Capacitive flexible pressure sensor based on geometric zero poisson's ratio structure

Abstract

The application discloses a capacitive flexible pressure sensor based on a geometric zero Poisson's ratio structure and belongs to the technical field of intelligent sensing. The capacitive flexible pressure sensor comprises a lower flexible substrate, a lower electrode, a porous ionic electroactive layer, an upper electrode and an upper flexible substrate. The porous ionic electroactive layer comprises a three-dimensional porous elastomer network skeleton and ionic liquid or ionic gel distributed inside pores of the three-dimensional porous elastomer network skeleton, on a skeleton surface and / or in a pore inner wall. The three-dimensional porous elastomer network skeleton has a geometric zero Poisson's ratio or near-zero Poisson's ratio deformation characteristic. The ionic liquid or ionic gel is distributed in the three-dimensional porous elastomer network skeleton in a non-complete filling mode. The three-dimensional porous elastomer network skeleton with the geometric zero Poisson's ratio or near-zero Poisson's ratio is combined with the ionic liquid or ionic gel, so that in-plane transverse strain propagation when being locally pressed can be inhibited, and high-capacitance response can be generated by using an ionic electroactive interface.

Description

Technical Field

[0001] This invention relates to the field of intelligent sensing technology, and in particular to a capacitive flexible pressure sensor based on a geometric zero Poisson's ratio structure. Background Technology

[0002] Capacitive flexible pressure sensors, due to their advantages such as simple structure, fast response speed, low power consumption, and ease of integration, have significant application value in fields such as robotic electronic skin, intelligent grasping, human-computer interaction, wearable health monitoring, and pressure distribution detection. In recent years, with the continuous improvement of the sensing performance requirements of tactile sensing systems, how to improve the sensitivity, lower the detection limit, and expand the detection range while maintaining the flexibility of the sensor has become one of the research hotspots in this field.

[0003] As tactile sensing systems evolve towards high-density arrays, signal crosstalk between sensing units is becoming increasingly prominent. In array-type flexible pressure sensors, when a sensing unit is locally compressed, the soft substrate and elastic dielectric layer, in addition to compression along the thickness direction, typically experience significant in-plane transverse strain propagation, causing stress and deformation to transfer from the compressed unit to adjacent unloaded units. This mechanical coupling effect leads to non-target changes in the electrode spacing, contact interface, and local capacitance response of adjacent units, resulting in signal crosstalk and severely reducing the spatial resolution and positioning accuracy of the array.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure.

[0006] To achieve the above objectives, the present invention provides a capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure, comprising: a lower flexible substrate, a lower electrode disposed on the lower flexible substrate, a porous ionizing active layer, an upper flexible substrate, and an upper electrode disposed on the upper flexible substrate; the porous ionizing active layer comprises a three-dimensional porous elastomer network framework and ionic liquids or ionic gels distributed within the pores, on the surface of the framework, and / or on the inner walls of the pores of the three-dimensional porous elastomer network framework; the three-dimensional porous elastomer network framework has geometrically zero Poisson's ratio or near-zero Poisson's ratio deformation characteristics; the ionic liquids or ionic gels are distributed in the three-dimensional porous elastomer network framework in a non-completely filled manner.

[0007] In one embodiment of the present invention, within the range of 0% to 60% of normal compressive strain, the ratio of the absolute value of the in-plane transverse strain of the porous ionized active layer to the absolute value of the normal compressive strain is not greater than 0.15.

[0008] In one embodiment of the present invention, the three-dimensional porous elastomer network skeleton includes one or more of the following: a back-in honeycomb structure, a paper-cut lattice structure, a star-shaped hinge structure, a paper-folding cell structure, a rotating unit structure, a cross-shaped connecting hole array structure, and a three-dimensional interconnected network structure of open-pore foam or open-pore sponge.

[0009] In one embodiment of the present invention, the three-dimensional porous elastomer network skeleton includes periodically or quasi-periodically repeating cells with a cell size of 0.01 mm to 2 mm, a cell wall thickness of 20 μm to 1000 μm, an average pore size of 5 μm to 1000 μm, and a porosity of 30% to 95%.

[0010] In one embodiment of the present invention, the mass loading of the ionic liquid or ionic gel is 5% to 80% of the mass of the three-dimensional porous elastomer network skeleton.

[0011] In one embodiment of the present invention, the skeleton beams, skeleton nodes and / or inner walls of the pores of the three-dimensional porous elastomer network skeleton have surface microstructures; the surface microstructures include one or more of the following: surface roughness structure, microprotrusion, microgroove, micropit or micropore structure.

