A piezoelectric energy harvester based on nonlinear gradient negative poisson's ratio structure
The piezoelectric energy harvester designed with a nonlinear gradient negative Poisson's ratio structure solves the problem of uneven stress distribution, realizes efficient energy conversion of piezoelectric materials, improves power density, and is suitable for continuous power supply of IoT devices.
Patent Information
- Application Number
- CN202610528920.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-21
- Publication Date
- 2026-07-07
AI Technical Summary
The existing piezoelectric energy harvesters have uneven stress distribution, resulting in low utilization of piezoelectric materials and limited power density improvement. Furthermore, the existing negative Poisson's ratio structures have not fully optimized the thickness dimension.
A piezoelectric energy trap based on a nonlinear gradient negative Poisson's ratio structure is adopted. The thickness distribution of the matrix is designed by a nonlinear cubic polynomial function, and combined with the negative Poisson's ratio structure segment, stress homogenization is achieved, thereby enhancing the energy conversion efficiency of the piezoelectric material.
It significantly improves the output power density, realizes the efficient utilization of piezoelectric materials, enhances power output, and is suitable for continuous power supply of IoT devices.
Smart Images
Figure CN122348693A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of microelectromechanical systems and new energy technologies, specifically to a piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure. Background Technology
[0002] With the rapid development of technology, the Internet of Things (IoT), as a significant revolution in the information industry, has been widely adopted in fields such as industrial production and infrastructure monitoring. The core of realizing the application of IoT technology lies in the long-term stable operation of a large number of information sensing devices, which currently rely heavily on battery power. Traditional battery-powered methods suffer from limited lifespan, high replacement and maintenance costs, and environmental pollution. Energy harvesters can continuously collect energy from the surrounding environment, such as magnetic fields and vibrations, offering significant advantages such as simple assembly, high energy collection density, and ease of integration. Since the working environment of IoT systems contains numerous vibration sources that can continuously provide mechanical vibration energy, piezoelectric energy harvesting technology, which utilizes environmental vibration energy to generate electricity, has become a research hotspot.
[0003] Existing piezoelectric energy harvesters typically employ a rectangular cantilever beam structure with uniform thickness. However, when a cantilever beam with uniform thickness undergoes bending vibration, the stress is mainly concentrated at the root of the fixed end, while the stress level in areas far from the root is extremely low. This uneven stress distribution leads to low utilization of the piezoelectric material, limiting the output power density of the energy harvester.
[0004] To improve stress distribution, some existing technologies have proposed linear variable cross-section structures, where the beam thickness decreases linearly from the fixed end to the free end. While linear gradient structures improve the average stress to some extent, their thickness change rate is constant, failing to perfectly match the theoretically constant strength curve of a cantilever beam. Therefore, the surface stress distribution of linear gradient structures still fluctuates, failing to achieve the theoretically maximum material utilization. Furthermore, existing negative Poisson's ratio energy traps primarily focus on optimizing the planar lattice shape, neglecting nonlinear optimization design in the thickness dimension. Summary of the Invention
[0005] To address the issues of uneven stress distribution and limited power density improvement in existing piezoelectric energy harvesters, this invention provides a piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure. By introducing a specific nonlinear cubic polynomial thickness distribution, the surface stress of the structure is made extremely uniform, significantly improving the output power.
[0006] The technical solution adopted in this invention is as follows:
[0007] A piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure includes an elastic matrix, one end of which is fixed and the other end is free. The elastic matrix structure includes a nonlinear variable thickness section and a negative Poisson's ratio structure section, and a piezoelectric transducer is provided at the upper end of the negative Poisson's ratio structure section.
[0008] Preferably, the thickness T of the elastic matrix decreases non-linearly and monotonically along the length direction x from the fixed end to the free end, and the contour of this non-linear change is defined by a cubic polynomial function. The cubic curve contour determined by the multi-objective optimization algorithm can accurately approximate the theoretical model of the isostatic beam, ensuring that the stress at each point on the beam remains consistent during vibration.
[0009] Preferably, the cubic polynomial function is , where x is the distance from the free end, and T(x) is the matrix thickness at that location; A, B, C, and D are all constant coefficients.
[0010] D represents the thickness of the free end, with a value ranging from 1.00mm to 2.60mm.
[0011] C is the coefficient of the linear term, with a value ranging from 0.010 mm to 0.020 mm;
[0012] B is the coefficient of the quadratic term, with a value range of 0.00002mm-0.00003mm;
[0013] A is the coefficient of the cubic term, with a value ranging from 0.000003mm to 0.000005mm.
[0014] Preferably, the negative Poisson's ratio structural segment is formed by a periodic array of multiple concave hexagonal cells; the concave hexagonal cell includes two parallel long sides and four short sides connecting the two long sides, the long sides are parallel to the width direction of the elastic matrix, and the short sides are concave towards the center of the concave hexagonal cell to form a concave corner structure.
