Stretchable strain sensor and method of manufacturing the same

Abstract

The application provides a stretchable strain sensor, which comprises a first elastic layer, a sensitive material layer, a second elastic layer, a non-elastic layer and a sensitive gap, wherein the first elastic layer, the second elastic layer and the non-elastic layer are sequentially stacked from bottom to top, the sensitive material layer is encapsulated in the second elastic layer, the sensitive gap is located in the non-elastic layer, and the sensitive material layer comprises a strain sensitive part, and the strain sensitive part is located in a region corresponding to the sensitive gap in a direction perpendicular to the thickness of each layer of the stretchable strain sensor. The sensitivity and the measurement range of the sensor can be flexibly adjusted during preparation, the structure and preparation of the sensor are simple, the processing is convenient, the sensor is suitable for roll-to-roll production, and has great application potential in the fields of wearable devices, implanted devices, robots and virtual reality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical devices, in particular, to a stretchable strain sensor and a preparation method thereof. BACKGROUND

[0002] The deformation measurement of each organ of the human body has great significance for sports monitoring and disease diagnosis and treatment. However, the deformation degree of different organs of the human body is quite different. For example, the deformation of organs such as the heart and the bladder is very large, and the strain thereof can reach more than 100%. For skin, muscle and other tissues and organs, the maximum deformation thereof can reach 50%, and for bones and teeth, the deformation thereof is usually not more than 0.1%. For a strain sensor, the measurement range and the measurement sensitivity are often a pair of contradictions. The measurement sensitivity of a sensor is usually high, and the measurement range thereof is relatively narrow. For a sensor with a large measurement range, the measurement sensitivity thereof is small.

[0003] At present, a stretchable strain sensor is usually realized by patterning a stretchable strain sensitive material on an elastic substrate. The electrical parameters such as resistance, capacitance and inductance of the strain sensitive material change during the deformation process. The deformation size loaded on the sensor can be calculated by measuring the electrical parameters. For example, a stretchable strain sensor can be prepared by printing a strain sensitive material on a soft and elastic substrate by inkjet printing, screen printing, laser etching and the like, or by injecting a strain sensitive material into a soft and elastic pipe. The existing strain sensitive materials usually include liquid metal, hydrogel, ionic liquid, carbon nanomaterial and metal nanowire conductive materials.

[0004] However, the main problem existing in the prior art is that these sensors can only be used for accurate measurement of a single strain range. For example, a stretchable strain sensor with liquid metal as the sensitive material has a relatively large strain measurement range, about 0-100%, and is suitable for deformation measurement of organs such as the heart and the bladder. However, the resolution of such a sensor is low, and it is difficult to accurately measure small deformation. For a stretchable strain sensor with carbon nanomaterial as the sensitive material, the sensitivity of the deformation measurement thereof is extremely high, and it is very suitable for small deformation measurement of less than 1%. However, when these sensors encounter a large deformation, they are usually directly damaged due to the large deformation.

[0005] The difficulty of solving the above problems and defects is that the strain sensitive material of a certain type of strain sensor directly determines the measurement sensitivity and the measurement range thereof. Even if the sensitive material is modified during the preparation process, the measurement sensitivity and the measurement range thereof will not change much. The significance of solving the above problems is that by preparing a sensitive gap structure in the strain sensor, the sensitivity and the measurement range of the sensor can be adjusted by adjusting the strain concentration degree in the structure to meet the full-range and full-precision strain measurement. SUMMARY

[0006] The present application provides a stretchable strain sensor, which has flexible sensitivity and measurement range in the preparation process, simple sensor structure and preparation, convenient processing, suitable for roll-to-roll production, and great application potential in wearable devices, implanted devices, robots, and virtual reality field.

[0007] The technical solutions of the present application are as follows:

[0008] According to one aspect of the present application, a stretchable strain sensor is provided, comprising a first elastic layer, a sensitive material layer, a second elastic layer, a non-elastic layer, and a sensitive gap, wherein the first elastic layer, the second elastic layer, and the non-elastic layer are sequentially stacked from bottom to top, the sensitive material layer is encapsulated in the second elastic layer, the sensitive gap is located in the non-elastic layer, and the sensitive material layer comprises a strain-sensitive part, which is located within the range of the region corresponding to the sensitive gap in the direction perpendicular to the thickness of each layer of the stretchable strain sensor.

