21 are concentric and arranged in sequence; the radial connection layer 22 is arranged along the diameter direction of the annular conductive layer 21, and the two ends are connected to the annular conductive layer with the largest diameter (i.e., the outermost annular conductive layer). Combined with bionics, the strain sensing functional layer is designed as a spider-web-shaped conductor to obtain good strain sensing performance. Specifically, the annular conductive layer can be an annular conductive layer or a roughly annular conductive layer, such as a regular octagonal conductive layer.

[0058] In some embodiments, the thickness of the spider-web-shaped conductor 2 does not exceed 10 μm.

[0059] In some embodiments, the substrate 5 is folded on both sides of the temperature-sensitive layer 4 to form folds 51. The folds are performed 3 to 10 times, with a 3 to 4 mm spacing between adjacent folds 51. Folding the substrate 5 on both sides of the temperature-sensitive layer to form folds 51 reduces mechanical loss of the entire sensor during stretching, as well as the impact of sensor tensile strain on temperature sensing.

[0060] In some embodiments, the material of the flexible substrate 1 is thermoplastic polyurethane;

[0061] The thickness of the soft substrate 1 is 0.1 to 0.2 mm;

[0062] The thickness of the temperature-sensitive layer 4 does not exceed 10 μm.

[0063] The thickness of the substrate 5 is 0.1 to 0.2 mm.

[0064] In some embodiments, the diameter of the largest annular conductive layer is 11-13 mm.

[0065] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned strain-temperature-pressure multimodal flexible sensor device, comprising the following steps:

[0066] S1. Mixing a conductive carbon paste with an ink having a positive conductivity coefficient to obtain a PTC (Positive Temperature Coefficient) ink; printing the PTC ink on a substrate and drying the ink to obtain an ink layer having a positive conductivity coefficient, i.e., a temperature-sensitive layer;

[0067] S2, folding the substrate on both sides of the temperature-sensitive layer to form a folded portion;

[0068] S3, printing the conductive carbon paste on the soft substrate and drying it to form a spider web-like conductor, which is the strain layer;

[0069] S4, adding carbon nanotubes and thermoplastic polyurethane into anhydrous ethanol and dispersing them to obtain a suspension;

[0070] S5, soaking the melamine sponge in the suspension and drying it to melt the thermoplastic polyurethane to obtain a sponge loaded with carbon nanotubes and thermoplastic polyurethane, which is the pressure-sensitive layer;

[0071] S6. Laminating the temperature-sensitive layer, the pressure-sensitive layer, and the strain layer in sequence to obtain a strain-temperature-pressure multimodal flexible sensor device.

[0072] In some embodiments, in the step of mixing the conductive carbon paste with the ink having positive conductivity characteristics, the mass ratio of the conductive carbon paste to the ink having positive conductivity characteristics is (1-3):(1-3).

[0073] In some embodiments, in the step of adding carbon nanotubes and thermoplastic polyurethane to anhydrous ethanol, the mass ratio of carbon nanotubes, thermoplastic polyurethane and anhydrous ethanol is (0.05-0.1):(0.25-0.3):(25-30).

[0074] In some embodiments, a melamine sponge is soaked in the suspension and then dried at 150-160° C. for 1-2 hours to melt the thermoplastic polyurethane.

[0075] In some embodiments, the PTC ink is printed on a substrate, and in the drying step, the drying temperature is 60 to 70° C.;

[0076] The conductive carbon paste is printed on a soft substrate, and in the drying step, the drying temperature is 60-70°C.

[0077] In some embodiments, the carbon nanotubes are MWCNTs (multi-walled carbon nanotubes).

[0078] In some embodiments, the method for preparing the strain-temperature-pressure multimodal flexible sensor device of the present invention comprises the following steps:

[0079] S1. Mixing a conductive carbon paste and an ink having a positive conductivity coefficient in a mass ratio of 1:1 and stirring them evenly to obtain a PTC ink for printing a temperature-sensitive square conductor (i.e., a temperature-sensitive layer);

[0080] S2. Use a screen printer to print a 1 cm long and 1 cm wide square conductor on a substrate (such as printing paper) using PTC ink. After printing, dry it at 70°C for 1 hour to obtain an ink layer with positive conductivity, which is the temperature-sensitive layer.

