An integrated serpentine micro-crack three-dimensional flexible vibration sensor and a preparation method thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV OF SCI & TECH
- Filing Date
- 2026-03-10
- Publication Date
- 2026-06-09
Smart Images
Figure CN122171014A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the fields of flexible sensor technology, microstructure sensing and vibration monitoring, and specifically relates to an integrated serpentine microcrack three-dimensional flexible vibration sensor and its preparation method. Background Technology
[0002] With the development of the Internet of Things, human-computer interaction, and smart wearable technologies, the demand for flexible sensors that can conform to complex curved surfaces and achieve multi-dimensional vibration sensing is increasing. Traditional vibration sensors are mostly rigid structures, which are large, difficult to bend, and hard to conform to the curved skin of the human body or robot. They are also difficult to install, have a fixed installation direction, and are difficult to achieve array-based monitoring.
[0003] In recent years, flexible strain sensors based on microcrack structures have attracted widespread attention due to their high sensitivity. Existing technologies have employed biomimetic principles to fabricate microcracks or microgroove arrays on flexible substrates to improve sensor performance. For example, one approach involves constructing a rigid-flexible composite substrate using paper, stainless steel sheets, and polymer tape, then fabricating parallel microgrooves on the surface using a femtosecond laser, followed by spraying a carbon nanotube / graphene composite conductive layer to sense vibrations. This design validates the potential of microcrack structures to enhance dynamic vibration response, enabling monitoring in the hundreds of hertz frequency range.
[0004] However, in-depth analysis of existing technical solutions reveals several inherent defects that limit their application in scenarios requiring high reliability, high sensitivity, and multi-directional sensing. Firstly, regarding structural reliability, the use of multi-layered heterogeneous materials (such as metals, plastics, and paper) bonded together with adhesives carries the risk of interface delamination failure under long-term vibration loads or humid and hot environments, severely impacting the long-term stability and lifespan of the sensor. Secondly, in terms of sensitivity, such structures typically lack effective inertial mass design, resulting in limited response amplitude to weak vibration signals and an inability to amplify them, thus limiting sensitivity. Most critically, regarding multi-dimensional sensing capabilities, existing designs output a single signal because their structure itself cannot provide multiple independent and directionally discriminative mechanical channels, thus failing to achieve three-dimensional decoupling of the vibration vector.
[0005] Therefore, there is an urgent need in this field for a new type of sensor that has inherent structural reliability, can actively amplify inertial response, and can provide a multi-channel directional information encoding mechanism, while overcoming the shortcomings of existing flexible vibration sensors in terms of structural reliability, inertial response strength, and multi-dimensional vibration sensing capabilities. Summary of the Invention
[0006] To address the above problems, the present invention aims to provide an integrated serpentine microcrack three-dimensional flexible vibration sensor and its fabrication method.
[0007] The specific technical solution for achieving the objective of this invention is as follows:
[0008] An integrated serpentine microcrack three-dimensional flexible vibration sensor includes a flexible substrate layer, a composite conductive layer, and multiple electrodes;
[0009] The composite conductive layer is disposed on the flexible substrate layer, and multiple electrodes are disposed on the composite conductive layer for connecting to the outside and extracting signals;
[0010] The flexible substrate layer is used to amplify and sense three-dimensional vibrations, and the corresponding information is converted into electrical signals through the composite conductive layer and transmitted to the outside.
[0011] Furthermore, the flexible substrate layer includes a flexible sensitive region, an inertial mass region, and a support region;
[0012] The flexible sensitive area is a cantilever beam with central symmetry, the inertial mass area is a thick area located in the center of the inner side of the cantilever beam, and the support area is a thick area located at both ends of the outer side of the cantilever beam.
[0013] The flexible sensitive region, inertial mass region, and support region are continuous without interface in the material, and their thickness varies in a gradient, decreasing sequentially from the support region, inertial mass region, and flexible sensitive region.
[0014] Furthermore, the flexible sensitive area consists of four serpentine cantilever beams arranged in a centrally symmetrical manner. Each serpentine cantilever beam includes at least two arc-shaped bending segments. The spatial curvature and orientation of these beams are designed to make the stiffness response of the four beams to vibrations in the X, Y, and Z directions anisotropic.
