Flexible sensor with multi-layer porous net structure and preparation method of flexible sensor

Abstract

The invention belongs to the technical field of flexible sensors, and particularly discloses a flexible sensor of a multi-layer porous net structure and a preparation method of the flexible sensor, and the flexible sensor comprises a functional layer and two flexible packaging layers. The functional layer is arranged between the two flexible packaging layers, the functional layer comprises a plurality of porous sensing structures which are arranged in a laminated manner, and each porous sensing structure comprises a nanometer latticed supporting layer and a sensing layer which are arranged in a laminated manner; the surfaces, connected with the functional layer, of the two flexible packaging layers are each provided with a protrusion array. The sensor has a wide mechanical response range while high sensitivity of the sensor is maintained, is good in flexibility, ultrathin, small in size and light in weight, hardly affects mandibular movement, can accurately monitor occlusal force, hardly causes inconvenience to muscle joint movement of a human body, and is suitable for popularization and application. And the flexibility is maintained under various mechanical deformations such as distortion, stretching or compression, and the multi-axial force can be detected.

Description

Technical Field

[0001] The invention discloses a flexible sensor with a multi-layer porous mesh structure and a preparation method thereof, belonging to the technical field of flexible sensors. Background Art

[0002] Flexible sensors are sensors made of flexible materials, which have good flexibility and ductility, and can be bent or even folded freely. Due to the flexible materials and structures, flexible sensors can be arranged arbitrarily according to the application scenarios, and can conveniently detect the measured units. According to the usage, flexible sensors can be divided into flexible pressure sensors, flexible gas sensors, flexible humidity sensors, flexible temperature sensors, flexible light sensors, flexible PH / ion sensors, flexible biosensors, etc.

[0003] The existing flexible pressure sensors used in human health monitoring have a high sensitivity, but their response range is only 0-400kPa, while the maximum bite force range of the human body is 0-800N. Therefore, the response range of the existing flexible pressure sensors used for health monitoring is difficult to meet the monitoring of human bite force. In addition, if you want to achieve a wide mechanical response range, the finished flexible sensors prepared in the prior art are usually too thick. When it exceeds 3mm, it will significantly affect the movement of the mandible, making it difficult to accurately monitor the changes in bite force, resulting in inaccurate monitoring results. Summary of the invention

[0004] The purpose of the present invention is to provide a flexible sensor with a multi-layer porous mesh structure and a preparation method thereof, so as to solve the technical problem that it is difficult to simultaneously achieve high sensitivity and a wide mechanical response range in the existing flexible pressure sensors used in human health monitoring.

[0005] A first aspect of the present invention provides a flexible sensor of a multi-layer porous mesh structure, comprising a functional layer and two flexible packaging layers;

[0006] The functional layer is arranged between the two flexible packaging layers, and the functional layer includes a plurality of porous sensing structures arranged in layers, each of the porous sensing structures includes a nano-grid-shaped supporting layer and a sensing layer arranged in layers;

[0007] The surfaces of the two flexible packaging layers connected to the functional layer both have protrusion arrays.

[0008] Preferably, the protrusion array is a micro-pyramid array, a cone array, a micro-needle array, a sphere array, a hemispherical array or an irregular array made using sandpaper, flower petals or leaves as a template.

[0009] Preferably, the height of each micro-pyramid in the micro-pyramid array is 6um to 8um, and the side length of the square at the bottom of each micro-pyramid is 8um to 12um;

[0010] The spacing between adjacent micro-pyramids is 8um to 12um.

[0011] Preferably, the material of the support layer is a high molecular polymer, cellulose, a cellulose derivative, a metal compound or a conductive polymer;

[0012] The material of the sensing layer is a nano-conductive material, and the nano-conductive material is silver nanowire, carbon nanofiber, cellulose nanofiber or graphene nanofiber.

[0013] Preferably, it also includes a flexible conductive film layer;

[0014] The flexible conductive film layer is arranged on the protrusion array.

[0015] Preferably, the number of the porous sensing structures is four.

[0016] Preferably, the thickness of the flexible sensor with multi-layer porous mesh structure is less than or equal to 0.2 mm;

[0017] The mechanical response range of the flexible sensor with the multi-layer porous mesh structure is 0 to 1600 kPa.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned flexible sensor with a multi-layer porous mesh structure, comprising:

[0019] Step 1: preparing two flexible packaging layers by using a template stamp transfer method, wherein one side surface of each flexible packaging layer has a protrusion array;

[0020] Step 2: preparing a plurality of stacked porous sensing structures on a surface of a flexible packaging layer having a protrusion array, each porous sensing structure comprising a stacked nano-grid support layer and a sensing layer;

[0021] Step 3: assemble two flexible packaging layers, and the protrusion arrays of the two flexible packaging layers are connected to the porous sensing structure.

