With the threatening of global warming and energy crises, searching for renewable and green energy resources is one of the most urgent challenges to sustainable development of human civilization. Many portable devices may need micro- to milli-Watt scale power to operate. Battery is one of the best choices for many personal electronics and wearable electronics, the replacing, recycling and disposal can be a huge environmental problem. Thus, harvesting energy from environment may entirely replace battery and/or extend the lifetime of the battery for sustainable operation. The discovery of energy recovery systems is the top 10 world discoveries in science according to academicians of Chinese Academy of Science. It is now in the top six future and emerging technologies selected by European Commission for support in the next 10 years. One of company's strategies is to develop disruptive battery-less technologies for wearable/portable devices.
