Design and analysis of a small-scale magnetically levitated energy harvester utilizing oblique mechanical springs

In this work, we present an electromagnetic, vibration-powered energy harvester utilizing hardening and negative stiffness mechanisms simultaneously. Since most vibrational energy sources' frequency-response spectrum are broadband, the energy harvester is designed to generate electrical power across a wider frequency range. This nonlinear energy harvester consists of a magnetic mass in-between two stationary magnets. However, instead of using a guiding structure or tight-fit container, oblique mechanical springs are used to align the moving magnet and eliminate Coulomb dry friction. The hardening effect of the magnetic springs increases the resonant frequency of the system, and the negative stiffness behavior of the mechanical springs improves the harvester's response towards the lower frequency spectrum. A nonlinear dynamic model of the device is developed using conservation laws, and a proof-of-concept prototype is fabricated. Simulations and experiments show good agreement and exhibit broad frequency spectra. For a base excitation of 0.75 g, the proposed prototype generates a peak voltage and normalized power density of approximately 2.95 V and 0.136 mW/cm(3)g(2), respectively. Although the normalized power density is not optimized, the prototype performs well with respect to other state-of-the-art electromagnetic energy harvester designs. Optimization of the proposed hand-held energy harvester prototype allows for the replacement of chemical batteries used in wireless sensor networks and mobile applications.