[0012] In one embodiment of the present invention, the feature size of the surface microstructure is 0.1 μm to 200 μm.

[0013] In one embodiment of the present invention, the material of the three-dimensional porous elastomer network skeleton includes one or more of PDMS, Ecoflex, TPU, PU, ​​silicone rubber, natural rubber, and polyolefin elastomer, or the material of the three-dimensional porous elastomer network skeleton is one of open-cell polyurethane foam, open-cell silicone rubber foam, and open-cell TPU foam.

[0014] In one embodiment of the present invention, the ionic liquid includes one or more of imidazole ionic liquids, pyridine ionic liquids, quaternary ammonium salt ionic liquids, and quaternary phosphate salt ionic liquids; the ionic gel is a gel material formed by combining the ionic liquid with a polymer network.

[0015] In one embodiment of the present invention, the ionic liquid or ionic gel is introduced into the three-dimensional porous elastomer network skeleton by means of quantitative dripping, natural wetting, vacuum-assisted permeation, pre-compression-rebound adsorption, scraping, rolling, centrifugation-assisted removal, or in-situ gelation.

[0016] Compared with existing technologies, this invention, by setting a three-dimensional porous elastomer network skeleton with geometrically zero or near-zero Poisson's ratio deformation characteristics between the lower and upper electrodes, ensures that the in-plane lateral strain of the porous ionostatic active layer under normal compression is intrinsically limited by the geometric structure. This localizes the deformation of the loading unit within the compression region, fundamentally reducing the mechanical coupling paths between units. This deformation localization capability is inherent in the sensing layer structure itself and does not rely on external circuit compensation or algorithm correction, thus offering advantages such as fast response speed, no additional power consumption, and no increase in system complexity.

[0017] Meanwhile, this invention distributes ionic liquids or ionic gels in a non-fully filled manner within the pores, on the surface of the framework, and / or on the inner walls of the channels of a three-dimensional porous elastomer network framework. This allows the framework to retain compressible pores that can shrink under pressure, avoiding the volumetric incompressibility problem caused by complete filling. This enables the sensor to generate sufficient thickness-direction deformation in response to normal pressure. Furthermore, the ionic liquids or ionic gels distributed on the framework surface form continuous ionic conductive pathways at the electrode interfaces, ensuring that the sensor has a detectable capacitive response output. This non-fully filled distribution method gives the sensing layer both sufficient compressive deformation capability and effective interfacial response capability. Attached Figure Description

[0018] Figure 1 This is a layered schematic diagram of a capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the pressure response mechanism of a capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure according to an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of an open-pore foam / sponge type three-dimensional connected network skeleton according to an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of a three-dimensional honeycomb structure skeleton according to an embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of a three-dimensional paper-cutting lattice structure framework according to an embodiment of the present invention;

[0023] Figure 6 This is a schematic diagram of a three-dimensional star-shaped hinge structure skeleton according to an embodiment of the present invention;

[0024] Figure 7 This is a schematic diagram of a three-dimensional origami cellular structure skeleton according to an embodiment of the present invention;

[0025] Figure 8This is a comparative schematic diagram showing the lateral deformation propagation of a conventional porous active layer and the porous ionized active layer of the present invention under localized pressure.

[0026] Figure label:

[0027] 100 - Capacitive flexible pressure sensor; 10 - Lower flexible substrate; 20 - Lower electrode; 30 - Porous ionization active layer; 301 - Positive ion; 302 - Negative ion; 40 - Upper electrode; 50 - Upper flexible substrate. Detailed Implementation

[0028] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0029] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0030] Please see Figure 1 and Figure 2 A preferred embodiment of the present invention provides a capacitive flexible pressure sensor 100 based on a geometrically zero Poisson's ratio structure, comprising:

[0031] The structure comprises a lower flexible substrate 10, a lower electrode 20, a porous ionized active layer 30, an upper electrode 40, and an upper flexible substrate 50.

[0032] That is, it includes a lower flexible substrate 10, a lower electrode 20 disposed on the lower flexible substrate, a porous ionization active layer 30, an upper flexible substrate 50, and an upper electrode 40 disposed on the upper flexible substrate 50.

[0033] The upper electrode 40 and the lower electrode 20 constitute a capacitance detection structure, and the change in capacitance before and after pressure loading is used as the output signal.

[0034] The porous ionized active layer 30 includes a three-dimensional porous elastomer network framework and ionic liquids or ionic gels distributed inside the pores, on the surface of the framework and / or on the inner walls of the pores of the three-dimensional porous elastomer network framework.

