Energy Harvesting Systems
Thin-film energy management system fabricated at low temperatures (below 150 C) with an inherent potential for seamless integration with a range of mobile devices with the aim of extending their battery life. The overall system architecture and the TFT charging circuit are presented. An analytical description of the circuit is presented, where the effects of light intensity and bias stress on the output voltage stability are analyzed. In addition, we examine the dependence of the system efficiency on circuit design parameters. At the optimum efficiency point, stability of circuit output voltage under various light intensities and electrical stress is examined. Finally, the system is cycled through a light–dark cycle and its self-discharge is measured. Section VI concludes the work by considering possible systems applications.
Wireless power transfer is experimentally demonstrated by transmission between an AC power transmitter and receiver, both realised using thin film technology. The transmitter and receiver thin film coils are chosen to be identical in order to promote resonant coupling. Planar spiral coils are used because of the ease of fabrication and to reduce the metal layer thickness.
Thermoelectric Energy Harvesting Devices
Thermoelectric generators operate by converting a temperature difference to electricity as depicted above. Oxide thermoelectrics are an upcoming class of thermoelectric materials with the advantage of being abundant, transparent, and eco-friendly in comparison to the conventional bismuth and lead compounds, skutterudites, silicides, and clathrates. They can withstand temperatures up to 1200K without chemical instability in air, allowing for a wide range of applications. Thermoelectric generators are designed based on p-type and n-type oxide thermoelectric semiconductors with the aim of improving the thermoelectric figure of merit zT, which is a measure of the thermoelectric efficiency. Methods of improving zT include doping to increase carrier concentration and electrical conductivity; and reduction of grain size to the nanoscale to decrease thermal conductivity.