Fiber type sensor with adjustable strain sensitivity and sensing range and preparation method thereof

Abstract

The invention discloses a fiber-type sensor with adjustable strain sensitivity and sensing range and a preparation method thereof. The fiber-type sensor realizes strain resistance response of basic sensitivity through bulk resistance change caused by cross sectional area change of a conductive material layer when the fiber-type sensor is stretched and an expansion effect of microcracks on the surface of the conductive material layer. The preparation method of the fiber type sensor comprises the following steps: extruding a thermoplastic polyurethane organic solution into a water bath by using an injector to obtain a phase separation porous core fiber 1; immersing the core fiber into an organic solution containing a thermoplastic polyurethane and carbon nanotube mixture, taking out the core fiber, and transferring the core fiber to a non-woven fabric substrate; the substrate and the coated core fiber on the substrate are integrally placed in a water bath and then taken out, and the sensing fiber is obtained after the fiber is stripped; a metal foil packaging layer or a polymer packaging layer is used for wrapping fibers in a segmented mode, and the fibers are pre-stretched to form the fiber type sensor with sensing efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic fibers, and in particular relates to a fiber-type sensor with adjustable strain sensitivity and sensing range and a preparation method thereof. Background Art

[0002] As a new type of sensor form, fiber-type sensors are increasingly used in the field of wearable sensing due to their small size, easy bending, and convenient integration with textiles. Strain sensing fibers have the ability to capture large and small strains, and can be used to obtain changes in body surface curvature caused by human joint posture and physiological activities. However, capturing different types of human strain requires strain sensors to have different sensitivities and working windows. For example, the strains of breathing and pulse are weak, requiring the sensor to have high sensitivity performance within a small strain range; the strain amplitude of elbow bending and shoulder bending is large, requiring the sensor to adapt to a large strain sensing range and produce a small signal response to unit strain, so as to monitor the entire process of joint movement within the range. Therefore, it is urgent to develop a fiber-type sensor with adjustable strain sensitivity and sensing range to achieve effective monitoring of strain within a predetermined range in human strain. Summary of the invention

[0003] The object of the present invention is to provide a fiber-type sensor with adjustable strain sensitivity and sensing range and a preparation method thereof;

[0004] A fiber-type sensor proposed in the present invention comprises a porous core fiber, a sensing functional layer and an external packaging layer; the sensing functional layer is coated on the surface of the porous core fiber; the external packaging layer is covered on the surface of the sensing functional layer in sections and intervals; the sensing functional layer comprises a packaging area and an unpackaged area, the area where the sensing functional layer covering the external packaging layer is located is the packaging area, and the area where the sensing functional layer not covering the external packaging layer is located is the unpackaged area; the surface of the sensing functional layer in the unpackaged area has micro cracks.

[0005] The encapsulated area accounts for 30%-50% of the surface area of ​​the sensing functional layer, and the unencapsulated area accounts for 70%-50%.

[0006] Furthermore, the diameter of the porous core fiber is 400 microns to 600 microns, and the thickness of the sensing function layer is 10 microns to 50 microns.

[0007] Furthermore, the porous core fiber is a porous thermoplastic polyurethane fiber; the sensing function layer is a mixture of thermoplastic polyurethane and carbon nanotubes; the external packaging layer is a metal foil, a polyimide film or a polyvinylidene fluoride film. The metal foil is 0.074 mm thick, with three layers of wrapping and winding; the electrospun polyimide film is 0.1 mm thick, or the polyvinylidene fluoride film is 0.1 mm thick, and each packaging layer is 10 mm long.

[0008] Further, a partial area in the unpackaged area is selected, the partial area including the crack area and non-crack areas located on both sides of the crack area;

[0009] The length direction of the crack region is the same as the length direction of the sensing function layer; the two sides of the crack region refer to the directions perpendicular to the length direction of the crack region; when the unpackaged region is not stretched, the equivalent resistance δR of the selected partial region is expressed as follows:

[0010] δR=(Rb1 / / Rc1 / / Rb2);

[0011] Rc1 represents the equivalent resistance of the crack area when not stretched;

[0012] Rb1 represents the bulk resistance of the crack-free area on one side of the crack area when not stretched;

[0013] Rb2 represents the bulk resistance of the crack-free area on the other side of the crack area when not stretched;

[0014] After stretching, the resistances of Rc1, Rb2, and Rb1 all increase.

