Date of Award

8-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Thompson, Lonny L

Committee Member

Fadel , Georges M

Committee Member

Zhao , Huijuan

Abstract

The objective of this thesis is to maximize the energy harvested from a vibrating bimorph cantilever beam by optimizing the geometrical parameters and the material properties of the piezoelectric beam. A three-dimensional finite element (FEA) model is developed to design a vibrating bimorph cantilever beam for energy harvesting. The reference piezoelectric material used in the design is Lead Zirconate Titanate (PZT-5H) and the substrate sandwiched between the two piezoelectric plates is brass. Three types of models are analyzed and compared in this work by modifying the brass substrate geometry- a solid homogenous substrate, a regular honeycomb substrate and an auxetic honeycomb substrate. Complete transversely isotropic elastic and piezoelectric properties are assigned to the bimorph layers. A time harmonic pressure load is applied to the top surface of the beam that results in electrical-mechanical coupling by vibration. The electric potential on the surfaces of the bimorph piezoelectric beam is used to compute voltage generated.
Also in this thesis, an automated design workflow has been set-up to solve an optimization problem by integrating ABAQUS 6.10, the commercial finite element package with the commercial optimization software package VisualDOC 7.1. The optimizer, Non-dominated Sorting Genetic Algorithm II (NSGAII), depends on the number of population, iterations, probability of cross over and mutations.
The first objective of this work is to compare the finite element analysis results of the bimorph cantilever beams with these three substrates for similar loading and boundary conditions. The thickness of the substrates and the material properties are maintained equal for all three models. The second objective is to optimize the thicknesses of the PZT plates `tp' and the relative dielectric constant to maximize the power harvested (i.e. voltage output) for a given loading condition and plate dimensions (length and width). The constraint used for solving this non-linear multi-physics optimization problem is the ultimate tensile stress for the piezoelectric plates. The optimized parameters obtained from VisualDOC are verified using ABAQUS and the results are compared.

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