Alternative power sources for miniature and micro devices

Energy harvesting, which in the modern literature can be traced back to the late 1990s, has been thought of as a ground breaking substitute for exhaustible energy sources for powering miniature and micro devices. However, there are still very few areas in which harvesters, at either the MEMS or macro-scale, have made significant impact. In comparison, a different technological solution to the same problem, that of wireless power delivery, either as near- or far-field electromagnetic transfer, is already gaining traction in several areas from charging electric vehicles to powering mobile devices. In this paper, the state of the art in each of these areas is discussed, and the future research challenges considered in the context of powering nodes in a wireless sensor network for the internet of things. None of the technologies scale well as dimensions reduce but solar, inductive power transfer and inertial energy harvesters are the most promising technologies at mm to cm scale. Power delivery techniques such as inductive power transfer are readily able to supply mW power levels to WSN nodes if human exposure to magnetic fields is not of concern in a particular application.