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2019 Vol. 40, No. 5
Published: 2019-10-28
381
Dynamic design and performance study of in-plane piezoelectric vibration energy harvesting
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.020
Piezoelectric vibration energy harvesting, which converts energy of the mechanical motions and vibrations that are commonly available in the surrounding environment to electrical energy, can realize self-power sensing, control and actuation. With the advantages of convenience, energy saving, eco-friendliness and sustainability, it has broad application prospects in the fields of aerospace, biomedical engineering, environmental monitoring and military engineering. In recent years, a lot of efforts have been made in piezoelectric vibration energy harvesting. There is still a long way to go to practical application. One of the key issues is the integrated design of the energy harvester. To facilitate the integration of piezoelectric energy harvesting devices with other small electromechanical systems, in-plane piezoelectric vibration energy harvesting is proposed. The piezoelectric vibration energy harvester is designed to be flat and harvest vibration energy in a two-dimensional plane, which can significantly reduce the three-dimensional space with a large power output. An in-plane piezoelectric vibration energy harvester with bistable and force amplification mechanism is designed to improve output power and working bandwidth. These structures can be carved by laser on a flat plate. The deformation and stress of the structures are analyzed. The electromechanical coupling dynamics model of the in-plane piezoelectric vibration energy harvester is established by the energy method. The influences of key design parameters on the performance of the in-plane piezoelectric vibration energy harvester are analyzed. Equivalent piezoelectric coefficient, bistable potential well depth and width can be adjusted by changing design parameters. The dynamic responses of the in-plane piezoelectric vibration energy harvester under harmonic excitation of different accelerations and frequencies are numerically simulated. The results show that the in-plane piezoelectric vibration energy harvester can effectively harvest energy under low frequency weak excitation and wide frequency range through reasonable design. The in-plane piezoelectric vibration energy harvesting design method is conducive to the application and industrialization of portable, wearable self-powered devices.
2019 Vol. 40 (5): 381-389 [
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390
The Difference on Steady State Responses of a Strongly Nonlinear System via Harmonic Balance Method and Complexification-averaging Technique
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.030
Recently, many scholars introduce intentional strong nonlinearities in the studied objects to enhance vibration control or energy harvesting. The responses of strongly nonlinear systems deserve to be evaluated more accurately in order to predict nonlinear effects in theory. Besides, as is known, the nonlinear energy sink (NES) can transfer or absorb the broadband vibration energy of a structure at both high and low frequencies its cubic nonlinear stiffness. First, both the harmonic balance method and the complexification-averaging technique are adopted and compared for acquiring steady state responses of the nonlinear dynamic system. The studied strongly nonlinear system contains a two-degree-of-freedom primary structure, which is subjected to a harmonic excitation, and a NES-piezo device. The NES-piezo device is composed of the nonlinear energy sink (NES) and a piezoelectric energy harvester. The two kinds of approximate analytical results are compared with numerical results. It is found that the two methods have a little difference in steady state responses when the nonlinearity of the system is not very strong. But if the system shows strong nonlinearity, the complex-averaging technique fails to obtain the high order’s responses, while the harmonic balance method can do this. Based on the conclusion, harmonic balance method is adopted to analyze the effect of an adding NES-piezo device on broadband vibration reduction. Two vibration cases are compared. One case applies the NES-piezo device and the other case only uses the NES. Results indicate that using the NES-piezo device will not deteriorate the efficiency of broadband vibration reduction. Furthermore, the responses near the first order resonant frequency can be improved slightly. Besides, results also demonstrates the integration of broadband vibration reduction and piezoelectric energy harvesting by an appropriate NES-piezo device. This research work shows similarities and differences of two approximate methods in solving problems of strong nonlinearity. It will contribute to choosing an appropriate approach when facing different nonlinear situation. And the integration of broadband vibration reduction and piezoelectric energy harvesting provide a theory significance.
2019 Vol. 40 (5): 390-402 [
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403
Theoretical modelling and analysis of piezoelectric vibration energy harvester based on stepped variable thicknesses cantilever beam with magnetic force
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.028
Vibration energy harvesting can be designed as self-powered devices for low power electronic such as wireless sensor network and wearable electronics. Thus, it have attracted much attention in recent years. In this work, a piezoelectric vibration energy harvester (PVEH) based on stepped variable thicknesses cantilever beam with magnetic force is proposed. First, the nonlinear magnetic force is introduced and the energy functions are obtained by using Euler-Bernoulli beam theory. The Lagrange Equation is applied to establish the coupled electromechanical dynamics equation. Finally, the influence of the distance between two magnets on the vibration characteristics of the system is examined. Moreover, the mono-stable and bi-stable responses are analyzed, and the effects of the distance between two magnets and external excitation amplitude on the vibration and voltage responses are investigated. It can be concluded that the magnets distance is the main factor affecting the potential energy of the system. There can occur monostable and bistable responses by adjusting the magnets distance, thus effectively improving the energy harvesting characteristics of the PVEH. Compared with the traditional piezoelectric energy harvester with constant cross-section cantilever beam, the proposed PVEH with magnetic stepped variable thickness cantilever beam can emerge obvious nonlinear phenomena and achieve broadband frequency responses by optimizing the structural parameters.