[0015] Based on a fiber-type sensor of the present invention, the present invention also provides a method for preparing a fiber-type sensor, comprising the following steps:

[0016] Step 1: Preparation of porous core fiber

[0017] The thermoplastic polyurethane organic solution is extruded into a water bath, and after standing, the formed fibers are taken out and air-dried to obtain phase-separated porous core fibers;

[0018] Step 2: Preparation of sensing functional layer

[0019] The porous core fiber is immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane to prepare a sensing function layer on the surface of the porous core fiber;

[0020] Step 3: Prepare the external packaging layer

[0021] The sensing function layer is encapsulated at intervals to obtain an external encapsulation layer; a fiber covered with the sensing function layer and the external encapsulation layer is obtained.

[0022] Step 4, applying a pre-stretching of 0-500% strain to the fiber prepared in step 3 and then releasing it, so that micro cracks are generated on the surface of the sensing function layer to form a fiber-type sensor.

[0023] Furthermore, 1 part of carbon nanotubes, 1 part of thermoplastic polyurethane, and 40 parts of N,N-dimethylformamide organic solvent are taken, stirred and heated to obtain the conductive paste described in step 2.

[0024] Furthermore, in step 3, the sensing function layer is encapsulated with copper foil.

[0025] Furthermore, in step 3, electrospinning is used to construct a polyimide film to perform interval packaging on the sensing function layer. The specific steps are as follows:

[0026] The polyimide raw material is dissolved in N,N-dimethylformamide solvent, and 5% to 20% concentration of triethylammonium bicarbonate salt is added to adjust the conductivity of the solution to prepare a spinning solution. The working voltage of the electrospinning machine is set in the range of 7.5 to 20 kV, the flow rate is adjusted to 0.25 to 2 mL / h, and the distance from the nozzle to the collector is adjusted to 5 to 20 cm. The polyimide solution is ejected from the nozzle under the action of a high-voltage electric field to form fibers, and the original sensing fiber is placed on a metal plate to control the nozzle spinning pattern. After the solvent evaporates, the ejected polyimide microfibers are segmented and solidified into polyimide films in a uniformly spaced pattern on the single-side surface of the sensing fiber.

[0027] Furthermore, in step 3, near-field direct writing electrospinning is used to construct a polyvinylidene fluoride film to perform interval packaging on the sensing function layer. The specific steps are as follows:

[0028] The polyvinylidene fluoride raw material is dissolved in a mixed solvent of dimethylacetamide and acetone, wherein the mass ratio of dimethylacetamide to acetone is 4:1, the concentration of polyvinylidene fluoride is 14wt%, and 40nm silica nanoparticles are added as an additive;

[0029] The electric field strength is set to 3.0-4.0 kV, the receiving distance is 4-8 mm, and the solution flow rate is 0.20 mL / h-0.5 mL / h. The polyvinylidene fluoride solution is sprayed out from the nozzle under the action of the high voltage electric field to form fibers, and the original sensing fiber is placed on a metal plate to control the nozzle spray pattern. After the solvent evaporates, the sprayed polyvinylidene fluoride microfibers are segmented and solidified into polyvinylidene fluoride films in a uniformly spaced pattern on the single side surface of the sensing fiber.

[0030] Furthermore, the preparation method of the thermoplastic polyurethane organic solution in step 1 is as follows:

[0031] According to the weight percentage, 1 part of thermoplastic polyurethane particles and 4-5 parts of N,N-dimethylformamide are weighed, stirred and heated to obtain a thermoplastic polyurethane organic solution.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0033] 1. The present invention periodically covers the surface of a strain sensing fiber with a sensing function layer with a metal or polymer packaging layer in sections at certain intervals to form a fiber-type sensor with adjustable strain sensitivity and sensing range. This fiber-type sensor has the characteristics of segmented distribution of axial Young's modulus. The strain exerted on other parts of the fiber is amplified by the presence of a packaging layer with less elasticity and ductility, thereby regulating the strain sensitivity of the sensing fiber.

