Bidirectional Fluid-based Flexible Sensor Based on Poisson Squeezing Effect and Preparation Method

Abstract

A bidirectional fluidic flexible sensor based on the Poisson squeezing effect and a preparation method thereof. The flexible sensor includes a flexible substrate, and the surface of the flexible substrate is a cross-shaped microchannel. An array formed by drum-shaped discrete microstructures is arranged in the cross-shaped microchannel, and a conductive fluid is filled in the gaps between the drum-shaped discrete microstructures to form a conductive path. By arranging an array formed by drum-shaped discrete microstructures in the cross-shaped microchannel, the sensor can obtain two output signals with different directions when being stretched, thereby realizing multi-directional strain measurement, greatly improving the high direction selectivity, high anisotropy and sensitivity of the sensor, and broadening the strain sensing range; during the preparation, capillary force automatic filling and the thrust of a syringe are used to realize the filling of the conductive fluid, and such a filling method has stable performance and is easy to implement with a simple processing technology.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly relates to a bidirectional fluidic flexible sensor based on the Poisson extrusion effect and a preparation method thereof. Background Art

[0002] In recent years, flexible strain sensors have attracted extensive attention. They have broad application prospects in the fields of motion detection, human health monitoring, and human-computer interaction. However, traditional flexible strain sensors are limited by the deformation characteristics of isotropic materials and can only detect single-direction strain. Due to the direction installation error, it is easy to cause measurement distortion, and it is difficult to distinguish the coupled signal changes under multi-axis strain conditions. Although several flexible wearable sensors based on various nanomaterials have been developed currently, most of them can only effectively detect the strain in a specific direction. Before measurement, users must always define the measurement direction, which is isotropic in different strain directions and can only sense the tensile deformation in a single direction, and cannot realize the identification of different tensile directions, severely limiting their applications. Therefore, it is necessary to design a strain sensor with multi-dimensional capabilities and a high strain coefficient.

[0003] To address the above problems, the most common solution is to use a combination of flexible strain gauges with geometric designs composed of isotropic piezoresistive materials. However, due to the significant damage of the network of isotropic piezoresistive materials under high strain, regardless of the loading direction, they show limited effects, have a small sensing range, and are not sufficient to distinguish the changes under multi-axis strain conditions. Moreover, the difficulty in having the ability for multi-directional motion detection lies in the strong coupling change between the principal strain direction and the transverse resistance, which limits the accurate detection of complex human motions, including the real-time detection of direction and amplitude. Once off-axis strain occurs, it will affect the electrical signal of the strain sensor, resulting in distorted strain output.

[0004] In recent years, in order to develop anisotropic high-sensitivity strain sensors, scholars at home and abroad have proposed a strategy for constructing resistive strain sensors based on serpentine conductive networks. By using vacuum sputtering deposition technology to deposit thin metal serpentine lines on the reserved structure of polyimide film, n fold lines are taken on it, thereby amplifying the resistance change by n times, such as the resistance disclosed in the literature "LUO Y, FAN H, LAI X, et al. Flexible liquid metal-based microfluidic strain sensors with fractal-designed microchannels for monitoring human motion and physiological signals[J / OL]. Biosensors and Bioelectronics, 2024, 246:115905. DOI:10.1016 / j.bios.2023.115905". The currently widely commercialized thin-film resistive strain gauge is based on this working principle. Although this strain gauge can be very thin, it has a high production cost and is fragile when repeatedly bent, which limits its wide application potential. In order to solve the problem of large stretching, some studies have proposed a V-groove array based on a high aspect ratio, such as the sensor recorded in the literature "WU D, SU Y, LI R, et al. Anisotropic and Highly Sensitive Flexible Strain Sensors Based on Carbon Nanotubes and Iron Nanowires for Human–Computer Interaction Systems[J / OL]. International Journal of Molecular Sciences, 2023, 24(17): 13029. DOI:10.3390 / ijms241713029". The sensor exhibits significant anisotropy. During the measurement process, the applied strain causes the material to change greatly along the pre-designed trajectory, while other untreated directions cannot achieve the same deformation effect. Therefore, these periodic wrinkle structures show uneven wrinkle distribution, which is a significant disadvantage. In addition, there is also a wrinkle structure formed by pre-stretching the flexible substrate, which has the disadvantage of low sensor sensitivity in the low strain range. Therefore, developing a multi-directional strain sensor that can have both a high gauge factor and a large stretching range remains an unresolved problem. Summary of the invention

