Energy in the small: Integrated micro-scale energy sources

Embedded energy sources are a key enabler for applications with limited or no physical access to external energy supplies. For nanomorphic micron-scale systems, such as integrated analytical microsystems, implantable diagnostics, and drug delivery devices, the available volume for on-board energy supplies is very limited. Thus, the capacity of an energy supply, both in terms of energy stored and the rate at which it can deliver energy, can place severe constraints on system design. This chapter investigates fundamental scaling limits for a variety of micron-sized energy sources, which include the galvanic and fuel cells, the supercapacitor, and radioisotope sources. Further, it is sometimes possible to directly harvest energy from the surrounding environment when the delivery of the energy can be either unintentional or directed. In the unintentional category, energy sources might include ambient electromagnetic, solar, vibration, fluid flows, thermal gradients, etc. An overview of the energy available for harvesting from a variety of sources is also provided.