Analysis On The Nonlinear Multi-Field Coupling In Piezoelectric Compound Structures And Experimental Study On Piezoelectric Energy Harvesters

Due to their excellent electromechanical (EM) coupling, piezoelectric compound structures (PCS) have been widely applied in acoustical wave devices like piezoelectric energy harvesters, piezoelectric transformers and piezoelectric resonators, etc. Progress in this field has greatly promoted the more in-depth development of the modern intelligent structural control and wireless energy supply. Because there exists complicated multi-field coupling in PCS and this coupling gradually appears strongly nonlinear with the miniaturization and integrated circuit developments of microelectronic devices, solving those physical quantities in PCS becomes very difficult. In this dissertation, dynamic equations of PCS are established from the three-dimensional electroelastic theory together with the introduction of nonlinear deformation. Then, in-depth studies are conducted on the linear and nonlinear characteristics of several typical piezoelectric acoustic wave devices. A few new conclusions are drawn from the analysis. Finally, some experimental studies are focused on piezoelectric energy harvestors with the results in agreement with our previous theoretical analysis. The important research achievements are as follows:(1) A novel torsion-type low-frequency piezoelectric energy-harvesting structure is put forward, which can effectively extract energy from low-frequency ambient vibrations. The structure/circuit coupling model of such harvesters is established. The effects of various system parameters on harvester performances are clarified in detail.(2) Several typical nonlinearly-dynamic model of piezoelectric energy harvesters are established by introducing nonlinear deformation of PCS. Considering that the polarization voltage and boundary charge are caused by two deformations, bending and in-plane stretching, the voltage and charge caused only by bending are distinguished from the remainders. Then the output voltage and current of the energy-harvesting structure are redefined in terms of the identified polarization voltage and boundary charge by bending. Moreover, the nonlinearly-dynamic behaviors of several typical piezoelectric energy-harvesting structures in the vicinity of resonance are analyzed. The multi-valuedness and jumping of output power are revealed, and the important influences of system parameters on the nonlinear region of harvesters are clarified, which are useful in harvester design.(3) A nonlinearly-dynamic model of5-layer piezoelectric transformers is established and the nonlinearly-dynamic behavior of the piezoelectric transformer structure in the vicinity of resonance is analyzed. The multi-valuedness and jumping of output/input voltage ratio are revealed, and the important influences of system parameters on the nonlinear region of transformers are clarified, which are useful in transformer design.(4) An experiment model is established for a piezoelectric bimorph harvester. In the model, a linear vortex sensing circuit is applied to catch the displacement maximums via the EM similar relationship in a linear EM system. Then, a differential full-wave rectified microcontraller is self-designed to periodically control the switch in series with the SSHI. The voltage reversal has been successfully achieved through the controlled SSHI at the displacement maximums. Finally, the experiments on the nonlinear coupling between piezoelectric structure and energy-storage circuit are conducted. Experiment results has verified our previous theoretical analysis.In summary, we presents a torsion-type low-frequency energy harvesting structure. The linear and nonlinear characteristics of piezoelectric harvesters and piezoelectric transformers are investigated in depth through the integrated analysis with harvesting-structure/storage-circuit full coupling. A few meaningful conclusions have been drawn in the dissertation. The achievements not only are of important guiding significance for the optimal design of piezoelectric harvesters and transformers, but also have a larger role in promoting further cross-discipline and the integration.