Mechanical Engineer at US Army CERDEC CP&I
Appreciating the Ambient: Considering the Energy Harvesting Source
If we take the definition of energy harvesting to be, “the conversion of ambient energy into electricity”, then an energy harvester is fundamentally coupled, by definition and by design, to its application. Indeed, the two are closely related, since an energy harvester cannot exist without an ambient energy source from which to harvest its energy. As energy harvesting, as a field of study, has matured, focus has largely been given to deriving as much energy as possible, so as to justify the harvester’s existence. This focused pursuit of optimal power output has led to contempt for the ambient source. With the growing interest in wearable energy harvesters, it is no long tolerable to neglect the energy harvester’s effect on the source. Any wearable device must quite literally be “worth its weight”, and a design which has the net effect of increasing metabolic rate is not an energy harvester, as it is no longer powered by “ambient” energy, but rather is a deliberately powered device. A framework by which to describe an energy harvester’s effect on the source is presented, along with design considerations for minimizing the harvester’s impact on the source, with particular impetus is given to Soldier-wearable devices.