# Extreme Low-Frequency Ultrathin Acoustic Absorbing Metasurface

## TL;DR

This paper presents an ultrathin, multi-coiled acoustic metasurface achieving near-perfect absorption at 50 Hz, surpassing traditional designs by offering tunable impedance and broadband capabilities through innovative physical mechanisms.

## Contribution

It introduces a novel multi-coiled metasurface design that achieves ultra-low-frequency absorption with tunable impedance without increasing thickness.

## Key findings

- Achieves 99.99% absorption at 50 Hz
- Thickness is only {rac}{1.3} cm, or {rac}{527} of wavelength
- Demonstrates broadband absorption by coupling different unit cells

## Abstract

We introduce a multi-coiled acoustic metasurface providing a quasi-perfect absorption (reaching 99.99% in experiments) at extremely low-frequency of 50 Hz, and simultaneously featuring an ultrathin thickness down to {\lambda}/527 (1.3 cm). In contrast to the state of the art, this original conceived multi-coiled metasurface offers additional degrees of freedom capable to tune the acoustic impedance effectively without increasing the total thickness. We provide analytical derivation, numerical simulation and experimental demonstrations for this unique absorber concept, and discuss its physical mechanism which breaks the quarter-wavelength resonator theory. Furthermore, based on the same conceptual approach, we propose a broadband lowfrequency metasurface absorber by coupling unit cells exhibiting different properties.

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Source: https://tomesphere.com/paper/1908.01495