Thesis Defense – Haafiz Husker
Title: INFLATABLE ACOUSTIC METAMATERIAL
Author: Haafiz Husker
Dr. Amr Baz (Adviser – Chair)
Dr. Balakumar Balachandran
Dr. Hosam Fathy
Exam Time: May 20, 2021 (Thursday) at 9:30AM
Abstract: Acoustic metamaterials thus far have been either passive or employed stacking to produce wide range of results. With the advent of advanced additive manufacturing techniques, the ability to create novel metamaterials have increased. Usually these Acoustic Meta Material are passive like in case of Membrane-type and Plate-type metamaterials. They are usually thin membranes or plates consisting of periodic unit cells with added masses. Numerous studies have shown these metamaterials exhibit tunable anti resonances with transmission loss greater than their corresponding mass-law. In these studies, the tunability is usually produces with complex electrical architecture and furthermore, in most of the investigations it is assumed that the unit cell edges of the metamaterial are fixed.
In this study, an innovative method is explored to create an active metamaterial that can be easily tunned. The proposed method distinguishes itself from past contributions by employs a unique unit cell design that is fabricated via advanced additive manufacturing to create a meta-material that exhibits negative Poison’sratio with adjustable unit cell edges for greater transmission loss than its mass-law would otherwise suggest. The membrane like Meta-material is tuned by inflating itself with pressurized air. The pressurization leads to large non-linear deformation and geometric stiffing in the membrane apart from adding mass by expanding its elastic unit cell edges. Which is exploited to adjust the eigen-modes and sound loss of the structure.
The veracity of this proposed design is then investigated analytically and experimentally. The metamaterial is manufactured using elastic material called Agilus- 30 via Multi-jet Manufacturing and is tested in an impedance tube to see its trans- mission loss. Finite elemental analysis is done to reduce the computational effort in creating an analytical model. The finite element analysis is compared with the experimental results to arrive at a consensus. The proposed metamaterial is then tested in real life application by conducting frequency response on a headphone with the IAMM installed to truly understand, the performance of such a setup. The results of these tests indicate the range of performance across low and high frequency as well as the versatility of the metamaterial to be adapted into any size as per the requirement.