[0035] The three-dimensional porous elastomer network skeleton has geometric zero Poisson's ratio or near-zero Poisson's ratio deformation characteristics.

[0036] Ionic liquids or ionic gels are distributed in a partially filled manner within a three-dimensional porous elastomer network framework.

[0037] The following explanation is based on the principle: When external normal pressure is applied to the upper flexible substrate 50, the pressure is sequentially transmitted to the upper electrode 40 and the porous ionized active layer 30. Due to its geometrically zero or near-zero Poisson's ratio deformation characteristics, the three-dimensional porous elastomer network framework in the porous ionized active layer 30 exhibits in-plane lateral strain under normal compression, which is intrinsically limited by its geometric structure. Normal compressive strain is primarily released through the rotation, bending, or rearrangement of cell walls in the thickness direction, rather than through in-plane lateral expansion. This mechanical characteristic localizes the deformation of the porous ionized active layer 30 within the compressed region, making it difficult for it to propagate to adjacent in-plane regions. Simultaneously, the ionic liquid or ionic gel distributed on the surface of the framework and the inner walls of the pores retains a large number of compressible pores in a partially filled manner. Under pressure, as the framework is compressed along its thickness direction, the pore volume inside the framework decreases, and the ionic medium attached to the surface of the framework and the inner walls of the pores undergoes spatial rearrangement, changing the ionic conductivity pathways and interface states formed between the framework and the upper and lower electrodes. When an electrical signal is applied to the upper electrode 40 and the lower electrode 20 through an external detection circuit, the electrochemical state of the electrode / ion medium interface changes accordingly with the degree of compression, thereby causing a change in the output signal of the capacitance detection structure. By detecting this change in capacitance, the magnitude and / or spatial distribution of the normal pressure can be sensed.

[0038] In summary, this invention, by setting a three-dimensional porous elastomer network skeleton with geometrically zero or near-zero Poisson's ratio deformation characteristics between the lower electrode 20 and the upper electrode 40, ensures that the in-plane lateral strain of the porous ionostatic active layer 30 under normal compression is intrinsically limited by the geometric structure. This localizes the deformation of the loading unit within the compressed region, fundamentally reducing the mechanical coupling paths between units. This deformation localization capability is inherent to the sensing layer structure itself and does not rely on external circuit compensation or algorithm correction, thus offering advantages such as fast response speed, no additional power consumption, and no increase in system complexity.

[0039] Meanwhile, this invention distributes ionic liquids or ionic gels in a non-fully filled manner within the pores, on the surface of the framework, and / or on the inner walls of the channels of a three-dimensional porous elastomer network framework. This allows the framework to retain compressible pores that can shrink under pressure, avoiding the volumetric incompressibility problem caused by complete filling. This enables the sensor to generate sufficient thickness-direction deformation in response to normal pressure. Furthermore, the ionic liquids or ionic gels distributed on the framework surface form continuous ionic conductive pathways at the electrode interfaces, ensuring that the sensor has a detectable capacitive response output. This non-fully filled distribution method gives the sensing layer both sufficient compressive deformation capability and effective interfacial response capability.

[0040] Optionally, within the range of 0% to 60% of the normal compressive strain, the ratio of the absolute value of the in-plane transverse strain to the absolute value of the normal compressive strain of the porous ionized active layer is not greater than 0.15.

[0041] By limiting the ratio to no more than 0.15, this invention ensures that the sensing layer maintains extremely low lateral deformation even under large normal compressive strain, thus guaranteeing the localization of deformation of the loaded units in the array from a mechanical perspective.

[0042] In some embodiments, the value is preferably no greater than 0.10, more preferably no greater than 0.05; or its equivalent Poisson ratio is -0.10 to 0.15, preferably -0.05 to 0.10.

[0043] Optionally, the three-dimensional porous elastomer network framework includes one or more of the following: a back-in honeycomb structure, a paper-cut lattice structure, a star-shaped hinge structure, a paper-folding cell structure, a rotating unit structure, a cross-shaped connecting hole array structure, an open-pore foam or an open-pore sponge three-dimensional connected network structure.

[0044] Optionally, the material of the three-dimensional porous elastomer network skeleton includes one or more of PDMS, Ecoflex, TPU, PU, ​​silicone rubber, natural rubber, and polyolefin elastomers, or the material of the three-dimensional porous elastomer network skeleton is one of open-cell polyurethane foam, open-cell silicone rubber foam, and open-cell TPU foam.

