IMEC has fabricated an energy harvester to generate energy from mechanical vibrations by using micromachining technology. Output power as high as 40 micro-Watts was obtained, thereby achieving the range of required power for wireless sensor applications. The harvester comes with a model that can be used to optimize the device during design.
For an input vibration with a resonance frequency of 1.8kHz and an amplitude of 180nm, a maximum experimental output power of 40 micro-Watts was measured. This comes well in range of the amounts of power needed by wireless sensor applications, such as the pulse-oxymeter developed earlier by IMEC and IMEC-NL, operating from the Holst Centre in Eindhoven, The Netherlands.
More info here.