Elsevier

Physics Letters A

Volume 384, Issue 35, 17 December 2020, 126887
Physics Letters A

A sound absorption panel containing coiled Helmholtz resonators

https://doi.org/10.1016/j.physleta.2020.126887Get rights and content

Highlights

  • A sound absorption panel with coiled Helmholtz resonators is proposed.

  • The proposed structure offers a feasible possibility for absorbing undesired sound at low frequencies.

  • The present structure lowers the working frequency and keeps all design attractiveness of Helmholtz resonators.

  • The use of the double resonators assembled in parallel can effectively broaden the absorption bandwidth.

  • Theoretical and FE predictions match well with experimental measurements.

Abstract

This study proposes a promising design of sound absorption panels containing acoustic resonators. Each resonator is comprised of one small-sized and one large-sized tubes in series. The former can be viewed as the neck of a Helmholtz resonator, while the latter serves as a resonant chamber. Both tubes are bent up to fit in limited space of the panel. The 3D printing technology is exploited to fabricate samples for measurements. Frequency manipulation for the absorption peak can be achieved by adjusting the geometric parameters of tubes. Moreover, two pairs of resonators with different dimensions can broaden the bandwidth of absorption. Theoretical predictions on absorption characteristics agree well with numerical and experimental results. The proposed structure offers a feasible way of absorbing low-frequency sound without the need to use thick panels.

Introduction

The last decade has witnessed a growing interest in the study of low-frequency sound absorption. Conventionally, sound absorption took advantages of porous/fibrous materials or objects with gradient index. The above-mentioned subjects usually work well at high frequencies, but they work inefficiently at low frequencies [1], [2], [3], [4], [5]. The use of resonant structures, such as locally resonant sonic crystals [6], [7], decorated membrane resonators [8], [9], [10], split tube resonators [11], [12], micro-perforated panels [13], [14], [15], and Helmholtz resonators (HRs) with spiral or extended necks [16], [17], [18], [19], [20], [21], [22], provides an additional possibility for low-frequency sound absorption. Although HRs with spiral or extended necks can effectively lower their working frequency, they are rarely installed in a compact space, especially for thin panels. Recently, the concept of coiling up space has been applied to the manipulation of acoustic waves [23], [24], [25], [26], [27], [28], [29]. Extraordinary dispersion, including negative refraction and conical dispersion, has been found in those labyrinthine metamaterials. Another illustrative space-coiling example is acoustic metasurfaces. They usually consist of curled and one-end-closed channels [30], [31]. Thickness of this structure is subwavelength. An acoustic metasurface is able to tune its absorption bandwidth using the cross-sectional area of channel. To lower the operating frequency without increasing the total channel length, nonuniform or gradient cross sections were adopted [32], [33]. Other designs, such as multicoiled structures [34] or underdamped coiled space resonators covered by a surface sponge coating [35], can lead to nearly-perfect absorption. Alternatives of acoustic metasurfaces are to embed acoustic resonators with a classical, spiral, or folded cavity in perforated or microperforated plates [36], [37], [38], [39], [40]. Studies have shown that within a compact space, a space-coiling resonator is more efficient in reducing working frequency and improving sound absorption performance than conventional ones. In addition to attempting to establish the governing principles, the development of computational techniques to predict results has aroused much research interest [39], [40], [41].

Inspired by previous works, we propose a relatively simple structure, which still exhibits sound absorption capability in the low frequency regime. Instead of using complex geometry for cavities [40], the inner resonator is comprised of a small tube and a large tube in series. Both tubes are coiled up to fit the limited space. The small-sized tube can be viewed as the neck of resonator, while the large-sized one serves as the cavity. The operating frequency can be approximately estimated using the traditional formula for a Helmholtz resonator [42]. An analytical model is presented to predict sound absorption profile of the present structure. Theoretical predictions on absorption characteristics are verified by comparing those with simulation and experimental results. To effectively broaden the absorption bandwidth, a panel with double resonators arranged in parallel is introduced. The air velocity field associated with the maximum sound absorption is also examined in modeling.

Section snippets

Design model

Fig. 1(a) shows the proposed sound absorbing panel which consists of a thin covering board with a square hole, a main panel having two tubes of different sizes in series, and a back wall. For saving space, each tube is bent up. The large tube has three nearly 90 turns; the small tube has one sharp and one moderate 90 turns. The round turns at the corner of cavity are for maximized usage of space and consistency of the cross-sectional area. Though the cross-section of both tubes is square, d1

Single resonator

In the finite element (FE) analysis, commercial software COMSOL Multiphysics is utilized to conduct numerical simulations. The Acoustic Module is adopted in the computation. The simulated model is comprised of two tubes of different sizes connected in series. The small-sized and large-sized tubes can be viewed as the neck and cavity of a Helmholtz resonator, respectively. In the resonator region, boundary layer effects including viscous and thermal losses are considered. An oscillation sound

Conclusions

This study investigates the sound absorption performance of a panel containing coiled Helmholtz resonators. The compact structure is able to absorb low-frequency sound energy. The absorption peak frequency can be precisely predicted employing the concept of acoustic impedance. Analytical and numerical predictions agree well with experimental results. The peak frequency can be tailored by dimensions of tubes. When two resonators with different dimensions are exploited, dual absorption peaks can

CRediT authorship contribution statement

Jung-San Chen: Conceptualization, Funding acquisition, Methodology, Resources, Supervision, Writing - original draft. Yu-Bin Chen: Funding acquisition, Visualization, Writing - review & editing. Yu-Hsiang Cheng: Investigation, Software. Li-Chih Chou: Validation, Visualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Ministry of Science and Technology (MOST), Taiwan, under grant numbers MOST 106-2221-E-006-122-MY3 and 106-2628-E-007-006-MY3.

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