Three-dimensional flexible sensing structure and preparation method and application thereof
By designing a three-dimensional flexible sensing structure on a flexible substrate and utilizing the difference in electrical signals between the flexible square pillars and the conductive electrode pairs, the problem that existing flexible strain sensors cannot distinguish the strain direction is solved, and low-cost, high-efficiency strain measurement is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV OF TECH
- Filing Date
- 2024-10-12
- Publication Date
- 2026-07-21
Smart Images
Figure CN119509330B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sensors and detection instruments, specifically relating to a three-dimensional flexible sensing structure capable of measuring strain direction and strain magnitude, its preparation method, and its application. Background Technology
[0002] Flexible strain sensors, with their advantages of high sensitivity, high resolution, lightweight, and low cost, have become indispensable components in IoT and AI data acquisition systems, with applications spanning human-machine interfaces, medical diagnostics, and intelligent sensing. Common flexible strain sensors are composites of nano-assembled sensitive elements and elastic polymer substrates. The responsiveness of these sensitive materials depends on the changes in the intrinsic electronic transport of the sensitive elements caused by deformation under external mechanical stimulation. Since mechanical stimulation in every direction triggers an intrinsic deformation in the sensing material, most flexible strain sensors are almost unable to identify the strain direction. Therefore, these strain sensors are limited to situations with a clearly defined loading direction and are easily interfered with by additional mechanical stimulation in different directions. A small number of designs have used size-anisotropic sensitive materials to construct flexible strain sensors. These devices are sensitive only to strain signals along a single axis, thus effectively distinguishing the specific direction of strain. However, these sensitive designs not only require size anisotropy in the sensitive material but also exhibit poor directional selectivity. Furthermore, their fabrication relies on complex techniques such as electrospinning and directional photolithography, thus limiting the breadth of material selection and increasing manufacturing costs. Therefore, how to develop a flexible sensor with simple structure, low cost, excellent performance, and the ability to simultaneously measure strain direction and strain magnitude remains a pressing problem in the field of flexible sensing. Summary of the Invention
[0003] To address the technical limitation of existing flexible strain sensors in accurately detecting strain direction, this invention provides a three-dimensional flexible sensing structure capable of measuring both strain direction and magnitude, along with its fabrication method and applications. In this invention, when a flexible substrate is subjected to mechanical tensile loads in different directions, the three-dimensional frustum structure on the substrate provides additional shear strain constraint, converting the mechanical tensile load into a localized strain distribution on the substrate surface. These locally distributed strains induce varying amplitudes of response strain in the electrical signals of strain-sensitive materials at different locations on the flexible substrate surface. By synthesizing the response differences of the sensitive materials at various locations, the magnitude and direction of the strain acting on the flexible substrate surface can be accurately analyzed, thus solving the technical challenge of traditional strain sensors being unable to distinguish strain direction.
[0004] The technical solution adopted in this invention is as follows: A three-dimensional flexible sensing structure capable of measuring strain direction and strain magnitude includes a three-dimensional flexible substrate, a pair of flexible conductive electrodes, a strain-sensitive material, wires, and an external circuit for measuring resistance. The three-dimensional flexible substrate is formed by an array of multiple equally spaced flexible square pillars distributed on one side of the flexible film. Multiple sets of electrode units are disposed on the flexible thin film surface around the flexible square column. Each set of electrode units includes flexible conductive electrode pairs distributed on the surface of the flexible thin film. Flexible strain-sensitive materials are assembled and embedded on the flexible thin film in the region where each flexible conductive electrode pair is located. Each flexible conductive electrode pair is connected to an external circuit for resistance measurement by means of wires to form a strain response unit, thereby forming a flexible directional strain sensing array.
[0005] Furthermore, the thickness of the three-dimensional flexible substrate is 0.05-0.1 mm, the elastic modulus is 0.1-4000 MPa, the shear modulus is 0.1-10 GPa, and the material is a polymer material. The flexible square pillars are arranged in a horizontal and vertical row at uniform intervals on the flexible film. The base of the flexible square pillar is rectangular or square, with a side length of 0.5 mm to 10 mm. The height of the flexible square pillar is 0.5 mm to 5 mm. The ratio between the distance between two adjacent flexible square pillars and the side length of the base of the flexible square pillar is 0.2 to 5:1. The polymeric material includes polydimethylsiloxane (PDMS), polyimide (PI), or polyurethane (PU), and the flexible square pillars on the flexible film are prepared by three-dimensional printing or template curing.