[0005] To overcome the above-mentioned drawbacks of the prior art, the object of the present invention is to provide a bidirectional fluidic flexible sensor based on the Poisson squeezing effect and a preparation method thereof. By arranging an array of drum-shaped discrete microstructures in a cross-shaped microchannel, a conductive fluid is filled in the gaps between the drum-shaped discrete microstructures to form a conductive path, so that the sensor can obtain two output signals with different directions when being stretched, thereby realizing multi-directional strain measurement, greatly improving the high-direction selectivity and high anisotropy of the sensor, making the sensor have high sensitivity, wide range and high-direction selectivity, and the processing technology is simple and easy to implement.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A bidirectional fluidic flexible sensor based on the Poisson squeezing effect, comprising a flexible substrate, the surface of the flexible substrate is a cross-shaped microchannel, an array of drum-shaped discrete microstructures is arranged in the cross-shaped microchannel, and a conductive fluid is filled in the gaps between the drum-shaped discrete microstructures to form a conductive path. When the cross-shaped microchannel is longitudinally stretched, the cross-sectional length of the conductive path on the longitudinal flow channel increases and the width decreases, so the resistance increases; on the transverse flow channel, the cross-sectional length of the conductive path decreases and the width increases, so the resistance decreases; the difference in resistance changes between the transverse and longitudinal directions becomes larger, realizing high-direction selectivity; copper wires are connected to the end points of the conductive path, and a top encapsulation layer is bonded on the flexible substrate to form a closed integrated sensor.

[0008] When the array of the drum-shaped discrete microstructures is driven by strains at the top and bottom, non-uniform strains in the vertical direction are generated. Among them, at the connection of the drum-shaped discrete microstructures with the flexible substrate and the top encapsulation layer, the strain is the same as that of the cross-shaped microchannel; while gradually approaching the middle of the cross-shaped microchannel along the vertical direction, the strain shows a decreasing trend; as the flexible substrate shrinks in the width direction, adjacent drum-shaped discrete microstructures approach each other and even contact and close, realizing cross-sectional contraction. As the adjacent drum-shaped discrete microstructures further contact, the conductive fluid filled in the gap is gradually squeezed, resulting in a sharp decrease in the cross-sectional area of the conductive path and finally approaching zero, so that the resistance at both ends of the cross-shaped microchannel changes by several orders of magnitude, improving the sensitivity of the sensor.

[0009] When the drum-shaped discrete microstructures are acted on by an external force, the effective cross-sectional area of the conductive path changes Characterized as , where is the circumferential effective conductive arc length of the drum-shaped discrete microstructure, is the axial contraction deformation of the drum-shaped discrete microstructure. This formula for the change in effective cross-sectional area is applicable to the linear response stage before the gap of the drum-shaped discrete microstructure closes. The change in the effective cross-sectional area of this conductive path can achieve high sensitivity under small strains. At the same time, the extrusion existing in the contact part of adjacent drum-shaped discrete microstructures can slow down the cross-order-of-magnitude change in resistance and achieve a wide measurement range.

[0010] The cross-section of the drum-shaped discrete microstructure is a composite shape composed of a square and semi-circles on both sides. The arrangement of the array is side-by-side, forming a square array.

[0011] The flexible substrate is a molded polymer with high stretchability, including polydimethylsiloxane (PDMS) or ecoflex.

[0012] The conductive fluid is various liquid materials with conductivity and can flow freely in the cross-shaped microchannel, including ionic liquids, liquid metals, or carbon-based material dispersions.

