Resistance type whisker sensor, electronic skin and preparation method thereof

Abstract

The invention provides a resistance type whisker sensor, an electronic skin and a preparation method thereof, the resistance type whisker sensor comprises a substrate layer, a liquid metal-carbon nanotube sensitive material layer and a packaging layer, the liquid metal-carbon nanotube sensitive material layer is packaged between the substrate layer and the packaging layer, the liquid metal-carbon nano tube sensitive material forms a conductive network, the conductive network is composed of liquid metal particles and carbon nano tubes generated by laser ablation, and the liquid metal particles are connected through the carbon nano tubes. In the nature, many organisms realize high-precision tactile detection by virtue of tentacles, for example, beards of animals such as cats and rats can sense tiny changes of the surrounding environment and recognize the shape, texture and vibration information of objects, and the high-sensitivity tactile sensing capability plays an important role in survival and environmental adaptation of the animals. The invention provides the high-sensitivity electronic whisker, and provides the electronic skin based on the whisker sensor array.

Description

Technical Field

[0001] The present invention relates to the field of tactile sensing technology, in particular to a resistive whisker sensor, an electronic skin and a preparation method thereof. Technical Background Electronic Skin (E-Skin) is an intelligent perception system that mimics the functions of human skin. Its core lies in realizing the acquisition of multi-modal information such as tactile perception of the environment, temperature detection, humidity measurement, and strain response through flexible electronic technology and sensor networks. This technology has broad application prospects in the fields of bionic robots, intelligent medicine, wearable devices, human-computer interaction, etc. With the progress of artificial intelligence technology, the role of robots in industrial manufacturing, medical rehabilitation, social services, etc. is becoming increasingly important. How to endow machines with human-like tactile perception ability has become one of the core issues in current research.

[0003] The invention patent (publication number CN118654788, publication date September 17, 2024, application number 202411132284.X) discloses a piezoresistive flexible pressure whisker sensor. The present invention includes a circular base, a circular top cover, cilia, and a needle cone. The needle cone is fixed to the top of the circular base, and the top of the needle cone is inserted into a groove at the bottom of the circular top cover. A support cylinder is fixedly connected to the center of the top of the circular top cover. The cilia are inserted into the support cylinder and fixedly connected to the support cylinder. The diameter of the circular top cover is smaller than that of the circular base. A flexible film is connected and covered between the circular top cover and the circular base, and multiple groups of sensitive grids are pasted on the flexible film. The multiple groups of sensitive grids are evenly arranged along the circumferential direction of the flexible film. This patent has the following problems: The mechanical structure is complex. The receptor of the whisker sensor in this patent is located on the substrate, that is, around the root of the whisker, and includes multiple receptors, with a complex structure. It is necessary to cooperate with multiple sensors to identify the bending direction of the whisker. While the receptor of the whisker sensor of the present invention is located on the whisker, with a simple structure, and the bending in two directions can be identified by a single receptor.

[0004] The invention patent (publication number: CN119043530, publication date: November 29, 2024, application number: 202411175519.3) discloses a replaceable whisker triboelectric sensor based on liquid metal, which includes a sensor body and a whisker body. A convex block is provided at the upper end of the sensor body, and an insertion interface is provided in the middle of the convex block. A metal block is provided at the lower end of the whisker body, and the metal block is inserted into the insertion interface, and the metal block is detachably connected to the insertion interface. Liquid metal is provided inside the whisker body, and a lead for transmitting signals is provided below the liquid metal, and the lead is electrically connected to the sensor body. The following problems exist in this patent: The receptor of the whisker sensor in this patent is based on the principle of triboelectrification. Although an electrical signal will be generated when the whisker bends, the electrical signal will only be generated at the moment of bending. Even if the bending state is maintained subsequently, the electrical signal will not be maintained but will quickly decay to 0. Therefore, this type of sensor can only be used for dynamic measurement and is not suitable for static measurement. The whisker sensor of the present invention is a resistive sensor, and the electrical signal only depends on the state of the whisker at that time. Therefore, it is suitable for both dynamic measurement and static measurement.

[0005] The utility model patent (publication number: CN222086917, publication date: November 29, 2024, application number: 202420520349.7) discloses a one-dimensional rolled structure flexible strain sensor, which is prepared in the following manner: preparation of liquid metal ink; using screen printing technology to print a liquid metal circuit on a substrate material according to a predetermined designed pattern shape to generate the conductive layer; using a laser to cut the substrate material printed with the liquid metal circuit into a preset sensor size; hot-pressing an elastic protective film on the substrate material printed with the liquid metal circuit to obtain a two-dimensional planar sensor; rolling up the two-dimensional planar sensor from one side of the long side to obtain a one-dimensional rolled structure flexible strain sensor; adding a signal transmission interface to the flexible strain sensing structure to obtain a one-dimensional rolled structure flexible strain sensor. The disadvantage of this utility model is that it is a one-dimensional sensor, and the existing electronic skin has a single tactile perception ability.