[0045] The following are examples illustrating several applications of the three-dimensional porous elastomer network framework material of this application:

[0046] Application 1: Geometric zero Poisson's ratio porous ionized active layer based on open-pore PU foam.

[0047] Please see Figure 3 This embodiment provides a geometrically zero Poisson's ratio porous ionostatic active layer based on open-cell PU foam. Open-cell PU foam with a thickness of 0.05 mm to 3 mm, a porosity of 60% to 95%, and an average pore size of 2 μm to 200 μm is selected as the three-dimensional porous elastomer network framework. After undergoing 1% to 70% pre-compression cycling, the foam exhibits near-zero Poisson's ratio or low transverse strain characteristics within the 0% to 50% normal compressive strain range.

[0048] The wetting and adhesion of ionic liquids to the PU foam skeleton surface are improved by plasma treatment, mild chemical roughening, or solvent swelling-drying treatment. Subsequently, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, quaternary ammonium salt ionic liquids, or mixtures thereof, are introduced using quantitative dripping and vacuum-assisted permeation. After impregnation, excess free liquid is removed by rolling, centrifugation, or absorbent paper, ensuring that the ionic liquid is mainly distributed on the foam skeleton surface and within the interconnecting channels, rather than completely filling the channels. The preferred ionic liquid loading is 10%–80% of the skeleton mass.

[0049] A geometrically zero Poisson's ratio porous electrolytic active layer is placed between upper and lower flexible electrodes. The electrode materials can be copper foil, metal nanowire films, carbon nanotube films, graphene films, conductive fabrics, or liquid metal electrodes. A flexible substrate of PI, PET, TPU, PDMS, or Ecoflex is respectively placed on the outer side of the upper and lower electrodes, and an elastic encapsulation layer is placed at the edge to obtain a capacitive flexible pressure sensor.

[0050] The working principle of the sensor is as follows Figure 2 As shown, when external pressure is applied to the upper electrode 40, the porous ionized active layer 30 is mainly compressed along the thickness direction, the volume of the connecting channels decreases, the skeleton beams and skeleton nodes undergo local bending and rearrangement, the equivalent distance between electrodes decreases, and at the same time, the electric bilayer structure formed by the ionic liquid at the interface of the upper electrode 40 / ionic liquid and the interface of the lower electrode 20 / ionic liquid is reconstructed (positive ions 301 and negative ions 302), the interface polarization is enhanced, thereby causing a change in the overall capacitance value of the sensor.

[0051] Because the three-dimensional porous elastomer network skeleton exhibits relatively small lateral strain under compression, the deformation of the locally loaded region is primarily confined to that region and does not easily propagate to adjacent regions. For the array structure, the capacitance change of the loaded element is significantly greater than the erroneous response of adjacent elements, thus achieving detection with no or extremely low crosstalk.

[0052] Application 2: Capacitive flexible pressure sensor based on three-dimensional honeycomb structure.

[0053] Please see Figure 4 The difference between this embodiment and Application 1 is that the three-dimensional porous elastomer network skeleton is a re-entrant honeycomb structure. First, a re-entrant honeycomb master mold is prepared by 3D printing, with a cell size of 0.01mm to 2mm, a cell wall thickness of 20μm to 500μm, and a re-entry angle of 20° to 80°; then, an elastic re-entrant honeycomb skeleton is formed by molding with PDMS, Ecoflex, TPU, PU, ​​or silicone rubber.

[0054] After introducing ionic liquids or ionic gels into the reintroduced honeycomb skeleton, the structure undergoes thickness compression through cell wall rotation, local bending, and pore compression in synergy when subjected to local pressure, thus limiting in-plane lateral deformation. This makes it suitable for fabricating high-density array-type capacitive tactile sensors.

[0055] Application 3: Capacitive flexible pressure sensor based on three-dimensional paper-cutting lattice structure.

[0056] Please see Figure 5 The difference between this embodiment and Application 1 is that the three-dimensional porous elastomer network framework adopts a paper-cut lattice structure. TPU, PDMS, Ecoflex, or silicone rubber sheets with a thickness of 50μm to 1000μm are laser-cut or die-cut to form a periodic array of slits. The slit length is 0.05mm to 5mm, and the slit spacing is 0.1mm to 3mm. After stretching, molding, or heat setting, the sheet forms a three-dimensional paper-cut lattice.

[0057] Ionic liquids or ionogels are introduced into the gaps, channels, and framework surfaces of a paper-cut lattice. Under pressure, the paper-cut lattice achieves thickness compression through beam segment rotation, local flipping, and unit cell convergence, while simultaneously reducing in-plane transverse strain propagation. This embodiment is suitable for low-cost fabrication of large-area flexible sensing arrays using planar processing methods.

