Omnidirectional detection sensor based on anisotropic fiber structure and preparation method thereof

Abstract

The invention discloses an omnidirectional detection sensor based on an anisotropic fiber structure and a preparation method thereof, and belongs to the technical field of flexible sensors. The omnidirectional detection sensor comprises a plurality of single-layer sensors, each single-layer sensor comprises an ordered TPU fiber film and a conductive layer arranged on the ordered TPU fiber film, and the conductive layers are connected with electrodes; all the single-layer sensors are stacked up and down, and the upper and lower adjacent single-layer sensors are distributed in a staggered manner after rotating by a certain angle; a bonding layer is arranged between the upper and lower adjacent single-layer sensors; and packaging layers are arranged outside all the single-layer sensors. According to the invention, the orderly arranged TPU fiber films are prepared firstly, then the anisotropic conductive network is constructed by combining the multi-walled carbon nanotubes, and a plurality of single-layer sensors are stacked together in a staggered manner, so that the distinction degree of multidirectional strain signals is remarkably improved. The omni-directional detection sensor also has the advantages of wide detection range, quick response, high sensitivity and high cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, and particularly relates to an omnidirectional detection sensor based on an anisotropic fiber structure and a preparation method thereof. Background Art

[0002] In recent years, flexible strain sensors have become increasingly important due to their potential in wearable devices, health monitoring systems, and soft robots. These sensors are designed to detect mechanical deformations by converting strain into measurable electrical signals. However, traditional flexible strain sensors are mainly limited to uniaxial strain detection, which restricts their ability to accurately capture complex multi-directional strains. This limitation is particularly evident in applications that require precise identification of strain direction and magnitude, such as monitoring human joint movements or implementing multi-axis control of robotic systems.

[0003] To overcome these drawbacks, anisotropic strain sensors have been developed to distinguish strains in different directions. Although some progress has been made, existing anisotropic strain sensors still face challenges in achieving a balance among high sensitivity, excellent stretchability, and a wide detection range. In addition, integrating multiple sensing elements to achieve omnidirectional detection while maintaining simplicity, cost-effectiveness, and reliability remains a significant technical challenge. Summary of the Invention

[0004] In view of the above technical problems, the present invention proposes an omnidirectional detection sensor based on an anisotropic fiber structure, and a preparation method of the omnidirectional detection sensor.

[0005] The technical solution adopted by the present invention is as follows: An omnidirectional detection sensor based on an anisotropic fiber structure, which comprises a plurality of single-layer sensors. Each single-layer sensor includes an ordered TPU fiber film and a conductive layer disposed on the ordered TPU fiber film, and the conductive layer is connected to an electrode; All the single-layer sensors are arranged in an up-and-down stacked manner, and the adjacent single-layer sensors in the up-and-down direction are distributed in a staggered manner after rotating a certain angle; An adhesive layer is provided between the adjacent single-layer sensors in the up-and-down direction; An encapsulation layer is provided outside all the single-layer sensors.

[0006] The present invention also proposes a preparation method of the omnidirectional detection sensor based on an anisotropic fiber structure as described above, comprising the following steps: a. Dissolve TPU particles in a solvent, and then prepare an ordered TPU fiber film by electrospinning; b. Coat multi-walled carbon nanotubes on the surface of the TPU fiber film to form a conductive layer; c. The conductive layer is connected to the electrode through conductive silver paste, and a single-layer sensor is obtained by processing. d. A plurality of single-layer sensors are arranged in an up-and-down stacked manner, and the adjacent single-layer sensors in the up-and-down direction are arranged in a staggered distribution after rotating a certain angle, and are bonded with Ecoflex between the adjacent single-layer sensors in the up-and-down direction. e. The plurality of single-layer sensors stacked in step d are encapsulated with Ecoflex and then heated and cured to obtain an omnidirectional detection sensor.

