3D printing flexible capacitance pressure sensor based on negative Poisson's ratio array

Abstract

The invention discloses a 3D printing flexible capacitive pressure sensor based on a negative Poisson's ratio microstructure array, and belongs to the technical field of flexible sensing. The sensor comprises an upper bottom plate electrode, a negative Poisson's ratio microstructure array dielectric layer, a lower bottom plate electrode, a wire and an insulation packaging layer which are sequentially arranged from top to bottom. Wherein the dielectric layer is integrally formed through 3D printing and is composed of a plurality of negative Poisson's ratio array elements which are distributed in a gradient mode, and each array element comprises a spring-like sensitive unit which is concave inwards and a pressure bearing unit. The structure utilizes a negative Poisson's ratio effect to enhance shear resistance and stability, and realizes cooperation of low-voltage high sensitivity and high-voltage wide range through gradient design. The preparation method comprises the steps of modeling, printing, post-processing and packaging. The sensor has the advantages of low cost, high sensitivity, wide detection range and good cycling stability, and is suitable for the fields of electronic skin, wearable equipment, health monitoring and the like.

Description

Technical Field

[0001] This invention relates to flexible sensing technology for wearable devices, specifically to a flexible capacitive pressure sensor with a negative Poisson's ratio microstructure array as the dielectric layer. Background Technology

[0002] Flexible capacitive pressure sensors, as a type of mechanical quantity sensor, convert external pressure stimuli into readable electrical signals, playing an important role in fields such as human-machine interfaces, artificial skin, artificial intelligence, electronic skin, and smart healthcare.

[0003] However, there are still bottlenecks to overcome before flexible capacitive pressure sensors can be widely used: First, the manufacturing cost is not matched with the mass production capacity. Existing microstructured dielectric layers rely on precision processes such as photolithography and laser etching, and the cost of a single device far exceeds the cost threshold in the consumer electronics field. Second, the long-term stability is insufficient. The interface bonding between the flexible electrode and the dielectric layer is weak, and delamination is likely to occur after repeated bending or pressing cycles. Moreover, the microstructure is fragile and easily damaged and difficult to recover. Third, high sensitivity and wide detection range are often mutually exclusive. Because the traditional process uses a molding process for the dielectric layer, it is impossible to design complex microstructures.

[0004] In recent years, 3D printing technology has provided a new approach for the integrated molding of complex microstructures. We can design more tunable microstructures for sensors and explore the impact of different microstructures and their arrangements on sensor performance.

[0005] Therefore, 3D-printed capacitive pressure sensors primarily utilize 3D printing to design complex structural functions, adding ions to the complex structural medium and rare metals and carbon nanotubes to the complex structural electrodes. This allows for the design and fabrication of a pressure sensor with high sensitivity and a wide linear range. It can be used as an essential simulated electronic skin in the Internet of Things (IoT) and has certain application value in biological health monitoring and the medical field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the issues of high manufacturing cost, insufficient stability, and incompatibility between high sensitivity and wide detection range in the existing capacitive pressure sensors. The present invention provides a flexible capacitive pressure sensor that significantly reduces manufacturing cost while improving sensor stability, sensitivity, and detection range through a negative Poisson's ratio microstructure design and 3D printing integrated molding process.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is a 3D printed flexible capacitive pressure sensor based on a negative Poisson's ratio array, comprising an upper base plate electrode, a spring-like negative Poisson's ratio microstructure array dielectric layer, and a lower base plate electrode arranged sequentially from top to bottom; wires electrically connected to the upper base plate electrode and the lower base plate electrode; and an insulating encapsulation layer covering the outside;

[0008] The dielectric layer of the spring-like negative Poisson's ratio microstructure array is integrally formed by 3D printing technology and is composed of several negative Poisson's ratio array elements arranged in an array; the dielectric layer material is thermoplastic polyurethane elastomer TPU.