[0006] Furthermore, flexible conductive electrodes are arranged around the periphery of the flexible square pillar, with a thickness of 50-500 nm, and are made of gold, silver, copper, iron, aluminum or indium tin oxide. The conductive electrodes are printed on the three-dimensional flexible substrate, and the preparation method can be inkjet printing, screen printing, flexible printing, magnetron sputtering or electron beam thermal evaporation coating.
[0007] Furthermore, the strain-sensitive material exhibits either an ordered or disordered microstructure, with a resistivity ranging from 1 to 10. 6 Between Ω, it is composed of flexible conductive nanostructures, which can include metal nanoparticles, magnetic nanowires, carbon nanotubes, graphene, PVDF, chitosan or conductive ink. Strain-sensitive materials are covered on the surface of the flexible conductive electrode pair and the flexible film in its region. The preparation method is physical vapor deposition, electrospinning or chemical liquid phase synthesis.
[0008] Furthermore, the wire diameter is 10-100 μm, including acetal enameled wire, polyester enameled wire, or polyurethane enameled wire.
[0009] Furthermore, the resistance measurement external circuit has a sampling frequency of 1-2000 Hz and a resistance sampling range of 1-10 Hz. 8 Ω.
[0010] The method for fabricating a three-dimensional flexible sensing structure capable of measuring strain direction and magnitude includes the following steps: Step A: Select a polymer film for preparing a three-dimensional flexible substrate, ensuring its surface is smooth, clean, and free of obvious scratches; Step B: Bond multiple flexible square pillars of the same material in a uniformly spaced horizontal and vertical arrangement to one side of the polymer film, and distribute an array of multiple equally spaced flexible square pillars on one side of the flexible film to form the three-dimensional flexible substrate. Step C: Print flexible conductive electrode pairs on the surface of the polymer film, which serves as a three-dimensional flexible substrate, along the periphery near the flexible square pillars. The printing methods include inkjet printing, screen printing, magnetron sputtering, flexible printing, photolithography, or electron beam thermal evaporation. The materials used are metals such as gold, silver, copper, iron, aluminum, or indium tin oxide. Step D: Add a strain-sensitive material with a certain coverage to the polymer thin film in the area where the flexible conductive electrode is located. The material can be selected from metal nanoparticles, magnetic nanowires, carbon nanotubes (CNTs), graphene, PVDF, chitosan, or conductive ink by physical vapor deposition, electrospinning, or chemical liquid phase synthesis. Step E: After the strain-sensitive material is deposited, connect the flexible conductive electrode pair to the input terminal of the resistance measurement external circuit with a wire, and confirm that the connection is normal.
[0011] Furthermore, the three-dimensional flexible sensing structure can measure the strain direction and magnitude. A strain response unit in a certain direction is considered a transverse response unit, and those perpendicular to the transverse response units can be classified as longitudinal response units. When tensile strain is applied to the three-dimensional flexible substrate along the transverse strain units, the flexible truncated beams provide additional shear strain resistance, hindering the deformation of the film below the flexible truncated beams. This localizes the strain to the position of the transverse response units between the flexible truncated beams, while the longitudinal response units generate almost no strain. Based on the differential comparison of the electrical signals between the transverse and longitudinal response units, synchronous measurement of the strain magnitude and direction in the plane can be achieved. Applying tensile strain in the longitudinal direction results in the opposite strain distribution on the flexible film.
