To supply power to this great amoun

To supply power to this great amount of sensors in the IoT networks and SHM systems, vibrational energy harvesters would be considered as great solutions since they are designed to harvest energies from external vibration sources, to supply the harvested energies to a sensor or device or to charge a battery, and to make possible completely self sustainable wireless sensor nodes or devices free from wiring needs. An increasing number of studies have been conducted on micro-electro-mechanical systems (MEMS) vibrational energy harvesters (MEH) and several classical works can be found in literature, e.g. reviews by Beeby et al. (2006) and Mitcheson et al. (2008).Recently, a new cantilever-type MEMS electrostatic energy harvester using potassium ion electrets was developed and fabricated (Koga et al. 2017). The developed device having a 14.4 g proof mass could generate 115 μWRMS power by 0.003 GRMS acceleration and could establish an electric energy of 4.8 mJ stored in a 44 μF capacitor in 90 min in a charging experiment using an acceleration waveform measured on a field viaduct. The current study was a subsequent study using the MEH of the same type.