[0009] Each negative Poisson's ratio array element includes a sensitive component and a pressure-bearing component. The sensitive component includes four sensitive elements of the main cantilever beam. The four sensitive elements are evenly distributed around the negative Poisson's ratio array element, with the direction closer to the center of the array element as the inside and the direction farther from the center of the array element as the outside. Each sensitive element has an inwardly concave shape. When it receives downward pressure, each sensitive element slides laterally inward.

[0010] The pressure-bearing assembly comprises four pressure-bearing units, which are evenly distributed around the center of the negative Poisson's ratio unit. Each pressure-bearing unit is positioned next to a corresponding sensitive unit; it is used to provide structural support under high pressure.

[0011] Specifically, the sensitive unit is a three-dimensional structure composed of several square planes, and its side view is two vertically mirrored oblique trapezoids; the side view is mirrored with the short base of the oblique trapezoid as the axis, the short waist of the oblique trapezoid faces inward and the long waist faces outward; the connection between the two vertically mirrored oblique trapezoids is the smaller base surface, and the square base surface where the two long bases of the oblique trapezoid of the lower half of the side view are located serves as the fixed end of the main cantilever beam and is fixedly connected to the upper base plate.

[0012] This invention proposes a flexible capacitive pressure sensor with a negative Poisson's ratio microstructure array as the dielectric layer. By introducing a negative Poisson's ratio structure, the impact and shear resistance of the dielectric layer is enhanced, effectively improving the stability of the device. By introducing a spring-like structure with unequal width bending cantilever beams, the dielectric layer is made more easily deformable while maintaining excellent elasticity, exhibiting high resilience and effectively improving the device's sensitivity. By introducing a gradient structure, only the sensitive unit deforms and functions under low- and medium-pressure conditions, while under high-pressure conditions, both the pressure-bearing unit and the sensitive unit work together, allowing the dielectric layer to withstand higher pressures and effectively increasing the device's pressure detection range.

[0013] This invention also proposes a method for fabricating a 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio microstructure array.

[0014] The beneficial effects of this invention are that, through the integration of negative Poisson's ratio microstructure design and 3D printing molding process, the stability, sensitivity and detection range of the sensor are improved while the manufacturing cost is significantly reduced. It has the advantages of high sensitivity, wide detection range, obvious micro-pressure detection and easy recovery, which promotes its practical application in flexible electronics and wearable devices. Attached Figure Description

[0015] Figure 1 This is a physical image of the present invention packaged in a 3×3 array;

[0016] Figure 2 This is a schematic diagram of the overall structure of the present invention;

[0017] Figure 3 This is a graph showing the relative capacitance of the device of the present invention as a function of pressure.

[0018] Figure 4 This is a sensitivity comparison diagram of the gradient negative Poisson's ratio dielectric layer used in this invention and other microstructure dielectric layers.

[0019] Figure 5 The response curve of the device of the present invention under 8000 cycles of 10N pressure;

[0020] Figure 6 This is a graph showing the capacitor recovery of the device of the present invention under 10 cycles of 1N pressure.

[0021] Figure 7 This relates the cantilever beam angle of the device to the device sensitivity. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The negative Poisson's ratio effect refers to the phenomenon that when a material is stretched, it expands laterally within its elastic range; while when it is compressed, it contracts laterally.

[0024] like Figure 1 As shown in the figure, an embodiment provides a physical diagram of a flexible capacitive pressure sensor with a negative Poisson's ratio microstructure array as the dielectric layer, including a spring-like negative Poisson's ratio microstructure array dielectric layer, an upper base plate electrode, a lower base plate electrode, wires, and an insulating PU film encapsulation layer.

[0025] The dielectric layer material is thermoplastic polyurethane elastomer (TPU), and post-processing uses a thermosetting method. Specifically, the TPU dielectric material is Elastic 50A Flexible resin, which has good elasticity and effectively improves the sensitivity and stability of the device. Gold electrodes are used, silver wires are used, and the insulating layer is encapsulated with a medical-grade PU film.

[0026] like Figure 2 As shown, the embodiment uses SolidWorks software to model and design the printed dielectric layer structure.