[0034] 2. The sensing function layer is composed of a mixture of thermoplastic polyurethane and carbon nanotubes. When stretched, cracks expand on the surface, and the equivalent circuit of the cracks is converted from parallel to series, which improves the strain sensitivity of the fiber sensor. At the same time, the density of the original surface cracks can be adjusted by different pre-stretching degrees, thereby changing the sensitivity and sensing range of the fiber sensor. The existing patents include a description of constructing microcracks on a thin film sensor by pre-stretching, but fail to explain the method of adjusting the sensing performance of the strain sensor (especially the fiber sensor) by pre-stretching treatment to different degrees.

[0035] 3. The construction of the sensing function layer in the fiber-type sensor preparation method is constructed by the method of substrate water bath phase separation and then peeling. The thermoplastic polyurethane core fiber is immersed in a conductive coating solution, taken out after a period of time and transferred to a non-woven fabric substrate; the substrate and the coated fiber on it are placed in a water bath for 5 minutes and then taken out, and the internal sensing fiber is obtained after the fiber is peeled off. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the 3D structure of the fiber-type sensor of the present invention;

[0037] Figure 2 It is a schematic diagram of the cross-sectional structure of the fiber-type sensor of the present invention;

[0038] Figure 3 It is a schematic diagram of the preparation principle of the fiber-type sensor of the present invention;

[0039] Figure 4 It is a scanning electron microscope photo of the crack and a schematic diagram of the change of the equivalent circuit topology during the crack generation process;

[0040] Figure 5 It is the working mechanism and equivalent circuit diagram of the fiber type strain sensor of the present invention;

[0041] Figure 6 This is a performance test diagram of the effect of the packaging layer ratio of the fiber-type sensor of the present invention on the sensing sensitivity and sensing range;

[0042] Figure 7 are scanning electron micrographs of cracks on the fiber surface after the unencapsulated area was pre-stretched by 300% and 500% and released;

[0043] Figure 8 This is a performance test diagram of the fiber-type sensor of the present invention, showing the effect of the pre-stretching degree on the sensing sensitivity and sensing range; DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0045] Embodiment 1

[0046] like Figure 1 As shown, a fiber sensor with adjustable strain sensitivity and sensing range of the present invention comprises a phase-separated porous core fiber 1, a sensing function layer 2 and an external packaging layer 3;

[0047] The sensing function layer 2 is coated on the surface of the porous core fiber 1, and the external packaging layer 3 is periodically and segmentally coated on the surface of the sensing function layer 2 at certain intervals. Figure 2 As shown, the encapsulated area accounts for 30%-50% of the surface area of ​​the sensing function layer 2, and the unencapsulated area accounts for 70%-50%; the length of each encapsulated layer is 10 mm.

[0048] The porous core fiber 1 is a porous thermoplastic polyurethane fiber with a diameter of 400-600 microns, and the sensing function layer 2 is a mixture of thermoplastic polyurethane and carbon nanotubes with a thickness of 10-50 microns.

[0049] The material of the external packaging layer 3 is a 0.074 mm thick metal foil, or a 0.1 mm thick electrospun polyimide film, or a 0.1 mm thick near-field electrospun polyvinylidene fluoride film. The length of each packaging layer is 10 mm, and each packaging layer is wrapped and wound with a total of three layers. Figure 1 (a) is the sensing fiber encapsulated by metal foil. Figure 1 (b) is a sensing fiber encapsulated on one side by electrospinning or near-field electrospinning. The surface of the sensing function layer 2 not covered by the external encapsulation layer 3 has micro cracks.

[0050] like Figure 5 As shown, the working mechanism and equivalent circuit of the fiber-type strain sensor of the present invention are given. A partial area in the unpackaged area of ​​the sensing functional layer 2 is selected, and the resistance is recorded as δR. The partial area includes a crack area and a crack-free area;

[0051] When the sensing functional layer 2 is not stretched, the resistance of the selected area is expressed as follows:

[0052] δR=(Rb1 / / Rc1 / / Rb2);

[0053] Rc1 represents the equivalent resistance of the crack area when not stretched;

[0054] Rb1 represents the bulk resistance of the crack-free area on one side of the crack area when not stretched;

[0055] Rb2 represents the bulk resistance of the crack-free area on the other side of the crack area when not stretched;

