An Electronic Circuit for Trickle Charge Harvesting From Littoral Microbial Fuel Cells

In this paper, the design of an electronic circuit for harvesting energy trickling from benthic sources and the long-term performance in powering sensors and devices in a littoral tidal basin are considered. The process has to contend with the randomness, diurnal variations, and low levels and voltages in available energy compared to what is required by oceanographic sensors. The system has two components: a circuit for conditioning the power and a large area electrode array in a littoral basin. The circuit has two stages and is able to overcome the leaks in capacitors used to store the power; the energy is stored first in a small capacitor and then in a large one so that voltages compatible with sensors are produced. The footprint of the anode is 10 m² and is inserted into the sediment and the cathode resides in the salt water above the sediment. Several different sensors and actuators have been autonomously powered by the stored energy (4.2 kJ at 12 V). A beacon and an underwater acoustic sensor (5 h of activation of combined hydrophone and three-axis accelerometer sensors, every 40 h; duty cycle has been doubled with recent improvements) have been powered over one to two months. Also, in-water propulsion (for 165 s at a time) of a 25-W biorobotic flapping fin propulsor has been achieved. The system is suitable primarily for powering sensors. It has been operated for more than three years at useful duty cycles, indicating sustainability for autonomous usage.