[0015] Furthermore, the serpentine cantilever beam is provided with a regularly arranged array of biomimetic microcracks generated by laser induction, and the composite conductive layer covers the biomimetic microcrack array;
[0016] The cracks in the biomimetic microcrack array change width when vibrated.
[0017] Furthermore, when the sensor performs vibration sensing:
[0018] The input vibration is amplified by the inertial mass region, and the three-dimensional displacement is encoded into multi-channel differentiated strain modes by the serpentine cantilever beam array in the flexible sensitive region.
[0019] The biomimetic microcrack array on the serpentine cantilever beam generates changes in crack width due to vibration, and the composite conductive layer covering it converts the strain into an electrical signal.
[0020] Finally, the complete three-dimensional vibration information was decoded from the multi-channel electrical signal using a decoupling algorithm.
[0021] Furthermore, when the sensor vibrates with a certain acceleration along with the object being measured, the inertial mass region will displace relative to the support region due to the action of inertial force.
[0022] The displacement of the inertial mass region acts on the roots of the four serpentine cantilever beams in the flexible sensitive region. Due to the different spatial orientations of each beam and the different stiffness characteristics determined by the serpentine structure, the same displacement induces different proportions of axial strain on different serpentine cantilever beams. and bending strain This allows us to obtain the three-dimensional displacement vectors of the four serpentine cantilever beams in the flexible sensitive area. coding: ;
[0023] Microcrack strain amplification and conductive network modulation: Macroscopic strain on a serpentine cantilever beam is transmitted to the microcrack region on its surface, causing a significant change in the crack width w of the V-shaped crack. This leads to a sudden change in the number of conductive pathways penetrating the crack in the composite conductive layer, resulting in a high-gain change in the overall resistance R of a single serpentine cantilever beam with strain. The resistance changes of the four cantilever beams constitute the observation vector. Based on the observation vector, the vibration acceleration components of the measured object in three orthogonal directions are calculated, thus completing the three-dimensional vibration sensing.
[0024] Furthermore, the microcracks are in an arc-shaped array, with a crack width of 20-50 μm, a depth of 10-80 μm, and a spacing of 200-600 μm.
[0025] Furthermore, the composite conductive layer is composed of graphene, multi-walled carbon nanotubes and polydimethylsiloxane, wherein the mass ratio of graphene to carbon nanotubes is 10:1 to 1:1, and the overall thickness of the conductive layer is 20-70 μm.
[0026] This solution also provides a method for fabricating the aforementioned integrated serpentine microcrack three-dimensional flexible vibration sensor, comprising the following steps: Step 1: Selectively cut the entire polyimide film surface using an ultraviolet laser to prepare a basic structure containing a serpentine cantilever beam, an inertial mass region, and a support region. Then, perform laser scanning in the serpentine cantilever beam region to induce the formation of a microcrack array. Step 2: Perform a second laser selective thinning on the lower surface of the cut polyimide film to obtain a support area, a serpentine cantilever beam, and an inertial mass area structure with varying thicknesses. Step 3: Prepare graphene / carbon nanotube / PDMS composite conductive paste, and use a spraying process to spray it onto the sensitive area of the substrate to form a continuous conductive layer;
[0027] Step 4: Fabricate multi-channel electrodes corresponding to the four sets of conductive sensing units on the support layer and mass block, and connect them with wires;
[0028] Step 5: Perform vibration performance calibration and three-dimensional decoupling test.
[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0030] (1) Fundamental innovation in structural integration: The three-dimensional flexible vibration sensor in this design abandons the traditional lamination and assembly approach, and creatively adopts a single-material laser differential processing technology to manufacture an integrated structure that includes a thin-walled cantilever beam, a thick-area mass block, and a support layer in one go. This structure eliminates all adhesive interfaces, eradicates the risk of delamination, and enables the sensor to have excellent environmental stability and fatigue durability. It also achieves seamless integration and precise control of inertial mass, laying a mechanical foundation for high sensitivity.