[0022] Preferably, the support layer is a nano-grid structure layer prepared by an electrospinning method using an electrospinning solution;

[0023] The sensing layer is a nano-grid structure layer obtained by spin coating nano-conductive material.

[0024] Preferably, after step 1, the method further includes:

[0025] A flexible conductive film layer is arranged on the surface of each flexible packaging layer having the protrusion array.

[0026] Compared with the prior art, the flexible sensor with a multi-layer porous mesh structure of the present invention has the following beneficial effects:

[0027] The functional layer of the present invention is a nano-grid structure, which not only has a rich pore structure, but also can further increase the specific surface area. When under pressure, the nano-grid-like porous sensing structure contacts step by step to form a complex fiber conduction path that crisscrosses, significantly enhancing the conductivity of the functional layer; at the same time, the porous structure can also absorb and disperse external pressure through the deformation of the pores, so that the sensor can maintain stable performance within a wide mechanical response range; further, the porous structure also has good air permeability and water permeability, and can maintain stable performance in a humid or corrosive environment, and is suitable for monitoring bite force. The present invention also uses two flexible packaging layers with a protrusion array outside the nano-grid-like functional layer for packaging. Under the action of external pressure, the tip of the protrusion array is significantly deformed by low pressure and the mutual contact with the conductive path of the functional layer makes the resistance change more significant. Compared with the planar structure, it significantly improves the sensitivity of the piezoresistive sensor. Therefore, the flexible sensor with a multi-layer porous mesh structure of the present invention has high sensitivity while having a wide mechanical response range. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of the preparation of a flexible sensor with a multi-layer porous mesh structure according to an embodiment of the present invention.

[0029] Figure 2 Schematic diagram of the sensing mechanism of the flexible sensor with a multi-layer porous mesh structure according to an embodiment of the present invention.

[0030] Figure 3 Figures are internal structural diagrams of the functional layer of an embodiment of the present invention, wherein (a) is a distribution diagram of silver nanowires, (b) is a distribution diagram of PAN NFs obtained by electrospinning a 10% mass fraction PAN / DMF solution, (c) is a distribution diagram of PAN NFs obtained by electrospinning a 20% mass fraction PAN / DMF solution, (d) is a base diagram of the PDMS micro-pyramid structure in a planar state; (e) is a cross-sectional morphology diagram of the micro-pyramid; and (f) is a structural diagram of the functional layer obtained by stacking four porous sensing structures.

[0031] Figure 4The current change graphs of the flexible sensors corresponding to the functional layers composed of different numbers of porous sensing structures when pressures of 0, 1, 2, 5, 10, 20, 50 and 100g weights are gradually applied at a voltage of -1 to 1V, wherein (a) is the current change graph of the flexible sensor corresponding to the functional layer composed of one porous sensing structure; (b) is the current change graph of the flexible sensor corresponding to the functional layer composed of two stacked porous sensing structures; (c) is the current change graph of the flexible sensor corresponding to the functional layer composed of three stacked porous sensing structures; (d) is the current change graph of the flexible sensor corresponding to the functional layer composed of four stacked porous sensing structures; (e) is the current change graph of the flexible sensor corresponding to the functional layer composed of five stacked porous sensing structures; (f) is the current change graph of the flexible sensor corresponding to the functional layer composed of six stacked porous sensing structures.

[0032] Figure 5 (a) is a sensitivity comparison diagram of a flexible sensor with a micro-pyramid array and a sensor with both surfaces of the packaging layer being flat, and (b) is a current-voltage curve diagram of the flexible sensor of the present invention under different pressures (0-75kPa) and a voltage range of -1V to 1V.

[0033] Figure 6 (a) is a diagram of the rapid loading / unloading response time of the flexible sensor of the present invention under a pressure of 1.25 kPa, (b) is a diagram of the relative current change of the flexible sensor of the present invention under a step-applied pressure (0-450 g-0), (c) is a diagram of the relative current change of the flexible sensor of the present invention under a step-applied stress (0-5 kg-0), and (d) is a diagram of the response of the flexible sensor of the present invention to a periodically applied force pulse.