[0007] The beneficial technical effects of the present invention are as follows: The present invention prepares an orderly arranged TPU fiber film through electrospinning technology, and then combines multi-walled carbon nanotubes (MWCNTs) to construct an anisotropic conductive network, and designs a multi-layer orthogonal stacked sensing unit, which significantly improves the discrimination of multi-directional strain signals. Moreover, due to the fiber orientation difference and the conductive path fracture mechanism, the omnidirectional detection sensor of the present invention exhibits significant sensitivity differences in the directions parallel and perpendicular to the fiber direction, and can achieve high-precision classification in the range of 0° to 180°. It has a wide detection range, fast response, high sensitivity and high cycle stability, and can effectively solve the problems of traditional flexible strain sensors such as too high similarity of multi-directional strain signals and insufficient direction recognition accuracy caused by isotropic conductive networks.

[0008] The principles of the above-mentioned fiber orientation difference and conductive path fracture mechanism are as follows: The parallel arrangement of the ordered TPU fiber film endows the substrate with high anisotropy. When the strain is applied along the fiber direction (parallel), the fibers are stretched but remain continuous, and the connection points of the MWCNT conductive network are less fractured, and the resistance change is small; when the strain is applied perpendicular to the fiber direction, the fiber spacing increases, and the conductive paths of the MWCNTs network are significantly fractured (the contact points are reduced or disconnected), resulting in a large resistance change. This anisotropic response enables the sensor to generate unique electrical signals under strains in different directions, thereby achieving high-precision direction discrimination.

[0009] In addition, there are also multi-layer stacks in the prior art for omnidirectional strain detection, but the single-layer sensors used need to print the sensing layer onto a flexible substrate according to a preset pattern. This complex printing process is easily affected by coating uniformity, and the assembled sensors have problems such as insufficient sensitivity. The present invention adopts an orderly arranged TPU fiber film + coated multi-walled carbon nanotube conductive layer + multi-layer orthogonal stacking, which can effectively solve the above problems. The obtained sensor has high sensitivity, wide detection range and high cycle stability, and the preparation method is simple and flexible, and is easy to implement.

[0010] The preparation process of the present invention can flexibly adapt to the performance requirements of sensors by regulating the fiber arrangement and stacking angle, without the need for complex micro-structure processing, and has excellent stretchability. It can be extended to the design of various types of sensors such as resistive and capacitive sensors, providing a high-resolution and high-reliability omnidirectional detection solution for human motion monitoring, robot tactile perception, and intelligent wearable devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic flow chart of the preparation method of the single-layer sensor in the present invention; Figure 2 is a diagram of the TPU fiber film prepared in a specific embodiment of the present invention, where (a) is a physical diagram of the ordered TPU fiber film, (b) is a SEM micrograph of the ordered TPU fiber film, (c) is a partial enlarged view of (b), and (d) is a SEM micrograph of the disordered TPU fiber; Figure 3 is a schematic diagram of the orthogonal stacking of three single-layer sensors; Figure 4 is a test chart of the response time of the omnidirectional detection sensor prepared in a specific embodiment of the present invention; Figure 5 is a test chart of the sensitivity of the omnidirectional detection sensor prepared in a specific embodiment of the present invention in the stretching range of 0 - 300%; Figure 6 is a schematic diagram of the direction division of the omnidirectional detection sensor prepared in a specific embodiment of the present invention; Figure 7 is an image of the voltage change when the omnidirectional detection sensor is stretched in different stretching directions. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The present invention discloses an omnidirectional detection sensor based on an anisotropic fiber structure and its preparation method to solve the problem that traditional flexible strain sensors have too high similarity of multi-directional strain signals and insufficient direction recognition accuracy due to isotropic conductive networks. Specifically, the present invention prepares an ordered TPU fiber film by electrospinning technology, constructs an anisotropic conductive network in combination with multi-walled carbon nanotubes, and designs a three-layer orthogonal stacking sensing unit to significantly regulate the resistance response characteristics when stretched in different directions by using the significant difference in fiber orientation. The omnidirectional detection sensor of the present invention exhibits significantly different sensitivities in the directions parallel and perpendicular to the fiber direction, greatly improving the multi-channel signal discrimination, and has excellent stretchability and a wide working range and other properties. The preparation process of this sensor is simple and flexible, and can be extended to resistive and capacitive sensing designs. The present invention provides a high-resolution and high-reliability omnidirectional strain detection solution for human motion monitoring, robot multi-directional tactile perception, and intelligent wearable devices.