[0015] Preferably, the piezoelectric transducer is a piezoelectric composite structure, which includes a piezoelectric ceramic layer and a metal substrate layer from top to bottom; the material of the piezoelectric ceramic layer is lead zirconate titanate PZT-5A, and the material of the metal substrate layer is brass; the piezoelectric transducer is fully bonded to the upper surface of the negative Poisson's ratio structure segment by an epoxy resin adhesive layer, and the epoxy resin adhesive layer fills the pores of the negative Poisson's ratio structure segment, so that the piezoelectric transducer and the negative Poisson's ratio structure segment form a tight mechanical coupling, ensuring the effective transmission of mechanical deformation during vibration.
[0016] Preferably, the elastic matrix is made of polylactic acid (PLA), and the elastic matrix is integrally formed by 3D printing. The infill rate of the 3D printing is not less than 90% to ensure the structural strength and mechanical properties of the elastic matrix. A mass block is fixedly connected to the free end face of the elastic matrix. The mass block is made of structural steel. The setting of the mass block can effectively reduce the resonance frequency of the elastic matrix, making it more suitable for low-frequency vibration environments. Attached Figure Description
[0017] Figure 1 This is a three-dimensional schematic diagram of the overall structure of the present invention.
[0018] Figure 2 This is a side view of the present invention, showing the nonlinear thickness variation curve of the elastic matrix.
[0019] Figure 3 This is a schematic diagram of the negative Poisson's ratio structure hole of the present invention.
[0020] Figure 4 This is a comparison diagram of stress distribution between the embodiment of the present invention and existing linear gradient structures.
[0021] Figure 5 This is an exploded structural diagram of the present invention.
[0022] Labeling explanation: 1-Mass block; 2-Elastic matrix; 3-Piezoelectric ceramic layer; 4-Metal substrate layer; 5-Fixing end; 6-Epoxy resin layer. Detailed Implementation
[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The scope of protection of the present invention is not limited to the following embodiments. All equivalent transformations made based on the technical solutions of the present invention fall within the scope of protection of the present invention.
[0024] like Figure 1 and Figure 2 As shown, this embodiment provides a piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure, including a nonlinear gradient negative Poisson's ratio structure elastic substrate 2, an epoxy resin layer 6 bonded to the top of the elastic substrate 2, a piezoelectric sheet bonded to the top of the epoxy resin layer 6, the piezoelectric sheet including a piezoelectric ceramic layer 3 and a metal substrate layer 4, a mass block 1 fixed to the front end of the elastic substrate 2, and a fixed end 5 at the root of the elastic substrate 2.
[0025] The nonlinear gradient negative Poisson's ratio structure elastic matrix 2 is made of polylactic acid.
[0026] The piezoelectric ceramic layer 3 of the piezoelectric element is made of lead zirconate titanate PZT-5A, and the metal substrate layer 4 is made of brass.
[0027] Mass block 1 and fixed end 5 are made of stainless steel.
[0028] The core innovation of this embodiment lies in the nonlinear thickness design of the elastic matrix 2. In order to obtain the optimal power generation performance under specific vibration conditions, this invention optimizes the thickness profile through a multi-objective genetic algorithm, and obtains an optimal cubic nonlinear curve.
[0029] Let the effective length of the elastic matrix 2 be L = 76 mm, and define the origin of the coordinate system x as located at the free end (i.e., x = 0 is the free end, and x = 76 is the fixed end). The matrix thickness T(x) (unit: mm) varies with position x (unit: mm) strictly according to the following formula:
[0030]
[0031] The specific parameters are explained below:
[0032] The constant term D = 1.68318 mm: This is the thickness of the free end. Compared to traditional designs, this thinner tip helps reduce structural stiffness, making it more prone to vibration.
[0033] The coefficient of the first term, C = 0.014588 mm, is the initial slope that controls the change in thickness.
[0034] The coefficients of the quadratic and cubic terms introduce nonlinear characteristics, causing the thickness curve to exhibit a specific shape that is steeper or gentler than the linear gradient near the fixed end, thereby accurately correcting the stress concentration effect at the root.
[0035] like Figure 3 As shown, the elastic substrate 2 is composed of a periodic array of multiple concave hexagonal cells. Each concave hexagonal cell includes two parallel long sides and four short sides connecting the two long sides. The long sides are parallel to the width direction of the elastic substrate 2, and the short sides are concave towards the center of the concave hexagonal cell to form a concave corner structure. When the elastic substrate 2 is subjected to bending and stretching, the negative Poisson's ratio structure segment expands in the lateral direction, causing the piezoelectric ceramic layer 3 to be subjected to tensile stress in both the longitudinal and lateral directions, thereby achieving superimposed enhancement of charge output.
