A frequency-adjustable inverse-bow piezoelectric-electromagnetic composite energy harvesting device

Abstract

The present application belongs to the field of micro energy collection, and relates to a frequency-adjustable reverse-bow-shaped piezoelectric-magnetic composite energy collection device, which comprises a reverse-bow-shaped elastic beam, a piezoelectric transducing unit, a first electromagnetic conversion mechanism and a second electromagnetic conversion mechanism; the structure of the first electromagnetic conversion mechanism is completely same as that of the second electromagnetic conversion mechanism; the piezoelectric transducing unit is arranged on the reverse-bow-shaped elastic beam; and the first electromagnetic conversion mechanism and the second electromagnetic conversion mechanism are respectively fixedly arranged at the two end portions of the reverse-bow-shaped elastic beam. The present application provides the frequency-adjustable reverse-bow-shaped piezoelectric-magnetic composite energy collection device which can significantly improve the energy conversion efficiency and total power density in unit volume, can realize maintaining high level of energy capture in a wider frequency range, can improve the overall participation and power generation efficiency of the piezoelectric material, and can ensure always being in the best power generation state.

Description

Technical Field

[0001] This invention belongs to the field of micro-energy harvesting and relates to a composite energy harvesting device, particularly a frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device. Background Technology

[0002] With the rapid development of Internet of Things (IoT) technology, wireless sensor network nodes deployed in fields such as underground coal mines, industrial automation, and structural health monitoring have created an urgent need for self-powered technology. Environmental vibration energy, as a widely available and readily accessible green energy source, can be converted into electrical energy through piezoelectric or electromagnetic transduction mechanisms, becoming an effective way to solve the problem of long-term power supply for low-power electronic devices.

[0003] Currently, most existing vibration energy harvesting devices adopt traditional cantilever beam or simply supported beam structures.

[0004] Regarding transduction mechanisms: most devices employ only a single piezoelectric (e.g., piezoelectric energy harvester) or electromagnetic transduction (e.g., electromagnetic energy harvester). While piezoelectric energy harvesters offer advantages such as simple structure and high voltage output, their current output is weak and their output impedance is high under low-frequency vibration environments. Electromagnetic energy harvesters, on the other hand, while providing higher current and stable performance at low frequencies, suffer from lower output voltage and relatively bulky size. Clearly, a single transduction mechanism is insufficient to achieve high power density and wide bandwidth energy capture under complex vibration environments.

[0005] In terms of structural geometry design: most existing beam-type energy harvesters are linear straight beams or simple circular arc beam structures. The strain distribution of these structures is often non-uniform, and due to limitations in linear dynamic characteristics, their efficient energy harvesting bandwidth is extremely narrow. When the environmental excitation frequency shifts even slightly, the device's output power decreases exponentially. Although some studies have introduced nonlinear structures (such as magnetostrictive nonlinearity and buckling structures), they often face problems such as high requirements for start-up excitation amplitude and difficulty in precisely controlling the nonlinear response.

[0006] Regarding environmental adaptability: The vibration frequencies in actual industrial sites (such as mine machinery and equipment or exhaust ventilation ducts) often have wide bandwidth, randomness, or vary with operating conditions. Existing energy harvesting devices have their natural frequencies fixed after manufacturing. Due to the lack of an effective frequency tuning mechanism, the device cannot actively adapt to the real-time environmental frequency, resulting in extremely low energy harvesting efficiency in variable frequency vibration environments.

[0007] In summary, designing an energy harvesting device that combines the advantages of both piezoelectric and electromagnetic transduction, possesses excellent geometric nonlinear gain characteristics, and can be tuned in real time according to the environmental excitation frequency is a technical challenge that urgently needs to be solved in the field of micro-energy harvesting technology. Summary of the Invention

[0008] In order to solve the above-mentioned technical problems in the background art, the present invention provides a frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device that significantly improves the energy conversion efficiency and total power density per unit volume, can achieve a high level of energy capture over a wider frequency range, can improve the overall participation of piezoelectric materials and power generation efficiency, and can ensure that it is always in the optimal power generation state.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device is characterized in that: the frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device includes a recurve bow-shaped elastic beam, a piezoelectric transducer unit, a first electromagnetic conversion mechanism, and a second electromagnetic conversion mechanism; the structure of the first electromagnetic conversion mechanism is exactly the same as that of the second electromagnetic conversion mechanism; the piezoelectric transducer unit is disposed on the recurve bow-shaped elastic beam; the first electromagnetic conversion mechanism and the second electromagnetic conversion mechanism are respectively fixedly disposed at both ends of the recurve bow-shaped elastic beam.

