An internal resonance based broadband vibration energy harvester is proposed by introducing an auxiliary oscillator to the main nonlinear harvesting oscillator. Compared to conventional nonlinear energy harvesters, the natural frequencies of this two-degree-of-freedom nonlinear system can be easily adjusted to be commensurable which will result in more resonant peaks and better wideband performance. Experimental measurements and equivalent circuit simulations demonstrate that this design outperforms its linear counterpart. In addition to the open-circuit voltage, the optimal resistance to obtain the maximum power is determined. Nearly 130% increase in the bandwidth is achieved compared to the linear counterpart at an excitation level of 2 m/s2. The findings provide insight for the design of a broadband energy harvester when there is nonlinearity and internal resonance.

This article investigates a dual-beam vibration energy harvester in which two piezoelectric cantilever beams are coupled by magnets. The analytical solution of such a vibration energy harvester system is derived. The dynamic responses and energy harvesting performances in quasi-linear, monostable and bistable regions are evaluated. With the analytical model validated by numerical simulation, a comprehensive parametric analysis is conducted to evaluate the effects of base excitation, ratio of natural frequencies and electromechanical coupling, revealing the benefits and limitations of the dual-beam vibration energy harvester, which was not possible before without the analytical tool. The magnetic interaction provides the nonlinearity and can achieve high-energy oscillations for both beams at the same time for power enhancement. However, the analysis also ascertains that the trade-off between the dual beams should be made given the change of base excitation, ratio of natural frequencies and electromechanical coupling. For a certain range of excitation, the increased output of one beam is always accompanied by the decreased output of the other for the high-energy oscillations in both monostable and bistable configurations. By and large, the operational bandwidth is enlarged for both beams owing to the co-occurrence of high-energy oscillations of the dual beams, while the performance of the system as a whole is somewhat restricted by the trade-off.

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A piezoelectric vibration energy harvester (PVEH) is capable of converting waste or undesirable ambient vibration energy into useful electric energy. However, conventional PVEHs typically work in a narrow frequency range, leading to low efficiency in practical application. This work proposes a PVEH based on the principle of the nonlinear energy sink (NES) to achieve broadband energy harvesting. An alternating current circuit with a resistive load is first considered in the analysis of the dynamic properties and electric performance of the NES-based PEVH. Then, a standard rectifying direct current (DC) interface circuit is developed to evaluate the DC power from the PVEH. To gain insight into the NES mechanism involved, approximate analysis of the proposed PVEH systems under harmonic excitation is sought using the mixed multi-scale and harmonic balance method and the Newton–Raphson harmonic balance method. In addition, an equivalent circuit model (ECM) of the electromechanical system is derived and circuit simulations are conducted to explore and validate the energy harvesting and vibration absorption performance of the proposed NES-based PVEH. The response is also compared with that obtained by direct numerical integration of the equations of motion. Finally, the optimal resistance to obtain the maximum DC power is determined based on the Newton–Raphson harmonic balance method and validated by the ECM. In general, the NES-based PVEH can absorb the vibration from the primary structure and collect electric energy within a broad frequency range effectively.

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