[0058] Application 4: Capacitive flexible pressure sensor based on a three-dimensional star-shaped hinge structure.

[0059] The difference between this embodiment and Application 1 is that the three-dimensional porous elastomer network framework is a star-shaped hinge structure (e.g., Figure 6 ) or origami cell structure (such as Figure 7 The origami cell is a three-dimensional network composed of multiple creases and panels. When subjected to normal compression, thickness compression is achieved through the rotation of creases and the closing of panels. The star-shaped hinge structure consists of a central node and radial beams. When subjected to normal compression, low lateral strain is achieved through the bending of beams and the coordinated rotation of nodes.

[0060] The aforementioned skeletons can all be prepared by mold replication, 3D printing molding, hot pressing folding, or elastomer casting, and ionic liquids or ionic gels can be introduced by impregnation or in-situ gelation to form a geometrically zero Poisson's ratio porous ionized active layer.

[0061] Application 5: Array crosstalk testing method.

[0062] The sensor of this invention is fabricated as a 3×3, 4×4, or higher density array. A normal pressure P is applied to one of the loading units, and the capacitance change ΔC0 of the loading unit and the maximum capacitance change ΔCa of the adjacent unloaded unit are recorded. The crosstalk coefficient K is defined as K = ΔCa / ΔC0 × 100%. In a preferred embodiment, when the pressure is in the range of 10 Pa to 100 kPa, K is not greater than 20%; more preferably not greater than 10%; and even more preferably not greater than 5%.

[0063] Under the same conditions, ordinary porous ionized layers that do not employ a geometrically zero or near-zero Poisson's ratio framework are more prone to lateral deformation propagation under localized pressure, and their adjacent unit error responses are significantly increased (e.g., Figure 8 (As shown).

[0064] Optionally, the three-dimensional porous elastomer network framework includes periodically or quasi-periodically repeating cell cells with a cell size of 0.01 mm to 2 mm, a cell wall thickness of 20 μm to 1000 μm, an average pore size of 5 μm to 1000 μm, and a porosity of 30% to 95%.

[0065] Among them, cell size refers to the characteristic length of a single repeating unit, which determines the deformation unit scale of the skeleton; cell wall thickness refers to the cross-sectional thickness of the beams or walls that make up the cell, which directly affects the bending stiffness and buckling critical load of a single cell; average pore size refers to the characteristic size of the pores inside the skeleton, which affects the wetting depth and distribution uniformity of the ionic liquid; porosity refers to the proportion of pore volume to the total volume of the skeleton, which determines the overall compressibility and compression stroke of the skeleton.

[0066] If the cell size is too large or the cell wall is too thin, the stiffness of individual cells is insufficient, and the skeleton is prone to non-uniform buckling or even collapse under normal compression, losing its intrinsic deformation mode of geometric zero Poisson's ratio. If the cell size is too small or the cell wall is too thick, the overall stiffness of the skeleton is too large, making it difficult to generate sufficient normal compressive strain within the normal pressure range, resulting in a significant decrease in sensor sensitivity. If the porosity is below 30%, the compressible space of the skeleton is insufficient, limiting the normal compression stroke. If the porosity is above 95%, the skeleton structure is too sparse, lacking mechanical integrity, and prone to irreversible plastic deformation after repeated compression. This invention, through the above parameter combination, ensures that the skeleton has sufficient porosity for compression while its cell structure is large enough to exert a geometric zero Poisson's ratio deformation constraint at the microscopic level, enabling the sensing layer to simultaneously meet the dual requirements of normal compressive sensitivity and in-plane lateral deformation suppression.

[0067] Optionally, the mass loading of the ionic liquid or ionic gel is 5% to 80% of the mass of the three-dimensional porous elastomer network skeleton.

[0068] The mass loading ratio of the ionic liquid or ionic gel to the mass of the three-dimensional porous elastomer network framework is a quantitative indicator of the degree of incomplete filling. A loading range of 5% to 80% ensures that the ionic medium is predominantly surface-attached within the framework, while retaining pores. This loading range also ensures that sufficient ionic medium forms continuous ionic conductive pathways on the framework surface and pore walls, while still preserving enough compressible pores to allow for significant thickness deformation under normal pressure. This optimizes the structural synergy between the deformation localization function of the "geometrically zero Poisson's ratio framework" and the "interfacial capacitance response function of the incompletely filled ionic medium."