[0011] The aforementioned first electromagnetic conversion mechanism includes a fixed base plate, a magnet, a supporting fixed block, an induction coil, a guide shaft, and a supporting slider. The supporting fixed block is fixedly mounted on the fixed base plate. A guide shaft is provided on the supporting fixed block. The axial direction of the guide shaft is parallel to the plane of the fixed base plate. The induction coil is fixedly mounted on the supporting fixed block. The axial direction of the induction coil is parallel to the axial direction of the guide shaft. The supporting slider is opposite to the supporting fixed block and slidably mounted on the fixed base plate. The sliding direction of the supporting slider is parallel to the axial direction of the guide shaft. The magnet is fixedly mounted on the supporting slider and moves synchronously with the supporting slider. The end of the deflection arch-shaped elastic beam is mounted on the supporting slider. When the deflection arch-shaped elastic beam is deformed by an external force, the magnet on the supporting slider extends into or is pulled out of the induction coil.

[0012] The aforementioned first electromagnetic conversion mechanism further includes a pre-position adjustment mechanism connected to the support slider; the pre-position adjustment mechanism includes a drive slider, a pre-tension spring, a slide rail, and a limiting mechanism; the slide rail is laid on a fixed base plate; the axis of the slide rail is parallel to the axis of the guide shaft; the support slider and the drive slider are sequentially arranged on the slide rail from front to back and move along the axis of the slide rail; the pre-tension spring is placed between the support slider and the drive slider; the limiting mechanism is placed on the slide rail and limits the position of the drive slider; preferably, the limiting mechanism is a limiting pin or a wedge block.

[0013] The aforementioned drive slider includes a support box; the bottom of the support box is disposed on a slide rail and moves along the axial direction of the slide rail; a cavity is provided inside the support box; one end of the preload spring is fixedly disposed on the support slider, and the other end is fixedly disposed in the cavity inside the support box through a circular plate.

[0014] The aforementioned pre-position adjustment mechanism also includes a drive mechanism connected to the drive slider.

[0015] The aforementioned driving mechanism includes a gear, a connecting pipe, a rotating rod, a toothed plate, and an L-shaped connecting plate; the toothed plate is laid on a fixed base plate; the axial direction of the toothed plate is parallel to the axial direction of the guide shaft; the rotating rod is connected to the gear through the connecting pipe and drives the gear to rotate around the axial direction of the connecting pipe; the gear meshes with the toothed plate; the L-shaped connecting plate is fitted onto the outside of the connecting pipe; one end of the L-shaped connecting plate is fixedly connected to the support box, and the other end is movably mounted on the fixed base plate and slidably connected to the fixed base plate; when the rotating rod rotates, the rotating rod drives the support box to move axially along the slide rail through the gear, the connecting pipe, and the L-shaped connecting plate.

[0016] The aforementioned fixed base plate is provided with a limiting groove; the axial direction of the limiting groove is parallel to the axial direction of the guide shaft; the foot of the L-shaped connecting plate is provided with a slider that matches the structure of the limiting groove; the slider is embedded in the limiting groove and moves along the axial direction of the limiting groove; preferably, the cross-section of the limiting groove is rectangular, triangular or dovetail-shaped.

[0017] The aforementioned drive mechanism also includes a support plate mounted on the connecting pipe, the support plate being movably mounted on the fixed base plate and slidably connected to the fixed base plate; the L-shaped connecting plate is provided with a through-hole; a limit block is provided on the top of the support plate; the limit block is embedded in the through-hole.

[0018] The piezoelectric transducer unit described above is a piezoelectric sheet arranged along the length of a deflection arch-shaped elastic beam; preferably, the piezoelectric transducer unit includes at least a first piezoelectric sheet group and a second piezoelectric sheet group; the first piezoelectric sheet group is placed in the crest region of the deflection arch-shaped elastic beam; the second piezoelectric sheet group is placed in the curvature transition region at the end of the deflection arch-shaped elastic beam.

[0019] An energy harvesting cluster, characterized in that: the energy harvesting cluster includes multiple frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting devices arranged in a matrix as described above.

