Geniş Bantlı ve Düşük Frekanslı Mekanik Titreşimler için Esnek Piezoelektrik Enerji Hasadı Sistemi Tasarımı ve Üretimi

Abstract

ABSTRACT DESIGN AND FABRICATION OF A FLEXIBLE PIEZOELECTRIC ENERGY HARVESTING SYSTEM FOR BROADBAND AND LOW-FREQUENCY MECHANICAL VIBRATIONS Hasan Göksenin ÇETİN Master of Science, Department of Mechanical Engineering Supervisor: Asst. Prof. Dr. Bilsay SÜMER September 2015, 100 pages Nowadays, methods for generating electrical energy from alternative energy sources have become important for powering small electronic devices. Primary energy sources available in the environment can be listed as solar, thermal, wind, acoustic and mechanical energies. Mechanical vibrations are generally used as an energy source of such devices since they are practical, not dependent on weather conditions, have high safety and long shell life. Three principal mechanisms for transforming vibration energy into electrical energy can be listed as electromagnetic, electrostatic and piezoelectric transduction. Since piezoelectric materials have higher energy density capacities, no requirement for an external power source, producible in small sizes and are suitable for low frequency vibration applications, they are generally used in vibration based energy harvesting systems. Piezoelectric energy harvesting systems are widely produced by sandwiching an elastic layer between two rigid piezoelectric layers which is called a bimorph structure. Unlike prior efforts, this study presents a novel piezoelectric energy harvesting system where polymer pillars stand on a piezoelectric polymer backing layer. In this configuration, polymer pillars behave like a set of oscillators on the iv vibrating structure, which provide absorption of vibration energy and act as an energy sink. Then, the stored elastic energy is converted to electrical energy in the clamped boundary via stress concentration on the piezoelectric layer. Energy harvesting system designed in this study is very flexible, lightweight and has low-density, since only polymer material is used in the whole structure. In this thesis, an analytical and numerical modeling of the energy harvesting system is developed. Analytical model is investigated for a single degree of freedom system of a single pillar structure under free, harmonic and step base excitation vibrations. Besides this, piezoelectric material and viscoelastic damping models are also studied. Then, numerical modeling with finite element methods is performed to study the modal, harmonic and transient vibration analysis of the single and multiple pillar structures. Results from the vibration analyses of analytical and numerical models are also compared. The energy harvesting system is obtained for the single and multiple pillar structures using a combination of a soft molding and additive manufacturing techniques. Then, a special test setup is prepared in order to perform vibration tests of the energy harvesting system. Each structure is tested under different harmonic base excitation vibrations including frequency sweep, voltage and power measurement tests. Results are also compared with the numerical simulation results. In addition to these, a commercial energy harvesting system is also tested using the same test setup and results are compared with the energy harvesting systems designed in this thesis. Finally, energy harvesting systems designed in this study are also compared according to their power density, figure of merit, efficiency etc. Keywords: Mechanical vibrations, piezoelectric, energy harvesting, polymer pillar