[0012] Furthermore, the three-dimensional flexible substrate of the three-dimensional flexible sensing structure is fixed in a stretchable stepper motor device. The relative resistance changes of the flexible conductive electrode pairs and strain-sensitive materials of the transverse and longitudinal response units on the surface of the three-dimensional flexible substrate are measured under different strain rates. The resistance change rate-strain rate curve is plotted, where the vertical axis represents the resistance change rate ΔR / R0 of the flexible conductive electrode pairs and strain-sensitive materials, R0 is the resistance of the flexible conductive electrode pairs and strain-sensitive materials in the original state, and ΔR is the difference between the resistance of the flexible conductive electrode pairs and strain-sensitive materials in the stretched state and the resistance in the original state; the horizontal axis represents the strain rate of the flexible film of the three-dimensional flexible substrate. A linear regression curve is plotted based on the vertical and horizontal axes. By calculating the slope of the linear regression curve, the sensitivity coefficient GF of the flexible conductive electrode pairs and strain-sensitive materials to strain can be obtained and input into the resistance measurement external circuit to realize the calibration of the three-dimensional flexible sensing structure to strain and the differentiation of different strain directions.
[0013] Furthermore, the three-dimensional flexible sensing structure is applied in motion monitoring, machine operation, voice recognition, or rehabilitation training.
[0014] The beneficial effects achieved by this invention are as follows: 1) Through a simple three-dimensional sensing structure design, strain can be simultaneously measured for both the direction and magnitude of strain in traditional isotropic flexible strain-sensing materials, demonstrating high versatility. This invention utilizes flexible frustums to induce non-uniformity in the strain distribution within the film plane during strain application, thereby inducing different amplitude response signals from various strain response units. Ultimately, the direction and magnitude of the strain are determined based on these differences in response signals. This design is applicable to most strain-sensitive materials and represents a universally applicable flexible directional strain sensing solution.
[0015] 2) Flexible sensitive materials can be selected according to different needs, with high adjustability and strong designability.
[0016] 3) The assembly method is simple, the material cost is low, and it can realize large-scale industrial production.
[0017] This design proposes a strain sensing design based on a three-dimensional flexible sensitive structure. Strain is controlled by designing cylinders of varying sizes, numbers, and spacing to construct a sensor capable of sensing and distinguishing strain direction. These three-dimensional structures are often assembled on the surface of a substrate capable of significant deformation. The deformation of the substrate causes changes in the resistance of the strain-sensitive material at different locations around the cylinders, thereby enabling the measurement of strain occurring on the substrate, as well as micro-forces and pressures applied to the substrate. Based on this, the applicant has invented a three-dimensional flexible sensing structure design and application capable of measuring strain direction and magnitude. This design utilizes a sensing element on a three-dimensional flexible substrate to provide a resistive response to strain induced by tension. The design incorporates a three-dimensional flexible truss structure on a solidified, flat, thin flexible substrate. Strain response units in a certain direction are considered transverse response units, while units perpendicular to the transverse response units are classified as longitudinal response units. When tensile strain is applied to the three-dimensional flexible substrate along the transverse strain units, the flexible trusses provide additional shear strain, hindering film deformation below the trusses and localizing the strain at the transverse response unit positions between the trusses, while the longitudinal response unit positions generate almost no strain. Applying tensile strain in the longitudinal direction results in the opposite strain distribution on the flexible film. By comparing the differential electrical signals between the transverse and longitudinal response units, simultaneous measurement of the magnitude and direction of strain in the plane can be achieved. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the design and application of a three-dimensional flexible sensing structure capable of measuring strain direction and magnitude according to the present invention: 1. Three-dimensional flexible substrate; 2. Electrode; 3. Strain-sensitive material; 4. Wire; 5. External circuit for resistance measurement.
[0019] Figure 2 These are the corresponding curves of strain change, which are parallel to and perpendicular to the tensile direction, respectively, as described in this invention.
[0020] Figure 3 These are the repeated test curves of the design described in this invention under different strain rates.
[0021] Figure 4 This is the real-time response curve of the design described in this invention during human joint activity. Detailed Implementation
[0022] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0023] Example 1: A flexible sensor with a three-dimensional frustum structure capable of measuring strain direction and magnitude was fabricated. The fabrication steps are as follows: 1) A flexible polymer film is used as a three-dimensional flexible substrate 1. The selected film is a PDMS film with a thickness of 0.5 mm, an elastic modulus of 3 MPa, and a clean, smooth surface without obvious scratches. 2) Multiple flexible square pillars of the same material, arranged in a uniformly spaced horizontal and vertical row, are cured and bonded to the upper surface of the three-dimensional flexible substrate 1. The flexible square pillars are made of PDMS with an elastic modulus of 3 MPa and a height of 1 mm. The base of each flexible square pillar is a square with a side length of 8 mm, and the distance between two adjacent flexible square pillars is 20 mm. (Comparison) Figure 1 In the middle, nine flexible square pillars are solidified and bonded to the upper surface of the three-dimensional flexible substrate 1, arranged in a horizontal and vertical pattern of three pillars.
