Double negative acoustic metastructure for attenuation of acoustic emissions

Abstract

Acoustic metamaterials hold great potential for attenuation of low frequency acoustic emissions. However, a fundamental challenge is achieving high transmission loss over a broad frequency range. In this work, we report a double negative acoustic metastructure for absorption of low frequency acoustic emissions in an aircraft. This is achieved by utilizing a periodic array of hexagonal cells interconnected with a neck and mounted with an elastic membrane on both ends. An average transmission loss of 56 dB under 500 Hz and an overall absorption of over 48% have been realized experimentally. The negative mass density is derived from the dipolar resonances created as a result of the in-phase movement of the membranes. Further, the negative bulk modulus is ascribed to the combined effect of out-of-phase acceleration of the membranes and the Helmholtz resonator. The proposed metastructure enables absorption of low frequency acoustic emissions with improved functionality that is highly desirable for varied applications.

The Present and Future Role of Acoustic Metamaterials for Architectural and Urban Noise Mitigations

“…In early stages, membrane type metamaterials were popular for low frequency noise attenuation and showed tremendous potential for several applications like indoor noise, aircraft cabin noise mitigation [49][50][51][52]. Kumar et al [53,54] demonstrated a membrane type double negative acoustic metamaterial for low frequency noise attenuation. The structure consists of periodically arranged unit cells, with each unit cell comprising two hexagonal cavities interconnected with a cylindrical hollow neck and an elastic membrane stacked on both ends.…”

Low-frequency perfect sound absorption achieved by a modulus-near-zero metamaterial

“…The effective parameters of the metamaterial are highly dependant on the geometry of the structure based on the basic resonant elements. The conception of double-negative 32,33 or double-zero 34 effective parameters has been developed and adapted in the absorption of sound waves. Duan et al .…”

Recent Advances in Acoustic Metamaterials for Simultaneous Sound Attenuation and Air Ventilation Performances

“…Reprinted with permission from Lee et al [50], © 2020 American Physical Society. The double membrane-hexagonal cavity and the dual negative spectra are reprinted with permission from Kumar et al [79], © 2020 AIP Publishing LLC.…”