[0034] Figure 7 (a) is a current response diagram of the flexible sensor of the present invention at different compression frequencies (1-10 Hz) under the same compression stress, and (b) is a current response diagram of the flexible sensor of the present invention after 2000 compression-release cycles under a pressure of 0.25 kPa.

[0035] Figure 8 Figure 3 is a diagram of using the flexible sensor of the present invention to monitor human muscle and joint movements, where (a) is the current response diagram of the fingers, (b) is the current response diagram of the wrist, (c) is the current response diagram of the knee joint, (d) is the current response diagram of the corner of the eye, (e) is the current response diagram of the temporalis muscle movement (relaxation and contraction), and (f) is the current response diagram of opening and closing the mouth.

[0036] Fig. 9The flexible sensor of the present invention is used to monitor the current response diagram of the bite force of the tooth model and the actual tooth bite force of the subject, wherein (a) is the current response diagram of the incisors in the tooth model, (b) is the current response diagram of the premolars in the tooth model, (c) is the current response diagram of the molars in the tooth model, (d) is the current response diagram of the incisors of the subject, (e) is the current response diagram of the premolars of the subject, and (f) is the current response diagram of the molars of the subject. DETAILED DESCRIPTION

[0037] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0038] A first aspect of an embodiment of the present invention provides a flexible sensor with a multi-layer porous mesh structure, comprising a functional layer and two flexible packaging layers; wherein the functional layer is arranged between the two flexible packaging layers, and the functional layer comprises a plurality of stacked porous sensing structures, each porous sensing structure comprises a stacked nano-mesh support layer and a sensing layer; the surfaces where the two flexible packaging layers are connected to the functional layer both have a protrusion array.

[0039] The functional layer of the present invention is a nano-grid structure, which not only has a rich pore structure, but also can further increase the specific surface area. When under pressure, the nano-grid-like porous sensing structure contacts step by step to form a complex fiber conduction path that crisscrosses, significantly enhancing the conductivity of the functional layer; at the same time, the porous structure can also absorb and disperse external pressure through the deformation of the pores, so that the sensor can maintain stable performance within a wide mechanical response range; further, the porous structure also has good air permeability and water permeability, and can maintain stable performance in a humid or corrosive environment, and is suitable for monitoring bite force. The present invention also uses two flexible packaging layers with a protrusion array outside the nano-grid-like functional layer for packaging. Under the action of external pressure, the tip of the protrusion array is significantly deformed by low pressure and the mutual contact with the conductive path of the functional layer makes the resistance change more significant. Compared with the planar structure, it significantly improves the sensitivity of the piezoresistive sensor. Therefore, the flexible sensor with a multi-layer porous mesh structure of the present invention has high sensitivity while having a wide mechanical response range.

[0040] The number of the porous sensing structures in the embodiment of the present invention may be 1-10, and illustratively, may be 2, 4, 6, 8, 10, etc., and preferably 4. When the number of the porous sensing structures is 4, the flexible sensor can have a mechanical response range of 0-1600 kPa while ensuring high sensitivity.

[0041] The protrusion array of the embodiment of the present invention is a micro-pyramid array, a cone array, a micro-needle array, a ball array, a hemispherical array or an irregular array made by using sandpaper, petals, leaves, etc. as templates. Since the tip of the micro-pyramid has a significant deformation to low pressure when under pressure and is a step-by-step deformation form, it can significantly improve the sensitivity and response speed of the flexible sensor of the present invention. Therefore, the embodiment of the present invention preferably uses a micro-pyramid array. The height of each micro-pyramid in the micro-pyramid array is 6um to 8um, preferably 7um; the side length of the square at the bottom of each micro-pyramid is 8um to 12um, preferably 10um; the spacing between adjacent micro-pyramids is 8um to 12um, preferably 10um. The micro-pyramid array with the above parameters can optimize the sensitivity and mechanical response range of the flexible sensor.

[0042] Furthermore, the protrusion array of the embodiment of the present invention can also be a surface micro-nano structure (micro-convex structure, thorn structure and folded structure) constructed using a substrate and a micro-nano structure (microsphere structure, sea urchin structure and cell structure) constructed using a conductive material; in addition, using plants as templates can also obtain microstructures on the surface of plants to improve sensitivity, such as lotus leaves, rose petals, sunflower pollen, etc.