[0013] A manufacturing method of a two-way fluid-based flexible sensor based on the Poisson extrusion effect includes the following steps:

[0014] The first step, preparation of the microchannel mold: Obtain the microchannel mold through 3D printing technology. The microchannel mold (1) has an array formed by drum-shaped discrete microstructures, and the drum-shaped discrete microstructures are in the structure of the cross-shaped microchannel (7);

[0015] The second step, preparation of the flexible substrate: Mold the microchannel mold to obtain the flexible substrate. The surface of the flexible substrate (2) is a cross-shaped microchannel, and an array formed by drum-shaped discrete microstructures is arranged in the cross-shaped microchannel;

[0016] The third step, encapsulation of the top encapsulation layer: Encapsulate the top encapsulation layer (4) on the upper part of the flexible substrate to obtain a tightly bonded and sealed cross-shaped microchannel structure housing;

[0017] The fourth step: Filling of the conductive fluid: Open small holes at the ends of three branches of the cross-shaped microchannel for air extraction, and use the remaining fourth end without opening as the injection end of the conductive fluid. Inject the conductive fluid. Under the action of capillary force and injection thrust, the conductive fluid automatically fills the entire cross-shaped microchannel to form a conductive path;

[0018] The fifth step: Integrated encapsulation: Connect copper wires to the endpoints of the conductive path, then pour encapsulation layer material at the connection to form an interconnection, and perform port encapsulation to obtain a two-way fluid-based flexible sensor based on the Poisson extrusion effect.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The design of the cross-shaped microchannel in the present invention enables the sensor to obtain two output signals with different directions when being stretched, and the resistance signals have obvious differences. Through dual-signal analysis, multi-directional strain measurement is achieved, greatly enhancing the high-direction selectivity and high anisotropy of the sensor.

[0021] (2) The drum-shaped discrete microstructure in the present invention converts the gap change behavior in the width direction into the change of the cross-section of the conductive path. As the flexible substrate shrinks, the cross-section of the conductive path gradually narrows and even the drum-shaped discrete microstructures come into contact. At the critical strain, the resistance increases by several orders of magnitude, greatly improving the sensitivity of the sensor and breaking through the limitation that only depends on the Poisson's ratio of the material.

[0022] (3) Compared with the conventional cylindrical structure, the drum-shaped discrete microstructure in the present invention effectively improves the sensitivity at low strains. At the same time, due to the mutual extrusion of the arc parts of the drum-shaped discrete microstructures, the cross-section of the conductive path when the discrete individuals come into contact is not too small, broadening the strain sensing range.

[0023] (4) The squeezing in and squeezing out of the conductive fluid during stretching in the present invention reduces the hysteresis, and can effectively avoid the mismatch of mechanical properties at the interface, without potential interface failure problems, greatly enhancing the stability of the multi-directional strain sensor.

[0024] (5) Regarding the filling of the conductive fluid during the preparation of the present invention, the combined action of capillary force automatic filling and the thrust of injection is adopted. Such a filling method has stable performance and is simple and easy to implement in processing.

[0025] In summary, based on the Poisson extrusion effect, the present invention greatly enhances the high-direction selectivity and high anisotropy of the sensor; the improved change behavior of the cross-section of the conductive path improves the sensitivity and wide measurement range of the sensor; the squeezing in and squeezing out of the conductive fluid during stretching enhances the stability of the multi-directional strain sensor, and the processing technology of the present invention is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the microchannel mold and the flexible substrate of the present invention.

[0027] Figure 2 It is a schematic structural diagram after the flexible substrate and the top encapsulation layer are bonded.

[0028] Figure 3 It is a schematic diagram of the conductive fluid filling process of the present invention.

[0029] Figure 4 It is a schematic structural diagram after the preparation and encapsulation of the present invention are completed.

[0030] Figure 5 It is a schematic cross-sectional diagram of the structure of the present invention during stretching.

[0031] Figure 6 This is a schematic cross-sectional view of the structure of the present invention during stretching.

[0032] Figure 7 This is a top view of the structure of the cross-shaped microchannel of the present invention.

[0033] Figure 8 This is a top view of the structure of the cross-shaped microchannel after stretching of the present invention.

