Vibration energy harvesting using magnetic spring based nonlinear oscillators: Design strategies and insights

Abstract

The rising technologies of wearable electronics resulted in urgent demand for developing eco-friendly power sources that can utilize free energies around us including ambient vibrations. Magnetic springs are amongst the most common techniques used to build vibration energy harvesting systems that convert vibrational energy into useful electric power. Here, we present an experimental and theoretical platform for design guidelines and analysis of magnetic springs encountered in vibration energy harvesting systems. An energy harvester prototype consisting of an oscillating solid magnet levitated between two stationary ring magnets is constructed and used for experimental evaluation. Results show excellent agreement between model and experiment. The use of the analytical force model to represent magnetic force nonlinearities is essential at high accelerations. While the magnetic damping coefficient varies during dynamic operation and is dependent on the position of the levitated magnet, it is shown that approximating this coefficient as a constant provides accurate prediction of the dynamic behavior of the system. Approximate analytical expressions for linear and nonlinear stiffness coefficients are obtained. Results suggest that linear and nonlinear stiffness coefficients are coupled. The outer diameter of the stationary ring magnet can be used to tune the nonlinearity of the energy harvesting system to obtain linear, hardening nonlinear, or softening nonlinear response. This work serves as a tool for designers to understand the behavior of magnetic spring based harvesting systems and evaluate their performance in light of their design parameters. This work also can serve other energy systems that utilize magnetic springs including energy sinks.