Design, FEM Modeling and Optimization of MEMS based Wideband Vibrational Energy Harvester for Low Power Applications

Abstract

This thesis presents the design, model and finite element analysis for Electrostatic Vibration Energy Harvester (EVEH). Due to the advancement in the CMOS technology the power ratings for microelectronics are becoming increasingly low due to their reduced size and supplying power to remote microsystems is becoming challenging. A device is needed which can harvest the ambient forms of energy from the surrounding to electrical energy or to make the devices self-powered in order to get rid of batteries. From the beginning of 21st century research efforts were made to find the mechanisms to harvest these ambient forms of energies. Usually three main transduction mechanisms for vibration based energy harvesters exists which are piezoelectric, electrostatic and electromagnetic, among these techniques electrostatic energy harvester is considered better due to its ease of integration with microelectronics. The novelty of the proposed harvester in this thesis is that it utilizes three degrees of freedom with amplification in displacement of proof mass and designed in a way that maximum number of transduction units (comb drives) are attached with absorber masses. A low cost commercially available fabrication process Metal MUMPs provided by MEMSCAP is selected. Usually three types of processes are provided by MEMSCAP those are SOIMUMPs, PolyMUMPs and MetalMUMPs, all differs with each other in a material usage for structural layer and minimum feature size. This MetalMUMPs process has minimum feature size of 8 μm and thickness of 20 μm with a structural layer of nickel. The resonance frequency of the harvester is around 3.9 kHz and very low acceleration amplitude of 0.1 g. The area of the proposed device is 7.48 mm2 and overlapping length of the combs attached is 25 μm. The total mass of the device is 9.4 mg with device volume of 0.140 mm3 having normalized power density of 0.0032 mW/cm3g-2. The total harvested power for applied load of 0.1 g was calculated to be 4.2 nW.