An Atmospheric Energy Harvester System: Linear Model and Test

Energy harvesters are steadily gaining popularity as a power source for microelectronic circuits, particularly in wireless sensor nodes and autonomous devices. Energy harvesting from small temperature and/or pressure variations, coupled with an appropriate energy storage unit, can generate sufficient electric power to operate low power electronics. Ongoing research in this area seeks to improve the power capacity and conversion efficiencies of such systems. In this project, a phase change vapor based atmospheric energy harvester with an electromechanical power transformer has been developed. An ethyl chloride fluid system converts the pressure generated, in response to nominal environmental changes, into usable electric power through a mechanical driveline-spring unit and attached DC generator. Published numerical results have indicated 9.6 mW power generation capacity over a 24 hour period for a low frequency sinusoidal temperature input with ±1°C variation at standard pressure. A prototype electromechanical unit was fabricated and experimentally tested; 30 mW electric power for a resistance load was recorded using an emulated input corresponding to 50 bidirectional cyclic atmospheric variations (∼175 hour period). Linearized models were derived to help evaluate the system’s transient characteristics and these mathematical results agreed favorably with the experimental behavior.