[0009] Optionally, in the above-mentioned stretchable strain sensor, the first elastic layer is selected from one or more of thermoplastic polyurethane material, ethylene-vinyl acetate copolymer material, silicone-based elastic material, polystyrene-based elastic material, polyolefin-based elastic material, ethylene-acrylic acid copolymer material, and latex-based elastic material.

[0010] Optionally, in the above-mentioned stretchable strain sensor, the second elastic layer is selected from one or more of thermoplastic polyurethane material, ethylene-vinyl acetate copolymer material, silicone-based elastic material, polystyrene-based elastic material, polyolefin-based elastic material, ethylene-acrylic acid copolymer material, and latex-based elastic material.

[0011] Optionally, in the above-mentioned stretchable strain sensor, the sensitive material layer is selected from one or more of liquid metal, hydrogel, graphene, carbon nanotube, silver nanowire, gold nanowire material, and micro-nano structure.

[0012] Optionally, in the above-mentioned stretchable strain sensor, the second elastic layer comprises an opening / window for exposing the external connection site of the sensitive material layer.

[0013] Optionally, in the above-mentioned stretchable strain sensor, the non-elastic layer is selected from one or more of photosensitive resin, polyimide, polyvinyl chloride, polyethylene terephthalate, polyolefin, and polyamide.

[0014] Optionally, in the above-mentioned stretchable strain sensor, the width of the sensitive gap is 0.001-50 millimeters.

[0015] Optionally, in the stretchable strain sensor, the thickness of the first elastic layer is 10-500 microns, and the thickness of the second elastic layer is 10-500 microns.

[0016] According to another aspect of the present application, a preparation method of the above-mentioned stretchable strain sensor is provided, comprising the following steps: S1. printing a sensitive material layer on a first elastic layer by using inkjet printing, screen printing, stencil, 3D printing or soft lithography technology; S2. coating an uncured second elastic layer on the first elastic layer to encapsulate the sensitive material layer, and curing the second elastic layer; and S3. preparing a non-elastic layer on the second elastic layer, and obtaining a sensitive gap by etching, corroding or cutting process.

[0017] According to another aspect of the present application, a preparation method of the above-mentioned stretchable strain sensor is provided, comprising the following steps: S1. printing a sensitive material layer on a first elastic layer by using inkjet printing, screen printing, stencil, 3D printing or soft lithography technology; S2. coating an uncured second elastic layer on the first elastic layer to encapsulate the sensitive material layer, and curing the second elastic layer; and S3. preparing a non-elastic layer on the second elastic layer, and obtaining a sensitive gap by etching, corroding or cutting process.

[0018] According to the technical solution of the present application, the beneficial effects are:

[0019] The present application designs a sensitive gap on the stretchable strain sensor, and prepares a strain sensitive material in the sensitive gap. The concentration of deformation on the strain sensitive material is adjusted by adjusting the width of the sensitive gap, so as to achieve the purpose of adjusting the measurement range and the measurement sensitivity of the stretchable strain sensor. The sensitivity and the measurement range depend on the width of the sensitive gap, and the length, the sensitivity and the measurement range of the sensor can be flexibly adjusted during the preparation process. The stretchable strain sensor has simple structure and convenient processing, and is suitable for roll-to-roll production. It has great application potential in the fields of wearable devices, implanted devices, robots and virtual reality.

[0020] In order to better understand and illustrate the concept, working principle and application effect of the present application, the present application will be described in detail below by specific embodiments combined with the accompanying drawings: BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced as follows.

[0022] Figure 1 is a schematic diagram of the structure of the stretchable strain sensor before and after stretching according to the present application;

[0023] Figure 2 is a schematic diagram of the stretchable strain sensor with different width sensitive slits according to the present application;

[0024] Figure 3 is a relationship between the resistance change and the strain of the stretchable strain sensor with different width sensitive slits according to the present application;

[0025] Figure 4 is a change of the resistance change rate of the stretchable strain sensor with a 10mm wide sensitive slit according to the present application under different strains. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical method and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and specific examples. These examples are merely illustrative, but not limiting to the present application.