[0031] (2) Innovative Design of Spatial Anisotropic Stiffness: This scheme is the first to introduce serpentine geometry into the elastic element design of a multi-axis vibration sensor. By precisely designing the curvature, orientation, and spatial orientation of the four serpentine cantilever beams, an elastic system with controllable anisotropy in stiffness matrix is actively constructed. This allows the displacement of the same mass block in different X, Y, and Z directions to excite the four beams to produce unique proportional combinations of tensile, compressive, and bending strains, thereby "encoding" the three-dimensional vibration information to four spatial locations. This spatial encoding mechanism based on stiffness anisotropy is the physical core of this sensor's ability to achieve three-dimensional vector decoupling.
[0032] The present invention will be further described below with reference to specific embodiments. Attached Figure Description
[0033] Figure 1 This is a top view schematic diagram of the overall structure of the integrated serpentine microcrack three-dimensional flexible vibration sensor of the present invention.
[0034] Figure 2 This is a cross-sectional schematic diagram of the integrated serpentine microcrack three-dimensional flexible vibration sensor of the present invention.
[0035] Figure 3 This is a schematic diagram illustrating the resistance change mechanism of the composite conductive layer in the microcrack region of the integrated serpentine microcrack three-dimensional flexible vibration sensor of the present invention.
[0036] Figure 4 This is a schematic diagram of the laser cutting front path planning during the fabrication process of the integrated serpentine microcrack three-dimensional flexible vibration sensor of the present invention. Detailed Implementation
[0037] Example
[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.
[0039] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.
[0040] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.
[0041] Combination Figure 1 and Figure 2 An integrated serpentine microcrack three-dimensional flexible vibration sensor includes a flexible substrate layer, a composite conductive layer, and multiple electrodes.
[0042] The composite conductive layer is disposed on the flexible substrate layer, and multiple electrodes are disposed on the composite conductive layer for connecting to the outside and extracting signals;
[0043] In this embodiment, the composite conductive layer is composed of graphene, multi-walled carbon nanotubes and polydimethylsiloxane, wherein the mass ratio of graphene to carbon nanotubes is 10:1 to 1:1, and the overall thickness of the conductive layer is 20-70 μm; the conductive layer forms an independent conductive network on each cantilever beam, and the networks are isolated by insulating regions.
[0044] The flexible substrate layer is used to amplify and sense three-dimensional vibrations, and the corresponding information is converted into electrical signals through the composite conductive layer and transmitted to the outside.
[0045] In addition, the flexible substrate layer includes a flexible sensitive area, an inertial mass area, and a support area;
[0046] The flexible sensitive area is a centrally symmetrically distributed cantilever beam; the inertial mass area is a thick region located in the center of the inner side of the cantilever beam, which in this embodiment is represented by a mass block; and the support area is a thick region located at both ends of the outer side of the cantilever beam. Figure 1 The supporting layer in;
[0047] The flexible sensitive region, inertial mass region, and support region are continuous without interface in the material, and their thickness varies in a gradient, decreasing sequentially from the support region, inertial mass region, and flexible sensitive region.
[0048] In this embodiment, the flexible sensitive area consists of four serpentine cantilever beams arranged in a centrally symmetrical manner. Each serpentine cantilever beam includes at least two arc-shaped bending segments, and the beam width is 1-4 mm. The spatial curvature and orientation are designed so that the stiffness response of the four beams to vibrations in the X, Y, and Z directions is anisotropic. In this embodiment, in the integrally formed PI flexible substrate, the thickness of the serpentine cantilever beam region is 100-200 μm, and the thickness of the mass block and support layer region is 100-500 μm.
[0049] The serpentine cantilever beam is provided with a regularly arranged array of biomimetic microcracks generated by laser induction, and the composite conductive layer covers the biomimetic microcrack array.
[0050] The cracks in the biomimetic microcrack array change width when vibrating.
[0051] In this embodiment, the microcracks are an arc-shaped array with a crack width of 20-50 μm, a depth of 10-80 μm, and a spacing of 200-600 μm.
