Harvesting mechanical energy for ambient intelligent devices

This paper deals with mechanical energy harvesters, power management and energy storage devices as important building blocks for wireless autonomous sensor networks. The basic task of the harvester is to convert vibrational into electrical energy. As these energy harvesting devices shrink in dimensions, while still providing sufficient energy, they will be key enablers for wireless autonomous sensor networks. For such a purpose, vibration harvesters are being investigated which feature a footprint of 1 cm(2) and an average power harvesting level of 100 mu W. A detailed description of the design and fabrication for the piezoelectric, electrostatic and electromagnetic harvester is given. Furthermore, the interaction between a piezoelectric vibration energy harvester, the power converter and the energy storage system is investigated. A system level approach, including mechanical and electrical domains, is pursued for impedance matching between both domains in order to investigate the physical design aspects of the energy harvester on the electrical domain. Two matching methods, such as complex and real matching, are presented and compared to each other. Finally, several energy storage systems are briefly presented in order to store the irregular available scavenged energy and supply the functional circuitry in the system like sensor(s), signal processing and transceiver. In order to reduce power consumption, the transceiver operates in pulsed load condition which makes the energy storage system crucial.