Scavenging or harvesting  energy from the in vivo environment is an important method for powering high energy-consuming ambulatory and sustainable biometric sensors and implants. Mechanical energy is abundant in the human body, but is difficult to harness due to severe design constraints. The purpose of this project is to prove feasibility of providing reliable and continuous power to high-power consuming in vivo devices long term (>2mW, >5 years). Possible sources of energy include mechanical vibration, fluidics, sonic/ultrasonic waves, and muscular contraction.