[0043] The material of the inner support layer of the porous sensing structure is a polymer, cellulose, a cellulose derivative, a metal compound or a conductive polymer, and can be prepared in various forms, such as a hollow tube, a sphere, or attached with other conductive materials. The polymer can be polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), polysulfone (PSF); the cellulose derivative can be cellulose acetate, cellulose nitrate, cellulose acetate, cellulose acetate butyrate and cellulose xanthate; the metal compound can be a metal oxide (such as RuO, Co3O4, Fe2O3), a metal sulfide (such as CuS, MoS2), a metal nitride (such as VN, TiN, Mo x N); the conductive polymer may be polyacetylene (PA), polyparaphenylene vinylene (PPV), polyaniline (PANi), or polypyrrole (PPy).

[0044] The embodiment of the present invention utilizes the solution of the above-mentioned material in combination with an electrospinning method to prepare a nanofiber mesh of the corresponding material to obtain a support layer.

[0045] The material of the sensing layer in the embodiment of the present invention is a nano-conductive material, and the nano-conductive material is silver nanowire, carbon nanofiber, cellulose nanofiber or graphene nanofiber. The nano-conductive material is coated on the supporting layer by spin coating.

[0046] The material used for the flexible encapsulation layer in the embodiment of the present invention can be any flexible, safe and non-toxic material, for example, polydimethylsiloxane (PDMS), polyimide (PI), polyester (PET), etc., preferably polydimethylsiloxane (PDMS).

[0047] In order to improve the conductivity and sensitivity of the flexible sensor of the present invention, the embodiment of the present invention further provides a flexible conductive film layer, which as an electrode layer can make the transmission of electrical signals more stable, and can significantly improve the stability and sensitivity of the sensor; the flexible conductive film layer is provided on the protrusion array. The material of the flexible conductive film layer is silver nanowires, carbon nanofibers, cellulose nanofibers or graphene nanofibers. Under the action of force, the conductive materials contact each other to increase the conductive channel, thereby reducing the resistance and increasing the current response, thereby improving the conductivity and sensitivity.

[0048] When traditional pressure sensors measure human body movements, they need to ensure sensitivity and mechanical response range, so their thickness often exceeds 3mm. When used for bite force monitoring, the large thickness will affect the mandibular movement and cannot accurately measure the bite force. At the same time, they lack comfort, flexibility, portability and durability. Therefore, the methods commonly used in clinical practice to check bite abnormalities include bite paper, wax sheets, etc., which have low accuracy, poor repeatability, and lack real-time data collection. The shape of the flexible sensor with a multi-layer porous mesh structure of the present invention can be rectangular or square, preferably square. When the size of the square is less than or equal to 2*2cm and the thickness is less than or equal to 0.2mm, it can still have a wide mechanical response range (0-1600kPa) and high sensitivity. Therefore, it is suitable for monitoring bite force, can accurately measure bite force, and has comfort, flexibility, portability and durability.

[0049] The present invention can also prepare an integrated circuit, which uses a flexible sensor array to monitor the occlusal contact of each tooth position of the dentition, and then WiFi, Bluetooth, NFC, NB-IoT, Sigfox, LoRa, MTC, and ZigBee can be used for wireless transmission to collect the data monitored by the sensor.

[0050] The second aspect of the present invention provides a method for preparing the above-mentioned multi-layer porous mesh structure flexible sensor, such as Figure 1 As shown, including:

[0051] Step 1: Prepare two flexible packaging layers by using a template stamp transfer method, wherein one side surface of each flexible packaging layer has a protrusion array.

[0052] Exemplarily, the above step 1 specifically includes:

[0053] Step 1.1: Prepare and clean a silicon template.

[0054] The silicon template in the embodiment of the present invention is a template with a protrusion array on one side surface. After the silicon template is prepared, it is ultrasonically washed in acetone, ethanol and deionized water for 30 minutes respectively to completely clean the impurities.

[0055] Step 1.2: Prepare a flexible encapsulation layer using a silicon template.

[0056] In an embodiment of the present invention, a PDMS precursor and a curing agent are evenly mixed in a ratio of 10:1, slowly poured into a silicon template, excess PDMS mixed liquid is removed, the substrate is kept flat, vacuumed for 1 hour to eliminate bubbles, polymerized in an oven at 80 degrees Celsius for 10 minutes to completely cure, and then carefully peeled off to obtain a PDMS micro-pyramid array with a flat substrate and an array structure facing upward, and plasma treated for 3 minutes to obtain a flexible packaging layer.

