UC San Diego

As a result of the documented performance limitations of conventional linear piezoelectric energy harvesters, researchers have focused their efforts towards device designs that can better capture broadband energy. The approaches used can be classified into three categories: frequency tuning, multi-modal energy harvesting, and nonlinear energy harvesting1. Of the nonlinear harvesting approaches studied, bistable energy harvesters have been shown to have the most robust performance when subjected to broadband harmonic & stochastic excitation2-4. A conventional method for developing a nonlinear bistable restoring force is through use of magnetic repulsion. In these studies, a common theme of high-energy orbit breakdown occurs during a frequency upsweep. The issue at hand is the inability of the device inertial forces to overcome the potential energy barrier (separatrix) inherent to a bistable potential energy. This paper proposes the use of a high-permeability electromagnet for adaptively controlling the bistable magnetic repulsion force to expand the frequency bandwidth for high-energy harmonic oscillations. Numerical simulations of the nonlinear oscillator are used to study the system response under varying parameters of separation distance and electromagnetic coil current. An analytical model of the magnetic moment of an electromagnet is developed for use in studying the force interaction between repulsing magnets and to determine the parametric space that generates buckling loads in a cantilever bimorph energy harvester. © 2014 SPIE.