Bidirectional fluid type flexible sensor based on Poisson extrusion effect and preparation method

Abstract

The invention discloses a two-way fluid type flexible sensor based on Poisson extrusion effect and a preparation method, the flexible sensor comprises a flexible substrate, the surface of the flexible substrate is a cross-shaped micro-channel, an array formed by drum-shaped discrete microstructures is arranged in the cross-shaped micro-channel, conductive fluid is filled in gaps of the drum-shaped discrete microstructures to form a conductive path, and the conductive path is connected with the flexible substrate. The array formed by arranging the drum-shaped discrete microstructures in the cross-shaped micro-channel enables the sensor to obtain two output signals in different directions when the sensor is stretched, thereby achieving the multi-direction strain measurement, greatly improving the high-direction selectivity, high anisotropy and sensitivity of the sensor, and widening the strain sensing range. During preparation, filling of the conductive fluid is achieved through capillary force automatic filling and the thrust effect of an injector, the filling mode is stable in performance, and the processing technology is simple and easy to achieve.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a bidirectional fluid-type flexible sensor based on Poisson extrusion effect and a preparation method thereof. Background Art

[0002] In recent years, flexible strain sensors have attracted widespread 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 strain in a single direction. The directional installation error can easily lead to measurement distortion, and it is difficult to distinguish the coupled signal changes under multi-axis strain conditions. Although several flexible wearable sensors based on many nanomaterials have been developed, most of them can only effectively detect strain in a specific direction. Before measurement, the user must always define the measurement direction. They are isotropic in different strain directions and can only sense tensile deformation in a single direction. They cannot recognize different tensile directions, which seriously limits their application. Therefore, it is necessary to design a strain sensor with multi-dimensional capabilities and a high strain coefficient.

[0003] The most common solution to the above problems is to use a geometrically designed flexible strain gauge combination composed of isotropic piezoresistive materials. However, since the network of isotropic piezoresistive materials will experience significant damage under high strain, they show limited effect regardless of the loading direction, have a small sensing range, and are insufficient to distinguish changes in multi-axis strain conditions. Moreover, the difficulty in having multi-axis motion detection capabilities lies in the strong coupling changes in the principal strain direction and lateral resistance, which limits the accurate detection of complex human body movements, including 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] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a bidirectional fluid-type flexible sensor based on the Poisson extrusion effect and a preparation method thereof, by arranging an array formed by drum-shaped discrete microstructures in a cross-shaped microchannel, and filling the gaps between the drum-shaped discrete microstructures with conductive fluid to form a conductive path, so that the sensor obtains two output signals with different directions when stretched, thereby realizing multi-directional strain measurement, greatly improving the high directional selectivity and high anisotropy of the sensor, so that the sensor has high sensitivity, wide range and high directional selectivity, and the processing technology is simple and easy to implement.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A bidirectional fluid-type flexible sensor based on the Poisson squeeze effect comprises a flexible substrate, 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. When the cross-shaped microchannel is subjected to longitudinal stretching, the cross-sectional length of the conductive path on the longitudinal direction of the flow channel increases and the width decreases, thereby increasing the resistance; the cross-sectional length of the conductive path on the transverse direction of the flow channel decreases and the width increases, thereby reducing 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 packaging layer is bonded to the flexible substrate to form a closed integrated sensor.

[0007] The array formed by the drum-shaped discrete microstructures 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 microstructure at the connection with the flexible substrate and the top packaging layer is the same as that of the cross-shaped microchannel; while the strain gradually decreases as it approaches the middle of the cross-shaped microchannel in the vertical direction; with the shrinkage of the flexible substrate in the width direction, adjacent drum-shaped discrete microstructures approach each other or even contact and close, achieving cross-sectional shrinkage; with the further contact of adjacent drum-shaped discrete microstructures, the conductive fluid 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 to change across orders of magnitude, thereby improving the sensitivity of the sensor.

[0008] When the drum-shaped discrete microstructure 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, is the axial shrinkage deformation of the drum-shaped discrete microstructure. The 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 is closed. The change in the effective cross-sectional area of ​​the conductive path can achieve high sensitivity under small strain. At the same time, the extrusion of adjacent drum-shaped discrete microstructures in the contact part can slow down the cross-order magnitude change of resistance and achieve a wide range.

[0009] The cross section of the drum-shaped discrete microstructure 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.

[0010] The flexible substrate is a molded polymer with large stretchability, including polydimethylsiloxane (PDMS) or ecoflex.

[0011] The conductive fluid is any type of liquid material with conductivity and can flow freely in the cross-shaped microchannel, including ionic liquid, liquid metal or carbon-based material dispersion.