[0057] In order to improve the conductivity and sensitivity of the prepared flexible sensor, after the copper electrode is attached to the flexible packaging layer, the embodiment of the present invention also provides a flexible conductive film layer on the side of the flexible packaging layer having the protrusion array. Specifically, a method of stretching, spin-coating the nano-conductive material and then retracting it is used to simplify the preparation of the micro-nano structure flexible conductive film layer, wherein the nano-conductive material is preferably silver nanowires (Ag NWs).

[0058] The above preparation method is repeated to prepare two flexible packaging layers.

[0059] Step 2: preparing a plurality of stacked porous sensing structures on a surface of a flexible packaging layer having a protrusion array, wherein each porous sensing structure comprises a stacked nano-grid support layer and a sensing layer.

[0060] Exemplarily, the above step 2 specifically includes:

[0061] Step 2.1, preparing electrospinning solution.

[0062] In the embodiment of the present invention, polyacrylonitrile (PAN) powder and N,N-dimethylformamide (DMF) solution are mixed in a mass ratio of 2:10, and a uniformly mixed PAN solution is obtained by magnetic stirring for 6 hours, namely, an electrospinning solution, and the mass fraction of the electrospinning solution is 20%.

[0063] Step 2.2: Prepare a nano-grid structure layer, which is the support layer, by using an electrospinning method.

[0064] In the embodiment of the present invention, an electrospinning method is used to prepare polyacrylonitrile fiber network (PANNFs), a voltage of 12 kV is applied between the syringe and the receiving plate, the flow rate of the injection pump is adjusted to 1.2 ml / h, the distance between the needle and the receiver is 15 cm, the spinning time is 10 min, and a PAN NFs layer is prepared by spinning on the surface of a flexible packaging layer having a protrusion array as a support layer, and the layer is placed in an oven at 80°C for 2 hours to dry the DMF solvent.

[0065] Step 2.3: Prepare a sensing layer on the support layer prepared in step 2.2.

[0066] In the embodiment of the present invention, a silver nanowire (Ag NWs) sensing layer is prepared on a supporting layer by a spin coating method. The solvent of the silver nanowire is isopropanol with a concentration of 1 mg / ml. The rotation speeds of the two-stage spin coating are 500 r / min and 1500 r / min, respectively. The spin coating time is 10 s and 20 s, respectively. After two spin coatings, a relatively uniformly distributed sensing layer can be obtained. The layer is then placed in an oven at 80 degrees Celsius and dried for 2 hours to dry the isopropanol solvent in the Ag NWs.

[0067] Step 2.4, prepare three layers of porous sensing structure consisting of a support layer and a sensing layer on the sensing layer prepared in step 2.3 to obtain a functional layer with four layers of porous sensing structure.

[0068] Step 3: assemble two flexible packaging layers, and the protrusion arrays of the two flexible packaging layers are connected to the porous sensing structure.

[0069] Illustratively, in an embodiment of the present invention, the flexible packaging layer obtained in step 2 is assembled with a flexible packaging layer obtained in step 1. During assembly, the protrusion arrays of the two flexible packaging layers are connected to the porous sensing structure. Then, the edges are carefully sealed with a PDMS mixed liquid (precursor and curing agent 10:1) and placed in an oven at 80 degrees Celsius for polymerization for 10 minutes to obtain a packaged flexible piezoresistive sensor.

[0070] The size of the flexible sensor prepared in the embodiment of the present invention is a 2*2cm square with a total thickness of about 0.2mm. It is small in size, light in weight, flexible and ultra-thin, and has almost no effect on the movement of muscles and joints, nor on the movement of the mandible during bite force monitoring.

[0071] The flexible sensor prepared in the embodiment of the present invention is composed of a multi-layer porous network structure formed by alternately stacking polyacrylonitrile nanofibers and silver nanowires and a polydimethylsiloxane (PDMS) micro-pyramid structure array. When pressure is applied, the polydimethylsiloxane (PDMS) micro-pyramid array realizes step-by-step deformation, and the multi-layer porous network structure exhibits multi-level deformation, thereby achieving a wide sensing range while maintaining high sensitivity. The principle mechanism of the sensor prepared by the present invention is as follows Figure 2 shown.

