Electrostatic And Piezoelectric Micro Energy Harvesters For Environmental Vibrational Energy Scavenging

Abstract

Nowadays wireless sensors are widely used in all kinds of fields such as biomedical, commercial and military. Micro energy harvesters converting the wasteful energy from environment into electricity enable the possibility of self-powered wireless sensor systems. This dissertation aims to develop micro energy harvesters to harness wasted mechanical vibrational energy. An electrostatic micro energy scavenger was designed to incorporate MEMS comb-drive in-plane overlap as well as in-plane gap closing topologies into one hybrid structure. The device geometry and dimensions were optimized to maximize the energy harvesting efficiency. UV-LIGA process combined with nickel electroplating was utilized to fabricate the devices. A shaker platform in conjunction with a calibrated accelerometer was used to measure the harvested AC voltage with varying acceleration. A peak to peak value of 0.800 V was generated under an external acceleration magnitude of 78.4 m/s2 at a vibration frequency of 1.90 kHz. The electromechanical simulations agreed with the measured data. Design, fabrication and characterization of a piezoelectric zinc oxide nanowire (ZnO NW) micro energy generator was performed. Low temperature hydrothermal growth of vertically aligned nanowires was integrated with MEMS surface micromachining technology to fabricate the membrane proof-mass structure and the piezoelectric sensor structure. Zinc oxide nanowires were compressed or released by the top layer of membrane proof-mass in response to external vibration. A peak output power of 70 pW was observed across an optimal 7 MΩ load when the device was excited with a peak acceleration of 1.4 g at 40 Hz which is the structural resonant frequency of the helicopter. The corresponding output voltage between the top and the bottom electrodes was 21.4 mV.