[0020] The advantages of this invention are:

[0021] This invention provides a frequency-tunable inverted bow-shaped piezoelectric-electromagnetic composite energy harvesting device, comprising an inverted bow-shaped elastic beam, a piezoelectric transducer unit, a first electromagnetic conversion mechanism, and a second electromagnetic conversion mechanism. The structures of the first and second electromagnetic conversion mechanisms are identical. The piezoelectric transducer unit is mounted on the inverted bow-shaped elastic beam. The first and second electromagnetic conversion mechanisms are respectively fixed at both ends of the inverted bow-shaped elastic beam. The inverted bow-shaped elastic beam used in this invention employs a specific inverted geometric configuration, altering the stress distribution pattern of traditional straight beams or single circular arc beams. During vibration, the inverted portion can induce a significant geometrical nonlinear strain gradient, resulting in a substantial increase in the average strain energy density of the piezoelectric material bonding area, thereby achieving higher energy output under the same excitation intensity. The combination of the geometrical nonlinearity of the inverted bow-shaped elastic beam structure and the damping modulation effect of the composite transducer unit enables the system to exhibit nonlinear bistable or multistable response characteristics under wide-band vibration environments. This breaks the limitation of traditional linear collectors that resonate only within extremely narrow frequency bands, greatly broadening the effective operating frequency band. Simultaneously, this invention incorporates a piezoelectric transducer and an electromagnetic conversion mechanism on a curved, arched elastic beam, forming a piezoelectric-electromagnetic composite transducer. Specifically: the piezoelectric transducer utilizes the high strain characteristics of the curved, arched elastic beam to provide a high-voltage output, overcoming the voltage threshold required for low-power sensor startup; the electromagnetic conversion mechanism utilizes the large-amplitude vibration in the middle of the curved, arched elastic beam to provide a large-current output, increasing the system's overall power; the organic combination of the piezoelectric transducer and the electromagnetic conversion mechanism achieves complementary impedance characteristics, improving the energy injection efficiency to the downstream energy storage circuit. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device provided by the present invention;

[0023] Figure 2 This is an enlarged structural schematic diagram of the pre-position adjustment mechanism used in this invention;

[0024] Figure 3 This is an enlarged structural schematic diagram of the driving mechanism used in this invention;

[0025] Figure 4 This is an exploded structural diagram of the L-shaped connecting plate and support plate used in this invention;

[0026] in:

[0027] 1-Fixed base plate; 2-Drive slider; 3-Preload spring; 4-Support slider; 5-Magnet; 6-Support fixing block; 7-Induction coil; 8-Guide shaft; 9-Recurved bow-shaped elastic beam; 10-Piezoelectric sheet; 12-Limiting groove; 13-Electromagnetic transducer mechanism; 14-Circular plate; 15-Support box; 16-Gear; 17-Connecting pipe; 18-Rotating rod; 19-Gear plate; 20-Support plate; 21-Slide rail; 22-L-shaped connecting plate; 23-Limiting block; 24-Strip hole; 25-Support plate; 26-Slider. Detailed Implementation

[0028] See Figure 1 This invention provides a frequency-adjustable recurve-type piezoelectric-electromagnetic composite energy harvesting device. The frequency-adjustable recurve-type piezoelectric-electromagnetic composite energy harvesting device includes a recurve-shaped elastic beam 9, a piezoelectric transducer unit, a first electromagnetic conversion mechanism, and a second electromagnetic conversion mechanism. The structure of the first electromagnetic conversion mechanism is exactly the same as that of the second electromagnetic conversion mechanism. The piezoelectric transducer unit is disposed on the recurve-shaped elastic beam 9. The first electromagnetic conversion mechanism and the second electromagnetic conversion mechanism are respectively fixedly disposed at both ends of the recurve-shaped elastic beam 9.

[0029] See Figure 1The inverted bow-shaped elastic beam 9 used in this invention has an overall upward-arching circular arc shape, and near the first and second electromagnetic conversion mechanisms, it has a transition arc that bends outward (downward), forming a typical inverted bow geometry. The inverted bow-shaped elastic beam 9 can effectively disperse local stress concentration under large-amplitude excitation, reducing the risk of brittle fracture of the piezoelectric ceramic. Unlike straight beams or single-circular-arc beams, the inverted bow-shaped elastic beam 9 used in this invention has a unique "strain amplification" effect under compression, generating extremely high strain gradients in specific transition areas of the beam, i.e., exhibiting strong geometric nonlinearity under compressive deformation. This not only lowers the activation threshold of the piezoelectric material but also utilizes the nonlinear large deformation characteristics to induce the system to generate bistable or higher-order vibration modes, significantly improving energy harvesting efficiency under low-frequency vibration. Compared to linear structures, the inverted beam can trigger large deformation with a smaller excitation amplitude, and its potential energy curve has a flatter bottom characteristic. This results in a lower activation threshold and higher strain energy density in low-frequency environments, thereby significantly improving the output power of the piezoelectric unit. The inverted bow-shaped elastic beam used in this invention employs a specific inverted geometric configuration, altering the stress distribution pattern of traditional straight beams or single circular arc beams. During vibration, the inverted portion induces a significant geometrical nonlinear strain gradient, substantially increasing the average strain energy density in the piezoelectric material bonding area, thereby achieving higher electrical energy output under the same excitation intensity. The combination of the geometrical nonlinearity introduced by the inverted bow-shaped elastic beam structure and the damping modulation effect of the composite transducer unit enables the system to exhibit nonlinear bistable or multistable response characteristics under wide-bandwidth vibration environments. This breaks the limitation of traditional linear collectors resonating only within an extremely narrow frequency band, greatly broadening the effective operating frequency band.

