Experimental analysis on the transduction coefficient of a non-linear electromagnetic energy harvesting device with softening stiffness

Nonlinear energy harvesting devices in the form of stiffness nonlinearity have emerged as among the effective solutions to overcome the performance limit of linear energy harvesting devices. However, up to now, researches on the nonlinear devices are only focusing on the ability to widen the bandwidth while the limit of employing linear transduction coefficient in a nonlinear system has yet to be heavily discussed. This paper investigates on the transduction coefficient for both linear and nonlinear systems of an electromagnetic energy harvesting device as a function of the excitation frequency. It is proven that the transduction coefficient of the nonlinear device is larger than its equivalent linear device, especially in the multi-stable solutions region. In common practice, the nonlinearity in the nonlinear system is considered weak, and its transduction coefficient is assumed to converge to the one produced by the linear system. The limits to which the transduction coefficient of a linear system can be employed on the nonlinear system were drawn based on the experimental analysis conducted on the proposed device. The device was designed to perform as a linear or nonlinear system, where the degree of nonlinearity was changed by varying the gap between the magnets. The limit of the transduction coefficient was determined from the analysis of the harmonic ratio. The results show that the linear transduction coefficient is valid to be employed to the nonlinear system when the harmonic ratio is less than five per cent at the multi-stable solutions region