[0081] S3, printing a conductive carbon paste on a flexible substrate (such as a TPU film) to obtain a spider web-shaped conductor, and drying it at 70° C. for 1 hour to obtain a strain layer;

[0082] S4, folding the substrate on both sides of the temperature-sensitive layer to form a folded portion;

[0083] S5. Add 0.05 g of MWCNT (multi-walled carbon nanotube) powder and 0.25 g of TPU powder (500 mesh size) to 25 g of anhydrous ethanol and sonicate at room temperature for 1 h to obtain a MWCNT / TPU suspension.

[0084] S6. Immerse the melamine sponge in the MWCNT / TPU suspension, squeeze it, and then release it, repeating this process several times to ensure that the sponge is fully immersed in the suspension. After the impregnation is completed, remove the sponge and place it in an electric blast drying oven at 150°C for 1 hour. 150°C is a temperature that ensures that the 500-mesh TPU powder can melt. After drying, remove the composite sponge and cool it to room temperature to obtain the MWCNT / TPU@melamine sponge, which is the pressure-sensitive layer.

[0085] S7. Use silicone rubber glue and double-sided tape to vertically bond the temperature-sensitive layer, pressure-sensitive layer, and strain layer to obtain a strain-temperature-pressure multimodal flexible sensor device. During testing, a wire needs to be drawn from both ends of the square conductor (i.e., the temperature-sensitive layer) and both ends of the spider-web structure conductor (i.e., the strain layer) to facilitate testing.

[0086] Specifically, refer to Figure 4 As shown, it is a schematic flow chart of the preparation method of the strain-temperature-pressure multimodal flexible sensor device of the present invention. Figure 4 (a) shows the printing of temperature-sensitive square conductors (i.e., temperature-sensitive layers) and the folding of substrates (e.g., printing paper); (b) shows the preparation of MWCNT / TPU suspensions and MWCNT / TPU@melamine sponges; and (c) the printing of spiderweb-structured conductors (i.e., strain layers).

[0087] refer to Figure 3 As shown, it is a physical picture of the strain-temperature-pressure multimodal flexible sensor device prepared by the present invention.

[0088] The main innovations of the method for preparing the strain-temperature-pressure multimodal flexible sensor device prepared by the present invention are as follows:

[0089] First, the structural design incorporates patterning and functionalization of the upper and lower electrodes in a conventional flexible pressure-sensing device, giving the upper electrode (a spiderweb-like conductor) and the lower electrode (a layer of ink with positive conductivity) additional sensing functions. This broadens the sensing dimension of the entire device, enabling the sensor to achieve integrated sensing of strain, temperature, and pressure. This innovative structural design, while endowing the device with multiple sensing functions, maintains its integrity and compactness, and experimentally demonstrates the low coupling between these sensing functions.

[0090] Second, a printing (i.e., screen printing) process was chosen to pattern the sensor's electrode plates. This process is low-cost, simple to operate, and compatible with a wide range of materials, allowing for mass production of identical patterns at once. Furthermore, the combined impregnation and high-temperature drying process is also low-cost and environmentally friendly. The primary materials used in the sensor's fabrication are all low-cost, green, and non-toxic, making the entire sensor fabrication process economically efficient and environmentally friendly.

[0091] Third, combining bionics, the strain sensing functional layer is designed into a spider web structure, so that it can obtain good strain sensing performance, and by folding the substrate of the temperature sensing functional layer (i.e., the temperature-sensitive layer), the mechanical loss of the entire sensor during the stretching process and the influence of the device's tensile strain on the temperature sensing function are reduced.

