Design and implementation of an out-of-plane electrostatic vibration energy harvester with dual-charged electret plates

Abstract This paper presents the design, simulation and implementation of an out-of-plane electrostatic power generator with dual-charged electret plates for low-level ambient kinetic energy harvesting. The rotational symmetrical resonator includes one movable disk-shaped circular mass and a series of spiral springs for suspension. The whole device is fabricated by CMOS compatible silicon micromachining technology with an overall volume of about 0.12 cm³. The two-plate device has both positive and negative charged electret plates. Experimental analysis shows that the present prototype is able to achieve an output power of 0.34 μW at a low resonance of 66 Hz at 0.5g, which corresponds to a normalized power density of 11.67 μW cm^-3 g^-2. With an acceleration changing from 0.1 to 0.5g, it is observed the operating half-power bandwidth increases by 2.6 times from 2.5 to 6.5 Hz. This may be attributed to the spring softening nonlinearity induced by the strong electrostatic force. The results could potentially provide an intriguing design methodology for developing nonlinear MEMS devices for broadband random energy harvesting.