Optimization of an Electromagnetic Generator for Underwater Energy Harvester

Energy harvesting devices can increase autonomy of submersible marine sensors. However, only the water movements can be used as energy source, since neither solar or temperature gradients are available bellow surface waters. A Linear Electromagnetic Generator (LEG), in a milliwatt energy harvester, is presented. Any moving parts are in contact with water, thus avoiding biofouling problems in the harvester. In this work, a 100mm length, 60mm diameter, cylindrical LEG was designed to maximize output power, and analyzed the effects of magnets size and geometry as well as coils position, at several working conditions. Two coils were used, with an internal resistance of 130 Ω in 1500 turns, together with N38-N42 magnets. A mean electrical power of 25 mW (100 mW peak) was experimental measured in the optimized configuration, in realistic conditions, which is enough to power almost any electronic low-power sensor.