[0052] Overall, the sensor in this solution is a flexible thin-film device that integrates structure, sensing, and conductivity, and from top to bottom includes:
[0053] The outermost layer consists of graphene and multi-walled carbon nanotubes as conductive fillers, which are uniformly dispersed and solidified in a polydimethylsiloxane elastic matrix. This layer has good conductivity, mechanical flexibility and high adhesion to the substrate.
[0054] Located beneath the conductive layer, it is an array of physical trenches directly generated on the surface of the polyimide substrate through laser induction. Cracks are arranged in the sensitive section of the cantilever beam, whose V-shaped or U-shaped cross-sections exhibit drastic width changes under strain.
[0055] Integrated polyimide structural layer: the core framework of the device. Employing a thickness-zoned design.
[0056] Flexible sensitive area (serpentine cantilever beam): It is relatively thin (100-200 μm), easy to bend and deform, and is the carrier of strain and cracks.
[0057] Inertial mass region (central mass block): Increased thickness (200-300 μm) to provide inertial mass.
[0058] Rigid fixing area (two-sided support area): The thickness is significantly thicker than the mass block (200-400 μm), used for device mounting and electrical connection, and provides a cavity to facilitate device vibration along the z-axis.
[0059] Electrode and interface layer: Above the support layer and the conductive functional layer on the surface of the mass block on both sides of each cantilever beam, conductive silver paste or copper tape are used to connect wires for connecting external measurement circuits.
[0060] The core design of the vibration sensor in this scheme is based on the second-order vibration system model of mass-spring-damper in classical mechanics, and innovatively extends it with spatial three-dimensional representation and structural integration. The dynamic behavior of the system is described by the following coupling equations:
[0061] For the three translational degrees of freedom of the system, its motion can be expressed as:
[0062]
[0063] in, The mass matrix represents the displacement vector of the central inertial mass region relative to the sensor mounting base (support area) in the X, Y, and Z directions. It mainly depends on the geometry and density of the centrally integrated polyimide mass block, whose function is to provide sufficient inertia when subjected to external vibration acceleration. When applied to the sensor substrate, the mass block experiences inertial force. This results in relative displacement. This invention utilizes locally thick regions actively formed through laser processing as mass blocks, significantly increasing [the mass]. This allows for a larger displacement output under the same input acceleration, laying a mechanical foundation for high-sensitivity detection.
[0064] Stiffness matrix This is the essence of the entire design, determined by the elastic properties of four spatially symmetrically distributed serpentine cantilever beams. The primary function of the serpentine structure is to effectively increase the equivalent length of the beams within a limited planar dimension, thereby reducing their axial and bending stiffness and making the sensor more sensitive to minute inertial forces. More importantly, the serpentine beams introduce controllable stiffness anisotropy in three-dimensional space. By precisely designing the radius, curvature, and orientation of the serpentine segments, the tensile, compressive, and bending stiffness contributions of each beam in the X, Y, and Z directions can be controlled, which allows for a more precise control of the stiffness matrix. The off-diagonal elements are not zero, meaning the motion of the system in the three directions is elastically coupled. This coupling relationship allows the mass block to have displacements in any direction. Each of these processes induces a unique combination of strain modes (tension, compression, and bending) on the four beams, providing a mapping relationship for subsequent inverse solving of the three-dimensional displacement vector using electrical signals.
[0065] Damping matrix The main reason for this is the viscoelastic internal friction of the polyimide material itself and the air damping, which modulates the frequency response characteristics and transient response of the system.
[0066] Specifically, when the sensor detects vibration:
[0067] The input vibration is amplified by the inertial mass region, and the three-dimensional displacement is encoded into multi-channel differentiated strain modes by the serpentine cantilever beam array in the flexible sensitive region.
[0068] The biomimetic microcrack array on the serpentine cantilever beam generates changes in crack width due to vibration, and the composite conductive layer covering it converts the strain into an electrical signal.
[0069] Finally, the complete three-dimensional vibration information was decoded from the multi-channel electrical signal using a decoupling algorithm.
