DESIGN AND ENERGY CAPTURE CHARACTERISTICS OF MAGNETICALLY COUPLED BISTABLE WIDE BAND PIEZOELECTRIC ENERGY HARVESTER

In order to improve the efficiency and practicality of energy harvester simultaneously, the compatibility of the vibration characteristics of the energy harvester and the environment is of utmost importance. The complex dynamic behaviors of nonlinear system lay important foundation for designing efficient energy harvesters. However, once the structures are designed and fabricated, their work frequencies are decided and invariable, and cannot be adjusted to adapt the vibration in environment. A movable hinge support and nonlinear magnetic force are introduced in this paper to design a wide band piezoelectric energy harvester with bistable states. The vibration properties of the designed energy harvester can match with the wide vibration frequencies in environment by widening its working band. In order to make sure the low frequency and wide band energy capture ability, we analyze the influences of structural length ratio, distance between magnets, load impedance, frequency and amplitude of external excitation on the linear stiffness, nonlinear stiffness and dynamic behaviors characteristics of the designed energy harvester system in detailed. Experiments are tested to validate our design and results. Firstly, the designed magnetically coupled bistable wide band piezoelectric energy harvester is simplified as a Euler-Bernoulli beam. Then, the nonlinear dynamic equations of the system are deduced by the Lagrange equation, which can be solved via harmonic balance method. The optical length ratio according to different frequency of external excitation are forecasted theoretically and validated via experimental tests. Numerical and experimental results show that the introduced nonlinear magnetic force makes the system exhibit negative stiffness, which enables the system to switch between monostable and bistable states and finally realize energy capturing in low frequency. What’s more, it can change the length ratio of the designed system by adjusting the location of the movable hinge support, which can make the system capture energy with a wide band from 0 to 16 Hz.