Sound absorption is an important topic in acoustic physics. One-dimensional sound absorption devices based on Decorated Membrane Resonator (DMR) provide an effective approach for sound absorption. In this thesis, I introduce the theoretical analysis and the experimental study of one-dimensional sound absorption and in the last chapter the study on perfect sound turning.

The general absorption properties of one-dimensional acoustic structure were investigated. In the one-dimensional system, acoustic functional devices can be classified as two types of monopole and two types of dipole based on the response symmetry and the pressure or particle velocity continuity condition. A 50% absorption upper limit for the individual monopole and dipole under one incidence was theoretically a...[ Read more ]

Sound absorption is an important topic in acoustic physics. One-dimensional sound absorption devices based on Decorated Membrane Resonator (DMR) provide an effective approach for sound absorption. In this thesis, I introduce the theoretical analysis and the experimental study of one-dimensional sound absorption and in the last chapter the study on perfect sound turning.

The general absorption properties of one-dimensional acoustic structure were investigated. In the one-dimensional system, acoustic functional devices can be classified as two types of monopole and two types of dipole based on the response symmetry and the pressure or particle velocity continuity condition. A 50% absorption upper limit for the individual monopole and dipole under one incidence was theoretically analyzed. Experimental verification of this limit and the conditions required to reach this limit were introduced.

From the viewpoint of the transfer matrix, the zero eigenvalue implies the potential for total absorption. One kind of this zero eigenvalue is achieved by a single dipole or monopole on which two coherent inputs are required. This kind of absorption is referred to as Coherent Perfect Absorber (CPA), with which the absorption for two coherent incidences is 100% and the one-incidence absorption is 50%. Both dipolar and monopolar examples are analyzed and experimentally tested.

The composite absorbers can achieve perfect absorption regardless of the incidence by assembly of a monopole and a dipole resonator on the same panel functioning at the same frequency. Perfect absorption is realized by the destructive interference of the monopole and dipole resonators to eliminate transmission and matching the average impedance to that of the air on the incident side to eliminate reflection. This kind of perfect absorbers belongs to the second kind of zero eigenvalue of transfer matrix for which both r and t are zero.

A device that turns the coherent incidents from two opposite directions is introduced. The frequency is tunable and the energy turn coefficient can reach 96.7%. The ratio between the scattered wave amplitude and the incident wave amplitude is less than 3%.