[0024] 3) Print flexible conductive electrode pairs 2 on the upper surface of the three-dimensional flexible substrate 1 at corresponding positions near the periphery of the flexible square pillars, for comparison. Figure 1 In the middle, four flexible conductive electrode pairs are printed around the four sides of the flexible square column.
[0025] The flexible conductive electrode pair 2 used is an interdigitated electrode with an electrode gap of 0.2 mm. It is prepared by vacuum mask evaporation process. The electrode material is silver with a thickness of 400 nm and an electrode resistance of 10 Ω. Each pair of interdigitated electrodes is insulated from each other. 4) A strain-sensitive material 3 with the same coverage should be added to the surface of the three-dimensional flexible substrate in the region where each flexible conductive electrode 2 is located. The strain-sensitive material 3 is a Pd nanoparticle lattice, and the deposition process used is nanocluster beam deposition. Atoms generated by sputtering on a 99.999% pure palladium target are nucleated and grown into palladium clusters after colliding with a buffer gas, and then deposited between the interdigitated electrodes. The particle size of the deposited nanoclusters is controlled at 3-5 nm, with a coverage of 70% in the region where the two conductive electrodes 2 are located, and a resistance of 10 ohms. 6 Ω.
[0026] 5) The three-dimensional flexible substrate 1, after the Pd nanocluster lattice is deposited, is placed in an atmospheric pressure environment, and the flexible conductive electrode pairs 2 and the input terminal of the resistance measurement external circuit 5 are connected one by one by wires 4 (the wires 4 are enameled wires).
[0027] 6) Place the three-dimensional flexible substrate 1, which is connected to the wire 4 and the resistance measurement external circuit 5, in an environment with normal temperature and pressure. Fix the three-dimensional flexible substrate 1 in a stretchable stepper motor device. Change the stretching distance of the stepper motor through the LabVIEW program, and then test the corresponding response behavior of the flexible conductive electrode pair 2 and the strain-sensitive material 3 in the strain rate range of 0-5%. Take the stretching direction as the parallel stretching direction, and the direction perpendicular to the parallel stretching direction is the vertical stretching direction.
[0028] By applying a tensile force parallel to the tensile direction to a three-dimensional flexible substrate 1, the strain rate of the PDMS film on the three-dimensional flexible substrate 1 is kept within the strain rate range of 0-5%. The relative resistance changes of the flexible conductive electrode pair 2 and the strain-sensitive material 3 on the surface of the three-dimensional flexible substrate 1 in the parallel and perpendicular tensile directions are measured at different strain rates, and the resistance change rate-strain rate curves are plotted. The results are as follows: Figure 2 As shown in the figure, the relative resistance change curves of the flexible conductive electrode pair 2 and the strain-sensitive material 3 on the surface of the three-dimensional flexible substrate 1 are parallel and perpendicular to the stretching direction, respectively. The horizontal axis is the strain rate of the PDMS film strain, and the vertical axis is the rate of change of the resistance of the conductive electrode 2 and the strain-sensitive material 3. A linear regression curve is plotted based on the vertical and horizontal axes, and the sensitivity coefficient GF to strain is obtained by calculating the slope of the linear regression curve.
[0029] Sensitivity coefficient at Figure 2 The slope of the linear regression curve of the resistance-strain curve, denoted by GF, can be seen in the strain curve. The larger the value, the higher the sensitivity within that strain range.
[0030] 7) Place the three-dimensional flexible substrate 1, with the wires 4 and the external resistance measurement circuit 5 connected, in a normal temperature and pressure environment. Fix the three-dimensional flexible substrate 1 in a stretchable stepper motor device. Change the stretching distance of the stepper motor using LabVIEW program, and test the corresponding repetitive response behavior of the flexible conductive electrode 2 and the strain-sensitive material 3 at strain rates of 0.1%, 0.2%, 0.5%, 0.8%, and 1%, respectively. Plot the resistance change rate curve as shown in the figure. Figure 3 As shown.