[0027] The dielectric layer of the spring-like negative Poisson's ratio microstructure array is integrally formed using 3D printing technology. The dielectric layer structure consists of several negative Poisson's ratio array elements with spring-like properties arranged in an array, with the array elements arranged in a 3×3 array in the embodiment. This constitutes a dielectric layer composed of multiple spring-like units with negative Poisson's ratio properties arranged in an array. Each negative Poisson's ratio array element includes a sensitive component and a pressure-bearing component. The sensitive component includes a sensitive unit with four main cantilever beams. The dielectric layer material utilizes Elastic50A Flexible material, which has good elasticity, and the negative Poisson's ratio structure has excellent shear resistance, ensuring the structural stability of the device during cyclic pressure testing.

[0028] Four sensitive elements are evenly distributed around the negative Poisson's ratio array element, with the direction closer to the center of the array element being the inside and the direction farther from the center of the array element being the outside. Each sensitive element has an inwardly concave shape. When subjected to downward pressure, each sensitive element slides laterally inward. This is used to efficiently convert minute pressure changes into significant capacitance changes in a low-pressure range through its spring-like structure that is prone to large elastic deformation, thereby achieving high sensitivity and low detection limit of the sensor.

[0029] Specifically, the sensitive unit in this embodiment consists of 11 square planes. The side view is a three-dimensional structure of two vertically mirrored inclined trapezoids, with the short base of the inclined trapezoid serving as the mirror axis. The short legs of the inclined trapezoids face inward, and the long legs face outward. The connection between the two vertically mirrored inclined trapezoids is the smaller base surface. The square base surface containing the two long bases of the inclined trapezoid in the lower half of the side view serves as the fixed end of the main cantilever beam and is fixedly connected to the upper base plate.

[0030] Figure 2 The two sides of the slanted trapezoid in the figure are inclined to one side, which is a preferred embodiment. If the two sides of the slanted trapezoid are inclined, the invention can also be realized as long as the shorter side faces inward and the longer side faces outward.

[0031] The pressure-bearing assembly includes four pressure-bearing units, which are evenly distributed around the center of the negative Poisson's ratio unit. Each pressure-bearing unit is located next to a corresponding sensitive unit. This provides structural support under higher pressure, thereby extending the upper limit of the sensor's pressure detection and protecting the sensitive unit from overload damage.

[0032] The shape of the pressure-bearing unit can be flexibly selected according to requirements, including spherical, rectangular, and conical shapes, as long as they can provide structural support under high pressure, the purpose of this invention can be achieved. An embodiment provides an optimal design, employing the same shape as the lower half of the sensitive unit. That is, an auxiliary cantilever beam with an overall inwardly inclined trapezoidal structure. The arrangement of the auxiliary cantilever beams is consistent with that of the main cantilever beams.

[0033] The slanted trapezoidal structure used in this embodiment has the following dimensions: height 1mm, upper base width 0.2mm and length 1mm, lower base width 0.4mm and length 1mm, long waist 1.15mm, and short waist 1.07mm. The angle between the long waist and the upper base plate is 60 degrees.

[0034] Specifically, the base plate electrode is made of silver tape and is attached to the upper and lower base plates of the device to form a continuous conductive layer;

[0035] The conductor is made of silver wire with a diameter of 0.5 mm and is attached between the electrode plate and the insulation layer;

[0036] The PU film encapsulation layer is made of medical PU film tape and is attached to the surface of the electrode plate of the device to form an insulating layer.

[0037] Specifically, the dielectric layer height is 2mm, and the bottom area of ​​the dielectric layer is 1.5mm × 1.5mm.

[0038] Specifically, the thermosetting method involves curing in a hot oven at 60°C for 6 minutes.

[0039] To achieve a comprehensive improvement in sensor performance, this invention has undergone systematic optimization from the perspectives of structural design and mechanical response principles, specifically in the following two aspects:

[0040] 1. The principle of enhanced stability of negative Poisson's ratio microstructures

[0041] The negative Poisson's ratio structure used in this invention, when subjected to vertical pressure, exhibits a unique inwardly concave cantilever beam that expands laterally, thereby:

[0042] (1) Resistance to shear deformation: The structure expands in the plane, which counteracts the tendency of lateral slippage caused by pressure and enhances the bonding stability of the electrode dielectric layer interface.