[0072] To confirm the successful preparation of PAN NFs / Ag NWs, a comprehensive material characterization was performed at various stages of the preparation process, and the corresponding insets show their low-magnification images. Figure 3 shown. Figure 3 (a) shows the uniform distribution of silver nanowires. In the present invention, the electrospinning parameters and the concentration of PAN / DMF solution are the main factors affecting the diameter, pore size and distribution density of PANNFs. Figure 3 (b) shows the uniform distribution of PAN NFs obtained by electrospinning a 10% mass fraction PAN / DMF solution. Figure 3 (c) in the figure shows the uniform distribution of PANNFs electrospun from a 20% mass fraction PAN / DMF solution, whose diameter is about twice that of PANNFs electrospun from a 10% mass fraction PAN / DMF solution. Since the diameter of PAN NFs directly affects the mechanical response range of the flexible sensor, a 20% mass fraction PAN / DMF solution is ultimately selected in the embodiment of the present invention. Figure 3 (d) shows the substrate of the PDMS micro-pyramid structure in a planar state. Figure 3 (e) is the cross-sectional morphology of the micro-pyramid in the overall sensor structure, that is, the micro-pyramid unit is a square with a bottom side length of 10um and a height of 7um. The spacing between each micro-pyramid unit is 10um. Complex and interlaced Ag NWs can be seen on the micro-pyramid, which is connected to the Ag NWs sensing layer below. Figure 3 (f) shows a four-layer PAN NFs / Ag NWs functional layer on the horizontal plane. The inset in the upper right corner is a cross-section of the functional layer, indicating that the diameter difference between PAN NFs and AgNWs is large, and PAN NFs can stably carry Ag NWs.

[0073] Compared with the piezoresistive effect of composite materials of conductive fillers and polymers or their porous structures, the functional layers of multilayer porous structures are more susceptible to pressure. The diameter, distribution, density and porosity of PAN NFs can be adjusted by adjusting the concentration of PAN / DMF solution, electrospinning parameters and environment. The fiber diameter of 20% PAN / DMF solution electrospinning is significantly higher than that of 10% PAN / DMF solution electrospinning ( Figure 3 As shown in (c), the sensitivity and mechanical response limit of the sensor to pressure can be intuitively changed by changing the aspect ratio and concentration of silver nanowires and adjusting the number of PANNFs / Ag NWs functional layers.

[0074] In order to study the effect of the number of porous sensing structure layers of the functional layer on the sensitivity, the present invention tests the change in current of sensors with 1-6 layers of porous sensing structure under -1 to 1V voltage and gradually applies 0, 1, 2, 5, 10, 20, 50, 100g weight pressure, such as Figure 4 As shown. When the pressure is constant, its resistance is constant, indicating that its sensor performance is stable. When the number of layers of the porous sensing structure of the sensor increases, when weights of 0-100g are gradually applied, the change in current decreases with the increase in the number of layers of the porous sensing structure, indicating that its sensitivity decreases. Since the measurement of bite force requires not only a wide mechanical response range, but also the precise measurement of tiny pressures, the present invention ultimately selects a 4-layer porous sensing structure, and the mechanical response range at this time is 0-1600kPa, which is sufficient to include the maximum bite force limit of the human body. In addition, it still has a relatively significant current change in response to tiny pressures.

[0075] In order to better study the performance enhancement mechanism of the flexible sensor of the present invention, the embodiment of the present invention first studies the influence of the micro-pyramid array structure and the non-micro-pyramid array structure on the performance of the flexible pressure sensor. Figure 5 As shown in (a), under a lower pressure range, the sensitivity of the sensor with a micro-pyramid array structure is higher than that of a flat thin film electrode, which is attributed to the 3D deformation of the micro-pyramid array structure. The micro-pyramid array structure is evenly distributed on the PDMS film. When subjected to pressure, the multi-layer porous nanofiber network of the micro-pyramid structure and the functional layer deforms step by step, while ensuring the wide mechanical response range and high sensitivity of the sensor. It can be seen that within the pressure range of 0-236 kPa, the sensor sensitivity of the thin film electrode with a micro-pyramid array structure (0.02 kPa -1 ) is higher than the sensitivity of flat thin film electrodes (0.008 kPa -1 )( Figure 5 (a)). At 236-430 kPa, the sensitivity of the sensor with the micro-pyramid array structure increases from 0.016 kPa for the flat film electrode.-1 Increase to 0.03kPa -1 The present invention realizes deformation response to slight pressure and heavy pressure through deformation of micro-pyramid structure, inconsistency of elastic modulus and diameter between Ag NWs and PAN NFs, greatly broadens its pressure response range (0-1600N), and uses micro-pyramid structure instead of planar structure to improve its sensitivity under different pressure ranges. The IV curve of the sensor shows excellent linear ohmic characteristics and has stable response to static pressure under different pressures in the voltage range of -1V to 1V ( Figure 5 In (b), as the pressure increases from 0 kPa to 75 kPa, the IV curve becomes steeper and the sensor resistance decreases, confirming the previous analysis.