[0013] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0014] As Figure 1-3 shown, an omnidirectional detection sensor based on an anisotropic fiber structure includes a plurality of single-layer sensors. Each single-layer sensor includes an ordered TPU fiber film and a conductive layer disposed on the ordered TPU fiber film. The conductive layer is connected to an electrode. All the single-layer sensors are arranged in an up-and-down stacked manner, and the adjacent single-layer sensors above and below are arranged in a staggered distribution after rotating a certain angle. A bonding layer is provided between the adjacent single-layer sensors above and below. An encapsulation layer is provided outside all the single-layer sensors.

[0015] The ordered TPU fiber film serves as a flexible substrate or base layer, and a plurality of fiber monomers therein are arranged in parallel, as Figure 2 shown in (a)-(c) therein. The electrode is disposed along the direction perpendicular to the fiber monomers. The electrode is a copper electrode or copper foil, and the copper electrode is connected to the conductive layer through conductive silver paste.

[0016] The conductive layer or conductive network is formed by coating multi-walled carbon nanotubes. Both the bonding layer and the encapsulation layer are made of Ecoflex material, and the thickness of the encapsulation layer can be set to 0.5-1 mm.

[0017] As Figure 3 shown, a total of three single-layer sensors are provided, which are the first single-layer sensor, the second single-layer sensor, and the third single-layer sensor in sequence from bottom to top. Taking the orientation of the first single-layer sensor as a reference, the second single-layer sensor rotates 90° relative to the first single-layer sensor, and the third single-layer sensor rotates 45° relative to the first single-layer sensor. That is, each layer is oriented in the directions of 0°, 45°, and 90° relative to the reference axis X-axis.

[0018] The anisotropic arrangement of the above fibers in combination with the multi-walled carbon nanotube conductive layer enables the sensor to exhibit different electrical responses to strains applied in different directions. Multiple anisotropic sensing element layers are stacked in specific directions (such as 0°, 45°, and 90°) to achieve comprehensive omnidirectional strain detection. The electrodes connected to each layer are used to measure the resistance change under strain.

[0019] This sensor is a strain sensor capable of detecting multi-directional mechanical deformation and can be applied to fields such as wearable electronic devices, health monitoring, soft robots, and human-computer interaction systems.

[0020] In summary, the present invention addresses the deficiencies of traditional strain sensors by introducing a novel flexible strain sensor with anisotropic properties based on an ordered thermoplastic polyurethane (TPU) fiber film. By leveraging the directional sensitivity of the anisotropic fiber structure and adopting a multi-layer design, the present invention provides a robust solution for omnidirectional strain detection. The sensor exhibits high sensitivity, excellent stretchability, and a broad working range, making it highly suitable for advanced applications in multi-directional strain recognition.

[0021] As Figure 1 shown, the present invention also provides a method for preparing an omnidirectional detection sensor based on an anisotropic fiber structure, comprising the following steps: a. Dissolve TPU particles in a solvent, and then prepare an ordered TPU fiber film by electrospinning. The fiber monomers in the ordered TPU fiber film are arranged in parallel with a controllable spacing.