[0034] Figure 9 This is a performance characterization diagram of different structures of the sensor of the present invention.

[0035] Figure 10 This is a performance characterization diagram of the present invention during stretching in different directions.

[0036] Figure 11 This is a sensitivity fitting diagram of the present invention during stretching in different directions.

[0037] In the figure, microchannel mold 1; flexible substrate 2; drum-shaped discrete microstructure 3; top encapsulation layer 4; conductive fluid 5; port encapsulation 6; cross-shaped microchannel 7; reference direction 8; longitudinal channel resistance 9; transverse channel resistance 10. Detailed implementation mode

[0038] The present invention will be described in detail below with reference to the accompanying drawings.

[0039] Refer to Figure 5 , A two-way fluid-based flexible sensor based on the Poisson squeezing effect, including a flexible substrate 2 as a stretching carrier, the surface of the flexible substrate 2 is a cross-shaped microchannel 7, an array formed by drum-shaped discrete microstructures 3 is arranged in the cross-shaped microchannel 7, and a conductive fluid 5 is filled in the gaps between the drum-shaped discrete microstructures 3 in the cross-shaped microchannel 7 to form a conductive path. When the cross-shaped microchannel 7 is longitudinally stretched, the cross-sectional area of the conductive path on the longitudinal channel increases in length and decreases in width, so the resistance increases; the cross-sectional area of the conductive path on the transverse channel decreases in length and increases in width, so the resistance decreases; the difference in resistance changes between the transverse and longitudinal directions becomes larger, realizing high direction selectivity; copper wires are connected to the end points of the conductive path, and a top encapsulation layer 4 is bonded on the flexible substrate 2 to form a closed integrated sensor.

[0040] When the array formed by the drum-shaped discrete microstructures 3 is driven by strains at the top and bottom, non-uniform strains are generated in the vertical direction. Among them, at the connection between the drum-shaped discrete microstructures 3 and the flexible substrate 2 and the top encapsulation layer 4, the strain is the same as that of the cross-shaped microchannel 7; while gradually approaching the middle of the cross-shaped microchannel 7 along the vertical direction, the strain shows a decreasing trend; as the flexible substrate 2 shrinks in the width direction, the adjacent drum-shaped discrete microstructures 3 approach or even contact and close to each other, realizing cross-sectional contraction; as the adjacent drum-shaped discrete microstructures 3 further contact, the conductive fluid 5 filled in the gap is gradually squeezed, resulting in a sharp reduction in the cross-sectional area of the conductive path and finally approaching zero, so that the resistance at both ends of the cross-shaped microchannel 7 changes by several orders of magnitude, obtaining highly sensitive strain sensing.

[0041] When the drum-shaped discrete microstructures 3 are subjected to external forces, the effective cross-sectional area of the conductive path changes Characterized as , where is the circumferential effective conductive arc length of the drum-shaped discrete microstructures 3, is the axial contraction deformation amount of the drum-shaped discrete microstructures 3. This formula for the change in the effective cross-sectional area is applicable to the linear response stage before the closure of the microstructure gap. The change in the effective cross-sectional area of this conductive path can achieve high sensitivity under small strains; at the same time, the extrusion existing in the contact part of the adjacent drum-shaped discrete microstructures 3 can slow down the change of the resistance by several orders of magnitude and realize a wide measurement range.

[0042] A manufacturing method of an anisotropic bidirectional fluid-based flexible strain sensor based on the Poisson extrusion effect includes the following steps:

[0043] The first step, preparation of the microchannel mold 1: Select black resin to fill the resin tank of the 3D printer, ensure that the first layer covering the printing platform is covered, start the printer, lower the printing platform to the resin tank to make the resin evenly adhere, ensure the same thickness, and perform preliminary curing with 20% ultraviolet light intensity to form the bottom layer; Import the 3D model data of the microchannel mold 1 into the slicing software, set the layer thickness to 0.1 mm for slicing, irradiate the resin with ultraviolet light, move the platform up after each layer is printed, and supplement new resin; After the basic printing is completed, increase the ultraviolet light intensity to the maximum for further curing; After taking out the model, soak it in the organic cleaning solution for 30 minutes, then perform ultrasonic cleaning for 10 minutes, and finally dry it with compressed nitrogen, and then perform hydrophobic treatment to obtain the microchannel mold 1. The microchannel mold 1 has an array formed by the drum-shaped discrete microstructures 3, and the drum-shaped discrete microstructures 3 are in the structure of the cross-shaped microchannel 7; as Figure 1 shown.