[0092] Based on the above advantages, the strain-temperature-pressure multimodal flexible sensor device of the present invention can achieve a stable measurement window of 0-35%, the strain sensitivity (GF, Gauge Factor) in the strain range of 0-20% is 75.56, and the GF in the strain range of 20-35% is 207.23. In addition, during the cooling process of 50℃-30℃, the resistance change of the strain sensing functional layer (i.e., the spider web-shaped conductor) is only -6.3%, indicating that temperature has little effect on the strain sensing function; in terms of temperature monitoring function, the sensor of the present invention has a 0.437%℃ -1 The sensitivity of the sensor is very good, and its resistance hardly changes under 35% cyclic stretching, which proves the low coupling between strain sensing and temperature sensing functions. For pressure sensing, the sensor has a pressure detection window of 1-200kPa and an accuracy of 18.25%kPa in the range of 1-5kPa. -1 The high sensitivity of the square conductor (i.e., the temperature-sensitive layer) is shown, and the resistance change of the square conductor (i.e., the temperature-sensitive layer) is only 4.1% during the cooling process from 50 to 30°C, which proves the weak temperature dependence of the pressure sensing function of the sensor.

[0093] The following further illustrates the strain-temperature-pressure multimodal flexible sensor device and its preparation method of the present invention using specific examples. This section further illustrates the present invention with reference to specific examples but should not be construed as limiting the present invention. Unless otherwise specified, the techniques employed in the examples are conventional techniques well known to those skilled in the art. Unless otherwise noted, the reagents, methods, and equipment employed in the present invention are conventional in the art.

[0094] In the following examples, the raw materials and their suppliers are shown in Table 1:

[0095] Table 1 - Manufacturers of various raw materials

[0096] Product Name Related parameters / specifications Manufacturer TPU film 100μm thick Shenzhen Hongye New Materials Co., Ltd. Printing paper 100μm thick Deli Group Co., Ltd. Melamine sponge <![CDATA[2mm thick, density 7.5kg / m 3 > Shanghai Zhenmo New Materials Co., Ltd. Conductive carbon paste JC-2110 Shenzhen Jieyongcheng Technology Co., Ltd. PTC electric heating ink Field-808Y Shenzhen Tengyu High-tech Materials Co., Ltd. TPU powder 500 mesh BASF of Germany Anhydrous ethanol Analytical pure AR Chengdu Kelong Chemicals Co., Ltd. Conductive silver paste AS7126 Shanren New Material Technology Co., Ltd. Multi-walled carbon nanotubes Tube diameter 3-15mm, tube length 15-30mm Shenzhen Suiheng Technology Co., Ltd. graphite powder Particle size 1μm Qinghe County Huiguang Metal Materials Co., Ltd.

[0097] Example 1

[0098] This embodiment provides a strain-temperature-pressure multimodal flexible sensor device, including:

[0099] soft substrate;

[0100] A strained layer, which is located on the surface of the soft substrate and is a spider-web-shaped conductor;

[0101] The pressure-sensitive layer is located on the surface of the strain layer away from the soft substrate. The pressure-sensitive layer is a melamine sponge loaded with carbon nanotubes and thermoplastic polyurethane. The length, width and height of the melamine sponge are 1 cm, 1 cm and 0.2 cm respectively.

[0102] The temperature-sensitive layer is located on the surface of the pressure-sensitive layer away from the soft substrate, and the temperature-sensitive layer is an ink layer with a positive conductivity coefficient;

[0103] a substrate, the surface of which, close to the soft substrate, is in contact with the temperature-sensitive layer;

[0104] The soft substrate is a TPU (thermoplastic polyurethane) film substrate with a thickness of 0.1 mm;

[0105] The spiderweb-shaped conductor includes four concentric annular conductive layers and two radial connecting layers; the radial connecting layer 22 is arranged along the diameter direction of the annular conductive layer and connected to the annular conductive layer with the largest diameter at both ends; the width of the annular conductive layer 21 is 0.5 mm, the width of the radial connecting layer is 0.5 mm, the spacing between two adjacent concentric annular conductive layers 21 is 1.3 mm, the average thickness of the spiderweb-shaped conductor 2 is 5 μm, and the diameter of the largest annular conductive layer is 11 mm;

[0106] The substrate is folded on both sides of the temperature-sensitive layer to form folded portions 51, wherein the number of folds is 6, the fold spacing between adjacent folded portions is 3 mm, and a "V" shape is formed between adjacent folded portions;

[0107] The temperature-sensitive layer is a cuboid with a length of 1 cm, a width of 1 cm, and a thickness of 5 μm;

[0108] The substrate is printing paper, and the thickness of the substrate is 0.1 mm.

