Electrostatic generator with free micro-ball and elastic stoppers for low-frequency vibration harvesting

We present a new MEMS electrostatic vibration harvester that exploits mechanical frequency amplification by multiple-mass impacts in combination with elastic stoppers. When the system is shaken at low frequency (10-60 Hz) a tungsten micro-ball impacts within the oscillating proof mass of the harvester transferring kinetic energy to the gap-closing comb transducer which in turns resonates at its natural frequency (92 Hz). In addition, elastic stoppers amplify the proof mass and ball velocity throughout collision with the fixed frame. Output power between 0.25 and 0.45 μW is achieved at 0.3-g amplitude and only 15 V bias in the range of 10-60 Hz with a -3db bandwidth of 50 Hz.