[0044] The cross-section of the drum-shaped discrete microstructure 3 is a composite shape composed of a square and two semi-circles on both sides. The array arrangement is side-by-side, forming a square array. The size of the individual drum-shaped discrete microstructure 3, the radian of the drum-shaped structure, and the size of the gap will all affect the magnitude of the critical strain and the sensitivity in the interval near the critical strain, which are selected according to specific requirements.

[0045] Second step, preparation of the flexible substrate 2: The microchannel mold 1 is replicated to obtain the flexible substrate 2. Weigh it with an electronic analytical balance. Mix the PDMS prepolymer (Dow Corning Sylgard 184 component A) and its supporting hydrogen-containing silicone oil cross-linking agent (Sylgard 184 component B) in a mass ratio of 10:1, stir evenly for 10 minutes, and pour it onto the prepared microchannel mold 1. Then degas the assembly for 10 minutes, imprint it, and heat it at 50 °C for 4 hours, and then demold to form the flexible substrate 2, which has an array composed of a flexible cross-shaped microchannel structure and the drum-shaped discrete microstructure 3, as Figure 1 shown.

[0046] The replication uses a molding polymer with high stretchability, including polydimethylsiloxane PDMS or ecoflex, and the corresponding polymer is selected according to the required stretching range.

[0047] Third step, encapsulation of the top encapsulation layer 4: Mix the PDMS prepolymer (Dow Corning Sylgard 184 component A) and its supporting hydrogen-containing silicone oil cross-linking agent (Sylgard 184 component B) in a mass ratio of 10:1, stir evenly for 10 minutes, and degas for 10 minutes. Spin-coat a part of it on polyethylene terephthalate (PET) at a speed of 500 rpm for 20 s, degas for 5 minutes, and then heat it at 90 °C for 2 hours to prepare the top encapsulation layer 4 of the microfluidic sensor. For the remaining part of the PDMS mixture, spin-coat it on the top encapsulation layer 4 (the parameter setting is to spin-coat at a speed of 500 rpm for 10 s first, and then spin-coat at a speed of 1500 rpm for 40 s), pre-cure it at 120 °C for 1 minute, invert the flexible substrate 2 on it, and heat it at 90 °C for 2 hours to form a chemical bond. Then, peel off the PET on the surface to obtain a sealed cross-shaped microchannel structure housing. It can be seen from the cross-sectional view that the flexible substrate 2 and the top encapsulation layer 4 are completely and tightly bonded together, as Figure 2 shown.

[0048] Fourth step, filling of the conductive fluid 5: At the end of each of the three branches of the closed cross-shaped microchannel 7, a small hole with a diameter of 0.5 mm is opened for air extraction. The current device is subjected to oxygen plasma treatment to temporarily change the PDMS from hydrophobic to hydrophilic, and the contact angle at the solid-liquid interface changes from an obtuse angle to an acute angle. Then, a syringe is used to inject the conductive fluid 5 ([EMIM][OTF], 98%, Aladdin Industrial Corporation) into the remaining unopened fourth-end channel of the cross-shaped microchannel 7. Under the action of capillary force and the thrust of the syringe, the conductive fluid 5 automatically fills the openings of the other three-end channels, obtaining a structured microchannel filled with the conductive fluid 5, as Figure 3 shown.

[0049] The conductive fluid 5 is various liquid materials with conductivity and can flow freely in the cross-shaped microchannel 7, including ionic liquids, liquid metals, and carbon-based material dispersions. The higher the conductivity of the material, the larger the obtained range. It can be selected according to specific requirements.

