Preparation method of flexible electromagnetic shielding type force sensor based on coaxial structure

Abstract

The invention discloses a preparation method of a flexible electromagnetic shielding type force sensor based on a coaxial structure, and belongs to the field of flexible electronics and intelligent sensors. According to the method, a coaxial wet spinning process is adopted, a core-sheath structure conductive fiber is constructed, a core layer is made of a multi-walled carbon nanotube (CNT) and thermoplastic polyurethane (TPU) composite material, and a sheath layer is made of a nickel-coated carbon nanotube (Ni-CNT) and TPU composite material. By regulating and controlling the proportion of the core sheath, the construction of the gradient conductive network is realized, and the sensing sensitivity, the electromagnetic shielding performance and the mechanical flexibility are improved. The obtained Ni-CNT-coated CNT fiber is made into fabric and integrated in a sensing glove, and multi-finger bending detection and wireless man-machine interaction control are achieved. The sensor has the advantages of high sensitivity, wide strain detection range and excellent electromagnetic shielding effectiveness, is suitable for the fields of intelligent wearing, anti-interference man-machine interface and fire-fighting equipment, and can also be expanded to complex application scenes such as aerospace teleoperation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible sensors, electromagnetic shielding materials and smart wearable devices, and in particular to a preparation method of a flexible electromagnetic shielding type force sensor based on a coaxial structure. BACKGROUND With the rapid development of flexible electronics, flexible force sensors have been widely used in human-computer interaction, medical monitoring, smart wear, virtual reality, intelligent manufacturing and other fields. Especially in remote control and intelligent operation in complex environments, such as fire rescue, industrial inspection and remote operation systems in aerospace, higher requirements are put forward for the performance stability and anti-interference ability of sensors. The structure of traditional flexible sensors is mostly a single conductive network, and its electromagnetic shielding performance is poor, which is difficult to work stably in a high-intensity electromagnetic interference environment. At the same time, in order to improve the conductivity, methods such as metal coating or high filling ratio conductive particles are usually used. Although these methods can provide certain shielding ability, they often lead to a decrease in the flexibility of the device, a decrease in the air permeability, and even affect the comfort and wearability. In recent years, the application of nano-carbon materials in flexible sensors has attracted widespread attention. Carbon nanotubes (CNT) have excellent electrical conductivity and mechanical properties, and are an ideal material for building flexible conductive networks. Nickel-coated carbon nanotubes (Ni-CNT) not only maintain the flexibility of CNT, but also have significant electromagnetic shielding performance, which is an important functional component for building new flexible electromagnetic shielding materials. By reasonably combining CNT and Ni-CNT to form a gradient conductive network with a core-sheath structure, the strain response sensitivity of the sensor can be improved, and its signal stability in an electromagnetic complex environment can be enhanced, ensuring the reliable operation of the sensor in a high-noise interference condition. This has important significance for remote mechanical arm control, extravehicular maintenance, astronaut gesture recognition and other high-precision remote operation sensing systems in aerospace. However, there is currently a lack of wearable force sensor preparation methods based on Ni-CNT@CNT core-sheath structure with good flexibility, electromagnetic shielding and sensing stability. Therefore, it is of important engineering application prospect to develop a new type of flexible force sensor with reasonable structure, simple preparation and suitable for complex environments. SUMMARY

[0002] The application aims to provide a preparation method of a flexible electromagnetic shielding type force sensor based on a coaxial structure. The coaxial wet spinning technology is adopted. The multi-walled carbon nanotubes (CNT) are dispersed in a thermoplastic polyurethane (TPU) solution as a fiber core layer. The nickel-coated carbon nanotubes (Ni-CNT) are dispersed in the TPU solution as a fiber outer layer (sheath layer), so as to construct a three-layer coaxial core-sheath structure conductive fiber with gradient conductive performance. The structure uses the CNT to construct an efficient strain response network, realizes sensitive and linear resistance change, and simultaneously improves the electromagnetic wave absorption capacity and overall mechanical strength through the Ni-CNT, so as to form an integrated sensing material with flexibility, high conductivity and electromagnetic interference (EMI) shielding capacity. The prepared fiber can be prepared into a wearable fabric through a weaving process, and is further integrated into a flexible sensing glove, so as to realize real-time monitoring and wireless signal transmission of high sensitivity, wide dynamic range and low delay for multi-point finger bending and complex actions, has excellent human adaptability and high anti-interference performance, and is especially suitable for application requirements of high-reliable flexible sensors in the fields of human-computer interaction, virtual reality, industrial control and aerospace. BRIEF DESCRIPTION OF DRAWINGS

[0003] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0004] Figure 1 The application provides a preparation method of a flexible electromagnetic shielding type force sensor based on a coaxial structure. DETAILED DESCRIPTION

[0005] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0006] In complex scenes such as aerospace teleoperation and fire rescue, higher requirements are put forward for the performance stability and electromagnetic shielding capacity of the flexible force sensor due to high electromagnetic interference and extreme environmental influence. The application constructs a Ni-CNT@CNT core-sheath structure conductive fiber through the coaxial wet spinning technology, realizes a preparation path of a three-layer flexible composite sensor, has the advantages of softness, stability, high sensitivity and excellent shielding performance, and is suitable for high-reliable human-computer interaction in complex environments.

[0007] Step 101, prepare the core layer raw material solution. Dissolve 13% mass fraction of thermoplastic polyurethane TPU in N,N-dimethylformamide DMF as the base solution. Under stirring, add 20% mass fraction of multi-walled carbon nanotubes MWCNT to it, continue magnetic stirring for 2 hours, then treat in an ultrasonic disperser for 30 minutes to obtain a stable and uniform MWCNT / TPU core layer conductive solution, which is dark gray in color.

