The role of coupling strength in the performance of electrodynamic vibrational energy harvesters

This paper explores the role of a key dimensionless design parameter, denoted 'coupling strength', that governs the power generation performance of electrodynamic (electromagnetic) vibrational energy harvesters. The importance of coupling strength-and not just the electrodynamic transduction coefficient-on the output power and efficiency of the vibration energy harvesting device is presented analytically using a standard electromechanical model and validated using experimental results. It is shown that, up to a certain point, increasing the coupling strength of the harvester substantially increases the output power, resulting in improved electrodynamic coupling effectiveness and device efficiency. An electrodynamic harvester is designed such that the coupling strength can be varied through manual adjustments without altering the input vibration characteristics. Experimentally, the harvester is tested at a constant input acceleration amplitude of 0.74 m s(-2) at the device natural frequency of 28.1 Hz. By increasing the coupling strength of the device from 2.6 to 49.2, the output power increased from 0.64 to 1.06 mW. The corresponding electrodynamic coupling effectiveness increased from 0.53 to 0.92, and the mechanical-to-electrical device efficiency increased from 21% to 45.3%.