[0022] The solvent is obtained by mixing N,N-dimethylformamide and tetrahydrofuran in a volume ratio of 1:1. Dissolve the TPU particles in the solvent to obtain a spinning solution, and the mass fraction of the spinning solution is 10% - 20%. Prepare an ordered TPU fiber film by electrospinning the spinning solution. The process parameters of electrospinning are as follows: the positive voltage is 10 - 15 kV, the negative voltage is -2 - -5 kV, and the roller rotation speed is 1500 - 2500 rpm.

[0023] b. Coat multi-walled carbon nanotubes on the surface of the TPU fiber film to form an anisotropic conductive network, i.e., a conductive layer. Specifically, prepare an aqueous solution of multi-walled carbon nanotubes, and the concentration of the aqueous solution of multi-walled carbon nanotubes is 5wt% - 15wt%. Uniformly coat the aqueous solution of multi-walled carbon nanotubes on the surface of the TPU fiber film and dry it at 50 - 60°C for 10 - 15 minutes to obtain the conductive layer.

[0024] c. Connect the conductive layer to the electrodes through conductive silver paste to process a single-layer sensor. Copper electrodes can be used as the electrodes, and the copper electrodes are arranged along the direction perpendicular to the fiber extension.

[0025] d. Stack a plurality of single-layer sensors in an up-and-down arrangement, and the adjacent single-layer sensors in the up-and-down direction are arranged in a staggered distribution after rotating a certain angle. Bond them with Ecoflex between the adjacent single-layer sensors in the up-and-down direction to form a multi-layer orthogonal stacked structure. Of course, the Ecoflex elastomer also serves as an isolation function.

[0026] e. Package the plurality of single-layer sensors stacked in step d with Ecoflex, and then heat and cure them. Control the heat curing temperature to be 50 - 60°C, the heat curing time to be 1 - 3 hours, and the thickness of the packaging layer to be 0.5 - 1 mm to obtain the omnidirectional detection sensor.

[0027] The present invention will be further described below in conjunction with specific embodiments: 1. Materials and equipment; Substrate: Thermoplastic polyurethane (TPU, Elastollan 1185A, BASF); Solvent: N,N-dimethylformamide (DMF) and tetrahydrofuran (THF, volume ratio 1:1, Aladdin reagent); Conductive material: Multi-walled carbon nanotube aqueous solution; Encapsulation material: Ecoflex 0030 (Smooth-on); Equipment: Electrospinning machine (positive and negative high-voltage power supply), Scanning electron microscope (SEM, Carl Zeiss Ultra55), Multi-channel data acquisition system (DAQ970A, Keysight Technologies).

[0028] 2. Preparation steps of the omnidirectional detection sensor based on the anisotropic fiber structure: Step 1: Preparation of an ordered TPU fiber film (as Figure 1 ); (1) Preparation of the spinning solution: Dissolve TPU particles in a DMF / THF mixed solvent (volume ratio 1:1), stir at 50 °C for 10 hours until completely dissolved to obtain the spinning solution. The mass percentage concentration of TPU particles in the spinning solution is 15%.

[0029] (2) Electrospinning parameters: Positive voltage 12 kV, negative voltage -3 kV; Needle-collector distance 15 cm, roller rotation speed 2000 rpm; Flow rate 0.02 ml / min, environmental temperature and humidity 25 °C / 45%.

[0030] (3) Collection of the fiber film: Collect through a rotating roller covered with release paper to obtain a parallel-aligned TPU fiber film, which enhances anisotropy, as shown in (a)-(c) of Figure 2 . At the same time, an unordered fiber film collected at a roller rotation speed of 200 rpm was compared, showing poor mechanical properties, as shown in (d) of Figure 2 .

[0031] Step 2: Construction of the conductive network; (1) Coating of MWCNTs: Uniformly brush-coat a 10 wt% carbon nanotube solution on the surface of the TPU film and dry at 50 °C for 10 minutes.

[0032] (2) Electrode connection: Fix copper foil electrodes (size 10×5 mm) with conductive silver glue, set along the direction perpendicular to the fibers, and the electrode spacing is 20 mm.