[0012] A method for manufacturing a bidirectional fluid-type flexible sensor based on Poisson extrusion effect comprises the following steps: The first step is to prepare a microfluidic mold: a microfluidic mold is obtained by 3D printing technology, wherein the microfluidic mold (1) has an array formed by drum-shaped discrete microstructures, and the drum-shaped discrete microstructures are in the structure of a cross-shaped microfluidic channel (7); The second step is to prepare a flexible substrate: the microfluidic channel mold is remolded to obtain a flexible substrate, the surface of the flexible substrate (2) is a cross-shaped microfluidic channel, and an array formed by drum-shaped discrete microstructures is arranged in the cross-shaped microfluidic channel; The third step is encapsulation of the top encapsulation layer: encapsulating the top encapsulation layer (4) on the upper part of the flexible substrate to obtain a tightly bonded and closed cross-shaped microfluidic structure shell; Step 4: Filling of conductive fluid: small holes are opened at the ends of the three branches of the cross-shaped microchannel to evacuate air, and the remaining fourth end without a hole is used as the injection end of the conductive fluid. The conductive fluid is injected. Under the action of capillary force and injection thrust, the conductive fluid automatically fills the entire cross-shaped microchannel 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.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The design of the cross-shaped microfluidic channel of the present invention enables the sensor to obtain two output signals with different directions when stretched, and the resistance signals are significantly different. Dual signal analysis can realize multi-directional strain measurement, greatly improving the high directional selectivity and high anisotropy of the sensor.

[0014] (2) The drum-shaped discrete microstructure of the present invention converts the gap change behavior in the width direction into a change in the cross-section of the conductive path. As the flexible substrate shrinks, the cross-section of the conductive path gradually narrows and even contacts the drum-shaped discrete microstructure. At the critical strain, the resistance increases by an order of magnitude, greatly improving the sensitivity of the sensor and breaking through the limitation of relying solely on the Poisson's ratio of the material.

[0015] (3) Compared with the conventional columnar structure, the drum-shaped discrete microstructure of the present invention effectively improves the sensitivity at low strain. At the same time, since the arc parts of the drum-shaped discrete microstructure squeeze each other, the cross-section of the conductive path when the discrete individuals are in contact will not be too small, thereby widening the strain sensing range.

[0016] (4) The squeezing in and out of the conductive fluid during stretching reduces hysteresis and can effectively avoid the mismatch of mechanical properties at the interface. There will be no potential interface failure problem, which greatly improves the stability of the multi-directional strain sensor.

[0017] (5) The present invention adopts the combined effect of capillary force automatic filling and injection thrust to fill the conductive fluid. This filling method has stable performance and is simple and easy to process.

[0018] In summary, the present invention is based on the Poisson squeezing effect, which greatly improves the high directional selectivity and high anisotropy of the sensor; the improved cross-sectional change behavior of the conductive path improves the sensitivity and wide range of the sensor; the squeezing in and out of the conductive fluid during stretching improves 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

[0019] Figure 1 It is a schematic diagram of the structure of the microfluidic mold and the flexible substrate of the present invention.

[0020] Figure 2 It is a schematic diagram of the structure after the flexible substrate and the top packaging layer of the present invention are bonded.

[0021] Figure 3 This is a schematic diagram of the conductive fluid filling process of the present invention.

[0022] Figure 4 This is a schematic diagram of the structure after the packaging is completed in the present invention.

[0023] Figure 5 It is a schematic diagram of the structural cross-section of the present invention during stretching.

[0024] Figure 6 It is a schematic diagram of the structural cross-section of the present invention during stretching.

[0025] Figure 7 It is a top view of the structure of the cross-shaped microfluidic channel of the present invention.

[0026] Figure 8 This is a top view of the structure of the cross-shaped microchannel after stretching of the present invention.

[0027] Fig. 9 This is a performance characterization diagram of different structures of the sensor of the present invention.

[0028] Fig.10 It is a performance characterization diagram of the present invention when stretched in different directions.

[0029] Fig.11 This is a sensitivity fitting diagram of the present invention when stretched in different directions.

[0030] In the figure, microfluidic mold 1; flexible substrate 2; drum-shaped discrete microstructure 3; top packaging layer 4; conductive fluid 5; port packaging 6; cross-shaped microfluidic channel 7; reference direction 8; longitudinal channel resistor 9; and lateral channel resistor 10. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings.