[0031] Figure 3 One peak represents the tensile recovery, indicating the number of times the measuring device records the sample's electrical signal value under tensile stress.
[0032] Example 2: This example tests the ability of the flexible sensor prepared in Example 1 to monitor the magnitude and direction of strain in real time. During the test, the maximum length reached by the sensor without being stretched was used as the initial value, and the current in the flexible conductive electrode pair 2 and the strain-sensitive material 3 in this state was taken as the initial current I0. Subsequently, the sensor was placed on the skin at a human joint connection, and by repeatedly performing joint bending movements of different amplitudes and directions, the magnitude and direction of strain were changed from the initial state. Figure 4The changes in the sensor's output signal were recorded when the sensor sample was attached to the wrist and the wrist joint was swung downwards. It was found that during the wrist swing, the strain caused by the joint movement was concentrated in one direction, resulting in a significant change in the electrode signal parallel to that direction, while the signal change in the other direction was not obvious. This indicates that the design has a distinguishing effect on the strain direction. Furthermore, the degree of wrist flexion also directly affects the amplitude of the electrode signal change. The greater the degree of flexion, the greater the tensile strain of the sensor. Therefore, the magnitude of the strain can be determined based on the amplitude of the electrical signal change.
[0033] The above experiments demonstrate that the design of this invention can simultaneously measure the strain direction and strain magnitude.
[0034] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.
Claims
1. An application of a three-dimensional flexible sensing structure, characterized in that... The three-dimensional flexible sensing structure includes a three-dimensional flexible substrate (1), a pair of flexible conductive electrodes (2), a strain-sensitive material (3), a wire (4), and a resistance measurement external circuit (5). An array of multiple equally spaced flexible square pillars is distributed on one side of the flexible film to form the three-dimensional flexible substrate (1). Multiple sets of electrode units are provided on the flexible film surface around the flexible square column. Each set of electrode units includes flexible conductive electrode pairs (2) distributed on the surface of the flexible film. Flexible strain-sensitive material (3) is assembled and embedded on the flexible film in the area where each flexible conductive electrode pair (2) is located. Each flexible conductive electrode pair (2) is connected to the resistance measurement external circuit (5) by wires (4) to form a strain response unit, thereby forming a flexible directional strain sensing array. The flexible square pillars are arranged in a horizontal and vertical row at uniform intervals on the flexible film. The base of the flexible square pillar is rectangular or square, with a side length of 0.5 mm to 10 mm. The height of the flexible square pillar is 0.5 mm to 5 mm. The ratio between the distance between two adjacent flexible square pillars and the side length of the base of the flexible square pillar is 0.2 to 5:
1. The flexible conductive electrode pair (2) is arranged around the periphery of the flexible square pillar, with a thickness of 50-500nm, and is made of gold, silver, copper, iron, aluminum or indium tin oxide. The strain-sensitive material (3) described above has a microscopic state of either order or disorder, and its resistance is between 1 and 10. 6 Between Ω, it is composed of flexible conductive nanostructures, and the nanostructures can include metal nanoparticles, magnetic nanowires, carbon nanotubes, graphene, PVDF, chitosan or conductive ink. The three-dimensional flexible sensing structure can measure the strain direction and strain magnitude. The strain response unit in a certain direction is regarded as the transverse response unit, and the units perpendicular to the transverse response unit can be classified as the longitudinal response unit. When tensile strain is applied to the three-dimensional flexible substrate (1) along the transverse strain unit, the flexible square pillars will provide additional shear strain resistance, which will hinder the deformation of the film below the flexible square pillars and localize the strain to the position of the transverse response unit between the flexible square pillars. The longitudinal response unit position will hardly generate strain. According to the differential comparison of the electrical signals between the transverse and longitudinal response units, the synchronous measurement of the strain magnitude and direction in the plane can be realized. When tensile strain is applied in the longitudinal direction, the strain distribution on the flexible film is reversed.
