Date Approved

9-7-2021

Embargo Period

9-8-2021

Document Type

Thesis

Degree Name

M.S. Mechanical Engineering

Department

Mechanical Engineering

College

Henry M. Rowan College of Engineering

Advisor

Chen Shen, Ph.D.

Committee Member 1

Behrad Koohbor, Ph.D.

Committee Member 2

Hong Zhang, Ph.D.

Keywords

2D axisymmetric, acoustic energy harvesting, broadband acoustics, energy capture, grooved energy harvester, rainbow trapping

Subject(s)

Energy harvesting; Microharvesters (Electronics)

Disciplines

Mechanical Engineering

Abstract

Acoustic energy harvesters (AEHs) collect otherwise unused ambient acoustic waves for conversion into useful electrical energy. This promising technology has potential applications ranging from grid-independent electronics to structural health monitoring systems. AEHs capture specific acoustic frequencies of interest using structures with frequency-matched component geometries. Despite the multitude of potential geometries suitable for AEH structures, existing AEH research has predominantly focused on the acoustic wave trapping performance of unidimensional or linear bidimensional AEH structures.

This study intended to broaden AEH bandwidth and capture efficiency by investigating the acoustic rainbow trapping performance of a novel 2D axisymmetric AEH design. A Finite Element Method (FEM) approach was employed using COMSOL Multiphysics® v5.5 to evaluate the acoustic wave trapping performance of various groove, cylindrical pillar, and circular hole-based unit cell geometries across the 100 kHz - 220 kHz frequency range. The grooved unit cell groove/plate depth ratio and overall plate depth were optimized. A FEM simulation analyzed the acoustic rainbow trapping performance of a 2D axisymmetric AEH design comprised of a gradient array of these optimized unit cells. These FEM results were validated using an array of piezoMEMS sensors mounted to an aluminum AEH prototype.

The prototype displayed reliably predictable acoustic frequency trapping at defined locations. Through these results, this study demonstrated the viability of 2D axisymmetric AEHs in enhancing the acoustic rainbow trapping effect across a broadband frequency range of interest. However, there is much opportunity to refine this AEH design. This proof of concept presents a strong impetus for furthering 2D axisymmetric AEH research.

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