[0050] Fifth step, integrated packaging: Copper wires are pulled out at the four ends of the cross-shaped microchannel 7 as the two-end electrodes, and the PDMS prepolymer mixed with a curing agent is used for packaging. Finally, after waiting for four hours at room temperature, the prepolymer will cure, or after heating on a heating platform at 50 °C for about two hours, the prepolymer cures to form the port packaging 6, thus finally obtaining a closed integrated stretchable bidirectional fluid-based flexible strain sensor, as Figure 4 shown, where the closed cross-shaped microchannel 7 is a cross-shaped cross-channel structure.

[0051] As Figure 5 and Figure 6 shown, the array formed by the drum-shaped discrete microstructures 3 generates non-uniform strain in the vertical direction under the strain drive at the top and bottom. The strain change decreases as the position gets closer to the middle. As the microchannel substrate in the width direction shrinks, the adjacent structures approach each other, realizing cross-section shrinkage and even contact, achieving structure closure. At the same time, due to the mutual extrusion of the arc parts of the drum-shaped discrete microstructures 3, the cross-section of the conductive path when the discrete individuals are in contact is not too small.

[0052] The conductive fluid 5 filled in the cross-shaped microchannel 7 forms the resistance of the sensor. By outputting the resistance signal of the two channels during stretching, the stretching direction and stretching strain can be identified under different stretching states, as Figure 7 shown; it should be noted that in the present invention, the flexible substrate 2 is selected from the same flexible material as the top packaging layer 4; the microstructured channels significantly improve the resistance response characteristics, not only breaking through the original Poisson's ratio limit, but also obtaining a sensitivity across several orders of magnitude from the gating opening and closing of the microstructures, and broadening the strain sensing range of the sensor.

[0053] To further demonstrate the advantages of the two-way fluidic flexible sensor based on the Poisson squeezing effect of the present invention, it will be described below in conjunction with experimental data.

[0054] First, as Figure 8 shown, the direction of the transverse flow channel is defined as the reference direction 8, and then the angle of counterclockwise rotation with respect to this reference direction 8 is defined as the strain direction of the anisotropic two-way fluidic flexible strain sensor based on the Poisson squeezing effect. When the stretching direction is perpendicular to the reference direction 8, the length of the longitudinal flow channel gap increases, the width decreases, the length of the transverse flow channel gap decreases, and the width increases. The changes in the two flow channel resistances of the longitudinal flow channel resistance 9 and the transverse flow channel resistance 10 exhibit positive and negative properties, greatly enhancing the direction selectivity. Figure 9 Shows the resistance outputs of the present invention, the unstructured microchannel resistive strain sensor, and the microchannel resistive strain sensor with a cylindrical array under different strains. It can be seen from the data that the sensitivity of the present invention using a drum-shaped discrete microstructure has been improved by several orders of magnitude. Figure 10 Shows the resistance output of the longitudinal flow channel of the present invention under different stretching directions. It can be found that the present invention has different resistance output response trends, indicating that the sensor of the present invention has high anisotropy. Figure 11 Shows the strain coefficient GF under different stretching directions, indicating that the present invention has high direction selectivity.