[0036] Working principle and effect verification:
[0037] The energy trap is fixed to the surface of the environmental vibration source via the fixed end 5. When the environmental vibration excitation acts on the fixed end 5, the elastic substrate 2, as a cantilever beam, undergoes bending vibration. The mass block 1 vibrates synchronously with the free end of the elastic substrate 2, further amplifying the deformation of the elastic substrate 2. Due to the nonlinear thickness gradient design of the elastic substrate 2, the bending stiffness of each section varies synergistically with the cube of the lever arm length and thickness. This rate of change precisely offsets the influence of the linear increase of bending moment with distance, making the stress distribution on the surface of the elastic substrate 2 tend to be uniform. The entire area of the piezoelectric transducer participates in energy conversion. At the same time, when the elastic substrate 2 is bent and stretched, the negative Poisson's ratio structural section generates lateral expansion, causing the piezoelectric ceramic layer 3 to be subjected to tensile stress in both the longitudinal and transverse directions. Based on the positive piezoelectric effect, the piezoelectric ceramic layer 3 generates charge output in both directions, greatly reducing the generation and cancellation of opposite charges, and achieving superposition enhancement of charge output. Finally, the piezoelectric transducer converts the mechanical energy of mechanical vibration into electrical energy, providing continuous power for loads such as IoT sensing devices.
[0038] This embodiment verifies the performance of the energy trap through finite element simulation. The simulated vibration excitation acceleration is 0.5g (g is the acceleration due to gravity). The finite element simulation results are as follows: Figure 4 As shown, the left side is the stress distribution cloud map of the nonlinear gradient negative Poisson's ratio structure piezoelectric energy harvester of this embodiment, and the right side is the stress distribution cloud map of the existing linear gradient structure piezoelectric energy harvester (thickness increases linearly from 1.68318mm to 4.86439mm). The comparison shows that the surface stress distribution of the piezoelectric energy harvester of this embodiment is more uniform, the low stress area is basically eliminated, the average stress in the middle section of the beam is increased by about 15% compared with the existing linear gradient structure, and the maximum stress does not exceed the yield limit of polylactic acid (PLA) material, resulting in high structural mechanical safety.
[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure, comprising an elastic substrate, one end of which is a fixed end and the other end is a free end, a negative Poisson's ratio structure segment is provided on the elastic substrate, and a piezoelectric transducer element is coupled to the upper surface of the negative Poisson's ratio structure segment; characterized in that: The thickness T of the elastic matrix decreases non-linearly and monotonically along the length x from the fixed end to the free end; the contour of the non-linearly and monotonically decreasing change is defined by a cubic polynomial function, which makes the stress distribution on the surface of the elastic matrix tend to be uniform under vibration.
2. The piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure according to claim 1, characterized in that, The cubic polynomial function is expressed as: Where x is the axial distance from the free end of the elastic matrix, T(x) is the matrix thickness at that position, and A, B, C, and D are constant coefficients.
3. The piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure according to claim 2, characterized in that, The effective length of the elastic matrix is L, and the range of the independent variable x is... The range of values for the constant coefficients satisfies: D represents the thickness of the free end, with a value ranging from 1.00mm to 2.60mm. C is the coefficient of the linear term, with a value ranging from 0.010 mm to 0.015 mm; B is the coefficient of the quadratic term, with a value range of 0.00002mm-0.00003mm; A is the coefficient of the cubic term, with a value ranging from 0.000003mm to 0.000005mm.
4. The piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure according to claim 1, characterized in that, The negative Poisson's ratio structural segment is formed by a periodic arrangement of multiple concave hexagonal cells; each concave hexagonal cell includes two opposing long sides and four short sides connecting the long sides, the long sides being parallel to the width direction of the elastic matrix, and the short sides being concave towards the center of the cell to form a concave angle.
5. The piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure according to claim 1, characterized in that, The piezoelectric transducer is a piezoelectric sheet structure, which includes a piezoelectric ceramic layer and a metal substrate layer; the material of the piezoelectric ceramic layer is lead zirconate titanate PZT-5A, and the material of the metal substrate layer is brass. The piezoelectric transducer is bonded to the surface of the negative Poisson's ratio structure segment by an epoxy resin adhesive layer, and the epoxy resin adhesive layer fills the pores of the negative Poisson's ratio structure.
6. The piezoelectric energy harvester based on a nonlinear gradient negative Poisson's ratio structure according to claim 1, characterized in that, The elastic matrix is made of polylactic acid (PLA) and is integrally formed using 3D printing technology; a mass block is provided at the free end, and the mass block is made of structural steel.