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Vibration energy harvesters with bistable characteristics, which can convert mechanical energy to electric energy, are typically cantilever beams with magnetic repulsion. In order to enhance their low-frequency performance, a seesaw-type approach has been proposed, which can make the structure overcome the potential barrier more easily. In this paper, we establish electromechanical coupling equations of the whole system, and prove that the internal beam delivers mechanical energy to the primary beam based on time-domain analysis. Meanwhile, frequency-domain analysis and solutions are conducted to investigate the dynamical and electrical behaviors of the system based on the adjustment of different parameters. We find that both the mechanical and electrical responses are enhanced gradually with the decrease of the relative damping coefficient within the bounds of the discussion. And the maximum response amplitude can be increased by a factor of 11.3 just by adjusting the position of the internal beam. Furthermore, the length of the internal beam can affect the responses of the system visibly and regularly, and the maximum response amplitude remains unchanged when changing the length of the internal beam from 80 to 100 mm. All of this suggests that the mechanisms of a seesaw-type energy harvester will provide guidance for designing a more appropriate structure, depending on different applications.

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.