Author Type

Graduate Student

Date of Award

Spring 4-16-2026

Document Type

Dissertation

Publication Status

Version of Record

Submission Date

May 2026

Department

Ocean and Mechanical Engineering

College Granting Degree

College of Engineering and Computer Science

Department Granting Degree

Ocean and Mechanical Engineering

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Hassan Mahfuz

Abstract

Acoustic metamaterials are engineered materials designed to control and manipulate sound propagation. Many such systems incorporate acoustic foams due to their porous structure, low density, and high specific surface area, which promotes efficient sound absorption. However, a major limitation of conventional acoustic foams -particularly open-cell varieties- is their lack of waterproofing, rendering them unsuitable for underwater or moisture-prone environments. To address this limitation, a multilayered acoustic foam composite (MAFC) was developed as a lightweight, waterproof structure with enhanced sound absorption performance. The MAFC consists of five layers: the first and fifth layers are aluminum foam, providing structural integrity; the second and fourth layers are silicone rubber, ensuring waterproofing; and the central layer is polyurethane (PU) foam, serving as the primary sound-absorbing medium. To further improve acoustic performance, the PU foam was reinforced with carbon nanotubes (CNT) to enhance the sound absorption coefficient (SAC). Two aluminum foam densities and three CNT concentrations were investigated. The low-density MAFC without CNTs exhibited a peak sound absorption coefficient (αpeak) of 0.75 at 3300 Hz, while the medium-density configuration reached 0.78. With CNT reinforcement, αpeak increased to 0.91 for the low density MAFC at 0.1 wt% CNT and to 0.88 for the medium-density case. A similar enhancement was observed at 2900 Hz. In contrast, at lower frequencies, sound absorption remained largely insensitive to both foam density and CNT inclusion. The dissertation presents detailed fabrication procedures, experimental methods, data processing, and analysis of the acoustic performance of the proposed MAFC.

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