[0043] (2) Dispersing impact stress: The pressure load is borne by multiple inwardly bent cantilever beams, and the stress is dispersed along the structural network through their unique geometric configuration, avoiding local plastic deformation or fracture caused by stress concentration.

[0044] (3) Improved rebound capability: The spring-like cantilever beam can quickly recover its original shape by utilizing its elastic deformation energy when unloaded, thus supporting the structural integrity during cyclic testing.

[0045] 2. Piecewise pressure response principle of gradient structures

[0046] In the dielectric layer unit of this invention, each array element adopts a design of high-sensitivity unit + low-profile pressure-bearing unit, and the mechanical stiffness of the two units is distributed in a stepped manner, with a critical pressure value Pc (determined by structural geometric parameters and material stiffness) in between:

[0047] Low pressure stage (≤ critical value Pc): Only the upper sensitive unit undergoes elastic deformation. The large deformation of its flexible cantilever beam causes a significant change in capacitance, achieving high-sensitivity detection.

[0048] High pressure stage (> critical value Pc): The deformation of the sensitive unit tends to saturate, the lower pressure-bearing unit begins to contact and participate in bearing, the overall stiffness of the structure increases, the deformation rate slows down, and the capacitance-pressure curve enters the linear flat zone, thereby expanding the detection range to higher pressures.

[0049] In summary, the introduction of negative Poisson bit characteristics primarily ensures the durability and interface stability of the device from a structural mechanics perspective, while gradient design achieves decoupling and synergistic improvement of sensitivity and detection range from a response mechanism perspective. The combination of these two, supplemented by 3D printing integrated molding technology, constitutes the core solution of this invention: a high-performance, highly stable, and low-cost flexible pressure sensor.

[0050] This example provides a method for fabricating a capacitive pressure sensor with a complex microstructure dielectric layer, including the following steps:

[0051] Step 1: Use the 3D CAD software SolidWorks to create a 3D model, construct a dielectric layer with a complex microstructure, and export it as an STL file, a standard model file format for 3D printing.

[0052] Step 2: Use the dedicated slicing software PreForm to add support to the exported STL file, and upload it to the Formlabs brand photopolymerization 3D printer for printing;

[0053] Step 3: Clean the printed device with alcohol for 10 minutes and remove the support.

[0054] Step 4: After removing the support, let the device air dry at room temperature for 30 minutes.

[0055] Step 5: After air drying, heat the components in a 60℃ oven for 6 minutes;

[0056] Step 6: Apply electrodes and perform insulating encapsulation.

[0057] like Figure 3 The diagram shows the output characteristics of a flexible capacitive pressure sensor with a gradient negative Poisson's ratio microstructure array as the dielectric layer in this embodiment. Specific parameters are as follows: Pressure detection range: 50 Pa ~ 450 kPa, minimum detection limit: 50 Pa; Sensitivity: 6.673 pF / Pa at low pressure, 0.119 pF / Pa at high pressure.

[0058] like Figure 4 As shown, the negative Poisson's ratio structure dielectric layer in the embodiment has superior sensitivity compared to other microstructure dielectric layers, and the gradient negative Poisson's ratio greatly improves the pressure detection range of the device at the cost of sacrificing sensitivity in the high-pressure range. In summary, the flexible capacitive pressure sensor with a gradient negative Poisson's ratio microstructure array as the dielectric layer provided by the present invention has the advantages of high sensitivity and a wide pressure detection range.

[0059] like Figure 5 As shown, the sensor in the embodiment underwent 8,000 cycles of pressure testing, demonstrating excellent device durability.

[0060] like Figure 6 As shown, the sensor in the embodiment was subjected to a cyclic load of 1 Newton. It can be seen that the device has good stability and the capacitance value error is extremely low in multiple experiments.

[0061] Combination Figure 5 and Figure 6 It is evident that the sensor provided by this invention, by incorporating the impact and shear resistance characteristics of the negative Poisson's ratio microstructure, greatly enhances the durability and stability of the device.

