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Nonlinear vibration energy harvesting has been mainstream research owing to its characteristics of broadband and high-output. However, the majority of existing energy harvesters are independent nonlinear structures, or one nonlinear structure combined with a linear structure. This article proposed the method that introducing internal nonlinear resonance structure to traditional nonlinear cantilever beam, improving the performance of it in low frequency effectively. Comparison experiments demonstrate that this method can promote energy harvesting with respect to an increase in the working frequency bandwidth by a factor of 4.4. Moreover, the maximum average power density is increased to 3570%. Based on the governing equations, the numerical simulations are implemented, which shows that internal beam with magnet has better performance than internal beam without magnet and its maximum amplitude can be increased by a factor of 7.8. Besides, two internal beams with magnets have the ability of frequency tuning as well. The experiment results and the numerical simulation validate that the superiority of double nonlinear structure, which provides a design idea for energy harvester subsequently.

Harvesting the ambient broadband vibrational energy is the ultimate objective of multi-stable vibration energy harvesters. The potential energy of a multi-stable system has more potential wells corresponding stable equilibrium states than a linear energy harvester, and the lower excitation energy is required to overcome the potential barriers to broaden the working bandwidth. However, for traditional multi-stable harvesters, increasing the number of stable equilibrium states to improve energy harvesting efficiency in random frequency bands is difficult. Without the need of external magnets generating static magnetic field, we propose an annularly-distributed poly-stable array which makes stable equilibrium states grow exponentially in maximum number. The experiments indicate that, comparing with a corresponding linear energy harvester, the working frequency bandwidth widened to 283%, the power density increased by a factor of 577 and the electric field energy raised to 133%. The proposed array shows the superiority in broadband vibrational energy harvesting and provides a solution collecting the abundant energy renewable in nature.