Electrostatic MEMS Vibration Energy Harvesters inside of Tire Treads

An electret electrostatic MEMS vibration energy harvester for tire sensors mounted inside of the tire tread is reported. The device was designed so as to linearly change an electrostatic capacitance between the corrugated electret and output electrode according to the displacement of the proof mass. The electromechanical linearity was effective at reducing the power loss. The output power reached 495 μW under sinusoidal vibration despite the footprint size being as small as 1 cm(2). Under impact vibration inside of the tire tread, the output power reached 60 μW at a traveling speed of 60 km/h. It was revealed that a higher mechanical resonance frequency of the harvester adjusted within the frequency band of a low-power spectral density of impact vibration acceleration was effective for high efficiency harvest impact vibration energy.