[0056] After being stretched, the body resistance Rb1 and Rb2 of the crack-free area increase due to the decrease in cross-sectional area, and the body resistance Rb1 and Rb2 of the crack-free area change to Rb1' and Rb2'; Rc1 represents the equivalent resistance of the crack area when not stretched, and the crack area includes the crack itself generated during stretching, the part of the crack that is not completely broken during the stretching process, and the unpackaged area on both sides of the crack opening. After being stretched, the equivalent circuit topology of the crack area changes from parallel type to series type, and the resistance changes from Rc1 to Rc1'. When the fiber-type sensor is stretched, in addition to the increase in body resistance of the unpackaged sensing function layer 2 due to the change in cross-sectional area, the sensing function layer 2 also gradually expands due to the gradual expansion of surface microcracks, and the equivalent circuit topology of the conductive path changes from parallel type to series type, causing the surface equivalent resistance to increase rapidly. The packaging area is wrapped with three layers of single-sided sticky copper foil or aluminum foil, or a single-sided electrospun polyimide film with a thickness of 0.1 mm, or a single-sided near-field electrospun polyvinylidene fluoride film with a thickness of 0.1 mm. Since the Young's modulus of the packaging layer is greater than that of the core fiber and the sensing function layer 2 (the materials of the core fiber and the sensing function layer 2 both belong to the thermoplastic polyurethane-based polymer material system), the encapsulated fiber part has greater rigidity and is not easy to deform. The strain generated after stretching will be more concentrated in the unencapsulated area, amplifying the strain in this area, thereby increasing the sensitivity of the fiber-type sensor.

[0057] Embodiment 2

[0058] Based on the fiber-type sensor in the first embodiment, the present invention further provides a method for preparing a fiber-type sensor with adjustable strain sensitivity and sensing range, wherein the strain sensitivity is adjusted by the area ratio of the packaging area and the pre-stretching degree, and the sensing range is mainly affected by the area ratio of the packaging area, such as Figure 3 As shown, the following steps are included:

[0059] Step 1: squeeze the thermoplastic polyurethane organic solution into a water bath using a syringe, let it stand for 5 minutes, take out the formed fiber and dry it to obtain a phase-separated porous core fiber 1.

[0060] Step 2, immersing the porous core fiber 1 into a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane, taking it out and transferring it to a non-woven fabric substrate;

[0061] The organic solution containing a mixture of carbon nanotubes and thermoplastic polyurethane in this embodiment includes 1 part of carbon nanotubes, 1 part of thermoplastic polyurethane, and 40 parts of N,N-dimethylformamide organic solvent, which are obtained by magnetically stirring the three at 250 rpm and heating at 80 degrees Celsius for 12 hours.

[0062] The non-woven fabric substrate and the porous core fiber 1 coated thereon are placed in a water bath as a whole and allowed to stand for 5 minutes, and then taken out, and the porous core fiber 1 is peeled off from the non-woven fabric substrate to obtain the porous core fiber 1 with the sensing function layer 2 attached thereto;

[0063] Step 3, encapsulating the sensing function layer 2 in intervals and sections to obtain an external encapsulation layer 3; the area where the external encapsulation layer 3 is located is the encapsulation area, and the encapsulation area accounts for 0-50% of the total surface area of ​​the sensing fiber; the specific encapsulation method is:

[0064] Use copper foil packaging layer packaging, or use electrospinning to construct polyimide film packaging, or use near-field direct writing electrospinning (referred to as near-field spinning) to construct polyvinylidene fluoride film packaging;

[0065] Electrospinning is used to construct polyimide film encapsulation. The specific steps are as follows:

[0066] The polyimide raw material is dissolved in N,N-dimethylformamide solvent, and 5% to 20% (w / v) concentration of triethylammonium bicarbonate salt is added to adjust the conductivity of the solution to prepare a spinning solution, and the working voltage of the electrospinning machine is set in the range of 7.5 to 20 kV, the flow rate is adjusted to 0.25 to 2 mL / h, and the distance from the nozzle to the collector is adjusted to 5 to 20 cm. The polyimide solution is sprayed from the nozzle under the action of a high-voltage electric field to form a fiber, and the original sensing fiber is placed on a metal plate, and the nozzle spray pattern is controlled by a program. After the solvent evaporates, the sprayed polyimide microfibers are segmented and solidified into a polyimide film in a uniformly spaced pattern on the single-side surface of the sensing fiber, and the encapsulation area accounts for 0-30% of the total surface area of ​​the fiber;

