Design of a broadband piezoelectric energy harvester with piecewise nonlinearity

In this study, a novel broadband piezoelectric vibration energy harvester (VEH) is constructed using piecewise nonlinearity. The VEH consists of a piezoelectric cantilever beam and a cylindrical cam-roller-spring structure that can produce negative stiffness and piecewise nonlinearity. The designed piecewise nonlinear force consists of two sections. The first section keeps the nonlinear force small, so that the VEH generates a high peak power, and the second section makes the nonlinear force increase sharply, so that the VEH has a wide bandwidth. Therefore, the designed VEH has higher peak power and wider bandwidth than those VEHs based on smooth magnetic nonlinearity or spring nonlinearity. Firstly, a dynamic model is developed and the steady-state periodic responses are obtained by the average method. Then, the influences of the structure parameters of the cam-roller-spring on the performance of the VEH are studied. The results show that compared with the linear system, the piecewise nonlinearity can increase the peak voltage from 28.9 to 64.6 V, increasing by 123%; it can increase the peak power from 0.84 to 4.17 mW, increasing by 396%; and it can increase the operating frequency range from 0.99 to 6.48 Hz, increasing by 554%. Finally, the energy harvesting performance of the designed VEH is compared with the widely used magnet-type and spring-type VEHs, in which the nonlinear forces are smooth. The results show that the proposed VEH has a 9.67% increase in peak power, a 79.2% increase in the frequency band, and a 4.2% increase in maximum efficiency than the magnet-type VEH; and has a 23.5% increase in peak power, a 5.01% increase in the frequency band, and an 8.8% increase in maximum efficiency than the spring-type VEH.