[0008] Step 102, prepare the sheath layer raw material solution. Take the 13% TPU / DMF solution as the base system, add 40% mass fraction of nickel-coated carbon nanotubes Ni-CNT, and use the same stirring and ultrasonic conditions as step 101 to obtain a stable Ni-CNT / TPU sheath layer conductive solution, which is gray-blue in color.

[0009] Step 103, perform coaxial wet spinning. Select a coaxial nozzle device with an outer needle gauge of 15G and an inner needle gauge of 20G, and inject the MWCNT / TPU core layer solution and the Ni-CNT / TPU sheath layer solution into the inner needle and the outer needle respectively. The spinning rate is 0.13 mL / min (core layer) and 0.30 mL / min (sheath layer) respectively. After the composite solution is sprayed out, it enters the coagulation bath, which is a 6% isopropyl alcohol IPA and deionized water mixed solution, to realize interface coagulation molding at room temperature.

[0010] Step 104, fiber drying. After washing the obtained Ni-CNT@CNT coaxial structure fiber with deionized water to remove the surface residual solvent, place it in a ventilated dryer and dry it naturally at room temperature for 48 hours to obtain a continuous and uniform three-layer conductive coaxial structure flexible fiber.

[0011] Step 105, weaving and assembly. Use plain knitting technology to weave the fiber into a flexible fabric, cut it into corresponding sensing units (2.5 times the length of the finger) according to the length of the finger, and sew it onto a nylon base fabric glove to form an integrated multi-point sensing glove.

[0012] Step 106, system connection and signal processing. Use conductive silver paste to bond silver wires to both ends of each sensing fiber and connect them to an ESP32 microcontroller module. The controller includes voltage acquisition, low-pass filtering, AD conversion, and Wi-Fi wireless communication modules, which can convert hand movements into command signals to realize wireless control interaction with remote robots or unmanned systems.

[0013] Example 1: The sensing fiber was prepared by the above steps, wherein the core layer MWCNT was 20 wt%, and the sheath layer Ni-CNT was 40 wt%. The prepared fiber had a conductivity of about 12.5 S / m, a strain response range of 0-100%, a sensitivity GF of 5.93, and an electromagnetic shielding efficiency SE of 36.7 dB (X band). When integrated into a five-finger glove for bending recognition test, the response time of single-finger action change was less than 100 ms, the multi-finger combination recognition accuracy was 96%, and the signal stability did not decrease significantly in a simulated high interference environment (EM field intensity > 50 V / m).

[0014] Comparative Example 1: A single-layer fiber was constructed by adding only MWCNT in the same TPU / DMF system, and the MWCNT concentration was 20 wt%. The obtained fiber had a conductivity of 6.8 S / m, but due to the lack of Ni-CNT outer layer protection, its signal fluctuation was large in an electromagnetic interference environment, the strain sensitivity was only GF=2.45, the shielding efficiency was less than 10 dB, and it could not meet the action recognition application in a high interference environment.

[0015] Comparative Example 2: A conductive fiber was constructed by using Ni-CNT single component, and the mass fraction of Ni-CNT was 40 wt%. The obtained fiber had a conductivity of 10.7 S / m and a high shielding efficiency (SE=30 dB), but due to the lack of gradient regulation of the fiber structure, the mechanical ductility was poor, the fiber was broken at 30% strain, the strain response curve fluctuated greatly, and the repeatability and linearity were insufficient.

[0016] Comparative Example 3: The same raw material system (MWCNT and Ni-CNT were 20 wt% and 40 wt%, respectively) was used, but a common double-tube non-coaxial spinning technology was used for layering and molding. The obtained fiber was a "parallel layer structure" rather than a true coaxial structure, and the interface bonding was poor and the peeling phenomenon was obvious. The sensor showed obvious hysteresis at 50% strain, the GF was 3.12, the shielding performance SE was 21.5 dB, and the sensor repeatability was reduced.

[0017] As can be seen from the above comparison, the Ni-CNT@CNT three-layer coaxial structure conductive fiber proposed in the present application has obvious advantages in the comprehensive mechanical, electrical and anti-interference performance, and is suitable for high-performance wearable sensing systems in complex environments.

Claims

1. A method for preparing a flexible electromagnetic shielding type force sensor based on a coaxial structure, characterized by, The method comprises the following steps: Preparation of CNT and TPU composite core layer conductive solution, and Ni-CNT and TPU composite sheath layer conductive solution; Injecting the two conductive solutions into the inner needle and outer needle of the coaxial wet spinning device respectively; Extruding the obtained composite liquid into a coagulation bath to form a fiber structure; Drying the obtained core-sheath structure fiber to obtain a flexible force-sensitive sensing fiber.

2. The method of claim 1, wherein, The mass fraction of MWCNT in the core layer conductive solution is 20%.

3. The method of claim 1, wherein, The mass fraction of Ni-CNT in the sheath layer conductive solution is 20% to 60%.

4. The method of claim 1, wherein, The mass concentration of TPU in DMF is 13%.

5. The method of claim 1, wherein, The inner needle of the coaxial nozzle is 20G, the outer needle is 15G, and the injection rates are 0.13 mL / min and 0.30 mL / min respectively.

6. The method of claim 1, wherein, The coagulation bath is 6% IPA in deionized water, and the solution temperature is room temperature.

7. The method of claim 1, wherein, The natural drying time of the fiber is 48 hours.

8. The core-sheath structured flexible sensing fiber prepared according to the method of any one of claims 1 to 7, characterized in that, The fiber has a conductive gradient structure and can be used to prepare a wearable strain sensor.

9. A sensor made of the flexible sensor fiber according to claim 8, characterized in that The fiber is sewn on the surface of a sensing glove and connected to a control system through a lead wire to realize real-time monitoring of hand movements and output of control instructions.

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