[0109] The method for preparing the strain-temperature-pressure multimodal flexible sensor device comprises the following steps:

[0110] S1. Mixing a conductive carbon paste and an ink having a positive conductivity coefficient in a mass ratio of 1:1 and stirring them evenly to obtain a PTC ink for printing a temperature-sensitive square conductor (i.e., a temperature-sensitive layer);

[0111] S2. Use a screen printer to print a square conductor with a length of 1 cm, a width of 1 cm, and a thickness of 0.1 mm on a substrate (printing paper) using PTC ink. After printing, dry it at 70°C for 1 hour to obtain an ink layer with positive conductivity, which is the temperature-sensitive layer.

[0112] S3, printing the conductive carbon paste on the flexible substrate (TPU film) to obtain a spider web-shaped conductor, and drying it at 70°C for 1 hour to obtain a strain layer;

[0113] S4, folding the substrate on both sides of the temperature-sensitive layer to form a folded portion;

[0114] S5. Add 0.05 g of MWCNT (multi-walled carbon nanotube) powder and 0.25 g of TPU powder (500 mesh size) to 25 g of anhydrous ethanol and sonicate at room temperature for 1 h to obtain a MWCNT / TPU suspension.

[0115] S6. Immerse the melamine sponge in the MWCNT / TPU suspension, squeeze it, and then release it, repeating this process several times to ensure that the sponge is fully immersed in the suspension. After the impregnation is completed, remove the sponge and place it in an electric blast drying oven at 150°C for 1 hour. 150°C is a temperature that ensures that the 500-mesh TPU powder can melt. After drying, remove the composite sponge and cool it to room temperature to obtain the MWCNT / TPU@melamine sponge, which is the pressure-sensitive layer.

[0116] S7. Use silicone rubber glue and double-sided tape to vertically bond the temperature-sensitive layer, pressure-sensitive layer, and strain layer to obtain a strain-temperature-pressure multimodal flexible sensor device. During testing, a wire needs to be drawn from both ends of the square conductor (i.e., the temperature-sensitive layer) and both ends of the spider-web structure conductor (i.e., the strain layer) to facilitate testing.

[0117] Performance Characterization

[0118] like Figure 5As shown, it is a SEM image of the melamine sponge before being immersed in the MWCNT / TPU suspension in Example 1 and a SEM image of the melamine sponge after the immersion is completed and dried; Figure 5 It can be seen from the figure that the melamine sponge is loaded with MWCNTs after being immersed in the MWCNT / TPU suspension and dried.

[0119] A strain-temperature-pressure multimodal flexible sensor device was prepared according to the method in Example 1, and its strain sensing performance was tested. Specifically, the resistance changes at both ends of the sensor spider web structure conductor under different tensile strains (including the maximum stable tensile limit, step tensile curve and strain sensitivity) and the change of its resistance with temperature were tested (the resistance did not change significantly with temperature, indicating that temperature has limited effect on the strain sensing function). The results are as follows: Figure 6 shown.

[0120] Figure 6 (a) is the maximum stable stretching limit; (b) is the step response curve; (c) is the sensitivity; (d) is the effect of temperature on its resistance when the strain layer has almost no mechanical damage.

[0121] Specifically, Figure 6 It is a characterization of the strain sensing performance of the device. The change in the resistance of the spiderweb structure conductor with tensile strain can be used to detect the strain of the device. During the test, a bidirectional electric translation stage is used to apply tensile strain to the device, and the two ends of the spiderweb conductor are connected to a digital bridge for data collection. Finally, the test results are unified into the relative resistance change rate on the vertical axis, that is, the relative change from the initial resistance (R0), and expressed as a percentage, that is, ΔR / R0 (%), where ΔR is the relative resistance change and ΔR / R0 is the relative resistance change rate.