[0032] Reference Figure 5 A bidirectional fluid-type flexible sensor based on Poisson squeezing effect includes a flexible substrate 2 as a stretching carrier, a cross-shaped microchannel 7 on the surface of the flexible substrate 2, an array formed by drum-shaped discrete microstructures 3 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 subjected to longitudinal stretching, the length of the conductive path section on the longitudinal direction of the flow channel increases and the width decreases, thereby increasing the resistance; the length of the conductive path section on the transverse direction of the flow channel decreases and the width increases, thereby reducing the resistance; the difference in resistance change in the transverse and longitudinal directions becomes larger, achieving high directional selectivity; copper wires are connected to the end points of the conductive path, and a top packaging layer 4 is bonded to the flexible substrate 2 to form a closed integrated sensor.

[0033] The array formed by the drum-shaped discrete microstructures 3 will produce 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 when gradually approaching the middle of the cross-shaped microchannel 7 in the vertical direction; with the contraction of the flexible substrate 2 in the width direction, the adjacent drum-shaped discrete microstructures 3 are caused to approach each other or even contact and close, thereby realizing cross-sectional contraction; with the further contact of the adjacent drum-shaped discrete microstructures 3, 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, and finally approaching zero, thereby causing the resistance at both ends of the cross-shaped microchannel 7 to change across orders of magnitude, thereby obtaining highly sensitive strain sensing.

[0034] 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 conductive arc length of the drum-shaped discrete microstructure in three circumferential directions, is the axial shrinkage deformation of the drum-shaped discrete microstructure 3. The effective cross-sectional area change formula is applicable to the linear response stage before the microstructure gap 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 in the contact part can slow down the cross-order magnitude change of resistance and achieve a wide range.

[0035] A method for manufacturing an anisotropic bidirectional fluid-type flexible strain sensor based on Poisson extrusion effect comprises the following steps: The first step is to prepare the microfluidic mold 1: select black resin to fill the resin tank of the 3D printer to ensure that the first layer of the printing platform is covered, start the printer, lower the printing platform to the resin tank to make the resin adhere evenly, ensure consistent thickness, and use 20% ultraviolet light intensity for preliminary curing to form a bottom layer; import the 3D model data of the microfluidic mold 1 into the slicing software, set the layer thickness to 0.1mm for slicing, irradiate the resin with ultraviolet light, and move the platform up after each layer is printed to add 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 an organic cleaning solution for 30 minutes, then ultrasonically clean it for 10 minutes, and finally blow it dry with compressed nitrogen, and then perform hydrophobic treatment to obtain a microfluidic mold 1, which has an array formed by drum-shaped discrete microstructures 3, and the drum-shaped discrete microstructures 3 are in the structure of the cross-shaped microfluidic channel 7; as shown in FIG. Figure 1 shown.

[0036] 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; the size of the drum-shaped discrete microstructure 3, the curvature of the drum-shaped structure, and the size of the gap will affect the size of the critical strain and the sensitivity of the interval near the critical strain, which can be selected according to specific needs.

[0037] The second step is the preparation of the flexible substrate 2: the microfluidic mold 1 is molded to obtain the flexible substrate 2, which is weighed using an electronic analytical balance, and the PDMS prepolymer (Dow Corning Sylgard 184 A component) and its matching hydrogenated silicone oil crosslinker (Sylgard184 B component) are mixed in a mass ratio of 10:1, stirred evenly for 10 minutes, and poured onto the prepared microfluidic mold 1; the assembly is then degassed for 10 minutes, embossed, heated at 50°C for 4 hours, and demolded to form a flexible substrate 2 having a flexible cross-shaped microfluidic structure and an array consisting of drum-shaped discrete microstructures 3, as shown in FIG. Figure 1 shown.

[0038] The mold is made of a molding polymer with large stretchability, including polydimethylsiloxane (PDMS) or ecoflex, and the corresponding polymer is selected according to the required stretching range.

[0039] Step 3: Encapsulation of the top encapsulation layer 4: PDMS prepolymer (Dow Corning Sylgard 184 A component) and its matching hydrogenated silicone oil crosslinker (Sylgard 184 The PDMS component (component B) was mixed in a mass ratio of 10:1, stirred evenly for 10 minutes, degassed for 10 minutes, a portion was spin-coated on polyethylene terephthalate (PET) at a speed of 500 rpm for 20 seconds, degassed for 5 minutes, and then heated at 90°C for 2 hours to prepare the top packaging layer 4 of the microfluidic sensor. The remaining portion of the PDMS mixture was spin-coated on the top packaging layer 4 (the parameters were set to spin-coat at a speed of 500 rpm for 10 seconds and then at a speed of 1500 rpm for 40 seconds), pre-cured at 120°C for 1 minute, and the flexible substrate 2 was turned upside down and heated at 90°C for 2 hours to produce chemical bonding. Then, the PET on the surface was peeled off to obtain a closed cross-shaped microfluidic structure shell. It can be seen from the cross-sectional view that the flexible substrate 2 and the top packaging layer 4 are completely and tightly bonded together, as shown in FIG. Figure 2 shown.

