On a spring-assisted multi-stable hybrid-integrated vibration energy harvester for ultra-low-frequency excitations

This work presents a spring-assisted multi-stable nonlinear vibration energy harvesting technique by integrating two working mechanisms (i.e., electromagnetic and triboelectric generators) into an interactive manner. To overcome the technical barrier of vibration energy harvesters with poor environmental adaptability, this hybrid design approach enables to harness more vibration energy under random and low-level excitation levels. In addition, we further incorporate a metallic spring-based multi-stable dynamical system that can simplify the mechanical design for working well in real-engineering conditions. Implementing the strategy of multi-stable nonlinear behavior, shallower potential wells of the dynamical system can be achieved by adjusting (i) the interaction between the outer fixed magnets and the inner moving magnet; and (ii) the inner moving magnet and its separation with the springs. This flexible arrangement is able to enhance the working performance under an ultra-low excitation threshold (1–5 Hz). By a parametric study, the influence of geometric parameters on the proposed system is analyzed. The experimental results indicate that the present device can produce a peak power of 165.3 mW under 5 Hz and 1 g, implying the estimated peak power density of about 2261.3 W/m³. The new design proposed here offers another perspective on the mechanical design and dynamical characteristics for efficient vibration energy harvesting.