[0027] As shown in Figure 1 , the stretchable strain sensor according to the present application comprises a first elastic layer 1, a sensitive material layer 4, a second elastic layer 2, a non-elastic layer 3 and a sensitive slit 5, wherein the first elastic layer 1, the second elastic layer 2 and the non-elastic layer 3 are sequentially stacked from bottom to top, and the sensitive material layer 4 is encapsulated in the second elastic layer 2. The sensitive slit refers to a stretchable slit in the non-elastic layer made by etching, etching, cutting and the like, which is used to concentrate the deformation of the sensor at the slit. The non-elastic layer 3 includes a first part and a second part (corresponding to non-elastic regions) separated by the sensitive slit 5, i.e., the sensitive slit 5 (corresponding to the sensitive slit region) is formed between the non-elastic materials of the first part and the second part. The sensitive material layer 4 includes a strain sensitive part corresponding to the sensitive slit region and a conductive part in the non-elastic region, wherein the strain sensitive part is arranged in a serpentine or bent structure for sensing strain during deformation, and the conductive part of the sensitive material layer in the non-elastic region is used for conduction, which is convenient for connection with external devices. The strain sensitive part of the sensitive material layer 4 is concentrated in the sensitive slit 5, i.e., the strain sensitive part is located within the width range of the sensitive slit 5 in the direction perpendicular to the thickness of each layer of the stretchable strain sensor, in other words, the strain sensitive part is located within the range of the region corresponding to the sensitive slit in the direction perpendicular to the thickness of each layer of the stretchable strain sensor, when stretching both ends of the stretchable strain sensor, since the non-elastic layer 3 is not deformable, all the strain loaded on the stretchable strain sensor will be concentrated in the sensitive slit 5. The strain borne in the sensitive slit 5 will be much larger than the actual strain loaded on the stretchable strain sensor.

[0028] Compared to a strain sensor without the sensitive gap 5, the amplification factor of the strain induced by the sensitive gap on the sensitive material is as follows: Let the total length of the sensor be L, the width of the sensitive gap 5 be d, and the deformation length applied to the sensor be ΔL. Without the sensitive gap, the strain borne by the sensitive material is ΔL / L, while in the tensile strain sensor with the sensitive gap 5, the strain borne by the sensitive material is ΔL / d. Therefore, the strain borne by the sensitive material in the tensile strain sensor with the sensitive gap 5 is L / d times that of the tensile strain sensor without the sensitive gap. This means that under the same deformation, the sensitive gap 5 increases the sensitivity of the tensile strain sensor by a factor of L / d. Therefore, by adjusting the width of the sensitive gap and the length of the tensile strain sensor, the measurement sensitivity and measurement range of the tensile strain sensor can be flexibly adjusted.

[0029] The first elastic layer 1 is the deformable substrate of the strain sensor. The first elastic layer 1 is selected from one or more of thermoplastic polyurethane materials, ethylene-vinyl acetate copolymer materials, silicone rubber elastic materials, polystyrene elastic materials, polyolefin elastic materials, ethylene-acrylic acid copolymer materials and latex elastic materials, and has a thickness of 10-500 micrometers.

[0030] During the deformation process, the electrical parameters such as resistance, capacitance, and inductance of the variable sensitive material in the sensitive material layer 4 will change accordingly. The sensitive material layer is selected from one or more electronic materials such as liquid metal, hydrogel, graphene, carbon nanotube, silver nanowire, gold nanowire material, and micro-nano structured silver sheet.

[0031] The second elastic layer 2 is used to encapsulate the sensitive material layer 4. The second elastic layer 2 is selected from one or more of thermoplastic polyurethane materials, ethylene-vinyl acetate copolymer materials, silicone rubber elastic materials, polystyrene elastic materials, polyolefin elastic materials, ethylene-acrylic acid copolymer materials, and latex elastic materials, and has a thickness of 10-500 micrometers. The second elastic layer 2 typically includes holes or windows to expose external connection sites of the sensitive material layer 4.