[0040] The fourth step is to fill the conductive fluid 5: a small hole with a diameter of 0.5 mm is opened at each of the three branch ends of the closed cross-shaped microchannel 7 to evacuate air, and the current device is treated with oxygen plasma to temporarily change the PDMS from hydrophobic to hydrophilic, and the contact angle of the solid-liquid interface is changed from an obtuse angle to an acute angle. Then, a syringe is used to inject the conductive fluid 5 ([EMIM][OTF], 98%, Aladdin Industries) from the remaining unopened fourth end flow channel of the cross-shaped microchannel 7. Under the action of capillary force and the thrust of the syringe, the conductive fluid 5 is automatically filled into the openings of the other three end flow channels, and a structured microchannel filled with the conductive fluid 5 is obtained, as shown in FIG. Figure 3 shown.

[0041] The conductive fluid 5 is any type of liquid material with conductivity and can flow freely in the cross-shaped microchannel 7, including ionic liquid, liquid metal, and carbon-based material dispersion. The higher the conductivity of the material, the larger the range obtained, which can be selected according to specific needs.

[0042] The fifth step is integrated packaging: copper wires are pulled out from the four ends of the cross-shaped microchannel 7 as the two-end electrodes, and the PDMS prepolymer mixed with the curing agent is used for packaging. Finally, the prepolymer will solidify after waiting for four hours at room temperature, or the prepolymer will solidify after heating on a heating platform at 50°C for about two hours to form a port package 6, thereby finally obtaining a closed integrated stretchable bidirectional fluid-type flexible strain sensor, such as Figure 4 As shown, the closed cross-shaped microchannel 7 here is a cross-shaped cross-channel structure.

[0043] like Figure 5 and Figure 6 As shown, 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. The strain change decreases as the position approaches the middle. As the microfluidic substrate shrinks in the width direction, adjacent structures approach each other, achieving cross-sectional shrinkage or even contact, thereby achieving structural closure. At the same time, due to the mutual squeezing of the arc-shaped 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.

[0044] The conductive fluid 5 filled in the cross-shaped microchannel 7 forms the resistance of the sensor. By outputting signals of the resistance of the two channels when stretched, the stretching direction and the stretching strain can be identified under different stretching states. Figure 7 As shown; it should be noted that in the present invention, the flexible substrate 2 selects the same flexible material as the top packaging layer 4; the microstructured flow channel significantly improves the resistance response characteristics, not only breaking through the original Poisson's ratio limitation, but also obtaining cross-order sensitivity from the gated opening and closing of the microstructure, and broadening the strain sensing range of the sensor.

[0045] In order to further demonstrate the advantages of the bidirectional fluid-type flexible sensor based on the Poisson squeezing effect of the present invention, an explanation is given below in combination with experimental data.

[0046] First, if Figure 8 As shown, the direction of the transverse flow channel is defined as the reference direction 8, and then the angle of counterclockwise rotation of the reference direction 8 is defined as the strain direction of the anisotropic bidirectional fluid-type flexible strain sensor based on the Poisson extrusion effect. When the stretching direction is perpendicular to the reference direction 8, the length of the longitudinal flow channel gap increases and the width decreases, and 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 are positive and negative, which greatly enhances the directional selectivity. Fig. 9 The resistance output of the present invention, the unstructured microfluidic resistive strain sensor, and the columnar array microfluidic resistive strain sensor under different strains is demonstrated. From the data, it can be seen that the sensitivity of the present invention using drum-shaped discrete microstructures is improved by several orders of magnitude. Fig.10The resistance output of the longitudinal flow channel of the present invention under different stretching directions is shown, and it can be found that the present invention has different resistance output response trends, which indicates that the sensor of the present invention has high anisotropy. Fig.11 The gauge factors GF under different stretching directions are shown, which indicates that the present invention has high directional 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.

2. The bidirectional fluid type flexible sensor based on Poisson squeezing effect according to claim 1 is characterized in that: 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.

3. 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.

4. The bidirectional fluid flexible sensor based on Poisson squeezing effect according to claim 1, 2 or 3, characterized in that: 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.

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

6. The method for manufacturing a bidirectional fluid type flexible sensor based on Poisson squeezing effect according to claim 1 or 2, 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.

7. 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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