[0030] The working principle of this invention is as follows: When low-frequency vibrations occur in the external environment, the inverted bow-shaped elastic beam 9 is excited and reciprocates up and down. The piezoelectric transducer deforms with the bending of the beam and outputs high voltage; simultaneously, the first and second electromagnetic conversion mechanisms vibrate with the inverted bow-shaped elastic beam 9, causing their opposing magnets 5 to shuttle through the corresponding induction coils 7, thereby cutting magnetic lines of force to generate induced current. This invention captures nonlinear vibrations through the inverted structure of the inverted bow-shaped elastic beam 9, achieves full-band energy coverage through piezoelectric-electromagnetic dual-mode operation, and achieves real-time tracking of the resonance point through motor-driven span conversion, thus solving the technical bottlenecks of low efficiency and narrow bandwidth in traditional energy harvesters.

[0031] See Figure 1 as well as Figure 2The first electromagnetic conversion mechanism used in this invention includes a fixed base plate 1, a magnet 5, a supporting fixing block 6, an induction coil 7, a guide shaft 8, and a supporting slider 4. The fixed base plate 1 serves as the installation reference for the entire device, and the supporting fixing block 6 is fixedly mounted on the fixed base plate 1. The guide shaft 8 is mounted on the supporting fixing block 6, and its axial direction is parallel to the plane of the fixed base plate 1. The induction coil 7 is fixedly mounted on the supporting fixing block 6, and its axial direction is parallel to the axial direction of the guide shaft 8. The supporting slider 4 is slidably mounted on the fixed base plate 1 relative to the supporting fixing block 6, and its sliding direction is parallel to the axial direction of the guide shaft 8. The magnet 5 is fixedly mounted on the supporting slider 4 and moves synchronously with it. The end of the recurved bow-shaped elastic beam 9 is mounted on the supporting slider 4. See also, for an example... Figure 1 The magnet 5 on the support slider 4 can be mounted on the top of the support slider 4 via a connecting rod and rigidly fixed by fastening bolts. When the recurved bow-shaped elastic beam 9 deforms under external force, the magnet 5 on the support slider 4 extends into or is pulled out of the induction coil 7. It should be noted that the magnet 5, the support fixing block 6, and the induction coil 7 constitute the electromagnetic transducer mechanism 13.

[0032] For example, the first electromagnetic conversion mechanism also includes a pre-position adjustment mechanism connected to the support slider 4. This pre-position adjustment mechanism can adjust the distance between the first and second electromagnetic conversion mechanisms, thereby changing the structural stiffness of the inverted bow-shaped elastic beam 9. That is, when it is necessary to adjust the system's natural frequency to match the ambient frequency, the pre-position adjustment mechanism adjusts the distance between the first and second electromagnetic conversion mechanisms, changing the prestress state and initial geometry of the inverted bow-shaped elastic beam 9, thereby achieving continuous adjustment of the system's resonant frequency. The frequency-raising principle of this invention is that when the two support sliders 4 move inward (span decreases), the bending stiffness of the inverted bow-shaped elastic beam 9 increases significantly, according to the forced vibration frequency equation... The system's natural frequency With stiffness The frequency reduction principle of this invention is that increasing the outward movement of the two supporting sliders 4 (i.e., increasing the span) reduces the equivalent stiffness of the system, thereby shifting the resonant frequency of the inverted bow-shaped elastic beam 9 towards lower frequencies. It should be noted that the adjustment via the pre-position adjustment mechanism is not merely a change in physical dimensions, but also a real-time reconstruction of the equivalent stiffness matrix of the elastic beam. By fine-tuning the span, linear or nonlinear compensation of the system's natural frequency can be achieved, ensuring the device always locks the resonance point under complex frequency conversion conditions (such as pump station speed switching). Changing the base spacing via the pre-position adjustment mechanism not only adjusts the resonant frequency but also optimizes the relative displacement between the magnet and the induction coil, as well as the prestress level of the piezoelectric element. This multi-parameter coupled adjustment allows the device to maintain optimal electromechanical conversion efficiency under different operating conditions.