2019 Vol. 40 (5): 403-416 [
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417
Experimental Research on Piezoelectric Energy Harvester for Tip mass with Different Section Shapes in Low Water Flow Velocity
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.029
In this paper, a cantilever beam piezoelectric energy harvester suitable for low velocity water flow is designed. The five tips of the piezoelectric energy harvesters with the same mass and different section shape are experimentally studied in the open water channel. By changing the flow velocity in the water channel, the variations of power and frequency with the flow velocity for each energy harvester were obtained and compared. The results show that there is a starting flow velocity for every tip within the range of the experimental flow velocity, that the RMS power harvested by the piezoelectric energy harvester is about zero when the flow velocity is lower than the starting flow velocity; the power changes with the increase of the flow velocity, when the velocity is exceeding the starting flow velocity; the starting velocity of tip with similar section is relatively closer, the quadrangular prism is the lowest, cylinder is the next, triangular prism is the highest, that the energy harvest performance of energy harvesters with different tip is different, and the performance of triangular prism(70°) is the best, when the flow velocity is 0.54 m/s, the maximum power of 2.02 mW, which is 1.06, 2.58, 1.36 times as much as cylinder, quadrangular prism (50) and triangular prism (60°) respectively. The study can provide reference for the design of similar piezoelectric energy harvester.
2019 Vol. 40 (5): 417-426 [
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427
A new hybrid energy harvester for human motion power generation
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.022
Converting energy from human motions into usable electricity for powering the operation of sensors is always a hot topic in energy harvesting researches. Yet how to efficiently exploit human motion and improve the level of output power are still key problems to be solved as well as the environmental adaptability. Based on the feature of human walking or running, a new hybrid energy harvester is proposed and designed, with consideration of combining piezoelectric and electromagnetic mechanisms. The piezoelectric energy harvesting is based on the strain of a piezoelectric beam, while the electromagnetic generator employs the configuration of stacked magnetic group cutting the coil. The theoretical model for the hybrid energy harvesting system is constructed to describe the characteristics of output voltage on the base of lumped parameter model. The predicted results are compared with the experimental measurements. The comparison agrees well which indicates the feasibility of the present model. It is found that there are two peaks of output voltage within the excitation frequency region. The results show that these two peaks can be adjusted by varying the length of piezoelectric beam which is related with the nature frequency of energy harvester. In this way, the bandwidth of energy harvesting can be increased when the two peaks are closing to each other according to the excitation frequency in surroundings. In addition, human motion experiments display that the hybrid energy harvester can output high DC voltage in a short time, for instance, when the running speed is 5km/h, 1.1V DV voltage is produced in 3 seconds to drive the sensor to work. When the time length of running is 30 seconds, the sensor can work for 77 seconds by virtue of the hybrid energy harvester. The present hybrid energy harvester has abilities of quick charge and endurance which offers potential applications of charging battery or powering sensors.
2019 Vol. 40 (5): 427-440 [
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441
Research on Piezoelectric Energy Harvesting of Variable Triangular Cross-sections Based on Equivalent Circuit Method
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.019
With the gradual increase of the energy crisis, more research on piezoelectric energy harvester research is conducted. The common simulation methods which are used to study piezoelectric energy harvester can only study the performance when it is connected to a simple single-resistive load circuit. The coupling problem of high-intensity DC circuits cannot be solved. In order to overcome these problems. First, the main components of the piezoelectric energy harvester are equivalent to electronic components by the second-order van der Pol's governing equation. And then the equivalent circuit models corresponding piezoelectric energy harvesters with different triangular cross-sections are established, based on the equivalent circuit method, Next the correction of the established equivalent circuit model is verified by wind tunnel experiments. Finally, the influence of external circuit interface, the apex angle of bluff body, external resistances and inflow velocity on the output voltage, output power and response displacement of the galloping piezoelectric energy harvester are analyzed by the model. It is found that with the increase of external resistances, the output voltage gradually increases and the growth rate gradually decreases. The optimum load resistance of the AC-DC circuit is 1.05 MΩ and 1.4 MΩ respectively. When the wind speed is 7.03 m/s and the apex angle of bluff body is 90°, the peak output voltage and output power of the AC-DC circuit are 41.34 V ,0.974 mW, and 50.8 V, 0.616 mW respectively. As he apex angle of bluff body increases, the output voltage, output power and response displacement gradually increase and the increasing speed gradually decreases. The equivalent circuit model can efficiently and accurately study the output power, output voltage, response displacement and its influencing factors of piezoelectric vibration harvester with different structural parameters and external circuits interfaces. The proposed equivalent circuit model has certain significance in accelerating the research and application of piezoelectric vibration energy harvester.
