Title: Vibration based micro-scale piezoelectric energy harvesting system

Abstract

The growth in the field of VLSI has given a new range of portable electronic gadgets to mankind and connected the whole world with communication devices. The success of portable electronics devices is based on energy needs and power consumption. The energy need is accomplished with the batteries. The advancement in fabrication industry is doubling the number of transistors in every 18 months, while the energy density of batteries is comparatively flat during an equivalent period. Moreover, batteries contain heavy metals that are toxic and hazardous. The alternative to traditional batteries is to make use of the parasitic mechanical vibration energy available locally in the atmosphere. Industrial devices, cars, structures, and human movement release mechanical vibrations which could be excellent sources for collecting small amounts of power without impacting the source itself. The use of piezoelectric, electromagnetic and electrostatic transducers can convert mechanical vibration energy into electrical energy. Piezoelectric transducers offer more viable option because of their high energy density. Important factors governing the performance of piezoelectric energy harvester are choice of material, volume, shape, resonance frequency and output power. The objective of this research work is to design a piezoelectric energy harvesting system with a wide bandwidth and a current amplification energy harvesting circuitry which would be capable enough to autonomously power micro-scale devices throughout their lifetime. Through the simulative analysis it has been concluded that the stress generated on a cantilever is more than any other mechanical structures. A bimorph cantilever harvester is constructed with silicon substrate and zinc oxide as piezoelectric material. Volume of the bimorph is 341.4mm3 which is significantly less than micro-scale maximum volume of 1000mm3. The studies concluded to have a thin film and a longer device which could provide higher power and better matching of resonance frequency with ambient vibration sources. The output power of 0.5mW across a 4MΩ resistor produced by the bimorph piezoelectric cantilver energy harvester at around 90Hz resonance frequency. A novel piezoelectric energy harvester has been proposed in this work based on a conventional seesaw mechanism. See-saw harvester is linear in design compared to other broadband energy harvester which have nonlinearity in structures with magnets, stoppers introduced. The displacement, charge and voltage sensitivity of the proposed harvester is improved by 76%, 12% and 8% respectively. The bandwidth of the proposed structure is also large as compared to the conventional design. The proposed design has a better sensitivity bandwidth product per unit volume of 33.23%, 10.20% and 22.70%, in terms of displacement, charge and voltage respectively.