[0033] For example, the pre-position adjustment mechanism used in this invention includes a drive slider 2, a pre-tension spring 3, a slide rail 21, and a limiting mechanism; the slide rail 21 is laid on the fixed base plate 1; the axial direction of the slide rail 21 is parallel to the axial direction of the guide shaft 8; the support slider 4 and the drive slider 2 are arranged sequentially from front to back on the slide rail 21 and move along the axial direction of the slide rail 21; the pre-tension spring 3 is placed between the support slider 4 and the drive slider 2; the limiting mechanism is placed on the slide rail 21 and limits the position of the drive slider 2; preferably, the limiting mechanism is a limiting pin or a wedge block. When it is necessary to adjust the system's natural frequency to match the ambient frequency, the first electromagnetic conversion mechanism drives the drive slider 2 and the second electromagnetic conversion mechanism drive the drive slider 2 to move symmetrically along the guide shaft 8 by the pre-position adjustment mechanism. By adjusting the span between the two support sliders 4, the prestress state and initial geometry of the inverted bow-shaped elastic beam 9 are changed, thereby achieving continuous adjustment of the system's resonant frequency.

[0034] Please continue reading Figure 2 The driving slider 2 used in this invention includes a support box 15; the bottom of the support box 15 is disposed on the slide rail 21 and moves axially along the slide rail 21; a cavity is provided inside the support box 15; one end of the preload spring 3 is fixedly disposed on the support slider 4, and the other end is fixedly disposed in the cavity inside the support box 15 through a circular plate 14. The preload spring 3 provides an outward initial thrust to the oppositely disposed support slider 4. Furthermore, as a preferred embodiment, the pre-position adjustment mechanism used in this invention also includes a driving mechanism connected to the driving slider 2, which drives the driving slider 2 to move axially along the slide rail 21. This driving mechanism can be a manual structure or a motor-driven structure. For example, see [link to relevant documentation]. Figure 3 The driving mechanism used in this invention includes a gear 16, a connecting pipe 17, a rotating rod 18, a toothed plate 19, and an L-shaped connecting plate 22. The toothed plate 19 is laid on the fixed base plate 1. The axial direction of the toothed plate 19 is parallel to the axial direction of the guide shaft 8. The rotating rod 18 is connected to the gear 16 through the connecting pipe 17 and drives the gear 16 to rotate around the axial direction of the connecting pipe 17. The gear 16 meshes with the toothed plate 19. The L-shaped connecting plate 22 is fitted outside the connecting pipe 17. One end of the L-shaped connecting plate 22 is fixedly connected to the support box 15, and the other end is movably set on the fixed base plate 1 and slidably connected to the fixed base plate 1. When the rotating rod 18 rotates, the rotating rod 18 drives the support box 15 to move along the axial direction of the slide rail 21 through the gear 16, the connecting pipe 17, and the L-shaped connecting plate 22. Gear 16 and gear plate 19 form a gear rack pair, which can realize step adjustment of the relative position of the two support sliders 4 in the range of 0.1mm. It can accurately change the boundary conditions and prestress state of the inverted beam and has the advantages of fast response, wide adjustment range and high stability.

[0035] The preload spring 3 provides a continuous axial preload to the supporting slider 4, ensuring that the mating surfaces of the gear and rack are always in close contact, eliminating backlash in the mechanical transmission chain, and ensuring the linearity and repeatability of frequency regulation. Under extreme vibration conditions, the preload spring 3 changes the elastic constraint coefficient of the boundary conditions. By adjusting the spring compression, higher-order vibration modes of the system can be fine-tuned, and it acts as a dynamic buffer under large-amplitude impacts, preventing permanent plastic deformation or fracture of the elastic beam 9. The introduction of the preload spring 3 effectively eliminates mechanical backlash in the gear and rack transmission system, improving the accuracy of frequency regulation. At the same time, when the environmental excitation is too large, the preload spring 3 can play a certain buffering role, protecting the anti-curved elastic beam 9 and its surface piezoelectric transducer unit from damage due to overload. When the sensor detects a drift in the environmental excitation frequency, the meshing transmission between the gear 16 and the toothed plate 19 controls the two driving sliders 2 to move symmetrically along the guide shaft 8.