Claims

1. A bidirectional fluid-type flexible sensor based on Poisson squeezing effect, comprising a flexible substrate (2), characterized in that: The surface of the flexible substrate (2) is a cross-shaped microchannel (7), an array formed by drum-shaped discrete microstructures (3) is arranged in the cross-shaped microchannel (7), and the gaps between the drum-shaped discrete microstructures (3) are filled with a conductive fluid (5) to form a conductive path. When the cross-shaped microchannel (7) is stretched longitudinally, the cross-sectional length of the conductive path in the longitudinal direction increases and the width decreases, thereby increasing the resistance; the cross-sectional length of the conductive path in the transverse direction decreases and the width increases, thereby decreasing the resistance; the difference in resistance change in the transverse and longitudinal directions becomes larger, thereby achieving high directional selectivity; copper wires are connected to the end points of the conductive path, and a top encapsulation layer (4) is bonded to the flexible substrate (2) to form a closed integrated sensor; The array formed by the drum-shaped discrete microstructures (3) generates non-uniform strain in the vertical direction under the strain drive of the top and bottom, wherein the strain of the drum-shaped discrete microstructures (3) at the connection with the flexible substrate (2) and the top packaging layer (4) is the same as that of the cross-shaped microchannel (7); while the strain gradually decreases as it approaches the middle of the cross-shaped microchannel (7) in the vertical direction; as the flexible substrate (2) shrinks in the width direction, adjacent drum-shaped discrete microstructures (3) approach each other or even contact each other, thereby achieving cross-sectional shrinkage; as adjacent drum-shaped discrete microstructures (3) further contact each other, the conductive fluid (5) filled in the gap is gradually squeezed, resulting in a sharp decrease in the cross-sectional area of ​​the conductive path, which eventually approaches zero, thereby causing the resistance at both ends of the cross-shaped microchannel (7) to change by orders of magnitude, thereby improving the sensitivity of the sensor; The cross section of the drum-shaped discrete microstructure (3) is a composite shape consisting of a square and two semicircles on both sides, and the array is arranged side by side in a square array.

2. The bidirectional fluid type flexible sensor based on Poisson squeezing effect according to claim 1 is characterized in that: When the drum-shaped discrete microstructure (3) is subjected to an external force, the effective cross-sectional area of ​​the conductive path changes Characterized by ,in is the effective circumferential conductive arc length of the drum-shaped discrete microstructure (3), is the axial contraction deformation of the drum-shaped discrete microstructure (3). The effective cross-sectional area change formula is applicable to the linear response stage before the gap of the drum-shaped discrete microstructure (3) is closed. The effective cross-sectional area change of the conductive path can achieve high sensitivity under small strain. At the same time, the extrusion of adjacent drum-shaped discrete microstructures (3) at the contact part can slow down the cross-order magnitude change of resistance and achieve a wide range.

3. The bidirectional fluid flexible sensor based on Poisson squeezing effect according to claim 1 is characterized in that: The flexible substrate (2) is a molded polymer with large stretchability, including polydimethylsiloxane (PDMS) or ecoflex.

4. The method for manufacturing a bidirectional fluid type flexible sensor based on Poisson extrusion effect according to claim 1, characterized in that: The conductive fluid (5) is any type of liquid material that is conductive and can flow freely in the cross-shaped microchannel (7), including ionic liquid, liquid metal or carbon-based material dispersion.

5. The method for manufacturing a bidirectional fluid type flexible sensor based on Poisson squeezing effect according to claim 1, characterized in that: The following steps are involved: The first step is to prepare a microfluidic mold (1): a microfluidic mold (1) is obtained by 3D printing technology, wherein the microfluidic mold (1) has an array formed by drum-shaped discrete microstructures (3), and the drum-shaped discrete microstructures (3) are in the structure of a cross-shaped microfluidic channel (7); The second step is to prepare the flexible substrate (2): the microfluidic channel mold (1) is molded to obtain a flexible substrate (2), the surface of the flexible substrate (2) is a cross-shaped microfluidic channel (7), and an array formed by drum-shaped discrete microstructures (3) is arranged in the cross-shaped microfluidic channel (7); The third step is packaging of the top packaging layer (4): packaging the top packaging layer (4) on the upper part of the flexible substrate (2) to obtain a tightly bonded and closed cross-shaped microfluidic structure shell; Step 4: Filling the conductive fluid (5): A small hole is opened at each of the three branch ends of the cross-shaped microchannel (7) to evacuate air, and the remaining fourth end without a hole is used as the injection end of the conductive fluid (5). The conductive fluid (5) is injected, and under the action of capillary force and injection thrust, the conductive fluid (5) automatically fills the entire cross-shaped microchannel (7) to form a conductive path; Step 5: Integrated packaging: Connect copper wires to the end points of the conductive path, pour packaging layer materials on the connection points to form interconnections, perform port packaging, and obtain a bidirectional fluid flexible sensor based on the Poisson extrusion effect.

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