[0070] In addition, when the sensor moves with the object being measured at a certain acceleration During vibration, the inertial mass region experiences inertial force. The effect is to cause displacement relative to the support area. The displacement is determined by the system's dynamic equations, and its amplitude and phase are closely related to the frequency and acceleration of the input vibration, as well as the system's M, C, and K parameters.
[0071] Displacement of the inertial mass region As boundary conditions, the roots of the four serpentine cantilever beams acting on the flexible sensitive region exhibit different proportions of axial strain due to the different spatial orientations of each beam and the stiffness characteristics determined by the serpentine structure. and bending strain For example, for displacement in the X direction, the beams oriented along the X-axis are mainly stretched / compressed, while the beams oriented along the Y-axis are mainly bent; for displacement in the Z direction, all beams are bent; thus, the three-dimensional displacement vectors of the four serpentine cantilever beams in the flexible sensitive area are obtained. coding: ;
[0072] Microcrack Strain Amplification and Conductive Network Modulation: Macroscopic strain on a serpentine cantilever beam is transferred to the microcrack region on its surface, causing a significant change in the crack width *w* of the V-shaped crack. The conductivity mechanism of the nanocomposite conductive layer covering the crack relies on the tunneling effect and direct contact between conductive fillers (carbon nanotubes, graphene). The change in crack width *w* leads to a sudden change in the number of conductive pathways penetrating the crack in the composite conductive layer, resulting in a high-gain change in the overall resistance *R* of a single serpentine cantilever beam with strain. Figure 3 As shown;
[0073] Resistance changes of the four cantilever beams These four electrical signals are measured in real time and independently (typically converted into voltage signals via a Wheatstone bridge or a constant voltage source voltage divider circuit). These four electrical signals constitute the observation vector. Based on the observation vector, the vibration acceleration components of the measured object in three orthogonal directions are calculated, thus completing the three-dimensional vibration sensing.
[0074] Therefore, through simple matrix operations, the vibration acceleration components of the measured object in three orthogonal directions can be calculated in real time from the four-channel voltage signal, thus completing three-dimensional vibration sensing.
[0075] In certain application scenarios, this embodiment designs a sensor for monitoring weak vibrations of the spindle housing of a CNC milling machine, aiming to identify early faults such as tool wear and spindle imbalance.
[0076] Overall design and dimensions: The sensor is designed to be rectangular, with dimensions of 60mm (length) × 25mm (width), to fit the limited flat area on the surface of the machine tool housing;
[0077] The overall layout consists of a rectangular central inertial mass (4mm × 15mm) surrounded symmetrically by four identical three-circular-arc cantilever beams. The other ends of the beams connect to two rectangular rigid support layers (4mm × 15mm) on either side. This integrated configuration of central mass, symmetrical cantilever beams, and double-sided supports ensures that vibrational energy input from the support is efficiently transferred to the mass through the elastic deformation of the beams, thus inducing complex strains in the beams. The design of the cantilever beams (arc radius R = 4.5mm, width W = 3.0mm) allows them to achieve a larger equivalent length within a finite plane, significantly reducing axial and bending stiffness and improving sensitivity. Simultaneously, their specific spatial curvature is key to generating differentiated stiffness responses to vibrations in the X, Y, and Z directions. In terms of thickness, the gradient design of the cantilever beam region (125μm), the inertial mass region (200μm), and the support region (300μm) optimizes the flexible deformation, inertial mass, and installation rigidity, respectively. This thickness difference is achieved by selective thinning of the same material using laser, ensuring the integrity and reliability of the structure.
[0078] Integrated substrate parametric design:
[0079] Substrate: 300μm thick Kapton® HN type polyimide film is selected, which has excellent mechanical properties, thermal stability and chemical resistance.
[0080] Cantilever beam design: Four beams are symmetrically distributed on both sides. Each beam is a three-arc serpentine shape with an arc radius R = 4.5 mm and a beam width W = 3.0 mm. Through laser thinning, the target thickness of the beam area is 125 ± 3 μm. This thickness provides sufficient mechanical strength while ensuring flexibility.