2. The application as described in claim 1, characterized in that... The three-dimensional flexible substrate (1) has a thickness of 0.05-0.1 mm, an elastic modulus of 0.1-4000 MPa, a shear modulus of 0.1-10 GPa, and is made of a polymer material. The polymeric material includes polydimethylsiloxane (PDMS), polyimide (PI), or polyurethane (PU), and the flexible square pillars on the flexible film are prepared by three-dimensional printing or template curing.
3. The application as described in claim 1, characterized in that... Flexible conductive electrode pairs (2) are printed on a three-dimensional flexible substrate (1). The preparation method can be inkjet printing, screen printing, flexible printing, magnetron sputtering or electron beam thermal evaporation coating.
4. The application as described in claim 1, characterized in that... Strain-sensitive material (3) is covered on the surface of the flexible conductive electrode pair (2) and the flexible thin film in its region. The preparation method is physical vapor deposition, electrospinning or chemical liquid phase synthesis.
5. The application as described in claim 1, characterized in that... The conductor (4) has a diameter of 10-100 μm and includes acetal enameled wire, polyester enameled wire or polyurethane enameled wire.
6. The application as described in claim 1, characterized in that... The resistance measurement external circuit (5) has a sampling frequency of 1-2000Hz and a resistance sampling range of 1-10. 8 Ω.
7. The application as described in claim 1, characterized in that... The method for fabricating the three-dimensional flexible sensing structure includes the following steps: Step A: Select a polymer film for preparing a three-dimensional flexible substrate (1) with a smooth and clean surface and no obvious scratches; Step B: Bond multiple flexible square pillars of the same material in a uniformly spaced horizontal and vertical arrangement to one side of the polymer film, and distribute an array of multiple equally spaced flexible square pillars on one side of the flexible film to form the three-dimensional flexible substrate (1). Step C: Print flexible conductive electrode pairs (2) on the surface of the polymer film, which serves as a three-dimensional flexible substrate (1), along the periphery of the flexible square pillars. The printing methods include inkjet printing, screen printing, magnetron sputtering, flexible printing, photolithography, or electron beam thermal evaporation. The materials used are metals such as gold, silver, copper, iron, aluminum, or indium tin oxide. Step D: Add a strain-sensitive material (3) with a certain coverage to the polymer thin film in the region where the flexible conductive electrode pair (2) is located. The material is selected by physical vapor deposition, electrospinning or chemical liquid phase synthesis, such as metal nanoparticles, magnetic nanowires, carbon nanotubes (CNTs), graphene, PVDF, chitosan or conductive ink. Step E: After the strain-sensitive material (3) is deposited, connect the flexible conductive electrode pair (2) to the input terminal of the resistance measurement external circuit (5) with the wire (4) and confirm that the connection is normal.
8. The application as described in claim 1, characterized in that... The three-dimensional flexible substrate (1) of the three-dimensional flexible sensing structure is fixed in a stretchable stepper motor device. The relative resistance changes of the flexible conductive electrode pairs (2) and strain-sensitive materials (3) of the transverse and longitudinal response units on the surface of the three-dimensional flexible substrate (1) are measured under different strain rates. The resistance change rate-strain rate curve is plotted, where the vertical axis is the resistance change rate ΔR / R0 of the flexible conductive electrode pairs (2) and strain-sensitive materials (3), R0 is the resistance of the flexible conductive electrode pairs (2) and strain-sensitive materials (3) in the original state, and ΔR is the difference between the resistance of the flexible conductive electrode pairs (2) and strain-sensitive materials (3) in the stretched state and the resistance in the original state; the horizontal axis is the strain rate of the flexible film of the three-dimensional flexible substrate (1). A linear regression curve is plotted based on the vertical and horizontal axes. The sensitivity coefficient GF of the flexible conductive electrode pairs (2) and strain-sensitive materials (3) to strain can be obtained by calculating the slope of the linear regression curve and input into the resistance measurement external circuit (5) to realize the calibration of the three-dimensional flexible sensing structure to strain and the differentiation of different strain directions.
9. The application as described in claim 1, characterized in that... The three-dimensional flexible sensing structure is used in motion monitoring, machine operation, speech recognition, or rehabilitation training.