[0006] Currently, electronic skin is usually realized by printing / depositing a two-dimensional pressure sensor array on a flexible substrate. Among them, the selection of the sensor sensitive material directly determines the performance of the resistive skin. In recent years, researchers have developed a variety of highly sensitive, flexible, and durable conductive materials, such as carbon nanomaterials (graphene, carbon nanotubes, carbon black, etc.), liquid metals (such as EGaIn, Galinstan), metal nanomaterials (such as silver nanowires, gold nanoparticles, etc.), conductive polymers (such as PEDOT:PSS, polyaniline, etc.), and MXene (Ti3C2T x). The application of these new materials significantly improves the sensitivity, response speed, mechanical durability and flexible adaptability of resistive skin tactile perception. However, the existing electronic skin technology based on two-dimensional sensor arrays still faces the following key issues: First, the existing electronic skin has a single tactile perception capability: current electronic skins mostly use pressure, capacitance, piezoresistive and other sensors, which mainly perceive normal pressure signals, and have limited detection capabilities for shear force, vibration, flow field changes and other information, making it difficult to achieve high-precision multimodal perception. Second. The sensors in existing electronic skins have poor flexibility and compliance. Most electronic skins and their sensors are made of rigid or semi-rigid materials, which are not flexible enough, affecting their application on complex curved structures and making it difficult to adapt to dynamic interfaces. Third, the signal processing of sensor arrays is complex: electronic skin systems usually need to integrate a large number of sensor units, resulting in a large amount of signal data, making it difficult to achieve real-time, low-power data processing and sensor fusion. Fourth, the scalability of sensors is limited: traditional electronic skin sensors mostly use a two-dimensional layout and lack a three-dimensional structural design, which limits their application in dynamic environments.

[0007] To address these challenges, it is necessary to develop a resistive whisker sensor and its electronic skin. Different from traditional flexible tactile sensors, the core advantages of bionic whisker sensors lie in their flexible structure, rich perception modes, and strong environmental adaptability. They can provide detection capabilities that are closer to those of biological tentacles. Summary of the invention

[0008] The present invention proposes an electronic skin based on a whisker sensor array. In nature, many organisms rely on whiskers to achieve high-precision tactile detection. For example, the whiskers of animals such as cats and mice can sense small changes in the surrounding environment and identify the shape, texture and vibration information of objects. This high-sensitivity tactile perception ability plays a vital role in the survival and environmental adaptation of animals. Inspired by this, bionic whisker sensors have gradually become an important research direction in the field of tactile perception in recent years. Compared with traditional flexible pressure sensors, whisker sensors can detect small contact forces, shear forces, wind field changes and other information, and have wider application potential.

[0009] Therefore, the object of the present invention is to disclose a resistive whisker sensor. Another object of the present invention is to disclose an electronic skin with a resistive whisker sensor. Another object of the present invention is to disclose a method for preparing a resistive whisker sensor electronic skin.

[0010] Specifically, the object of the present invention is implemented according to the following technical solution. A resistive whisker sensor includes a base layer, a liquid metal-carbon nanotube sensitive material layer, and a packaging layer. Among them, the liquid metal-carbon nanotube sensitive material layer is encapsulated between the base layer and the packaging layer. The liquid metal-carbon nanotube sensitive material forms a conductive network, which is composed of liquid metal particles and carbon nanotubes. The liquid metal particles are connected by carbon nanotubes, and the carbon nanotubes form a conductive bridge between the liquid metal particles. The conductive network is mainly composed of two parts: liquid metal particles and carbon nanotubes. The liquid metal particles have excellent conductivity, while the conductivity of carbon nanotubes is relatively weak. The resistance of the conductive pattern mainly comes from the carbon nanotube part. Therefore, when the conductive network is stretched or compressed, the length of the carbon nanotube bridge will correspondingly elongate or shorten, resulting in a sharp increase or decrease in the resistance of the conductive network.

[0011] Among them, the liquid metal-carbon nanotube sensitive material layer is prepared by using liquid metal and polyacrylonitrile (PAN) as the base materials, preparing conductive ink by ultrasonic dispersion method, and constructing a conductive network by laser ablation technology.