[0081] Mass block design: Located at the center of the sensor, it is designed as a rectangle with dimensions of 4mm × 15mm. A laser processing strategy is used to maintain its thickness at 200μm, thus forming an effective inertial mass block.
[0082] Support area design: Located at both ends of the sensor, with dimensions of 4mm×15mm and a thickness of 300μm, providing a stable mounting base.
[0083] Microcrack array design: Microcracks perpendicular to the arc are designed on each cantilever beam. Target parameters: Crack width ≈ 30 μm, depth ≈ 30 μm, spacing between adjacent crack center points ≈ 300 μm. This density and size are designed to optimize strain sensitivity and response linearity.
[0084] Conductive layer design: A PDMS composite material synergistically reinforced with graphene and multi-walled carbon nanotubes is employed. The mass ratio of the two is set at 1:1. The large specific surface area of graphene is used to construct the basic conductive network, while carbon nanotubes act as one-dimensional conductors to enhance network connectivity and toughness. The target conductive layer thickness is 20 μm.
[0085] In addition, the three-dimensional vibration sensor of this solution can also be applied to:
[0086] 1. Industrial Robot Joint Vibration Monitoring and Fault Early Warning: Sensors are attached to the sixth axis (wrist) joint housing of an industrial robot. During repetitive grasping and placing operations, the three-dimensional vibration spectrum of the joint is continuously monitored. When early pitting occurs in the reducer gears or bearing wear appears, the amplitude of the vibration signal in specific frequency bands (such as the sideband of the gear meshing frequency) will significantly increase. The three-dimensional information provided by this sensor allows for more accurate location of the fault source (e.g., distinguishing between radial and axial vibrations), enabling predictive maintenance and preventing unexpected downtime.
[0087] 2. Intelligent Piano Teaching and Performance Analysis: Multiple miniaturized sensors (down to 10mm x 10mm) are embedded beneath the piano keys. During performance, the sensors not only capture the force of the keystrokes (corresponding to the peak Z-axis acceleration) but also sensitively detect the minute lateral movements of the fingertips at the moment of touch (X / Y-axis signals). This information is closely related to timbre and tone quality. By analyzing the three-dimensional vibration data, the performer's touch technique can be quantitatively evaluated, providing objective data support for digital and visualized piano teaching.
[0088] 3. Wind Turbine Blade Condition Monitoring: A series of sensors are attached in an array to the root surface of the wind turbine blades. During operation, the sensor network monitors the vibration modes in the flapping, swaying, and torsional directions of the blades in real time. Through the fusion analysis of the three-dimensional vibration data, blade imbalances, changes in mass distribution, or structural damage (such as cracks) can be identified, enabling online and distributed sensing of the wind turbine blade health status and ensuring the safe and efficient operation of wind power equipment.
[0089] In addition, this solution also provides a method for fabricating the aforementioned integrated serpentine microcrack three-dimensional flexible vibration sensor, including the following steps: Step 1: Selectively cut the entire polyimide film surface using an ultraviolet laser to prepare a basic structure containing a serpentine cantilever beam, an inertial mass region, and a support region. Then, perform laser scanning in the serpentine cantilever beam region to induce the formation of a microcrack array.
[0090] Among them, the laser cutting uses a power-tunable ultraviolet laser system, which controls the thickness of different areas by controlling the laser energy density and the number of scans.
[0091] This embodiment specifically includes:
[0092] a. Substrate fixation and cleaning: After cleaning the surface of the PI film with anhydrous ethanol, fix it flat on the substrate of the laser cutting machine with dust-free tape;
[0093] b. Structural contour cutting and release: Run the first laser program. Use an ultraviolet laser (λ=355nm), set the power to 100%, the scanning speed to 500mm / s, and the focused spot diameter to approximately 12μm. First, cut along the outer contour of the sensor, cutting through the overall contour of the four serpentine cantilever beams, the central mass block, and the two side support areas to release the structure;
[0094] c. Inducing Microcrack Generation: The second stage of the fine-machining process is executed. The laser power is drastically reduced to 5%, and an extremely high scanning speed (1500 mm / s) is used to rapidly scan the microcrack pattern. The instantaneous thermal shock of the laser induces directional, depth-controlled patterned cracks on the PI material surface. Online monitoring using an optical microscope is employed to adjust the power and number of repetitions until the crack morphology meets design requirements. Figure 4 As shown.