[0036] To prevent the L-shaped connecting plate 22 from shifting position during movement, see... Figure 3 as well as Figure 4 The present invention provides a limiting groove 12 on a fixed base plate 1. For example, a support plate 20 can be connected to the side of the fixed base plate 1 (it should be noted that the support plate 20 is fixedly connected to the fixed base plate 1), and the limiting groove 12 is laid on the support plate 20. The axial direction of the limiting groove 12 is parallel to the axial direction of the guide shaft 8. The foot of the L-shaped connecting plate 22 is provided with a slider 26 that matches the structure of the limiting groove 12. The slider 26 is embedded in the limiting groove 12 and moves along the axial direction of the limiting groove 12. For example, the cross-section of the limiting groove 12 is T-shaped, rectangular, triangular, or dovetail-shaped.

[0037] See Figure 3 The drive mechanism also includes a support plate 25 mounted on the connecting pipe 17. The support plate 25 is movably mounted on the fixed base plate 1 and slidably connected to the fixed base plate 1. An L-shaped connecting plate 22 is provided with a through strip hole 24. A limit block 23 is provided on the top of the support plate 25. The limit block 23 is embedded in the strip hole 24.

[0038] See Figure 1 The piezoelectric transducer used in this invention is a piezoelectric sheet 10 disposed along the length direction of the inverted bow-shaped elastic beam 9 (especially on the upper surface of the inverted bow-shaped elastic beam 9). Exemplarily, the piezoelectric transducer includes at least a first piezoelectric sheet group and a second piezoelectric sheet group; the first piezoelectric sheet group is located in the middle crest region of the inverted bow-shaped elastic beam 9; the second piezoelectric sheet group is located in the curvature transition region at the end of the inverted bow-shaped elastic beam 9. Both the first and second piezoelectric sheet groups include one or more piezoelectric sheets 10. The high strain gradient generated in the corresponding regions during vibration is utilized by both the first and second piezoelectric sheet groups to improve transducer efficiency.

[0039] See Figure 1 In operation, when the external environment (such as mine machinery or ventilation ducts) generates vibration excitation, this excitation is transmitted to the entire device through the fixed base plate 1. Due to the specific mass distribution and geometric stiffness of the inverted bow-shaped elastic beam 9, it undergoes forced vibration under excitation, driving the transducer elements mounted on it to move. The vibration causes the inverted bow-shaped elastic beam 9 to undergo periodic bending deformation. Because of the significant strain concentration at the crests and end bends of the inverted bow configuration, the piezoelectric transducer units attached to these locations experience tensile and compressive strain. Based on the positive piezoelectric effect, the dipole moments inside the piezoelectric material align in an orientation, generating alternating charges on the electrode surface, thus converting mechanical strain energy into electrical energy. During the vibration of the inverted bow-shaped elastic beam 9, the magnet 5 of the electromagnetic transducer mechanism 13 reciprocates left and right. This movement causes the magnet 5 to shuttle through the center of the electromagnetic transducer mechanism induction coil 7 fixed at the bottom. According to Farad's law of magnetic induction, the magnetic flux within the induction coil changes periodically, thereby generating an induced electromotive force. This method directly converts the beam's vibration velocity energy into current output. This invention utilizes the dual characteristics of "large displacement" and "high local strain" during the vibration of an inverted beam to complete the coordinated conversion between electromagnetic (based on velocity) and piezoelectric (based on strain) within the same mechanical vibration cycle, thereby maximizing the utilization of energy density.

[0040] Clearly, the frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device provided by this invention operates on the core principles of the positive piezoelectric effect, the law of electromagnetic induction, and nonlinear structural dynamics tuning. It is more suitable for monitoring coal mine electromechanical equipment where vibration amplitude fluctuations are large and frequency modulation accuracy requirements are extremely high. This invention integrates mechanical frequency modulation, piezoelectric energy conversion, and electromagnetic energy conversion within a limited space. Its compact structure and significantly higher power generation efficiency per unit volume compared to single-mode harvesting devices provide a solid power foundation for the miniaturization and integrated design of wireless sensor nodes.