[0032] The non-elastic layer 3 is used to construct the sensitive gap. The material of the non-elastic layer 3 is a material that is invariant or has very little deformation under stress, and is selected from one or more of photosensitive resin, polyimide, polyvinyl chloride, polyethylene terephthalate, polyolefin, and polyamide.

[0033] The width of sensitive gap 5 is 0.001-50 mm, such as... Figure 2 As shown, from top to bottom, these correspond to strain sensors with sensitive slit widths of 0.1 mm, 0.5 mm, and 1 mm, respectively. For sensitive slits larger than 0.2 mm ( Figure 2For the sensitive gap (the lowermost in FIG. 1) that is greater than 0.2 millimeter, the processing method can be achieved by laser cutting or wire cutting the non-elastic layer. Figure 2 For the sensitive gap (the uppermost in FIG. 1) that is less than 0.2 millimeter, a photosensitive resin (e.g., photoresist) is usually used as the non-elastic layer, and then a photoetching method is used to obtain the sensitive gap on the non-elastic layer. By adjusting the width of the sensitive gap in preparation, the sensitivity and measurement range of the stretchable strain sensor can be adjusted.

[0034] The layers are connected by one or more combinations of hot pressing, cold pressing, gluing, plasma bonding, chemical crosslinking, and spin coating.

[0035] The stretchable strain sensor of the present application designs a sensitive gap on the stretchable strain sensor and prepares a strain-sensitive material in the sensitive gap. By adjusting the width of the sensitive gap, the concentration of deformation on the strain-sensitive material is adjusted, so as to achieve the purpose of adjusting the measurement range and measurement sensitivity of the stretchable strain sensor.

[0036] The preparation method of the stretchable strain sensor of the present application includes:

[0037] S1. Printing a sensitive material layer on a first elastic layer. Inkjet printing, screen printing, stencil, 3D printing, soft etching, and the like are used to print the sensitive material on the first elastic layer.

[0038] S2. Coating an uncured second elastic layer material on the first elastic layer to encapsulate the sensitive material layer, and curing the second elastic layer. The coating is performed by spin coating, and the curing temperature is 80°C, and the curing time is 30 minutes.

[0039] S3. Preparing a non-elastic layer photoresist on the second elastic layer, and obtaining a sensitive gap by etching, corrosion, cutting, and the like. Specifically, the spin coating speed is 12000 r / min, the spin coating time is 30 seconds, and after spin coating, the temperature is 95°C and the curing time is 10 minutes; and a photoetching mask with a sensitive gap pattern is placed on the photoresist, and the photoetching machine is exposed for 90 seconds, and after exposure, the temperature is 95°C and the heating time is 10 minutes, and after heating, the photoresist is developed with a photoetching developer for 5 minutes, and the photoresist on the sensitive gap area of the photoresist is dissolved, and the sensitive gap 5 is obtained.

[0040] Another preparation method of the stretchable strain sensor of the present application includes:

[0041] S1. Printing a sensitive material layer on a first elastic layer and drying. Specifically, inkjet printing technology, screen printing, stencil, 3D printing, soft etching, and the like are used to print the sensitive material on the first elastic layer, and then placed in an oven at a temperature of 80°C for 20 minutes.

[0042] S2. Punching holes on the second elastic layer to expose the electrical connection sites of the sensitive material layer, and hot pressing the second elastic layer on the first elastic layer to encapsulate the sensitive material layer. Wherein, the hot pressing temperature is 130 degrees Celsius, and the pressure is 3 kg / square centimeter.

[0043] S3. Punching holes on the non-elastic layer to expose the electrical connection sites of the sensitive material layer, and etching, etching, cutting the sensitive gap on the non-elastic layer, and combining the cut non-elastic layer on the second elastic layer by hot pressing, cold pressing, gluing, ion bonding, etc. So that the strain sensitive part of the sensitive material layer is located in the sensitive gap. Wherein, the hot pressing temperature is 140℃, and the pressure is 3 kg / square; using a laser cutting machine to cut the sensitive gap on the non-elastic layer hot melt adhesive film.

