A Non-Uniform Planar Coil in Electromagnetic Vibration Energy Harvesting for Enhanced Output Power

Abstract

Planar electromagnetic vibration energy harvester (EVEH) is a promising technology for compact, low form factor self-powered wireless devices. However, planar EVEH has the limitation of non-fully utilized magnetic flux gradient and low output power due to its structure constraint and weak magnetic flux gradient capturing capability. Planar coil is the key component in harvesting magnetic flux gradient and determining the output electromotive force (EMF) voltage and output power. A novel non-uniform distributed planar (NUDP) coil is proposed to break the current limitation of output power for the planar coil. The boost in output power is realized with tight inner windings and loose outer windings. The breakpoint is determined based on power increasing rate for each winding. The optimal winding radius for both inner and outer coils is investigated using discrete non-linear constraint heuristic optimization method. The designed NUDP coil-based EVEH achieves peak-to-peak output voltage of 305 mV and output power of 1.163 mW at 64.3 Hz resonant frequency and 0.05 g acceleration. It realizes 16.3% higher output power and 19.4% higher output voltage than uniform distributed planar (UDP) coil under the same spring and magnet. The power density of the proposed prototype reaches 9.616 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is 15.025 times higher than the state-of-the-art EVEHs with the planar coil.