2019 Vol. 40 (5): 441-450 [
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451
Modeling and validation of a clip spring structure applied in ultra-low frequency vibration energy harvesters
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.017
This paper established an equivalent stiffness model for a clip spring structure, which was usually applied in a kind of piezoelectric vibration energy harvesters, mainly based on Mohr’s method. The accuracy of the model was validated by the universal tensile testing machine. Two ways to linearity simplify the stiffness of clamp springs were discussed: through fitting the tension curve and modifying the stiffness according to the resonant frequency. The research results showed that it was reasonable to consider it as a linear spring from the tension curve; while in the practical vibration energy harvesters, the stiffness of the clamp spring could be linearly modified according to the natural frequency of the oscillating system, the calculated amplitude-frequency response characteristics were similar to those of the nonlinear dynamic model. The research results provide theoretical support for the establishment of a simplified dynamic and electromechanical coupling models in the field of piezoelectric vibration energy harvesters.
2019 Vol. 40 (5): 451-457 [
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Modeling and Experimental Investigation of Radial Electromagnetic Energy Harvesting for Self-powered Bearing Condition Monitoring
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.024
Recent advancements of wireless sensor and low power microelectrics make a great contribution to intelligent and networking health monitoring technologies. Due to key component of rotating machinery, bearings play a significant role on keeping the health state of defense, railway and wind turbines equipments. Therefore, miniaturization and self-powered methods of bearing state monitoring are important enabling technologies. This paper presents a radical electromagnetic rotating energy harvester for bearing condition monitoring to solve the power resource of wireless sensor node in the future and then introduces the circular Halbach array to improve the magnetic field of coils for performance enhancement. Based on the magnetic charge theory and space coordinate transformation, the calculation method of radial magnetic field distribution for circular Halbach array is proposed. Then the model of output voltage of the proposed energy harvester is established by electromagnetic induction. Moreover, the effect of different parameters on output voltage is numerically investigated by the proposed theoretical model. Finally, finite element simulation and experimental results under different speeds demonstrate the effectiveness of proposed model and that the proposed device can obtain the maximum output power of 81.2mW at 1000rpm.
2019 Vol. 40 (5): 458-466 [
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Design and experimental verification of dynamic multi-stable piezoelectric wind energy harvester
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.031
Aiming to overcome the inefficiency of flutter energy harvester for altering speed wind, a dynamic multi-stable flutter piezoelectric wind-energy-harvester was proposed in this paper. This harvester consists of a cantilever with a rectangular plate, three magnets and a piezoelectric patch. To prove the harvester’s superior performance in scavenging wind energy, a prototype was fabricated, and the validation experiment was carried out with the wind speed altering. The results show that the wind energy harvester exhibits the bi-stable characteristic for low wind speed; whereas it exhibits the tri-stable characteristic for high wind speed, in which case a neutral equilibrium position emerges and becomes stable gradually. The dynamic multi-stable harvester could execute snap-through and even coherent resonance for the wind speed ranging from v=2.0 m/s to v=7.5 m/s, thus it could generate a high output over the wide range of wind speed.
2019 Vol. 40 (5): 467-477 [
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478
A MEMS Piezoelectric Energy Harvesting System Based on Impact Frequency Up-conversion Mechanism
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2019.021
This paper proposes a MEMS piezoelectric energy harvesting system (PEHS) working with the impact-based frequency up-conversion mechanism. By using this mechanism, the problem that the natural frequency of the piezoelectric cantilever does not match the external excitation frequency is solved and the efficiency of energy harvesting is improved. The PEHS mainly consists of a low frequency stainless-steel cantilever with resonant frequency of 25 Hz and a high frequency piezoelectric cantilever with resonant frequency of 935 Hz. These two cantilevers are placed in parallel. The conversion of low frequency environmental vibration to high frequency piezoelectric beam vibration is realized through the collision between the bottom stainless-steel cantilever and the top piezoelectric cantilever. During one collision cycle, the bottom stainless-steel cantilever is firstly triggered to resonate under the external low frequency vibration excitation, then the stainless-steel cantilever collides with the top piezoelectric cantilever and they move upwards together. The models of an energy harvesting system in which a low frequency driving cantilever impacts a high frequency generating cantilever are established and discussed. The output performances of the single piezoelectric cantilever at different accelerations and the output performances of the PEHS under different initial distances are tested. Experimental results demonstrate that under the external vibration of 935 Hz, the maximum output voltage of the single piezoelectric cantilever is 74 mV and the maximum output power is calculated to be 0.11 μW at 1.0 g acceleration. While the maximum open-circuit output voltage of the PEHS can be 1220 mV at a relatively low excitation frequency of 25 Hz, the operating bandwidth of the PEHS is widened to 4.7 Hz and the maximum output power is calculated to be 8.6 μW at an acceleration of 1.0 g. It indicates that the impact-based frequency up-conversion mechanism can effectively reduce the operating frequency, widen the operating bandwidth and improve the vibration energy harvesting efficiency of the PVEH under low frequency and low acceleration vibration environment.
2019 Vol. 40 (5): 478-487 [
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