[0069] Optionally, the skeleton beams, skeleton nodes, and / or the inner walls of the pores of the three-dimensional porous elastomer network skeleton have surface microstructures.

[0070] Surface microstructures include one or more of the following: surface roughness structures, microprotrusions, microgrooves, micropits, or micropores.

[0071] Surface roughness refers to the random undulations on the surface at the nanometer to micrometer scale; micro-protrusions, micro-grooves, micro-pits, and micro-pores all refer to micrometer-level surface morphologies with certain regular shapes, which are respectively manifested as protrusions on the surface, recessed channels, circular pits, and tiny holes.

[0072] It should be noted that when introducing ionic liquids in a partially filled manner, the ionic medium adheres only to the framework surface in a thin layer rather than completely filling the pores. If the framework surface is too smooth, the ionic liquid adhering to the surface is prone to migration, coalescence, or detachment during repeated compression-rebound cycles, leading to a significant decrease in the long-term cyclic stability and output signal consistency of the sensor. By setting the aforementioned microstructures on the framework surface, the actual contact area and mechanical anchoring points between the framework and the ionic liquid are increased, ensuring that the ionic liquid is stably anchored to the framework surface during compression-release cycles, making it less prone to slippage and detachment.

[0073] Optionally, the characteristic size of the surface microstructure is 0.1 μm to 200 μm.

[0074] The range of 0.1μm to 200μm ensures that the microstructure size is much larger than the molecular-level roughness (which can provide an effective physical anchoring effect), while being much smaller than the macroscopic scale of the skeleton cell and cell wall (without destroying the overall mechanical integrity of the skeleton).

[0075] Optionally, the ionic liquid includes one or more of imidazole ionic liquids, pyridine ionic liquids, quaternary ammonium salt ionic liquids, and quaternary phosphate salt ionic liquids; the ionic gel is a gel material formed by combining an ionic liquid with a polymer network.

[0076] Optionally, the porosity of the three-dimensional porous elastomer network skeleton is gradient-distributed along the thickness direction of the skeleton, and the average pore diameter on the side adjacent to the upper electrode is greater than the average pore diameter on the side adjacent to the lower electrode.

[0077] A gradient porosity distribution along the thickness direction means that the porosity of the framework changes gradually or stepwise from one side to the other, rather than being uniformly consistent throughout the thickness direction. The average pore size on the side adjacent to the upper electrode is larger than that on the side adjacent to the lower electrode, indicating a gradient in pore size. The pressure-applied side has larger pore sizes (i.e., a more porous structure), while the support side has smaller pore sizes (i.e., a denser structure). This asymmetric pore size distribution along the thickness direction creates an asymmetry in mechanical properties.

[0078] It should be noted that the large-aperture structure on the side adjacent to the upper electrode (the side where pressure is directly applied) has lower compressive stiffness and lower critical buckling stress, preferentially deforming in the low-pressure stage. This results in a highly sensitive initial response of the sensor to weak pressure signals, effectively lowering the detection limit. As the pressure increases, the large-aperture region is gradually compressed to a certain extent, and the lower small-aperture region (with higher compressive stiffness) begins to participate in load-bearing and provide higher support stiffness, thereby delaying the mechanical saturation of the sensor and effectively widening the upper limit of pressure detection. This gradient design enables a wide-range response characteristic of high sensitivity in the low-pressure range and unsaturation in the high-pressure range for a sensing layer of the same thickness.

[0079] In addition, the large-aperture side has more open space for the distribution and migration of ionic liquids, forming a richer ionic active region at the upper electrode interface, which is beneficial to enhancing the initial capacitance response signal; while the small-aperture side has a higher specific surface area, which can carry more ionic liquids to maintain the continuity of the interface response in the high-pressure section.

[0080] It is particularly important to emphasize that this gradient pore structure is a performance optimization design based on a geometric zero Poisson's ratio skeleton. The gradient change only occurs along the thickness direction and does not change the topological configuration of the skeleton. Therefore, the zero Poisson's ratio deformation characteristics in the skeleton plane are not affected. While the sensor achieves optimized sensitivity, it still retains the in-plane lateral deformation suppression and low crosstalk characteristics brought by the geometric zero Poisson's ratio skeleton.

[0081] Optionally, the cell size and / or cell wall thickness of the three-dimensional porous elastomer network skeleton exhibit a non-uniform gradient distribution in the in-plane direction and / or thickness direction.

[0082] Specifically, the skeleton is divided into multiple regions in the in-plane direction, and the cell size and / or cell wall thickness of different regions are different, so that the skeleton has different compressive stiffness in different regions in the in-plane; and / or the cell size and / or cell wall thickness of the skeleton changes continuously or stepwise from one side to the other along the thickness direction.