[0041] The core idea of ​​this invention lies in the deep integration of "nonlinear geometric gain" and "active mechanical frequency compensation". Traditional devices often choose between "environmental adaptability" and "energy conversion efficiency", while this solution simulates the biomechanical characteristics of a recurve bow, uses its natural curvature inflection point to concentrate strain energy, and combines the bottom sliding base to change the tension of the beam, thereby constructing a smart energy harvesting system with dynamically adjustable frequency and dual-mode energy composite.

[0042] This invention provides, in addition to the previously described frequency-tunable recurve-bow piezoelectric-electromagnetic composite energy harvesting device, an energy harvesting cluster formed based on this device. Depending on the operating conditions, multiple recurve-bow piezoelectric-electromagnetic composite energy harvesting devices can be used in a matrix configuration. This energy harvesting cluster can address dynamic operating conditions where the frequency varies with the load, such as in underground coal mines and industrial pumping stations. By actively tracking and real-time tuning the environmental excitation frequency, it solves the persistent problem of "disabling upon frequency deviation" in energy harvesting devices, ensuring the long-term reliable operation of the sensor's self-powered system.

[0043] This invention addresses the common problem that existing technologies often employ only a single piezoelectric or electromagnetic transduction method. While piezoelectric transduction offers high voltage, it results in extremely low current and struggles with impedance matching under high loads; electromagnetic transduction, while providing high current, suffers from very low output voltage, making it difficult to directly drive low-power electronic devices. This invention aims to achieve simultaneous high voltage and high current output under the same excitation source through a piezoelectric-electromagnetic composite structure design, leveraging the complementary properties of both methods. This significantly improves energy conversion efficiency and total power density per unit volume. Existing energy traps often employ linear cantilever beams or simple circular arc beams, which have extremely narrow resonance peaks and only exhibit high power generation efficiency at specific frequencies, exhibiting poor adaptability to random environmental vibrations. This invention aims to break the resonance limitations of linear systems by introducing a recurve bow-shaped nonlinear geometry. Utilizing the large deformation and geometric nonlinearity of the recurve beam under compression, it induces a wideband response, thereby maintaining a high level of energy capture over a wider frequency range. In traditional beam structures, stress often concentrates at the root or specific points during vibration, resulting in most of the piezoelectric material being in a low-strain state, thus failing to fully exploit its transduction potential. This invention aims to alter the stress transmission path within a beam by employing a unique curvature design in the shape of a recurve bow, thereby generating multiple high-strain regions within the beam during vibration. This enhances the overall participation of the piezoelectric material and improves its power generation efficiency. Existing devices have their natural frequency locked after manufacturing, making them unsuitable for complex scenarios such as coal mine excavators and industrial pumping stations where frequencies fluctuate with operating conditions. This invention addresses the technical challenge of energy harvesting devices failing to actively track and match environmental excitation frequencies by incorporating a mechanically adjustable frequency drive mechanism. This mechanism adjusts the span between the bases at both ends of the recurve bow, allowing for real-time changes to the system's initial state and equivalent stiffness. This ensures the device remains in optimal power generation condition.

Claims

1. A frequency-tunable recurve bow-type piezoelectric-electromagnetic composite energy harvesting device, characterized in that: The frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device includes a recurve bow-shaped elastic beam (9), a piezoelectric transducer unit, a first electromagnetic conversion mechanism, and a second electromagnetic conversion mechanism; the structure of the first electromagnetic conversion mechanism is exactly the same as that of the second electromagnetic conversion mechanism; the piezoelectric transducer unit is disposed on the recurve bow-shaped elastic beam (9); the first electromagnetic conversion mechanism and the second electromagnetic conversion mechanism are respectively fixedly disposed at both ends of the recurve bow-shaped elastic beam (9).

2. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 1, characterized in that: The first electromagnetic conversion mechanism includes a fixed base plate (1), a magnet (5), a supporting fixing block (6), an induction coil (7), a guide shaft (8), and a supporting slider (4); the supporting fixing block (6) is fixedly mounted on the fixed base plate (1); the guide shaft (8) is mounted on the supporting fixing block (6); the axial direction of the guide shaft (8) is parallel to the plane of the fixed base plate (1); the induction coil (7) is fixedly mounted on the supporting fixing block (6); the axial direction of the induction coil (7) is parallel to the axial direction of the guide shaft (8). Line; the support slider (4) is opposite to the support fixing block (6) and is slidably disposed on the fixed base plate (1); the sliding direction of the support slider (4) is parallel to the axial direction of the guide shaft (8); the magnet (5) is fixedly disposed on the support slider (4) and moves synchronously with the support slider (4); the end of the recurved bow-shaped elastic beam (9) is disposed on the support slider (4); when the recurved bow-shaped elastic beam (9) is deformed by external force, the magnet (5) on the support slider (4) extends into the induction coil (7) or is pulled out from the induction coil (7).

3. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 2, characterized in that: The first electromagnetic conversion mechanism further includes a pre-position adjustment mechanism connected to the support slider (4); the pre-position adjustment mechanism includes a drive slider (2), a pre-tightening spring (3), a slide rail (21) and a limiting mechanism; the slide rail (21) is laid on the fixed base plate (1); the axis of the slide rail (21) is parallel to the axis of the guide shaft (8); the support slider (4) and the drive slider (2) are arranged sequentially from front to back on the slide rail (21) and move along the axis of the slide rail (21); the pre-tightening spring (3) is placed between the support slider (4) and the drive slider (2); the limiting mechanism is placed on the slide rail (21) and limits the position of the drive slider (2); preferably, the limiting mechanism is a limiting pin or a wedge block.

4. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 3, characterized in that: The drive slider (2) includes a support box (15); the bottom of the support box (15) is set on the slide rail (21) and moves along the axial direction of the slide rail (21); the support box (15) has a cavity inside; one end of the preload spring (3) is fixedly set on the support slider (4), and the other end is fixedly set in the cavity inside the support box (15) through the circular plate (14).

5. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 4, characterized in that: The preposition adjustment mechanism also includes a drive mechanism connected to the drive slider (2).

6. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 5, characterized in that: The driving mechanism includes a gear (16), a connecting pipe (17), a rotating rod (18), a toothed plate (19), and an L-shaped connecting plate (22); the toothed plate (19) is laid on a fixed base plate (1); the axial direction of the toothed plate (19) is parallel to the axial direction of the guide shaft (8); the rotating rod (18) is connected to the gear (16) through the connecting pipe (17) and drives the gear (16) to rotate around the axial direction of the connecting pipe (17); the gear (16) and the toothed plate (18) are connected to the gear (16) through the connecting pipe (17) and drive the gear (16) to rotate around the axial direction of the connecting pipe (17); the gear (16) and the toothed plate (18) are connected to the gear (19) through the connecting pipe (18) and drive the gear (19) to rotate around the axial direction of the connecting pipe (17); the gear (16) and the toothed plate (19) are connected to the gear (19) through the connecting pipe (18) and drive the gear (19) to rotate around the axial direction of ... 9) Meshing; the L-shaped connecting plate (22) is fitted on the outside of the connecting pipe (17); one end of the L-shaped connecting plate (22) is fixedly connected to the support box (15), and the other end is movably set on the fixed base plate (1) and slidably connected to the fixed base plate (1); when the rotating rod (18) rotates, the rotating rod (18) drives the support box (15) to move axially along the slide rail (21) through the gear (16), the connecting pipe (17) and the L-shaped connecting plate (22).

7. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 6, characterized in that: The fixed base plate (1) is provided with a limiting groove (12); the axial direction of the limiting groove (12) is parallel to the axial direction of the guide shaft (8); the foot of the L-shaped connecting plate (22) is provided with a slider (26) that matches the structure of the limiting groove (12); the slider (26) is embedded in the limiting groove (12) and moves along the axial direction of the limiting groove (12); preferably, the cross section of the limiting groove (12) is rectangular, triangular or dovetail-shaped.

8. The frequency-tunable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to claim 7, characterized in that: The driving mechanism also includes a support plate (25) fitted on the connecting pipe (17), the support plate (25) being movably mounted on the fixed base plate (1) and slidably connected to the fixed base plate (1); the L-shaped connecting plate (22) is provided with a through strip hole (24); a limit block (23) is provided on the top of the support plate (25); the limit block (23) is embedded in the strip hole (24).

9. The frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting device according to any one of claims 1-8, characterized in that: The piezoelectric transducer unit is a piezoelectric sheet (10) arranged along the length of the inverted bow-shaped elastic beam (9); preferably, the piezoelectric transducer unit includes at least a first piezoelectric sheet group and a second piezoelectric sheet group; the first piezoelectric sheet group is placed in the crest region of the inverted bow-shaped elastic beam (9); the second piezoelectric sheet group is placed in the curvature transition region at the end of the inverted bow-shaped elastic beam (9).

10. An energy harvesting cluster, characterized in that: The energy harvesting cluster includes multiple frequency-adjustable recurve bow piezoelectric-electromagnetic composite energy harvesting devices arranged in a matrix as described in any one of claims 1-9.

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