[0095] Step 2: Perform a second laser selective thinning on the lower surface of the cut polyimide film to obtain a support area, a serpentine cantilever beam, and an inertial mass area structure with varying thicknesses.
[0096] In this embodiment, the process specifically includes: flipping the PI film to the back side and running the third program. The laser power is adjusted to 50%, a grating scanning mode (line spacing 20μm) is adopted, and the scanning speed is increased to 1000mm / s. Multiple scans are performed on the four cantilever beams and the mass block area. By controlling the number of scans, the thickness of the beam area is precisely reduced to the target value of 125μm in real time, the thickness of the inertial mass area is reduced to 200μm, and the support area is automatically shielded by the program and is unaffected by the scanning.
[0097] Step 3: Prepare a graphene / carbon nanotube / PDMS composite conductive paste, and use a spraying process to spray it onto the sensitive areas of the substrate to form a continuous conductive layer; specifically including:
[0098] a. Preparation of conductive paste: Accurately weigh 0.06g MWCNTs and 0.06g graphene, add them to 10g cyclohexane, stir magnetically for 5min, and then ultrasonically disperse in an ice-water bath (150W power) for 0.5h to obtain a uniformly dispersed nanofiller suspension. Simultaneously, add 0.6g PDMS prepolymer (Sylgard 184 component A) to 10g cyclohexane and stir magnetically for 30min to fully dilute. Then mix the nanofiller suspension with the PDMS dilution, stir magnetically for 30min, and then ultrasonically disperse in an ice-water bath (150W power) for 0.5h. Finally, add 0.06g PDMS curing agent (component B), and gently stir for 15min to avoid introducing air bubbles, thus obtaining a homogeneous conductive paste.
[0099] b. Mask Coating and Curing: Clean and dry the laser-processed sensor substrate, then treat the upper surface with oxygen plasma to improve adhesion to the conductive layer. Cover the non-electrically connected areas on the support area with a custom polyimide tape mask. Using an ultra-fine airbrush, at a pressure of 0.1 MPa and a distance of 15 cm, apply multiple thin layers at a uniform speed. Pause for 30 seconds after each layer, and apply approximately 1-3 layers to the target thickness. After coating, carefully remove the mask. Place the sample in a ventilated oven and program the temperature: first maintain at 40°C for 1 hour to allow the solvent to evaporate slowly, then cure at 80°C for 1 hour, and finally cure at 120°C for 2 hours to ensure complete cross-linking of PDMS and strong adhesion to the PI substrate.
[0100] Step 4: Fabricate multiple electrodes corresponding to the four sets of conductive sensing units on the support area and the inertial mass area, and connect them with wires, including:
[0101] a. Apply conductive silver paste (EPO-TEK H20E) precisely to both ends of the corresponding cantilever beams in the support area and inertial mass area using a dispensing machine to connect the wires to the conductive layer.
[0102] b. Place the entire assembly on a 150°C hot plate and heat for 30 minutes to allow the silver paste to sinter and solidify rapidly, forming an ohmic contact.
[0103] Step 5: Perform vibration performance calibration and three-dimensional decoupling test.
[0104] The embodiments described above are merely one implementation method of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.
Claims
1. An integrated serpentine microcrack three-dimensional flexible vibration sensor, characterized in that, It includes a flexible substrate layer, a composite conductive layer, and multiple electrodes; The composite conductive layer is disposed on the flexible substrate layer, and multiple electrodes are disposed on the composite conductive layer for connecting to the outside and extracting signals; The flexible substrate layer is used to amplify and sense three-dimensional vibrations, and the corresponding information is converted into electrical signals through the composite conductive layer and transmitted to the outside.
2. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 1, characterized in that, The flexible substrate layer includes a flexible sensitive area, an inertial mass area, and a support area; The flexible sensitive area is a cantilever beam with central symmetry, the inertial mass area is a thick area located in the center of the inner side of the cantilever beam, and the support area is a thick area located at both ends of the outer side of the cantilever beam. The flexible sensitive region, inertial mass region, and support region are continuous without interface in the material, and their thickness varies in a gradient, decreasing sequentially from the support region, inertial mass region, and flexible sensitive region.
3. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 2, characterized in that, The flexible sensitive area consists of four serpentine cantilever beams arranged in a centrally symmetrical manner. Each serpentine cantilever beam includes at least two arc-shaped bending segments. The spatial curvature and orientation of the beams are designed to make the stiffness response of the four beams to vibrations in the X, Y, and Z directions anisotropic.
4. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 3, characterized in that, The serpentine cantilever beam is provided with a regularly arranged array of biomimetic microcracks generated by laser induction, and the composite conductive layer covers the biomimetic microcrack array. The cracks in the biomimetic microcrack array change width when vibrated.
5. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 4, characterized in that, When the sensor senses vibration: The input vibration is amplified by the inertial mass region, and the three-dimensional displacement is encoded into multi-channel differentiated strain modes by the serpentine cantilever beam array in the flexible sensitive region. The biomimetic microcrack array on the serpentine cantilever beam generates changes in crack width due to vibration, and the composite conductive layer covering it converts the strain into an electrical signal. Finally, the complete three-dimensional vibration information was decoded from the multi-channel electrical signal using a decoupling algorithm.
6. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 4, characterized in that, When the sensor vibrates with a certain acceleration along with the object being measured, the inertial mass region will be displaced relative to the support region due to the inertial force. The displacement of the inertial mass region acts on the roots of the four serpentine cantilever beams in the flexible sensitive region. Due to the different spatial orientations of each beam and the different stiffness characteristics determined by the serpentine structure, the same displacement induces different proportions of axial strain on different serpentine cantilever beams. and bending strain This allows us to obtain the three-dimensional displacement vectors of the four serpentine cantilever beams in the flexible sensitive area. coding: ; Microcrack strain amplification and conductive network modulation: Macroscopic strain on a serpentine cantilever beam is transmitted to the microcrack region on its surface, causing a significant change in the crack width w of the V-shaped crack. This leads to a sudden change in the number of conductive pathways penetrating the crack in the composite conductive layer, resulting in a high-gain change in the overall resistance R of a single serpentine cantilever beam with strain. The resistance changes of the four cantilever beams constitute the observation vector. Based on the observation vector, the vibration acceleration components of the measured object in three orthogonal directions are calculated, thus completing the three-dimensional vibration sensing.
7. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 4, characterized in that, The microcracks are arranged in an arc-shaped array, with a crack width of 20-50 μm, a depth of 10-80 μm, and a spacing of 200-600 μm.
8. The integrated serpentine microcrack three-dimensional flexible vibration sensor according to claim 1, characterized in that, The composite conductive layer is composed of graphene, multi-walled carbon nanotubes and polydimethylsiloxane, wherein the mass ratio of graphene to carbon nanotubes is 10:1 to 1:1, and the overall thickness of the conductive layer is 20-70 μm.
9. A method for fabricating an integrated serpentine microcrack three-dimensional flexible vibration sensor as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Selectively cut the entire polyimide film surface using an ultraviolet laser to prepare a basic structure containing a serpentine cantilever beam, an inertial mass region, and a support region. Then, perform laser scanning in the serpentine cantilever beam region to induce the formation of a microcrack array. Step 2: Perform a second laser selective thinning on the lower surface of the cut polyimide film to obtain a support area, a serpentine cantilever beam, and an inertial mass area structure with varying thicknesses. Step 3: Prepare graphene / carbon nanotube / PDMS composite conductive paste, and use a spraying process to spray it onto the sensitive area of the substrate to form a continuous conductive layer; Step 4: Fabricate multi-channel electrodes corresponding to the four sets of conductive sensing units on the support area and the inertial mass area, and connect them with wires; Step 5: Perform vibration performance calibration and three-dimensional decoupling test.