[0122] First, a gradient of 5% strain (Strain is strain) is applied to stretch the device from its original length, such as Figure 6 As shown in (a), the device exhibits relatively stable strain performance before being stretched to 35%, and becomes unstable at 40%. Therefore, the stable strain sensing range of the device is 0-35%, with a large strain sensing window. The device is then subjected to gradient stretching, and the entire process of the device changing from original length to 35% strain and then back to original length is shown in Figure 2. Figure 6 As shown in (b), the device exhibits good dynamic response characteristics and distinct step-by-step responses to different strain values. In particular, the resistance change steps are more distinct and stable during the device's return to its original length. This indicates that the device exhibits a relatively stable response during the stretching and release process.

[0123] The resistance value of the lowest point at each strain (relatively stable) during the device stretching process with a 5% strain gradient was recorded, and the relative resistance change rate of the device under different strains was calculated. Figure 6 (c) shows the device's response signal under different strains and the fitted straight lines for each region. According to the definition of strain sensitivity (GF), the slope of the fitted straight line for different strain ranges can represent the GF within that range. The figure shows that the device's strain sensing process is divided into two main stages: the first stage is when the strain is 0-20%, at which the device's GF is 75.56; the second stage is when the strain is 20%-35%, at which the device's GF is 207.23. This data demonstrates the device's excellent strain sensitivity.

[0124] ΔR=GF·R0·Δε (Δε is the corresponding variable)

[0125] In order to verify whether the ambient temperature would interfere with the device's strain sensing function, the device was first heated to 50°C and then cooled to 30°C at room temperature. During the cooling process, the resistance changes at both ends of the spider web conductor were monitored. Figure 6 (d) shows that the relative resistance change rate of the spiderweb conductor is -6.3%. In contrast, when it is used for strain sensing, its relative resistance change rate exceeds 200% under only 5% strain conditions, which indicates that the fluctuation of ambient temperature has limited effect on the strain sensing performance compared with tensile strain.

[0126] A strain-temperature-pressure multimodal flexible sensor device was prepared according to the method in Example 1, and its temperature sensing performance was tested. Specifically, the resistance at both ends of the square conductor (i.e., the temperature-sensitive layer) of the sensor was tested as a function of ambient temperature. Next, the resistance at both ends of the square conductor was tested under repeated 35% tensile strain (there was almost no change, and the tiny peaks produced may be due to the slight jitter of the device during each stretch). Finally, physical images of the device under different tensile strains were taken (it can be seen that the strain of the device was indeed absorbed by the folded portion and did not affect the square conductor and the conductive sponge area). The results are shown in Figure 1. Figure 7 shown.

[0127] Figure 7 (a) shows the response signal and fitting straight line at different temperatures; (b) shows the resistance change of the temperature sensing functional layer of the device under repeated stretching of 35% strain; (c) shows the actual picture of the device under different strains (0-40%).

[0128] Figure 7It is a characterization of the temperature sensing performance of the device. The resistance of the square conductor will change with temperature, so by testing its resistance change, the change in external ambient temperature can be detected. At the beginning of the test, the wires leading from both sides of the square conductor are connected to the digital bridge, and then the heating platform is turned on to heat the device. During the entire heating process, a commercial thermometer is needed to measure the temperature change of the device and record it. The vertical axis is displayed in the form of a percentage of the relative change rate of resistance, that is, ΔR / R0 (%), where R0 is the initial resistance, and here is the resistance of the device at 30°C. The resistance-temperature response characteristics of this device in the temperature range of 30-50°C are evaluated with a gradient of 5°C. From the definition of temperature sensitivity (TCR), it can be seen that the temperature sensitivity of the resistive temperature sensing device can be characterized by the slope of the fitting straight line of the response output point, from Figure 7 (a) shows that the device has a 0.437% ℃ -1 sensitivity.

[0129] The sensitivity formula is: (ΔT is the temperature change relative to the initial temperature).

[0130] As mentioned above, to eliminate the interference of external tension on the temperature sensing function, the paper substrate is folded. In theory, the strain of the printing paper caused by external tension will be absorbed by the folded part, thus ensuring that the square conductor is not affected. To verify this theory, the device was photographed at its original length and under 10%, 20%, 30% and 40% strain conditions, as shown in the figure below. Figure 7 As shown in (c), as the device is stretched, the origami part gradually expands, absorbing the increased strain of the device, so that the composite sponge and the square conductor area do not deform due to stretching. The resistance change of the square conductor under a large strain of 35% is further tested. Figure 7 (b) shows that the relative resistance change rate of the square conductor during more than 10 stretching cycles is much lower than the relative resistance change rate caused by a 5°C increase in the device temperature, proving that the tensile strain of the device has almost no effect on the temperature sensing function.