[0033] Step 3: Integration and encapsulation of the multi-layer sensor; (1) Stacking structure: Three layers of conductive films are orthogonally arranged at 0°, 90°, and 45°, and an Ecoflex prepolymer (thickness 0.8 mm) is coated between the layers, as Figure 3 shown; (2) Curing conditions: Cured in an oven at 55 °C for 2 hours to form an integral flexible package (total thickness 2.5 mm).

[0034] The above-mentioned integral flexible package does not include a packaging layer; of course, after coating the Ecoflex prepolymer between the layers, the Ecoflex prepolymer can also be coated on the outside of all single-layer sensors to form a packaging layer when cured in the oven.

[0035] The above-mentioned omnidirectional detection sensor, namely the multi-directional strain sensor, is composed of three stacked anisotropic strain sub-sensors, and each layer responds to mechanical stimuli in different directions. Among them, the first two layers are responsible for detecting strain signals in the parallel (X-axis) and vertical (Y-axis) directions, while the third layer is more sensitive to strains at 45° angles to the X-axis and Y-axis, as Figure 3 shown. Each sub-sensor is composed of highly arranged TPU conductive films, which have excellent electrical conductivity and flexibility. The strain responses of the X-axis, 45° direction, and Y-axis are monitored through Channel 1, Channel 2, and Channel 3 respectively. This design enables the three sub-sensors to sense multi-directional strains and respond to multi-dimensional strain stimuli through orthogonal stacking and specific function allocation, thus providing a high-performance sensing solution for applications such as complex human movements and multi-directional recognition.

[0036] Performance tests were carried out on the omnidirectional detection sensors prepared in the above embodiments, and the results are as Figure 4-7 shown.

[0037] Figure 4 It is a response time test chart of the omnidirectional detection sensor. It can be seen from Figure 4 that at 5% strain, the response time is 30 ms and the relaxation time is 35 ms.

[0038] Figure 5 This is the sensitivity test chart of the omnidirectional detection sensor prepared in the specific embodiment of the present invention in the stretching range of 0 - 300%. It can be seen from Figure 5It can be seen that the sensitivity GF reaches a peak of 144.066 at 200%-300% strain (tensile in the horizontal axis), and the anisotropy is obvious in the range of 0-300%. In the figure, GF1, GF2, and GF3 respectively represent the sensitivities of the prepared omnidirectional sensors when stretched in the direction perpendicular to the fiber in the ranges of 0-140%, 140-200%, and 200-300%. GF represents the sensitivity of the prepared omnidirectional sensor when stretched 300% in the direction parallel to the fiber. This difference stems from the regulation of the MWCNTs conductive network by the fiber orientation, demonstrating the high-resolution response ability of the sensor in different directions.

[0039] Figure 6 It is a schematic diagram of the direction division of the omnidirectional detection sensor prepared in the specific embodiment of the present invention; Figure 7 It is an image of the voltage change when stretched in different directions. By observing the image, it can be clearly seen that as the stretching direction changes, the voltage responses of the three channels of the sensor show different changing trends. Specifically, under different tensile stress directions, the voltage responses of the three channels also exhibit their own unique characteristics. For example, when moving from 0° to 90°, the voltage response of channel 1 gradually weakens, while the voltage response of channel 3 gradually strengthens; for channel 2, the voltage response gradually strengthens from 0° to 45° and gradually weakens from 45° to 90°. This phenomenon can be attributed to the anisotropic structure of the sensor. It can be seen that the sensor of the present invention has an obvious differential response when stretched in the 0°-180° direction.

[0040] The parts not described in the above manner can be achieved by adopting or referring to the existing technologies.

[0041] Of course, the above description is only the preferred embodiment of the present invention. The present invention is not limited to listing the above embodiments. It should be noted that all equivalent substitutions and obvious deformation forms made by any person skilled in the art under the teaching of this specification fall within the substantial scope of this specification and should be protected by the present invention.