[0067] Near-field direct writing electrospinning (referred to as near-field spinning) is used to construct polyvinylidene fluoride film packaging. The specific steps are as follows:

[0068] The polyvinylidene fluoride raw material is dissolved in a mixed solvent of dimethylacetamide and acetone (mass ratio is 4:1), the polyvinylidene fluoride concentration is 14wt%, and 40nm silica nanoparticles are added as additives. The electric field strength is set to 3.0~4..0kV, the receiving distance is 4~8mm, the solution flow rate is 0.20mL / h~0.5mL / h, and the spinning temperature is 40℃. The polyvinylidene fluoride solution is sprayed out from the nozzle under the action of the high-voltage electric field to form fibers, and the original sensing fiber is placed on a metal plate, and the nozzle spraying pattern is controlled by a program. After the solvent evaporates, the ejected polyvinylidene fluoride microfibers are segmented and solidified into polyvinylidene fluoride films in a uniformly spaced pattern on the single-side surface of the sensing fiber, and the encapsulation area accounts for 0-30% of the total surface area of ​​the fiber;

[0069] Step 4, applying a pre-stretch of 0-500% strain to the fiber and then releasing it to generate micro cracks on the surface of the sensing layer, thereby forming a fiber-type sensor with sensing performance.

[0070] Figure 6 This is the relationship between the proportion of the metal packaging area and the sensing sensitivity and sensing range in the experimental test. It can be seen that with the increase in the proportion of the packaging area, the strain sensing sensitivity gradually increases, while the sensing range gradually decreases, thus realizing the adjustment of the sensing sensitivity and sensing range.

[0071] Figure 4 Scanning electron microscope image of the surface of the middle sensing functional layer 2. After undergoing 500% pre-tensile strain during the preparation process and then released, significant microcracks can be seen. Figure 4 The figure on the right is an equivalent circuit model of this crack area, which describes the process of gradual crack expansion of the sensing functional layer 2 after being stretched during use, and the corresponding resistance network gradually changes from a parallel type to a series type.

[0072] Figure 7 The following are scanning electron microscope images of the surface of the sensing function layer 2 after the sensing fiber was pre-stretched by 300% strain and 500% strain, respectively. As the degree of pre-stretching increases, the initial cracks of the fiber sensor increase, and the proportion of the parallel type in the equivalent circuit of the sensing function layer 2 increases. When subjected to strain, the crack area will simultaneously transform from the parallel type to the series type, thereby improving the sensitivity of the fiber sensor. Figure 8 This is the influence curve of pre-stretching on sensor sensitivity and sensing range obtained by experimental test. It can be seen that the greater the pre-stretching degree, the greater the sensitivity of the fiber strain resistor, while the effective sensing range does not change much. This is the second sensitivity adjustment method.

[0073] By adjusting the packaging layer ratio and pre-stretching in the present invention, the sensor sensitivity can be increased to 33-35 (sensitivity is defined as the relative resistance change rate divided by the strain size in the resistive sensor stretching test) to meet the detection requirements of weak strains such as human breathing and pulse. The sensor sensitivity can also be reduced to 25-28, and the sensor range is increased to 80% to meet the sensitivity and range requirements for detecting elbow bending and joint bending.

[0074] Embodiment 3

[0075] Based on the fiber-type sensor in Example 1, the present invention provides a method for preparing a fiber-type sensor with adjustable strain sensitivity and sensing range, which is as follows:

[0076] According to the weight percentage, 1 part of thermoplastic polyurethane particles and 4 parts of N,N-dimethylformamide were weighed on a balance and heated at 80 degrees Celsius for 12 hours while magnetically stirring at 200 revolutions per minute to obtain a thermoplastic polyurethane organic solution. The thermoplastic polyurethane organic solution was squeezed into a water bath with a syringe, and after standing for 5 minutes, the formed fiber was taken out and dried to obtain a phase-separated porous core fiber 1;

[0077] The porous core fiber 1 is immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane, and then transferred to a non-woven fabric substrate after being taken out; the substrate and the coated core fiber thereon are placed in a water bath as a whole and allowed to stand for 5 minutes, then taken out, and the sensing fiber is obtained after the fiber is peeled off;

[0078] A copper foil packaging layer is used to wrap the sensing fiber in sections at uniform intervals, with the packaging area accounting for 10% of the total surface area of ​​the fiber. The fiber is pre-stretched with 100% strain and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing efficiency.