[0012] The base layer (11) is at least one of polyethylene terephthalate (PET) film or polyimide (PI) film, and the packaging layer (13) is selected from at least one of polyurethane, polydimethylsiloxane or PET.

[0013] An electronic skin composed of a whisker sensor array includes a plurality of the above-mentioned whisker sensors. The plurality of whisker sensors are arranged in a certain direction and distance in an array arrangement on a soft substrate to form a whisker sensor array. Specifically, the conductive joints of the whisker sensors are vertically inserted and fixed on the soft substrate to form an array, and then the conductive joints of the sensor array are connected to the detection circuit in sequence through wires. Through the analysis software, the whisker sensors can sense the normal pressure and identify the pressure distribution. The sensor array is connected to the data acquisition circuit by row-column scanning, that is, the detection circuit is arranged in a row-column manner. When each row or column is activated, the signals of the sensors at the corresponding row-column intersections will be read and processed. The signal reading and processing are realized through a Wheatstone bridge circuit.

[0014] Optionally, in the above-mentioned whisker sensor electronic skin, the soft substrate is selected from at least one of polydimethylsiloxane (PDMS) substrates, thermoplastic elastomer substrates, or biodegradable plastic substrates.

[0015] Optionally, by arranging multiple whisker sensors in an array, each whisker sensor is at a different position in the array. Specifically, each whisker sensor rotates at different angles (such as 0°, 45°, 90°) around its vertical axis, so that the sensor array has different response degrees to shear forces in different directions; in the array, by changing the rotation angle of the whiskers (such as 0°, 45°, 90°), it can detect shear forces in different directions.

[0016] A preparation method for a resistive whisker sensor includes the following steps: Step 1. Preparation of conductive ink: Mix polyacrylonitrile (PAN) and liquid metal in an ink solvent, add a surfactant to prevent particle agglomeration, and perform ultrasonic treatment to convert the liquid metal into liquid metal micro-nano particles and uniformly mix them with PAN particles to obtain a uniform and stable conductive ink; Step 2. Patterning and laser ablation of the whisker sensor: Use patterning technology to print the above-prepared conductive ink on a rigid substrate. The printed pattern is in the shape of a slender snake, with an aspect ratio greater than 5. Place the printed pattern in an oven at 80°C to 150°C for drying. The dried pattern has no conductivity, and the dried pattern is subjected to laser ablation to form a conductive pattern; Step 3. Encapsulation of the whisker sensor: Use polyurethane, polydimethylsiloxane (PDMS), or polyethylene terephthalate (PET) to encapsulate the conductive pattern by spin coating, hot pressing, cold pressing, or ultrasonic bonding methods to complete the preparation of a single whisker sensor.

[0017] Method for preparing a whisker sensor electronic skin, including vertically inserting and fixing the above-mentioned multiple whisker sensors on a soft substrate in a certain direction and at a certain distance to form an array, so as to form a whisker sensor electronic skin.

[0018] Optionally, in the above preparation method, the soft substrate is selected from at least one of a polydimethylsiloxane (PDMS) substrate, a thermoplastic elastomer substrate, or a biodegradable plastic substrate.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. High-sensitivity perception: The whisker sensor of the present invention is based on a liquid metal-carbon nanotube composite conductive material. Since the carbon nanotubes form a bridge structure between the liquid metal particles, an obvious resistance change can be caused during bending deformation. Therefore, it can detect tiny contact forces in the micro-newton (μN) range, making it have significant advantages in fine tactile perception, wind speed detection, vibration detection, etc. For the liquid metal conductive material without a carbon nanotube bridge structure, there is no obvious resistance change during bending deformation.

[0020] 2. Multi-modal information acquisition: The whisker sensor can not only sense normal pressure, but also detect information such as shear force, vibration frequency, and hydrodynamic changes, providing richer tactile feedback for robots and intelligent prosthetics.

[0021] 3. Flexible and deformable: Compared with traditional rigid tactile sensors, the whisker sensor is prepared based on flexible materials, can adapt to complex surfaces, and still maintains good sensing ability during large-range bending or stretching.

[0022] 4. Strong scalability: The whisker sensors can be assembled into an array to achieve large-area and distributed tactile perception, and can be flexibly designed and adjusted according to application requirements.

[0023] These technical advantages make the whisker sensor-based electronic skin one of the key technologies for future robot tactile perception systems and are expected to be widely applied in fields such as bionic robots, intelligent prosthetics, and wearable intelligent devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of a single whisker sensor of the present invention; Figure 2 It is a microscopic change mechanism diagram of the liquid metal-carbon nanotube sensitive material in the whisker sensor of the present invention when deformed; Figure 3 It is a diagram of different resistance changes obtained when the whisker sensor of the present invention bends in different directions; Figure 4 It is an array diagram composed of whisker sensors of the present invention; Figure 5 It is an array diagram composed of 0° whisker and 90° whisker sensors of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be described in detail below with reference to the accompanying drawings and through specific embodiments.