Claims

1. An omnidirectional detection sensor based on anisotropic fiber structure, characterized in that: It comprises a plurality of single-layer sensors, wherein the single-layer sensors comprise an ordered TPU fiber film and a conductive layer arranged on the ordered TPU fiber film, wherein the conductive layer is connected to an electrode; All single-layer sensors are stacked up and down, and the upper and lower adjacent single-layer sensors are staggered after being rotated by a certain angle; An adhesive layer is provided between upper and lower adjacent single-layer sensors; An encapsulation layer is arranged outside all single-layer sensors.

2. The omnidirectional detection sensor based on anisotropic fiber structure according to claim 1, characterized in that: Several fiber monomers in the ordered TPU fiber film are arranged in parallel; the electrodes are arranged along a direction perpendicular to the fiber monomers, and the electrodes are copper electrodes, which are connected to the conductive layer through conductive silver glue.

3. The omnidirectional detection sensor based on anisotropic fiber structure according to claim 1, characterized in that: The conductive layer is formed by coating multi-walled carbon nanotubes.

4. The omnidirectional detection sensor based on anisotropic fiber structure according to claim 1, characterized in that: The adhesive layer and the packaging layer are both made of Ecoflex material, and the thickness of the packaging layer is 0.5-1 mm.

5. The omnidirectional detection sensor based on anisotropic fiber structure according to claim 1, characterized in that: There are three single-layer sensors in total, which are the first single-layer sensor, the second single-layer sensor and the third single-layer sensor from bottom to top. Taking the orientation of the first single-layer sensor as a reference, the second single-layer sensor is rotated 90° relative to the first single-layer sensor, and the third single-layer sensor is rotated 45° relative to the first single-layer sensor.

6. The method for preparing an omnidirectional detection sensor based on anisotropic fiber structure as claimed in any one of claims 1 to 5, characterized in that The following steps are involved: a. Dissolving TPU particles in a solvent, and then preparing an ordered TPU fiber film by electrospinning; b. Coating multi-walled carbon nanotubes on the surface of the TPU fiber film to form a conductive layer; c. The conductive layer is connected to the electrode through conductive silver glue to obtain a single-layer sensor; d. Arrange a plurality of single-layer sensors in an up-and-down stack, rotate the upper and lower adjacent single-layer sensors at a certain angle and stagger them, and use Ecoflex to bond the upper and lower adjacent single-layer sensors; e. The multiple single-layer sensors stacked together in step d are packaged with Ecoflex, and then heated and cured to obtain an omnidirectional detection sensor.

7. The method for preparing an omnidirectional detection sensor based on anisotropic fiber structure according to claim 6, characterized in that: In step a: the solvent is obtained by mixing N,N-dimethylformamide and tetrahydrofuran in a volume ratio of 1:1; TPU particles are dissolved in the solvent to obtain a spinning solution, and the mass fraction of the spinning solution is 10% to 20%.

8. The method for preparing an omnidirectional detection sensor based on anisotropic fiber structure according to claim 6, characterized in that: In step a, the process parameters of electrospinning are as follows: positive voltage is 10 to 15 kV, negative voltage is -2 to -5 kV, and drum speed is 1500 to 2500 rpm.

9. The method for preparing an omnidirectional detection sensor based on anisotropic fiber structure according to claim 6, characterized in that: In step b: prepare a multi-walled carbon nanotube aqueous solution with a concentration of 5wt% to 15wt%; evenly coat the multi-walled carbon nanotube aqueous solution on the surface of the TPU fiber film and dry it at 50 to 60°C for 10 to 15 minutes to obtain a conductive layer.

10. The method for preparing an omnidirectional detection sensor based on anisotropic fiber structure according to claim 6, characterized in that: In step e: the heating curing temperature is controlled to be 50-60° C., and the heating curing time is controlled to be 1-3 hours.

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