The recent potential benefit of nonlinearity has been to apply in order to improve the effectiveness of energy harvesting devices. For instance, at relatively high excitation levels, both low and high-energy responses can coexist for the same parameter combinations in a hardening type Duffing oscillator, and this provides a wider bandwidth and a higher energy harvesting effectiveness under periodic excitations. However, frequency or amplitude sweeps of the excitation must be used in order to reach a desirable high-energy orbit, and this gives a limitation on practical implementation. The motivating hypothesis has been that the frequency response curve can be shifted by tuning the stiffness of the system, and the jump from the low-energy orbit to the high-energy orbit can be triggered without changing the frequency or the amplitude of the excitation. This paper presents a stiffness tunable nonlinear vibrational energy harvester, whose equivalent linear stiffness can be tuned using variable damping control with an advantage that there is no need to consume extra energy. Theoretical investigations show the methodology for tuning stiffness, and simulation results have validated that the proposed method can be used to trigger a jump to the desirable state, and hereby this can improve the efficiency and broaden the bandwidth of the energy harvester.
