Published online by Cambridge University Press: 05 October 2014
Electronics is progressively penetrating more deeply into human lives: integration has made possible the wealth of many small mobile devices that society currently enjoys (e.g. smart phones, MP3 players, GPS navigation assistants, etc.). In this scenario, active RFID systems hold the promise of implementing smart environment and objects, and can ease processes in many applications fields, e.g. industrial processes, personal healthcare, environmental monitoring. Pervasive computing and wireless sensor networks are introducing their potential while power consumption has been greatly reduced thanks to energy-aware design techniques. The availability of low cost batteries has been one of the main drivers of these advances, even though it now represents one of the main limitations. In fact, power supplies still mainly rely on electrochemical cells with limited stored charge and are often impracticable to replace.
During the last years energy harvesting from ambient sources has proven to be a viable solution: the environment is an intrinsic source of low-density highly available energy  in either steady or intermittent and irregular forms such as, for example, vibrations , thermal gradients , indoor light , and electromagnetic radiation . At the current state of the art, most energy harvesters can provide in practical cases an output power density of about 10–100 µW/cm3 . In this scenario, mechanical vibrations represent a viable solution for powering low power electronic systems (e.g. wireless sensor nodes, personal healthcare devices, etc.).