[0083] Preferably, the cell size of the skeleton gradually increases from the central region to the edge region, giving the central region a higher cell density and compressive stiffness, and the edge region a lower cell density and compressive stiffness; and / or the cell wall thickness of the skeleton gradually increases from the pressure application side to the support side, making the cell wall on the pressure application side thinner and easier to deform under low pressure, and the cell wall on the support side thicker and providing support under high pressure. The gradient distribution is achieved by adjusting the printing parameters layer by layer during the 3D printing process, or by gradient template casting, or by spatial modulation of laser processing parameters.

[0084] This embodiment introduces cellular structural parameters with spatial gradient distribution into a single skeleton, thereby achieving differentiated response behavior of the sensor at different spatial locations and under different pressure ranges, effectively extending the sensor's measurement range and improving its linearity across the entire range.

[0085] Specifically, the in-plane regional gradient design allows the local stiffness of the pressure-bearing area to determine the sensitivity of the point when the sensor is subjected to localized point pressure. The small-cell, high-stiffness structure in the central region provides a stable capacitive response under high pressure, while the large-cell, low-stiffness structure in the edge region provides a high-sensitivity response under low pressure. This enables the same sensor to adapt to different pressure amplitudes at different spatial locations, making it particularly suitable for tactile sensing scenarios with uneven pressure distribution. The thickness gradient design achieves a layer-by-layer deformation mechanical response mode: the thin-walled cells on the pressure-applied side preferentially undergo elastic buckling and contraction under low pressure, providing a high-sensitivity initial capacitive response; as the pressure increases, the deformation is gradually transmitted to the lower layers, with the thick-walled cells successively participating in load-bearing and providing gradually increasing support stiffness. This keeps the sensor's capacitance-pressure curve approximately linear across the entire range, avoiding the nonlinear response characteristics of steep low-pressure sections and saturated high-pressure sections common in uniform structures, and significantly simplifying the design of the signal processing circuit. This gradient design is a further structural optimization based on a geometric zero Poisson's ratio skeleton. The gradient change does not change the topological symmetry of the skeleton, and the zero Poisson's ratio deformation characteristics and low crosstalk properties of the skeleton in the plane are fully preserved.

[0086] Optionally, when the capacitive flexible pressure sensor 100 in this invention is an array sensor, the porous ionized active layer 30 with a geometric zero Poisson's ratio structure confines the deformation of the loaded unit mainly to the pressure area and reduces the capacitive false response of adjacent unloaded units.

[0087] Preferably, the crosstalk coefficient of adjacent unloaded units is no greater than 20% of the output signal of the loaded unit, more preferably no greater than 10%, and even more preferably no greater than 5%; the crosstalk coefficient is the ratio of the maximum capacitance change of adjacent unloaded units to the capacitance change of the loaded unit.

[0088] The following describes the fabrication method of the capacitive flexible pressure sensor 100 provided by the present invention, including the following steps:

[0089] S1, Prepare or select a three-dimensional porous elastomer network framework.

[0090] A three-dimensional porous elastomer network skeleton with geometric zero Poisson's ratio or near-zero Poisson's ratio can be obtained through 3D printing, template casting, mold replication, laser cutting-expansion molding, hot pressing and folding, phase separation foaming, salt grain template foaming, freeze drying, or by directly selecting open-pore foam / sponge.

[0091] S2, adjusts the pore structure and transverse strain characteristics of the skeleton.

[0092] The three-dimensional porous elastomer network skeleton is cut, pre-compressed, heat-set, swelled and dried, surface roughened or plasma-treated to make it exhibit geometric zero Poisson's ratio or near-zero Poisson's ratio deformation within a predetermined compressive strain range, and to improve the adhesion stability of ionic liquids or ionic gels.

[0093] S3, introduce ionic liquids or ionic gels.

[0094] Ionic liquids or ionic gels are introduced into a three-dimensional porous elastomer network framework by means of quantitative dripping, natural wetting, vacuum-assisted permeation, pre-compression-rebound adsorption, scraping, rolling, centrifugation-assisted removal, or in-situ gelation. Excess free ionic liquids or ionic gels are removed and distributed in the pores, framework surface, and / or pore inner walls, while retaining some compressible pores.

[0095] S4, Assemble the sensor.

[0096] The resulting geometrically zero Poisson's ratio porous ionized active layer is placed on the lower electrode and then covered with the upper electrode. If necessary, an elastic encapsulation layer or barrier layer is placed on the edge or outer surface of the device to obtain a capacitive flexible pressure sensor.