[0076] Sensor in Figure 6 The sensor shows a fast loading / unloading response time at a pressure of 1.25 kPa in (a), where the loading response time is about 40 ms and the unloading response time is about 70 ms. The dynamic loading and unloading cycle test curves of the sensor under step pressure and in low, medium and high pressure areas are shown in Figure 1. Figure 6 As shown in (b) to (d) in Figure 1, it shows that the sensor has good repeatability and stability and can reliably measure a wide range of pressures within different pressure test ranges. Figure 7 As shown in (a), the electrical signal changes consistently at different frequencies (1, 2, 5 and 10 Hz) under a pressure of 1 kPa, with no frequency dependence, indicating that the sensor has a stable and fast response.

[0077] In order to explore the durability of the prepared flexible pressure sensor, Figure 7 As shown in (b), the frequency is set to 0.5 Hz, and a pressure of 0.25 kPa is applied to the sensor and repeated 2000 times. The zoomed-in figure shows the amplified electrical signal response of randomly extracted different time periods. After more than 2000 repeated pressure loading and unloading cycles, there is no obvious difference in the amplitude and waveform of the signal response, indicating that the sensor has high durability, which is crucial for practical applications. The above results clearly show that the sensor has excellent stability, reliable and significant response, wide mechanical response range and high sensitivity, and has significant repeatability under various pressures and different frequencies. It is an ideal device for monitoring human bite force and wearable pressure sensing applications.

[0078] In human health monitoring, highly sensitive sensors can monitor human physiological parameters in real time, such as heart rate, blood pressure, etc., while a wide mechanical response range enables the sensor to adapt to different intensities of exercise or external impact. In bite force detection, the present invention can simultaneously meet the requirements of accurate detection of micro bite force and maximum bite force.

[0079] like Figure 8As shown, the flexible sensor of the embodiment of the present invention can be used to monitor the movement of human muscles and joints, such as Fig. 9 As shown, the flexible sensor according to the embodiment of the present invention can be used to monitor the actual bite force of the human body.

[0080] In the process of monitoring the bite force, the present invention first uses a tooth model to simulate a standard oral occlusal contact situation, the incisors ( Fig. 9 (a)), premolars ( Fig. 9 (b)), molars ( Fig. 9 (c) in the figure). The pressure of about 150 kPa was applied to the incisor area, about 260 kPa was applied to the premolar area, and about 400 kPa was applied to the posterior area. The incisors and premolars were in short contact (1 second), and the molars were in continuous contact (10 seconds). The response signals of the incisors, premolars and molars under three different forces and different bite times were displayed. In addition, the bite force monitoring function of the sensor was tested on actual human subjects, and the incisors ( Fig. 9 (d)), premolars ( Fig. 9 (e)) and molars ( Fig. 9 In (f), the single bite response characteristics of each tooth show that molars bear greater forces than incisors and premolars, which is consistent with previous research results. The actual test verified the ability of the sensor to accurately monitor and quantify the bite force of each tooth. Due to the inconsistent morphology of incisors, premolars and molars, especially the complex cusp morphology of molars, the teeth will slide along the tooth surface morphology until uniform, extensive and uniform contact is achieved when the subjects bite. The differences in tooth position, anatomical morphology and habitual bite force of each person will produce unique bite recording signals, so it can be used as a "bite force ID card" for some private operations. Tooth morphology and bite habits are personalized, and the quantitative indicators of chewing can be roughly distinguished through a limited number of bite tests. The range of bite force has a solid anatomical basis, and its application is highly subjective due to individual differences. Abnormal bite contact is closely related to many diseases of the oral and maxillofacial system. For example, bruxism, clenching teeth, periodontal occlusal trauma, temporomandibular joint disorder, etc., monitoring the abnormality of occlusal contact through sensors can provide accurate and reliable basis for clinicians' diagnosis and treatment. The development of wireless intelligent bite force sensors for human-computer interaction is a promising direction in the future.