[0026] The principle concept of the present invention is based on a liquid metal-carbon nanotube sensitive material. By combining laser ablation technology, highly sensitive electronic whiskers are prepared. The electronic whiskers are further arranged in an array to form a large-area electronic skin for pressure distribution perception. In the array, the orientation of the whiskers is further adjusted for multi-modal mechanical perception. Finally, a highly sensitive tactile perception network constructed by flexible whisker sensors is used to achieve multi-modal and intelligent perception of environmental information. The present invention not only helps to break through the bottleneck of existing electronic skin technologies but also provides innovative solutions for fields such as intelligent robots, intelligent prosthetics, and flexible electronics.

[0027] As Figure 1 and Figure 2 shown, the resistive whisker sensor 1 of the present invention includes a base layer 11, a liquid metal-carbon nanotube sensitive material layer 12, and a packaging layer 13. Among them, a wiring area 14 and a sensor sensitive band 15 are provided on the sensor, and a conductive joint 16 is provided at the root; one end of the conductive joint 16 is connected to the liquid metal-carbon nanotube sensitive material layer 12, and the other end is used to connect to a detection circuit. Among them, the liquid metal-carbon nanotube sensitive material layer 12 is encapsulated between the base layer 11 and the packaging layer 13, and the liquid metal-carbon nanotube sensitive material layer 12 forms a conductive network.

[0028] The liquid metal-carbon nanotube sensitive material layer 12 is a conductive network constructed by using liquid metal and polyacrylonitrile (abbreviated as PAN) as basic materials, preparing conductive ink through ultrasonic dispersion method, and adopting laser ablation technology.

[0029] The liquid metal-carbon nanotube sensitive material layer 12 includes liquid metal particles 121 and carbon nanotubes 122. In the microscopic state, the liquid metal particles 121 are non-conductive due to the isolation of the oxide film. By introducing carbon nanotubes 122 between the liquid metal particles as conductive bridges to connect the liquid metal particles 121, a conductive network can be formed. The conductive bridges are carbon nanotubes 122 converted from PAN. The two ends of the carbon nanotubes 122 are connected to the liquid metal particles 121, and the carbon nanotubes 122 form conductive bridges between the liquid metal particles 121. As Figure 2 shown, the conductive network is mainly composed of two parts: liquid metal particles 121 and carbon nanotubes 122 generated by laser ablation. The liquid metal particles 121 are connected by carbon nanotubes 122 to build a stable conductive network. The originally non-conductive pattern becomes conductive after laser ablation because PAN is transformed into carbon nanotubes 122. The liquid metal particle part has excellent conductive ability, and the carbon nanotube part has relatively weak conductive ability. Therefore, the resistance of the conductive network of the liquid metal-carbon nanotube sensitive material layer 12 mainly comes from the carbon nanotube part, and the conductive pattern is in the shape of slender snake lines with an aspect ratio greater than 5. Therefore, when the conductive network is stretched or compressed, the distance between the liquid metal particles at both ends of the carbon nanotubes elongates or shortens (the length of the carbon nanotubes remains unchanged, and the distance between the liquid metal particles changes), resulting in a sharp increase or decrease in the resistance of the conductive network.

[0030] The base layer 11 is a material with stiffness, selected from at least one of polyethylene terephthalate (PET) film or polyimide (PI) film; The encapsulation layer 13 is a flexible material, selected from at least one of polyurethane, polydimethylsiloxane (PDMS), or polyethylene terephthalate (PET).

[0031] A single resistive whisker sensor 1 can bend in two directions, left and right. In space, a single resistive whisker sensor can identify deformations in two different directions. The single resistive whisker sensor is flat. There is a liquid metal-carbon nanotube sensitive material between the base layer 11 and the encapsulation layer 13. There is a wiring area 14, a sensor sensitive band 15 on the sensor, and a conductive joint 16 at the root. One end of the conductive joint 16 is connected to the liquid metal-carbon nanotube sensitive material layer 12, and the other end is used to connect the detection circuit.

