Energy budget and high-gain strategies for voltage-constrained electrostatic harvesters

Wireless micro-sensors and similar technologies must derive their energy from micro-scale sources (e.g., thin-film Li Ions, etc.) to function in volume-constrained environments like the human body. Unfortunately, confining the source to small spaces limits the total energy available to such an extent that operational life is often impractically short. Ambient energy offers an alternate and virtually boundless source, except small volumes restrain harvesting power. Voltage-constrained electrostatic CMOS harvesters, for example, draw energy from the work done against the mechanical plates of a MEMS variable capacitor at relatively slow rates, producing low output power. This paper discusses how much energy is available in such a system before and after harvesting and offers energy-conservation schemes for increasing its net energy gain (i.e., power output) during all operational phases.