[0044] Example 1

[0045] Use polydimethylsiloxane silica gel as the first elastic layer and the second elastic layer, use liquid metal as the sensitive material, and use photoresist as the non-elastic layer. The combination between different layers is carried out by spin coating.

[0046] Use inkjet printing technology to print liquid metal on polydimethylsiloxane silicon film (first elastic layer 1), then use a spin coater to spin coat the uncured polydimethylsiloxane silicon solution on the first elastic layer 1 to encapsulate the sensitive material 4, the spin coating speed is 2000 r / min, the spin coating time is 30 seconds, and after spin coating, it is placed in an oven at a temperature of 80℃ for 30 minutes. Next, spin coat a layer of non-elastic layer photoresist (SU8 2035, MicroChem Corp., US) on the second elastic layer 2, the spin coating speed is 12000 r / min, the spin coating time is 30 seconds, and after spin coating, it is placed in an oven at a temperature of 95 degrees Celsius for 10 minutes. Put the photoresist mask with sensitive gap pattern on the photoresist, use the photoetching machine to expose for 90 seconds, after exposure, heat at 95 degrees Celsius for 10 minutes, and after heating, develop it with photoetching developer for 5 minutes. The photoresist on the sensitive gap area of the photoresist is dissolved, and the sensitive gap 5 is obtained. Thus, the preparation of the stretchable sensor is completed.

[0047] Example 2

[0048] Use thermoplastic polyurethane as the first elastic layer and the second elastic layer, use liquid metal as the sensitive material, and use PVC material as the non-elastic layer. The bonding method between different layers is carried out by hot pressing.

[0049] Liquid metal ink (liquid metal particles dispersed in a solution of polyurethane) is printed on a thermoplastic polyurethane (first elastic layer) by using screen printing technology, and is dried in an oven at a temperature of 80 degrees Celsius for 20 minutes. Then another layer of thermoplastic polyurethane (second elastic layer) is hot-pressed on the first elastic layer by using hot-pressing technology, and the hot-pressing temperature is 130 degrees Celsius and the pressure is 3 kg / square centimeter. Before hot-pressing, holes need to be punched on the second elastic layer to expose the electrical connection sites of the liquid metal sensitive material layer. PVC hot melt adhesive film is used as a non-elastic layer, and a laser cutting machine is used to cut sensitive gaps with widths of 1 mm, 2.5 mm, 5 mm, 10 mm and 20 mm, respectively, on five pieces of PVC hot melt adhesive film. The cut PVC hot melt adhesive film is hot-pressed on the second elastic layer at 140 degrees Celsius and a pressure of 3 kg / square, and the main part (strain sensitive part) of the sensitive material is located in the sensitive gap. Before hot-pressing, holes also need to be punched on the PVC non-elastic layer to expose the electrical connection sites of the liquid metal sensitive material layer. Thus, five stretchable strain sensors with different sensitive gap widths are prepared.

[0050] Performance test:

[0051] The strain sensors with different sensitive gap widths in Example 2 are subjected to tensile test, and the resistance of the sensitive material is measured during the tensile process, as shown in Figure 3 , it can be seen that the narrower the sensitive gap, the greater the degree of increase in resistance with the increase in deformation, and the higher the sensitivity of the strain sensor.

[0052] As shown in Figure 4 , the change of the resistance change rate of the stretchable strain sensor with a sensitive gap width of 10 mm under different strains is measured, and the experimental results show that the strain sensor of the present application has fast response speed and good reproducibility.

[0053] In summary, the sensitivity and measurement range of the flexible stretchable sensor of the present application depend on the width of the sensitive gap and the length of the sensor, and the sensitivity and measurement range can be flexibly adjusted during preparation; and the sensor structure and preparation are simple and convenient to process, suitable for roll-to-roll production; and have great application potential in the fields of wearable devices, implanted devices, robots and virtual reality.

[0054] The above description is based on the best embodiment of the concept and working principle of the present application. The above embodiments should not be understood as limiting the scope of the present application, and other embodiments and combinations of implementation modes according to the concept of the present application all belong to the protection scope of the present application.

