A miniature harvester of vertical vibratory capacitive type achieving several tens microwatt for broad frequency of 20–40 Hz

The vertical harvester with double swastika-spring has a dielectric beneath a counter electrode. The discharge is avoided due to using the dielectric. Thus, the counter electrode can contact with an electret surface. The device can generate the power as far as the input acceleration is enough for the mass to reach the electret surface, even at the frequency apart from the resonant one. It leads to high output power for broad frequency bandwidth. There is almost no hysteresis between the up sweep curve and down sweep one. Thus, the device can generate a stable output against frequency change.