Harvesting circuits for miniaturized photovoltaic cells

Miniaturized systems like wireless microsensors suffer from short operational lifetimes because they lack space to store the energy that wireless transmission, signal conditioning, and monitoring require to operate across time. Harvesting ambient energy circumvents this limitation because the environment is a virtually boundless reservoir of energy. Of available sources, solar light produces the highest power density, and although artificial lighting is not as rich, thermal and magnetic sources produce even lower power densities and mechanical and chemical transducers are difficult to integrate. The problem is microscale photovoltaic (PV) cells only produce 1 and 100 μW/mm² for artificial and solar lighting, so the act of conditioning and transferring power can dissipate most, if not all, of the power available. The focus of this paper is to introduce and discuss the design challenges associated with harvesting circuits when harnessing, conditioning, and transferring power from tiny PV cells that only generate 1-100 μW.