[0032] When the end of the whisker sensor touches an object, the whisker will bend. Figure 3When the whisker sensor of the present invention bends in different directions, different resistance change diagrams are obtained. When the whisker sensor bends towards the encapsulation layer side (right bend, or Figure 2 the upward bend shown in Figure 2 ), the conductive pattern is compressed and the resistance decreases; at the microscopic level, relative to the undeformed state, the distance between the liquid metal particles decreases, and the length of the carbon nanotube bridges connecting adjacent liquid metal particles becomes shorter. As shown in Figure 2 ), since the resistance of the conductive pattern mainly comes from the carbon nanotubes, the compressed conductive pattern will have a significant resistance decrease. When the whisker sensor bends towards the substrate layer side (left bend, or Figure 3 the downward bend shown in Figure 2 ), the conductive pattern is stretched and the resistance increases, as shown in

[0033] ; at the microscopic level, relative to the undeformed state, the distance between the liquid metal particles increases, and the length of the carbon nanotube bridges connecting adjacent liquid metal particles becomes longer. As shown in Figure 4 ), the stretched conductive pattern will have a significant resistance increase. Compared with the conductive pattern without carbon nanotubes, the resistance of the conductive pattern hardly changes during the right bend and the left bend.

[0034] As shown in Figure 4 , the electronic skin composed of a resistive whisker sensor array of the present invention includes a plurality of resistive whisker sensors 1, and the plurality of resistive whisker sensors 1 are arranged on the soft substrate 2 in a certain direction and distance to form a whisker sensor array; specifically, the conductive joints of the plurality of resistive whisker sensors 1 are vertically inserted and fixed on the soft substrate 2 to form an array, and the conductive joints of the resistive whisker sensor array are connected to the detection circuit in sequence through wires. The detection circuit is arranged in a row-column manner. When activating one row or one column each time, the signals of the sensors at the corresponding row-column intersections will be read and processed. The signal reading and processing are realized through a Wheatstone bridge circuit. Through the analysis software, the resistive whisker sensor can sense the normal pressure and identify the pressure distribution. The connection of the conductive joints of the sensor array to the detection circuit, the detection circuit and the analysis software belong to the prior art and will not be elaborated here.

[0034] The soft substrate is an elastomeric substrate with a low modulus. Preferably, the soft substrate is selected from at least one of a polydimethylsiloxane (PDMS) substrate, a biodegradable plastic substrate, or a thermoplastic elastomer (such as a thermoplastic polyurethane elastomer TPU, styrene-butadiene-styrene block copolymer SBS) substrate. The biodegradable plastic substrate such as an ecoflex substrate is a biodegradable plastic of BASF Corporation.

[0035] Preferably, by arranging a plurality of resistive whisker sensors in an array, each resistive whisker sensor is at a different position in the array. Specifically, each resistive whisker sensor rotates at different angles around its vertical axis, such as 0°, 45°, 90°, so that the sensor array has different response degrees to shear forces in different directions; in the array, by changing the rotation angle of the whiskers, such as 0°, 45°, 90°, it can detect shear forces in different directions.

[0036] In order to accurately analyze the pressure distribution, the shape and material of the contacted object, as well as the direction and magnitude of the shear force of the whisker sensor array, the present invention uses a deep learning model mainly composed of CNN (Convolutional Neural Network) + Transformer (temporal feature modeling) for calculation.

[0037] Figure 4 This is an array diagram composed of 0° whisker sensors 1 of the present invention. The arrangement directions of the whisker sensors 1 are the same, and each whisker sensor is arranged left and right. Each whisker sensor can rotate forward and backward for detecting the movement in the front and back directions.

[0038] Figure 5An array diagram consisting of 0° whisker sensors and 90° whisker sensors for the present invention is shown. In the figure, there are multiple whisker sensors 1 arranged at 0° and multiple whisker sensors 1' arranged at 90°, forming an array composed of 0° whisker sensors and 90° whisker sensors.

[0039] In other embodiments, several whisker sensors arranged at 45° can also be provided. The spacing between the sensors arranged at 45° is 15 mm. For example, Figure 5 the sensors arranged at 90° therein are replaced with whisker sensors arranged at 45°.

[0040] A preparation method of a resistive whisker sensor includes the following steps Step 1. Preparation of conductive ink Mix polyacrylonitrile (PAN) and liquid metal in an ink solvent, and add a surfactant to prevent particle agglomeration. Use a cell disruptor to ultrasonically treat the mixture to convert the liquid metal into liquid metal micro-nano particles and uniformly mix them with PAN particles to obtain a uniform and stable conductive ink.

[0041] The mass fraction selection range of the ink solvent is 10wt% - 50wt%, and the ink solvent is selected from at least one of ethanol, butanol, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether.