[0131] A strain-temperature-pressure multimodal flexible sensor device was prepared according to the method in Example 1, and its pressure sensing performance was tested. Specifically, the current between one end of the sensor's spider-web structure conductor (i.e., the strain layer) and one end of the square structure conductor (i.e., the temperature-sensitive layer) was tested as a function of pressure, as well as the resistance of the pressure-sensitive structure (the temperature-sensitive layer, the pressure-sensitive layer, and the strain layer as a whole) as a function of temperature (it can be seen that its resistance exhibits weak temperature dependence). The results are shown in Figure 1. Figure 8 shown.

[0132] Figure 8(a) is the response signal and the segmented fitting straight line under different pressures; (b) is the temperature response curve of the sensor pressure-sensitive structure during the cooling process.

[0133] Specifically, Figure 8 To characterize the pressure sensing performance of the device. The resistance of the composite conductive sponge will decrease as the pressure increases, and the test of the resistance of the composite sponge needs to rely on a square conductor and a spider web structure conductor as the upper and lower electrodes. At the beginning of the test, the pins at one end of the spider web conductor and the pins at one end of the square conductor are connected to the digital bridge through a wire to test the real-time resistance of the pressure-sensitive structure, and an electric push-pull force gauge is used to apply pressure to it, and the correspondence between the resistance of the pressure-sensitive structure and the external pressure is recorded. Since the sponge is not in contact with the spider web electrode when there is no external pressure, in order to more clearly characterize the pressure-sensitive performance of the device, the tested resistance value needs to be converted into a current value (U is taken as 1V). When the device is without external pressure, the current is 0. At the initial stage of pressure application, the interface contact has not yet reached a stable state. Therefore, in the process of calculating the pressure sensitivity, the current value at 1kPa is taken as I0, and the vertical axis is the percentage of the relative change rate of current, that is, ΔI / I0 (%). Similar to the characterization methods of strain sensitivity and temperature sensitivity, pressure sensitivity can also be quantitatively characterized by the slope of the fitted straight line between the relative rate of change of current and pressure. Figure 8 As shown in (a), the response signals under different pressures are linearly fitted in different regions. It can be seen that the detection window of the device's pressure sensing function is 1-200kPa. Its pressure sensing is mainly divided into four response intervals: the pressure detection range of the initial response interval is 1-5kPa, at which the device sensitivity is 18.25% kPa -1 The pressure detection range of the second interval is 5-15kPa. The sensor sensitivity is 5.81% kPa -1 As the pressure increases to the third interval of 15-80 kPa, the device sensitivity is 1.35% kPa -1 In the fourth response range, the device shows obvious sensitivity attenuation, which drops to 0.56% kPa. -1 According to the above test results, the device exhibits differentiated sensitivity characteristics in different pressure ranges and exhibits excellent sensing performance in low-pressure areas.

[0134] To further explore the effect of temperature on pressure sensing, a small 183g copper block was first applied to the pressure-sensitive structure to generate current. The device was then placed on a heating platform. After the device was heated to 50°C, it was cooled to room temperature. A digital bridge was used to detect the resistance change during this process and convert it into a relative current change rate. Figure 8(b) shows that the system composed of composite conductive sponge and electrode exhibits excellent thermal stability. Its current change rate changes by only 4.1% in the temperature range of 50-30℃. In contrast, the system is very sensitive to pressure changes, such as Figure 8 As shown in (a), in the pressure range of 1-15 kPa, the response caused by a pressure change of only 1 kPa is higher than 4.1%.

[0135] It can be understood that the various technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0136] The above are merely preferred embodiments of the present application and only specifically describe the technical principles of the present application. These descriptions are intended only to explain the principles of the present application and should not be construed in any way as limiting the scope of protection of the present application. Based on the explanations herein, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application, as well as other specific implementations of the present application that can be conceived by those skilled in the art without inventive effort, shall be included within the scope of protection of the present application.