[0097] In this invention, the provided capacitive flexible pressure sensor 100 can be used for robotic electronic skin, flexible tactile arrays, intelligent grasping, human-computer interaction interfaces, wearable health monitoring, pressure distribution detection, or low crosstalk tactile imaging.

[0098] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0099] 1. This invention combines a three-dimensional porous elastomer network framework with a geometric zero or near-zero Poisson's ratio with an ionic liquid or ionic gel, which can both suppress the propagation of in-plane transverse strain under local pressure and generate a high capacitance response by utilizing the ionized interface.

[0100] 2. By defining the transverse strain ratio, equivalent Poisson's ratio, porosity, pore size, cell size, ion dielectric loading, and incomplete filling state, the present invention provides a more defined structural feature and verifiable performance boundary, which helps to distinguish it from ordinary zero Poisson's ratio dielectric layers and ordinary porous composite dielectric layers.

[0101] 3. The porous ionotropic active layer of the present invention retains interconnected compressible pores, which can simultaneously generate thickness compression, electrode spacing change, contact area change, electric bilayer reconstruction and interface polarization change under pressure, thus possessing high sensitivity, low detection limit and good cycle stability.

[0102] 4. This invention can be prepared using open-pore foam, elastomer template, paper-cut lattice, or folding structure or 3D printing mold making, etc., without relying on complex micro-nano processing technology, and is suitable for large-area preparation of flexible tactile arrays and robotic electronic skin.

[0103] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure, characterized in that, include: A lower flexible substrate, a lower electrode disposed on the lower flexible substrate, a porous ionization active layer, an upper flexible substrate, and an upper electrode disposed on the upper flexible substrate; The porous ionized active layer includes a three-dimensional porous elastomer network framework and ionic liquids or ionic gels distributed inside the pores, on the surface of the framework and / or on the inner walls of the channels of the three-dimensional porous elastomer network framework. The three-dimensional porous elastomer network skeleton has geometric zero Poisson's ratio or near-zero Poisson's ratio deformation characteristics; The ionic liquid or ionic gel is distributed in the three-dimensional porous elastomer network framework in a non-completely filled manner.

2. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, Within the normal compressive strain range of 0% to 60%, the ratio of the absolute value of the in-plane transverse strain to the absolute value of the normal compressive strain of the porous ionized active layer is no greater than 0.

15.

3. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, The three-dimensional porous elastomer network framework includes: It can be one or more of the following: honeycomb structure, paper-cut lattice structure, star hinge structure, origami cell structure, rotating unit structure, cross-connecting hole array structure, open-pore foam or open-pore sponge three-dimensional connected network structure.

4. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, The three-dimensional porous elastomer network framework comprises periodically or quasi-periodically repeating cells with a cell size of 0.01 mm to 2 mm, a cell wall thickness of 20 μm to 1000 μm, an average pore size of 5 μm to 1000 μm, and a porosity of 30% to 95%.

5. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, The mass loading of the ionic liquid or ionic gel is 5% to 80% of the mass of the three-dimensional porous elastomer network skeleton.

6. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, The skeleton beams, skeleton nodes and / or inner walls of the pores of the three-dimensional porous elastomer network skeleton have surface microstructures. The surface microstructure includes one or more of the following: surface roughness structure, micro-protrusion, micro-groove, micro-pit or micro-pore structure.

7. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 6, characterized in that, The characteristic size of the surface microstructure is 0.1 μm to 200 μm.

8. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, The material of the three-dimensional porous elastomer network skeleton includes one or more of PDMS, Ecoflex, TPU, PU, ​​silicone rubber, natural rubber, and polyolefin elastomers, or the material of the three-dimensional porous elastomer network skeleton is one of open-cell polyurethane foam, open-cell silicone rubber foam, and open-cell TPU foam.

9. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 1, characterized in that, The ionic liquid includes one or more of imidazole ionic liquids, pyridine ionic liquids, quaternary ammonium salt ionic liquids, and quaternary phosphate salt ionic liquids; The ionic gel is a gel material formed by combining the ionic liquid with a polymer network.

10. The capacitive flexible pressure sensor based on a geometrically zero Poisson's ratio structure as described in claim 9, characterized in that, The ionic liquid or ionic gel is introduced into the three-dimensional porous elastomer network skeleton through quantitative dripping, natural wetting, vacuum-assisted permeation, pre-compression-rebound adsorption, scraping, rolling, centrifugation-assisted removal, or in-situ gelation.

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