Ambient vibration energy harvesters: A review on nonlinear techniques for performance enhancement

Vibration energy harvesters are emerging as a promising solution for powering small-scale electronics, such as sensors and monitoring devices, especially in applications where batteries are costly or difficult to replace. However, current vibration energy harvesters are only effective within a limited frequency bandwidth, whereas most ambient vibrations occur randomly over a wide frequency range. Many techniques, such as tuning, coupling between modes, multimodal arrays and hybrid transduction methods, can be used for performance enhancement of vibration-based energy harvesters. Among these techniques is the introduction of nonlinearities to the energy harvesting system. In most cases, using nonlinear techniques for energy harvesting results in a larger frequency bandwidth when compared to a linear system. In certain systems, the introduction of nonlinearities can also result in a higher amplitude response. The aim of this paper is to conduct a critical review of nonlinear techniques which have been investigated for performance enhancement of energy harvesters in the past decade and present state of the art of energy harvesters which utilise this technique. This includes discussions of several techniques that have been employed for enhancing energy harvesting, such as stochastic loading, internal resonances, being multi-degree-of-freedom, mechanical stoppers and parametric excitations, which all lead to nonlinear behaviour and enhancement of the system. These techniques are capable of significantly extending the frequency bandwidth and, in some cases, increasing the amplitude response. The enhancement in performance results in devices that can harvest energy more efficiently from ambient vibrations.