Claims

1. A strain-temperature-pressure multimodal flexible sensor device, characterized in that: include: soft substrate; a strain layer, located on the surface of the soft substrate, wherein the strain layer is a spider-web-shaped conductor; a pressure-sensitive layer, located on a surface of the strain layer away from the soft substrate, wherein the pressure-sensitive layer is a sponge loaded with carbon nanotubes and thermoplastic polyurethane; a temperature-sensitive layer, which is located on a surface of the pressure-sensitive layer away from the flexible substrate, and is an ink layer having a positive conductivity characteristic; A base, whose surface close to the soft substrate is in contact with the temperature-sensitive layer.

2. The strain-temperature-pressure multimodal flexible sensor device according to claim 1, wherein: The spider-web-shaped conductor includes a plurality of concentric annular conductive layers and a plurality of radial connection layers; The radial connection layer is arranged along the diameter direction of the annular conductive layer, and its two ends are connected to the annular conductive layer with the largest diameter; The width of the quasi-annular conductive layer is 0.5-0.6 mm, the width of the radial connection layer is 0.5-0.6 mm, and the distance between two adjacent concentric annular conductive layers is 1.3-1.5 mm.

3. The strain-temperature-pressure multimodal flexible sensor device according to claim 1, wherein: The substrate is folded on both sides of the temperature-sensitive layer to form folded parts, wherein the number of folds is 3 to 10 times, and the fold spacing between adjacent folded parts is 3 to 4 mm.

4. The strain-temperature-pressure multimodal flexible sensor device according to claim 1, wherein: The material of the soft substrate is thermoplastic polyurethane; The thickness of the soft substrate is 0.1 to 0.2 mm; The thickness of the substrate is 0.1-0.2 mm.

5. The strain-temperature-pressure multimodal flexible sensor device according to claim 1, wherein: The diameter of the largest annular conductive layer is 11 to 13 mm.

6. A method for preparing a strain-temperature-pressure multimodal flexible sensor device according to any one of claims 1 to 5, characterized in that: The following steps are involved: The conductive carbon paste is mixed with ink having positive conductivity coefficient characteristics to obtain PTC ink; Print the PTC ink on the substrate and dry it to obtain an ink layer with positive conductivity, which is the temperature-sensitive layer. Folding the substrate on both sides of the temperature-sensitive layer to form a folded portion; The conductive carbon paste is printed on a soft substrate and dried to form a spider-web-like conductor, which is the strain layer; Adding carbon nanotubes and thermoplastic polyurethane into anhydrous ethanol and dispersing them to obtain a suspension; The melamine sponge is immersed in the suspension and dried to melt the thermoplastic polyurethane to obtain a sponge loaded with carbon nanotubes and thermoplastic polyurethane, which is the pressure-sensitive layer; The temperature-sensitive layer, the pressure-sensitive layer and the strain layer are laminated in sequence to obtain a strain-temperature-pressure multimodal flexible sensor device.

7. The method for preparing the strain-temperature-pressure multimodal flexible sensor device according to claim 6, wherein: In the step of mixing the conductive carbon paste with the ink having positive conductivity coefficient characteristics, the mass ratio of the conductive carbon paste to the ink having positive conductivity coefficient characteristics is (1-3):(1-3).

8. The method for preparing the strain-temperature-pressure multimodal flexible sensor device according to claim 6, wherein: In the step of adding carbon nanotubes and thermoplastic polyurethane into anhydrous ethanol, the mass ratio of the carbon nanotubes, thermoplastic polyurethane and anhydrous ethanol is (0.05-0.1):(0.25-0.3):(25-30).

9. The method for preparing the strain-temperature-pressure multimodal flexible sensor device according to claim 6, wherein: Soak the melamine sponge in the suspension and then dry it at 150-160°C for 1-2 hours to melt the thermoplastic polyurethane.

10. The method for preparing the strain-temperature-pressure multimodal flexible sensor device according to claim 6, wherein: The PTC ink is printed on the substrate, and in the drying step, the drying temperature is 60-70°C; The conductive carbon paste is printed on a soft substrate, and in the drying step, the drying temperature is 60-70°C.

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