[0042] The mass fraction of polyacrylonitrile (PAN) is 0.5wt% - 5wt%. PAN is a precursor material that is converted into carbon nanotubes (CNTs) during the ablation process for constructing a conductive bridge. The molecular weight range is 50,000 - 150,000 g / mol, and the particle size is 20 nanometers, 100 nanometers, 5 microns, 10 microns, or 50 microns. Add PAN to the conductive ink so that PAN is transformed into carbon nanotubes connecting liquid metal particles during the laser ablation step.

[0043] The mass fraction selection range of the liquid metal is 40wt% - 90wt%, and the liquid metal is selected from at least one of pure gallium (Ga), gallium-indium alloy (Ga-In), gallium-indium-tin alloy, and gallium-zinc alloy.

[0044] The mass fraction of the surfactant is 0 - 5wt%, and it is selected from at least one of sodium dodecyl sulfate, polyoxyethylene alkylphenol ether, polyvinylpyrrolidone, and sodium polyacrylate.

[0045] Step 2. Patterning and laser ablation of the whisker sensor Using patterning techniques such as screen printing, inkjet printing, and stencils, the above-prepared conductive ink is printed on a rigid substrate layer and dried to obtain a dried pattern. The substrate layer is, for example, a polyethylene terephthalate (PET) film or a polyimide (PI) film. To achieve the purpose of the whisker, the printed pattern is in the shape of a slender serpentine with an aspect ratio greater than 5. The printed pattern is placed in an oven at 80 - 150 °C for drying, and the dried pattern is non-conductive.

[0046] The dried pattern is subjected to laser ablation to form a conductive pattern. The types of lasers can include femtosecond lasers (wavelength 500 - 1500 nm), Nd:YAG lasers (wavelength 1064 nm), and CO2 lasers (wavelength 10.6 µm). The laser power density is controlled (1 - 10 W / cm²), and the pattern is scanned at a speed of 1 - 20 mm / s. During the process of laser ablation of the pattern, the laser causes the liquid metal particles to rupture, and under the action of high temperature, PAN is converted into carbon nanotubes that connect the liquid metal particles, thereby forming a conductive network composed of liquid metal-carbon nanotube sensitive materials. The carbon nanotubes will form a conductive bridge between the liquid metal particles, constructing a stable conductive network. The originally non-conductive pattern becomes conductive after laser ablation. The conductive network is mainly composed of two parts: liquid metal particles and carbon nanotubes. The liquid metal particle part has excellent conductivity, and the carbon nanotube part has relatively weak conductivity. Therefore, the resistance of the conductive pattern mainly comes from the carbon nanotube part. The laser ablation of the dried pattern is a special step of the present invention. In this step, PAN will be transformed into carbon nanotubes that connect the liquid metal particles.

[0047] Step 3. Encapsulation of the whisker sensor Flexible materials such as polyurethane, polydimethylsiloxane (PDMS), and polyethylene terephthalate (PET) are used to encapsulate the conductive pattern by methods such as spin coating, hot pressing, cold pressing, and ultrasonic bonding to complete the preparation of a single whisker sensor.

[0048] The thickness of the encapsulation layer needs to be less than the thickness of the substrate layer to ensure that the conductive pattern is not on the neutral plane when the whisker bends under force, thereby improving the signal response. When the end of the whisker sensor touches an object, the whisker will bend. Figure 3 For the whisker sensor of the present invention, when it bends in different directions, different resistance change graphs are obtained. When the whisker sensor bends towards the encapsulation layer side (right bend, or Figure 2 the upward bend as shown in Figure 2 ), the conductive pattern is compressed and the resistance decreases; at the microscopic level, compared with the undeformed state, the distance between the liquid metal particles decreases, and the length of the carbon nanotube bridge connecting adjacent liquid metal particles becomes shorter. As shown inFigure 2 As shown in the downward bend shown in [Figure], the conductive pattern is stretched and the resistance increases, as Figure 3 shown; at the microscopic level, relative to the undeformed state, the distance between liquid metal particles increases, and the length of the carbon nanotube bridges connecting adjacent liquid metal particles becomes longer, as Figure 2 shown, and the stretched conductive pattern will have a significant increase in resistance. Compared with the conductive pattern without carbon nanotubes, during the right bend and left bend, the resistance of the conductive pattern hardly changes.

[0049] Step 4. Arrange the whisker sensor array to form an electronic skin: Arrange the whisker sensors into a matrix array to form a large-area electronic skin, that is, arrange multiple whisker sensors in a certain direction and distance to form a whisker sensor array. It can be on a soft substrate layer, such as polydimethylsiloxane (PDMS) substrate or ecoflex substrate, vertically insert multiple whisker sensors to form a whisker sensor array, and then connect the conductive joints of the sensor array to the detection circuit in sequence through wires. Through analysis software, the whisker sensors can sense the normal pressure and identify the pressure distribution. In addition, it can also sense information such as vibration frequency and hydrodynamic changes. By different spacings and arrangements, the tactile resolution can be optimized.