[0062] like Figure 7 As shown, the influence of the angle of the cantilever beam of the negative Poisson's ratio unit of the sensor provided by the present invention on the device sensitivity was investigated. It was concluded that the device sensitivity is optimal when the cantilever beam is at a 60° angle to the bottom surface.

Claims

1. A 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array, characterized in that, include: The components arranged from top to bottom are: an upper base plate electrode, a spring-like negative Poisson's ratio microstructure array dielectric layer, and a lower base plate electrode. Wires electrically connected to the upper and lower base plate electrodes; And the insulating encapsulation layer covering the outside; The dielectric layer of the spring-like negative Poisson's ratio microstructure array is integrally formed by 3D printing technology and is composed of several negative Poisson's ratio array elements arranged in an array; the dielectric layer material is thermoplastic polyurethane elastomer TPU. Each negative Poisson's ratio array element includes a sensitive component and a pressure-bearing component. The sensitive component includes four sensitive elements of the main cantilever beam. The four sensitive elements are evenly distributed around the negative Poisson's ratio array element, with the direction closer to the center of the array element as the inside and the direction farther from the center of the array element as the outside. Each sensitive element has an inwardly concave shape. When it receives downward pressure, each sensitive element slides laterally inward. The pressure-bearing assembly comprises four pressure-bearing units, which are evenly distributed around the center of the negative Poisson's ratio unit. Each pressure-bearing unit is positioned next to a corresponding sensitive unit; it is used to provide structural support under high pressure.

2. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 1, characterized in that, The sensitive unit is a three-dimensional structure composed of several square planes. Its side view is two vertically mirrored oblique trapezoids. The side view is mirrored with the short base of the oblique trapezoid as the axis of reflection. The short waist of the oblique trapezoid faces inward and the long waist faces outward. The connection between the two vertically mirrored oblique trapezoids is the smaller base surface. The square base surface where the two long bases of the oblique trapezoid in the lower half of the side view are located serves as the fixed end of the main cantilever beam and is fixedly connected to the upper base plate.

3. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 2, characterized in that, The angle between the long waist of the sloping trapezoidal structure and the upper base plate is 60 degrees.

4. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 3, characterized in that, The height of the inclined trapezoidal structure is 1mm, the width of its upper base is 0.2mm and the length is 1mm, the width of its lower base is 0.4mm and the length is 1mm, the length of its long waist is 1.15mm and the length of its short waist is 1.07mm.

5. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 3, characterized in that, The pressure-bearing unit uses the same structure as the lower half of the inclined trapezoidal structure of the sensitive unit located on the same side.

6. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 1, characterized in that, The dielectric layer material is made of Elastic50A Flexible resin.

7. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 1, characterized in that, The upper and lower base plate electrodes are made of silver adhesive tape; the wires are silver wires with a diameter of 0.5 mm; and the insulating encapsulation layer is medical PU film tape.

8. The 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio array as described in claim 1, characterized in that, The overall height of the dielectric layer is 2mm, and the bottom area is 1.5mm × 1.5mm.

9. The method for fabricating a 3D-printed flexible capacitive pressure sensor based on a negative Poisson's ratio microstructure array as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. 3D Modeling: Use 3D CAD software to construct a 3D model of the dielectric layer of the spring-like negative Poisson's ratio microstructure array and export it as an STL format file; S2. Printing preparation and shaping: Use slicing software to add support and slice the STL file, and import it into the photopolymer 3D printer to print, and obtain an integral dielectric layer blank. S3. Post-processing: The printed dielectric layer preform is cleaned, the support is removed, it is left to air dry and then heat-cured. S4. Assembly and packaging: Electrodes are attached to the upper and lower surfaces of the dielectric layer, wires are connected, and insulating packaging is performed to obtain the flexible capacitive pressure sensor.

10. The preparation method according to claim 10, characterized in that, The process parameters for the thermosetting treatment in step S3 are: curing at 60°C for 6 minutes in a hot oven.

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