Subwavelength total acoustic absorption with degenerate resonators (1509.03711v1)

Abstract: We report the experimental realization of perfect sound absorption by sub-wavelength monopole and dipole resonators that exhibit degenerate resonant frequencies. This is achieved through the destructive interference of two resonators' transmission responses, while the matching of their averaged impedances to that of air implies no backscattering, thereby leading to total absorption. Two examples, both using decorated membrane resonators (DMRs) as the basic units, are presented. The first is a flat panel comprising a DMR and a pair of coupled DMRs, while the second one is a ventilated short tube containing a DMR in conjunction with a sidewall DMR backed by a cavity. In both examples, near perfect absorption, up to 99.7%, has been observed with the airborne wavelength up to 1.2 m, which is at least an order of magnitude larger than the composite absorber. Excellent agreement between theory and experiment is obtained.

• The paper demonstrates perfect sound absorption by using paired monopole and dipole degenerate resonators to achieve phase cancellation and impedance matching.
• Experimental results and simulations show up to 99.7% absorption using both flat panel and ventilated tube designs.
• The study advances acoustic metamaterials and suggests novel applications for compact absorber design and potential extension to electromagnetic waves.

An Analysis of Subwavelength Total Acoustic Absorption with Degenerate Resonators

The paper entitled "Subwavelength Total Acoustic Absorption with Degenerate Resonators" authored by Min Yang et al. undertakes the exploration of perfect sound absorption through an innovative approach involving the use of degenerate resonators. By leveraging subwavelength monopole and dipole resonators with matching resonant frequencies, the researchers achieved total absorption via the mechanism of destructive interference. This interference is coupled with impedance matching, thereby preventing backscattering and leading to the effective absorption of sound.

Overview

The paper introduces two configurations to demonstrate the principle of perfect absorption using decorated membrane resonators (DMRs): a flat panel and a ventilated short tube. Each of these configurations combines monopole and dipole resonators at degenerate resonant frequencies. In the flat panel setup, a DMR and a pair of coupled DMRs constitute the basic units, while the ventilated tube employs a DMR in conjunction with a sidewall DMR backed by a cavity. Remarkably, total absorption reaching up to 99.7% was observed, markedly surpassing the acoustic absorber's physical dimensions, which were significantly smaller than the sound wavelength.

Key Findings and Theoretical Implications

1. Perfect Absorption Mechanism: The core finding of this paper is the ability to achieve near-perfect sound absorption through degenerate resonators. The paper posits the construction of a composite resonator unit consisting of both monopole and dipole resonators, achieving phase cancellation on the transmission side for total absorption.
2. Experimental Validation: The practical demonstrations of these resonator configurations correlated well with theoretical predictions, showcasing excellent agreement between experimental results and numerical simulations. This validation underscores the effectiveness of using degenerate resonators to nullify both transmission and backscatter, leading to complete absorption.
3. Implications for Acoustic Metamaterials: The proposed methodology enhances our understanding of resonator-based acoustic absorbers, offering pathways to optimize subwavelength acoustic absorbers for practical applications. These findings open up avenues for designing compact, effective sound-absorptive materials without dependence on additional structures such as reflective walls.
4. Potential Application to Electromagnetic Waves: Although the paper is confined to acoustic waves, the authors speculate that the concept could be extended to electromagnetic waves, given the analogous properties between acoustics and electromagnetism.

Future Prospects

The paper presents exciting prospects for further enhancement of absorptive materials, particularly in miniaturized applications where space constraints necessitate innovative soundproofing solutions. Future research might explore extending these findings to broader frequency ranges and integrating them into diverse structural designs. Additionally, the paper provides a solid grounding for investigating similar absorption phenomena in optical and electromagnetic systems, potentially broadening the paper's applicability to communication technologies and noise control systems.

In conclusion, this paper contributes significantly to the field of acoustic metamaterials, providing empirical and theoretical insights into achieving subwavelength total acoustic absorption. Through meticulous experiments and simulations, the research delineates a pathway for efficient sound absorption using the strategic arrangement of degenerate resonators, highlighting potential multifaceted applications in engineering and material sciences.