[0050] A single whisker sensor can bend in both the left and right directions. In space, a single whisker sensor can identify deformations in two different directions. In order to enable the whisker sensor array to identify shear forces in different directions, the sensor array is designed by the following method.

[0051] By arranging multiple whisker sensors into an array, such as Figure 4As shown, the whisker sensors at different positions in the array are then rotated by different angles (such as 0°, 45°, 90°) around the vertical axis, so that the sensor array has different response degrees to shear forces in different directions, such as Figure 5 As shown. In the array, the rotation angle of the whiskers (such as 0°, 45°, 90°) is changed so that it can detect shear forces in different directions.

[0052] In order to accurately analyze the pressure distribution, the shape and material of the contacted object, and the direction and magnitude of the shear force of the whisker sensor array, the present invention uses a deep learning model mainly composed of CNN (Convolutional Neural Network) + Transformer (temporal feature modeling) for calculation.

[0053] Example 1 Ethanol (10 wt%) and methyl ethyl ketone (5 wt%) are selected as the ink mixing solvents. Polyacrylonitrile (PAN) powder is weighed so that its mass fraction is 3 wt%, and the particle size is selected as 100 nanometers. Liquid metal alloy (Ga-In-Sn) is selected with a mass fraction of 80 wt%. A surfactant (polyvinylpyrrolidone, 2 wt%) is added to prevent particle agglomeration. PAN and liquid metal are added to the ink solvent, and stirred at room temperature for 30 minutes to form a homogeneous mixture. The mixture is ultrasonically treated (frequency 20 kHz, time 5 minutes) using a cell disruptor to convert the liquid metal into micro-nano particles. The liquid metal particles after ultrasonic treatment are evenly distributed around the PAN particles to form a stable conductive ink. Using screen printing, the ink is printed on a flexible substrate of polyurethane to form a long strip pattern. The pattern is dried in an oven at 80 °C for 10 minutes. Using a femtosecond laser, controlling the laser power density (1 W / cm²), scanning the printed pattern at a speed of 5 mm / s. During the process of laser ablation of the pattern, the laser will cause the liquid metal particles to break, and under the action of high temperature, PAN is converted into carbon nanotubes, and the carbon nanotubes will form a conductive bridge between the liquid metals. The conductive pattern is encapsulated using a polyurethane film by a hot pressing method, and the thickness of the encapsulation layer is less than the thickness of the substrate to ensure obvious signal changes during bending. The sensor can respond to external stimuli such as touch and bending, and reflect the stress state of the sensor through resistance changes.

[0054] Example 2: Ethylene glycol ethyl ether acetate (10 wt%) was selected as the ink solvent, and polyacrylonitrile (PAN) powder was weighed to have a mass fraction of 5 wt% and a particle size of 300 nm. Liquid metal alloy (Ga-In) with a mass fraction of 83 wt% was selected. 2 wt% of sodium polyacrylate surfactant was added to prevent particle agglomeration and increase the wettability of the ink for printing. PAN and liquid metal were added to the ink solvent, and stirred at room temperature for 30 minutes to form a homogeneous mixture. The mixture was stirred using a high-speed mixer (rotation speed 10000 r / min, time 20 minutes) to convert the liquid metal into micron-sized particles, forming a stable conductive ink. Using the inkjet printing method, the ink was printed on a flexible PDMS substrate to form a serpentine pattern with an aspect ratio of 5. The pattern was dried in an oven at 80 °C for 10 minutes. Using a Nd:YAG laser (wavelength 1064 nm), controlling the laser power density at 2 W / cm², and scanning the printed pattern at a speed of 20 mm / s, under the action of the laser, the liquid metal microparticles ruptured and connected with the carbon nanotube network formed by PAN, achieving conductivity conversion. The conductive pattern was encapsulated using PDMS by spin coating, and the thickness of the encapsulation layer was less than that of the substrate to ensure a significant signal change during bending.

