Energy harvesting for assistive and mobile applications

Technology advances have enabled modification of the size and shape of the electronic components to the microscale, with commensurate scaling down of their power requirements to milliwatts and microwatt range. Consequently, many complex electronic systems and devices such as wearable medical and autonomous devices consume power in the range less than 200 mu W, and wireless sensor networks in the range mu W to 100 mW are operated on battery power. Due to the salient limitations of battery power, such as longevity of charge and where applicable, the requirement for periodic recharging, possibilities for utilization of autonomous energy sources is critical for operation of such devices. Ambient energy sources, such as vibrations (1 mu W to 20 mW), motion (wide range in power outputs), temperature gradient (0.5-10 mW), radiofrequency waves (>180 mu W/cm(2)), light (100 mu W/cm(2) to 100 mW/cm(2)), acoustics (0.003-0.11 mu W/cm(2)), and many other, have the potential to directly power the electronic device. Ambient energy harvesting, when used separately or in conjunction with batteries, will enhance the longevity of equipment operations requiring portable or autonomous power supply. This paper reviews the state of the art in energy-harvesting techniques, power conversion, and characterization of mini-and microscale self-sustaining power generation systems in the range 600 mu W to 5 W, specifically focusing on low-power system applications, for personal assistive and mobile technology devices.