[0079] Embodiment 4

[0080] Based on the fiber-type sensor in Example 1, the present invention provides a method for preparing a fiber-type sensor with adjustable strain sensitivity and sensing range, which is as follows:

[0081] According to the weight fraction, 1 part of thermoplastic polyurethane particles and 4 parts of N,N-dimethylformamide are weighed on a balance and heated at 100 degrees Celsius for 10 hours while magnetically stirring at 200 revolutions per minute to obtain a thermoplastic polyurethane organic solution. The thermoplastic polyurethane organic solution is extruded into a water bath with a syringe, and the formed fiber is taken out and dried after standing for 5 minutes to obtain a phase-separated porous core fiber 1; the porous core fiber 1 is immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane, and then transferred to a non-woven fabric substrate after being taken out; the substrate and the coated core fiber thereon are placed in a water bath as a whole, and then taken out after standing for 5 minutes, and the sensing fiber is obtained after peeling the fiber; an aluminum foil packaging layer is used to wrap the fiber in sections at uniform intervals, and the packaging area accounts for 30% of the total surface area of ​​the fiber, and the fiber is pre-stretched with a strain of 100% and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing efficiency.

[0082] Embodiment 5

[0083] Based on the fiber-type sensor in Example 1, the present invention provides a method for preparing a fiber-type sensor with adjustable strain sensitivity and sensing range, which is as follows:

[0084] According to the weight fraction, 1 part of thermoplastic polyurethane particles and 5 parts of N,N-dimethylformamide were weighed on a balance and heated at 80 degrees Celsius for 10 hours while magnetically stirring at 200 revolutions per minute to obtain a thermoplastic polyurethane organic solution. The thermoplastic polyurethane organic solution was extruded into a water bath with a syringe, and the formed fiber was taken out and dried after standing for 5 minutes to obtain a phase-separated porous core fiber 1; the porous core fiber 1 was immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane, and then transferred to a non-woven fabric substrate after being taken out; the substrate and the coated core fiber thereon were placed in a water bath as a whole, stood for 5 minutes, and then taken out, and the sensing fiber was obtained after the fiber was peeled off; a 0.1mm thick single-sided electrospun polyimide encapsulation layer was used to wrap the fiber in sections at uniform intervals, and the encapsulation area accounted for 30% of the total surface area of ​​the fiber, and the fiber was pre-stretched with a strain of 100% and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing efficiency. The steps of electrospinning to construct a uniformly spaced polyimide film encapsulation layer include dissolving the polyimide raw material in N,N-dimethylformamide solvent, adding 20% ​​(w / v) concentration of triethylammonium bicarbonate salt to adjust the conductivity of the solution to configure a spinning solution, setting the working voltage of the electrospinning machine within the range of 20kV, adjusting the flow rate to 2mL / h, adjusting the distance from the nozzle to the collector to 15cm, and the polyimide solution is ejected from the nozzle under the action of a high-voltage electric field to form a fiber, and the original sensing fiber is placed on a metal plate, and the nozzle spray pattern is controlled by a program. After the solvent evaporates, the ejected polyimide microfibers are segmented and solidified into a polyimide film in a uniformly spaced pattern on the single-side surface of the sensing fiber. The fiber is pre-stretched with a 100% strain and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing performance.

[0085] Embodiment 6

[0086] Based on the fiber-type sensor in Example 1, the present invention provides a method for preparing a fiber-type sensor with adjustable strain sensitivity and sensing range, which is as follows:

[0087] According to the weight fraction, 1 part of thermoplastic polyurethane particles and 5 parts of N,N-dimethylformamide were weighed on a balance and heated at 80 degrees Celsius for 10 hours while magnetically stirring at 200 revolutions per minute to obtain a thermoplastic polyurethane organic solution. The thermoplastic polyurethane organic solution was extruded into a water bath with a syringe, and the formed fiber was taken out and dried after standing for 5 minutes to obtain a phase-separated porous core fiber 1; the porous core fiber 1 was immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane, and then transferred to a non-woven fabric substrate after being taken out; the substrate and the coated core fiber on it were placed in a water bath as a whole, stood for 10 minutes, and then taken out, and the sensing fiber was obtained after peeling the fiber; a 0.1mm thick single-sided electrospun polyimide encapsulation layer was used to evenly wrap the fiber in sections, and the encapsulation area accounted for 30% of the total surface area of ​​the fiber, and the fiber was pre-stretched with a strain of 300% and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing efficiency. The steps of electrospinning to construct a uniformly spaced polyimide film encapsulation layer include dissolving the polyimide raw material in N,N-dimethylformamide solvent, adding 15% (w / v) concentration of triethylammonium bicarbonate salt to adjust the conductivity of the solution to configure a spinning solution, setting the working voltage of the electrospinning machine within the range of 15kV, adjusting the flow rate to 1.5mL / h, adjusting the distance from the nozzle to the collector to 15cm, and the polyimide solution is ejected from the nozzle under the action of a high-voltage electric field to form a fiber, and the original sensing fiber is placed on a metal plate, and the nozzle spray pattern is controlled by a program. After the solvent evaporates, the ejected polyimide microfibers are segmented and solidified into a polyimide film in a uniformly spaced pattern on the single-side surface of the sensing fiber. The fiber is pre-stretched with a 100% strain and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing performance.

[0088] Embodiment 7

[0089] Based on the fiber-type sensor in Example 1, the present invention provides a method for preparing a fiber-type sensor with adjustable strain sensitivity and sensing range, which is as follows:

[0090] According to the weight fraction, 1 part of thermoplastic polyurethane particles and 5 parts of N,N-dimethylformamide were weighed on a balance and heated at 80 degrees Celsius for 10 hours while magnetically stirring at 200 revolutions per minute to obtain a thermoplastic polyurethane organic solution. The thermoplastic polyurethane organic solution was extruded into a water bath with a syringe, and the formed fiber was taken out and dried after standing for 5 minutes to obtain a phase-separated porous core fiber 1; the porous core fiber 1 was immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane, and then transferred to a non-woven fabric substrate after being taken out; the substrate and the coated core fiber thereon were placed in a water bath as a whole, stood for 10 minutes, and then taken out, and the sensing fiber was obtained after the fiber was peeled off; a 0.1mm thick single-sided electrospun polyvinylidene fluoride encapsulation layer was used to wrap the fiber in sections at uniform intervals, and the encapsulation area accounted for 20% of the total surface area of ​​the fiber, and the fiber was pre-stretched with a strain of 500% and then released to generate microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing efficiency. The steps of constructing a uniformly spaced polyvinylidene fluoride film encapsulation layer by near-field direct writing electrospinning include dissolving the polyvinylidene fluoride raw material in a mixed solvent of dimethylacetamide and acetone (mass ratio of 4:1), the polyvinylidene fluoride concentration is 14wt%, and 40nm silica nanoparticles are added as additives. The electric field strength is set to 3.5kV, the receiving distance is 5mm, the solution flow rate is 0.25mL / h, and the spinning temperature is 40℃. The polyvinylidene fluoride solution is ejected from the nozzle under the action of a high-voltage electric field to form a fiber, and the original sensing fiber is placed on a metal plate, and the nozzle spray pattern is controlled by a program. After the solvent evaporates, the ejected polyvinylidene fluoride microfibers are segmented and solidified into a polyvinylidene fluoride film on the single-side surface of the sensing fiber in a uniformly spaced pattern. The fiber is pre-stretched with a 100% strain and then released to produce microcracks on the surface of the sensing layer, forming a fiber-type sensor with sensing efficiency.

[0091] The strain resistance response of basic sensitivity is achieved through the change in volume resistance caused by the change in the cross-sectional area of ​​the conductive material layer when stretched and the expansion of microcracks on the surface of the conductive material layer. At the same time, the sensitivity and sensing range of the fiber-type sensor can be adjusted by covering the packaging layer with different area ratios and applying different degrees of pre-stretching strain.

Claims

1. A fiber-type sensor, characterized in that: It includes a porous core fiber, a sensing function layer and an external packaging layer; The sensing function layer is coated on the surface of the porous core fiber; The external packaging layer is segmented and spaced to cover the surface of the sensing function layer; The sensing function layer includes a packaging area and an unpackaging area, the area where the sensing function layer is covered with the external packaging layer is the packaging area, and the area where the sensing function layer is not covered with the external packaging layer is the unpackaging area; The surface of the unpackaged area has cracks.