[0055] Sensor array construction. Multiple whisker sensors were used and vertically arranged on a flexible PDMS substrate to form an array. By changing the rotation angles of the whiskers at different positions in the array, whiskers with 0° rotation angle and 90° rotation angle were obtained. The 0° whisker is most sensitive to the shear force in the x direction and has a small response to the shear force in the y direction. The 90° whisker is most sensitive to the shear force in the y direction and has a small response to the shear force in the x direction. The whisker sensor can measure both the pressure (normal force) and the shear force (horizontal force) simultaneously. The resistance change of the whisker is not only related to the shear force but also affected by the bending caused by the vertical pressure. The sensor array was connected to the data acquisition circuit in a row-column scanning manner, that is, the detection circuit was arranged in a row-column layout. When activating one row or one column each time, the signals of the sensors at the corresponding row-column intersections were read and processed. The signal reading and processing were achieved through a Wheatstone bridge circuit. Finally, a deep learning model combining CNN and Transformer was used to analyze the signals of the whisker sensor array to accurately identify the shape, material, and pressure distribution of the contacted object, as well as the magnitude and direction of the shear force.

[0056] Unless otherwise defined, all technical and / or scientific terms used in this application have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. The materials, methods, and examples mentioned in this application are illustrative only and not restrictive. Although the present invention has been described in connection with specific embodiments, under the gist of the invention of this application, those skilled in the art can make appropriate substitutions, modifications, and variations, and such substitutions, modifications, and variations still fall within the protection scope of this application.

Claims

1. A resistive whisker sensor, characterized in that, It includes a base layer (11), a liquid metal-carbon nanotube sensitive material layer (12), and a packaging layer (13). Among them, the liquid metal-carbon nanotube sensitive material layer (12) is encapsulated between the base layer (11) and the packaging layer (13). The liquid metal-carbon nanotube sensitive material layer (12) forms a conductive network, and the conductive network is composed of liquid metal particles (121) and carbon nanotubes (122), and the liquid metal particles (121) are connected by the carbon nanotubes (122).

2. The resistive whisker sensor according to claim 1, wherein The liquid metal-carbon nanotube sensitive material layer (12) is prepared by using liquid metal and polyacrylonitrile (PAN) as base materials to prepare conductive ink through ultrasonic dispersion method, and a conductive network is constructed by using laser ablation technology.

3. The resistive whisker sensor according to claim 1, wherein The base layer (11) is at least one of polyethylene terephthalate (PET) film or polyimide (PI) film, and the packaging layer (13) is selected from at least one of polyurethane, polydimethylsiloxane or polyethylene terephthalate (PET).

4. A whisker sensor electronic skin, characterized in that, It includes a plurality of resistive whisker sensors (1) according to any one of claims 1 to 3. The plurality of resistive whisker sensors are arranged in an array arrangement on a soft substrate (2) to form a whisker sensor array.

5. The whisker sensor electronic skin according to claim 4, wherein, The soft substrate is selected from at least one of a silicone substrate, a polydimethylsiloxane (PDMS) substrate, a thermoplastic elastomer substrate or a biodegradable plastic substrate.

6. The whisker sensor electronic skin according to claim 4, characterized in that Each whisker sensor rotates at different rotation angles around the axis in its vertical direction.

7. The whisker sensor electronic skin according to claim 4, characterized in that, The rotation angles are 0°, 45° or 90°.

8. A preparation method of a resistive whisker sensor, characterized in that, It includes the following steps: Step 1. Preparation of conductive ink: Mix polyacrylonitrile (PAN) and liquid metal in an ink solvent, add a surfactant to prevent particle agglomeration, and perform ultrasonic treatment to convert the liquid metal into liquid metal micro-nano particles and uniformly mix them with PAN particles to obtain a uniform and stable conductive ink. Step 2. Patterning and laser ablation of the whisker sensor: Use patterning technology to print the above-prepared conductive ink on a rigid substrate. The printed pattern is in the shape of a slender snake, and the aspect ratio is greater than 5. Place the printed pattern in an oven at 80°C to 150°C for drying. The dried pattern has no conductivity, and the dried pattern is subjected to laser ablation to form a conductive pattern. Step 3. Encapsulation of the whisker sensor: Use polyurethane, polydimethylsiloxane (PDMS) or polyethylene terephthalate (PET) to encapsulate the conductive pattern by spin coating, hot pressing, cold pressing or ultrasonic bonding methods to complete the preparation of a single whisker sensor.

9. A preparation method of a whisker sensor electronic skin, characterized in that, It includes the following steps: Insert and fix a plurality of the whisker sensors prepared by the preparation method described in claim 8 vertically on a soft substrate in a certain direction and at a certain distance to form an array, so as to form a whisker sensor electronic skin.

10. The preparation method according to claim 9, characterized in that, The soft substrate is selected from at least one of a polydimethylsiloxane (PDMS) substrate, a thermoplastic elastomer substrate or a biodegradable plastic substrate.

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