Modeling And Experimenetal Research On Piezoelectric And Coupled Piezoelectric-electromagnetic Energy Harvester Based On Beam Structure

With the recent advances in the integrated circuit technology, there is a trend towards the miniaturization. Power supply for micro electromechanical systems (MEMS) has attracted interest from many researchers. To date, many wireless sensors are battery powered. However, the use of battery brings not only the troubles of short life and costly replacement work, but also limitation for miniaturization in MEMS. As a potential candidate, the mechanical vibration exists widely in daily life and it can be converted into electricity via electrostatic, electromagnetic and piezoelectric transductions. Harvesters using electrostatic transduction are easy to integrate into MEMS; however, their applications are restricted because of requiring the additional excitation power supplies. Compared with electrostatic energy harvesters, the piezoelectric energy harvesters (PEHs) and the electromagnetic energy harvesters (EMEHs) have the advantages of no external excitation power supplies. In addition, the PEH has the advantages of high power density and easy to fabricate and the EMEH has the advantages of small resistance and large output current. To date, the researches on vibration energy harvesting based on piezoelectric and elecrtromagnetic conversion mechanisms have received increasing attention from scholars at home and abroad.The useful power level can be achieved only when the excitation frequency is close or equal to the natural frequency of the energy harvester. However, the vast majority of practical vibration sources are present in the frequency-variant. Hence, a critical issue in vibration energy harvesting research is how to increase the bandwidths of the energy harvesters. In this paper, the focus are on three piezoelectric and electromagnetic energy harvesters based on the beam structures, namely, the cantilevered PEH with segmented electrode configuration (SEC), the PEH based on coupled beam structures and the coupled two-degree-of-freedom (2DOF) piezoelectric-electromagnetic energy harvester (P-EMEH). The mathematical models of three energy harvesters are established separately. The effect of the electrode configuration, structure design and the multi-principle approach on the resonant frequencies and power outputs are studied respectively. The validities of the mathematical models are validated by the experiments methods. The results provide theoretical and experimental foundation for improving the performance of the PEH and the coupled P-EMEH based on beam structures.Vibration modes of a cantilevered beam other than the first mode have certain strain nodes where the dynamic strain distribution changes sign. SEC can avoid the cancellation of the electrical outputs. As a PEH with multi-output-ports intended to deliver the power to a common load, an interfacing circuit including multiple rectifiers is required. For evaluating the performance of the PEH with standard rectifier circuit, at first, a mathematical model of cantilevered PEH with SEC is established based on piezoelectric theory and Rayleigh-Ritz method. Based on the mathematical model, the equivalent circuit model (ECM) of cantilevered PEH with SEC is established and the ECM parameters are determined from theoretical analysis and FEA. Furthermore, the ECM is established in SPICE software and the multi-model power outputs of the PEH with SEC are evaluated when considering the practical rectifier circuit. Finally, the validity of the mathematical model is validated by experiment method. The power outputs of SEC are compared with those from CEC. The results demonstrate the feasibility of using SEC as a simple and effective means to improve the performance of a cantilevered PEH at a higher mode.When designing a multimodal energy harvester, multiple resonance frequencies close to each other are rationally preferable. However, high-modes of the cantilevered PEH are far away from the first mode. The coupled elastic structures have multiple resonance frequencies close each other. In this paper, the mathematical model of a PEH coupled with a clamped-clamped beam with a central mass is established. The effect of the mass ratio of piezoelectric cantilever to the clamped-clamped beam with a central mass and the damping ratio of the clamped-clamped beam on resonance frequencies and peak power outputs are analyzed. The analytical results are compared with those from FEA. The results show that as the mass ratio increases, two resonance frequencies are closer each other and both two peaks increase; as the damping ratio of clamped-clamped beam increase, both two peaks reduce. For avoiding torsional vibration of the clamped-clamped beam, a single piezoelectric beam is turned into double piezoelectric beams of the symmetric configuration. The experiment models results verified the rationality of improved structure and the validity of the mathematical model.Except for the study on the performance of the PEH, in this paper, the performance of a coupled2DOF P-EMEH is studied. A mathematical model of2DOF P-EMEH is established based on piezoelectric theory and the law of electromagnetic induction. The system parameters are obtained from the experiment. The effects of the mass ratio, the natural frequency ratio and the electromechanical coupling coefficients on piezoelectric, coil and total power outputs are analyzed separately. The results show that as the mass ratio is reduced or the frequency ratio is increased, the first peak power outputs of2DOF P-EMEH are improved. As the electromechanical coupling coefficient of the PEH or EMEH is small, the power outputs of2DOF P-EMEH are improved when compared with2DOF PEH or2DOF EMEH. However, as the electromechanical coupling coefficients are very close to the saturation value, additional electromechanical transducer can’t improve power outputs of the original harvesters.