[0081] A flexible sensor of a preferred structure of the present invention is composed of a functional layer of a multi-layer porous mesh structure formed by alternating stacking of polyacrylonitrile nanofibers and silver nanowires and a poly-PDMS micro-pyramid structure array. When pressure is applied, the PDMS micro-pyramid array achieves step-by-step deformation, and the multi-layer nanofiber network structure exhibits multi-level deformation. This composite structure can not only maintain the high sensitivity of the sensor while having a wide sensing range, but also expand its application in the fields of human health monitoring and bite force detection. For example, in human health monitoring, the highly sensitive sensor can monitor the physiological parameters of the human body in real time, such as heart rate, blood pressure, etc.; and the wide mechanical response range enables the sensor to adapt to different intensities of exercise or external impact. In the bite force detection (usually in the range of 0-800N), the sensor can simultaneously meet the accurate detection of small bite force and maximum bite force.

[0082] The flexible sensor of the present invention is in the form of a 2*2cm square, has good flexibility and is ultra-thin, has a small size and light weight, hardly deforms the blade, hardly affects the movement of the mandible, can accurately monitor the bite force, and hardly causes any inconvenience to the muscle and joint movement of the human body. It maintains its flexibility under various mechanical deformations such as twisting, stretching or compression, and can detect multi-axial forces.

[0083] The above are only several embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above disclosed technical content to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A flexible sensor with a multi-layer porous mesh structure, characterized in that: It includes a functional layer and two flexible packaging layers; The functional layer is arranged between the two flexible packaging layers, and the functional layer includes a plurality of porous sensing structures arranged in layers, each of the porous sensing structures includes a nano-grid-shaped supporting layer and a sensing layer arranged in layers; The surfaces of the two flexible packaging layers connected to the functional layer both have protrusion arrays.

2. The flexible sensor with a multi-layer porous mesh structure according to claim 1, characterized in that: The protrusion array is a micro-pyramid array, a cone array, a micro-needle array, a sphere array, a hemispherical array or an irregular array made by using sandpaper, petals or leaves as a template.

3. The flexible sensor with a multi-layer porous mesh structure according to claim 2, characterized in that: The height of each micro-pyramid in the micro-pyramid array is 6um to 8um, and the side length of the square at the bottom of each micro-pyramid is 8um to 12um; The spacing between adjacent micro-pyramids is 8um to 12um.

4. The flexible sensor with a multi-layer porous mesh structure according to claim 1, characterized in that: The material of the support layer is a high molecular polymer, cellulose, a cellulose derivative, a metal compound or a conductive polymer; The material of the sensing layer is a nano-conductive material, and the nano-conductive material is silver nanowire, carbon nanofiber, cellulose nanofiber or graphene nanofiber.

5. The flexible sensor with a multi-layer porous mesh structure according to claim 1, characterized in that: Also includes a flexible conductive film layer; The flexible conductive film layer is arranged on the protrusion array.

6. The flexible sensor with a multi-layer porous mesh structure according to claim 1, characterized in that: The number of the porous sensing structures is 4.

7. The flexible sensor of the multi-layer porous mesh structure according to claim 6, characterized in that: The thickness of the flexible sensor with multi-layer porous mesh structure is less than or equal to 0.2 mm; The mechanical response range of the flexible sensor with the multi-layer porous mesh structure is 0 to 1600 kPa.

8. A method for preparing a flexible sensor with a multi-layer porous network structure as claimed in any one of claims 1 to 7, characterized in that: include: Step 1: preparing two flexible packaging layers by using a template stamp transfer method, wherein one side surface of each flexible packaging layer has a protrusion array; Step 2: preparing a plurality of stacked porous sensing structures on a surface of a flexible packaging layer having a protrusion array, each porous sensing structure comprising a stacked nano-grid support layer and a sensing layer; Step 3: assemble two flexible packaging layers, and the protrusion arrays of the two flexible packaging layers are connected to the porous sensing structure.

9. The method for preparing a flexible sensor with a multi-layer porous mesh structure according to claim 8, characterized in that: The support layer is a nano-grid structure layer prepared by an electrospinning method using an electrospinning solution; The sensing layer is a nano-grid structure layer obtained by spin coating nano-conductive material.

10. The method for preparing a flexible sensor with a multi-layer porous mesh structure according to claim 9, characterized in that: After step 1, also include: A flexible conductive film layer is arranged on the surface of each flexible packaging layer having the protrusion array.

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