Claims

1. A stretchable strain sensor comprising a first elastic layer (1), a layer of sensitive material (4), a second elastic layer (2), a non-elastic layer (3) and a sensitive slit (5), characterized in that, The non-elastic layer (3) is used to construct a sensitive gap (5), wherein the first elastic layer (1), the second elastic layer (2) and the non-elastic layer (3) are sequentially stacked from bottom to top, the sensitive material layer (4) is encapsulated in the second elastic layer (2), the sensitive gap (5) is located in the non-elastic layer (3), and the sensitive material layer (4) comprises a strain sensitive part, the strain sensitive part is located in the range of the corresponding area of the sensitive gap (5) in the direction perpendicular to the thickness of each layer of the stretchable strain sensor, when the two ends of the stretchable strain sensor are stretched, all the strain loaded on the stretchable strain sensor will be concentrated in the sensitive gap (5) because the non-elastic layer (3) is not deformable, the strain sensitive part of the sensitive material layer (4) is arranged in a serpentine or bent structure for sensing strain during deformation, and the conductive part of the sensitive material layer located in the non-elastic region is used for conducting electricity, thereby facilitating connection with external devices.

2. The stretchable strain sensor of claim 1, wherein, The first elastic layer (1) is selected from one or more of thermoplastic polyurethane material, ethylene-vinyl acetate copolymer material, silicone rubber elastic material, polystyrene-based elastic material, polyolefin-based elastic material, ethylene-acrylic acid copolymer material and latex-based elastic material.

3. The stretchable strain sensor of claim 1, wherein, The second elastic layer (2) is selected from one or more of thermoplastic polyurethane material, ethylene-vinyl acetate copolymer material, silicone rubber elastic material, polystyrene-based elastic material, polyolefin-based elastic material, ethylene-acrylic acid copolymer material and latex-based elastic material.

4. The stretchable strain sensor of claim 1, wherein, The sensitive material layer (4) is selected from one or more of liquid metal, hydrogel, graphene, carbon nanotube, silver nanowire, gold nanowire material and micro-nano structure.

5. The stretchable strain sensor of claim 1, wherein, The second elastic layer (2) comprises a hole for exposing the external connection site of the sensitive material layer.

6. The stretchable strain sensor of claim 1, wherein, The non-elastic layer (3) is selected from one or more of photosensitive resin, polyimide, polyvinyl chloride, polyethylene terephthalate, polyolefin and polyamide.

7. The stretchable strain sensor of claim 1, wherein, The width of the sensitive gap (5) is 0.001-50 mm.

8. The stretchable strain sensor of claim 1, wherein, The thickness of the first elastic layer (1) is 10-500 microns, and the thickness of the second elastic layer (2) is 10-500 microns.

9. The method of claim 1-7, wherein, The method comprises the following steps: S1. The sensitive material layer (4) material is printed on the first elastic layer (1) by using inkjet printing, screen printing, stencil, 3D printing or soft etching technology; S2. The uncured second elastic layer (2) material is coated on the first elastic layer (1) to encapsulate the sensitive material layer (4), and the second elastic layer (2) is cured; and S3. The non-elastic layer (3) photoresist is prepared on the second elastic layer (2), and the sensitive gap (5) is obtained by etching or cutting process.

10. The method of claim 1-7, wherein, The method comprises the following steps: S1. The sensitive material layer (4) material is printed on the first elastic layer (1) by using inkjet printing, screen printing, stencil, 3D printing or soft etching technology and dried; S2. Punching holes on the second elastic layer (2) to expose the electrical connection sites of the sensitive material layer (4), and hot-pressing the second elastic layer (2) on the first elastic layer (1) to encapsulate the sensitive material layer (4); and S3. Punching holes on the non-elastic layer (3) to expose the electrical connection sites of the sensitive material layer (4), and cutting the sensitive slit (5) on the non-elastic layer (3), and hot-pressing, cold-pressing, gluing or ion bonding the cut non-elastic layer (3) on the second elastic layer (2) so that the strain-sensitive part of the sensitive material layer (4) is located in the sensitive slit (5).

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