2. A fiber-type sensor according to claim 1, characterized in that: The encapsulated area accounts for 30%-50% of the surface area of ​​the sensing functional layer, and the unencapsulated area accounts for 70%-50%.

3. A fiber-type sensor according to claim 1, characterized in that: The porous core fiber is a porous thermoplastic polyurethane fiber; The sensing function layer is a mixture of thermoplastic polyurethane and carbon nanotubes; The external packaging layer is a metal foil, a polyimide film or a polyvinylidene fluoride film.

4. A method for preparing a fiber-type sensor as claimed in claim 3, characterized in that: The steps include: Step 1: Preparation of porous core fiber The thermoplastic polyurethane organic solution is extruded into a water bath, and after standing, the formed fibers are taken out and air-dried to obtain phase-separated porous core fibers; Step 2: Preparation of sensing functional layer The porous core fiber is immersed in a conductive slurry containing a mixture of carbon nanotubes and thermoplastic polyurethane to prepare a sensing function layer on the surface of the porous core fiber; Step 3: Prepare the external packaging layer The sensing function layer is packaged in intervals to obtain an external packaging layer; Step 4, applying a pre-stretching of 0-500% strain to the fiber prepared in step 3 and then releasing it, so that cracks are generated on the surface of the sensing function layer, thereby forming the fiber-type sensor.

5. The method for preparing a fiber-type sensor according to claim 4, characterized in that: Take 1 part of carbon nanotubes, 1 part of thermoplastic polyurethane and 40 parts of N,N-dimethylformamide organic solvent, stir and heat to obtain the conductive paste described in step 2.

6. The method for preparing a fiber-type sensor according to claim 4, characterized in that: In step 3, copper foil is used to perform interval packaging on the sensing function layer.

7. The method for preparing a fiber-type sensor according to claim 4, characterized in that: In step 3, electrospinning is used to construct a polyimide film to perform interval packaging of the sensing function layer. The specific steps are as follows: The polyimide raw material is dissolved in N,N-dimethylformamide solvent, and 5% to 20% concentration of triethylammonium bicarbonate salt is added to adjust the conductivity of the solution to prepare a spinning solution. The working voltage of the electrospinning machine is set in the range of 7.5 to 20 kV, the flow rate is adjusted to 0.25 to 2 mL / h, and the distance from the nozzle to the collector is adjusted to 5 to 20 cm. The polyimide solution is ejected from the nozzle under the action of a high-voltage electric field to form fibers, and the original sensing fiber is placed on a metal plate to control the nozzle spinning pattern. After the solvent evaporates, the ejected polyimide microfibers are segmented and solidified into polyimide films in a uniformly spaced pattern on the single-side surface of the sensing fiber.

8. The method for preparing a fiber-type sensor according to claim 4, characterized in that: In step 3, near-field direct writing electrospinning is used to construct a polyvinylidene fluoride film to perform interval packaging of the sensing function layer. The specific steps are as follows: The polyvinylidene fluoride raw material is dissolved in a mixed solvent of dimethylacetamide and acetone, wherein the mass ratio of dimethylacetamide to acetone is 4:1, the concentration of polyvinylidene fluoride is 14wt%, and 40nm silica nanoparticles are added as an additive; The electric field strength is set to 3.0-4.0 kV, the receiving distance is 4-8 mm, and the solution flow rate is 0.20 mL / h-0.5 mL / h. The polyvinylidene fluoride solution is sprayed out from the nozzle under the action of the high voltage electric field to form fibers, and the original sensing fiber is placed on a metal plate to control the nozzle spray pattern. After the solvent evaporates, the sprayed polyvinylidene fluoride microfibers are segmented and solidified into polyvinylidene fluoride films in a uniformly spaced pattern on the single side surface of the sensing fiber.

9. The method for preparing a fiber-type sensor according to claim 4, characterized in that: The preparation method of the thermoplastic polyurethane organic solution in step 1 is as follows: According to the weight percentage, 1 part of thermoplastic polyurethane particles and 4-5 parts of N,N-dimethylformamide are weighed, stirred and heated to obtain a thermoplastic polyurethane organic solution.

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