# Efficient broadband sound absorption exploiting rainbow labyrinthine metamaterials

**Authors:** F. Nistri, V. H. Kamrul, L. Bettini, E. Musso, D. Piciucco, M. Zemello, A. S. Gliozzi, A. O. Krushynska, N. Pugno, L. Sangiuliano, L. Shtrepi, F. Bosia  
**arXiv:** [2110.05026](https://arxiv.org/abs/2110.05026)  
**Date:** 2021-10-11  
**Summary page:** https://www.summarizepaper.com/en/paper/2110.05026v4/

## Key points

- Study showcases effective noise absorption capabilities of a 3-D printed panel with intricately arranged space-coiling labyrinthine acoustic elementary cells.
- Resonance frequency of unit cell exhibits linear scaling relationship with thickness and lateral size, allowing for easy adjustment of working frequency.
- Flat panel designed using data-driven approach with diverse cell dimensions in quasi-periodic lattice formation to create broader absorption spectrum covering frequencies between 800 and 1400 Hz.
- Panel design features thinner profile, lightweight construction, and modular nature for versatile applicability across various geometries compared to conventional solutions.
- Performance evaluation in reverberation room demonstrates exceptional sound absorption capabilities at desired operational frequencies, close to ideal values.
- Research highlights innovative design methodology for noise-mitigation panels and the efficacy of labyrinthine metamaterials in achieving tunable mid- to low-frequency sound attenuation.

## Summary

In the study titled "Efficient broadband sound absorption exploiting rainbow labyrinthine metamaterials," authors F. Nistri, V. H. Kamrul, L. Bettini, E. Musso, D. Piciucco, M. Zemello, A. S. Gliozzi, A. O. Krushynska, N. Pugno, L. Sangiuliano, L. Shtrepi and F.Bosia present a proof of concept experiment showcasing the effective noise absorption capabilities of a 3-D printed panel designed with intricately arranged space-coiling labyrinthine acoustic elementary cells of varying sizes. The research delves into the analytical and numerical analysis of these labyrinthine unit cells to determine their absorption characteristics before fabricating and subjecting them to experimental testing in an impedance tube setup to validate the dependence of absorption properties on cell thickness and lateral size. Notably,the resonance frequency of the unit cell is observed to exhibit a linear scaling relationship with both thickness and lateral size within the specified range,facilitating easy adjustment of the working frequency as needed. Utilizing this data-driven approach,a flat panel is meticulously designed by strategically arranging cells of different dimensions in a quasi-periodic lattice formation to leverage the acoustic "rainbow" effect – effectively combining the frequency responses of diverse cells to generate a broader absorption spectrum covering frequencies between 800 and 1400 Hz. Compared to conventional sound absorbing solutions,this novel panel design stands out for its thinner profile and lightweight construction while being modular in nature for versatile applicability across various geometries. The performance evaluation conducted in a small-scale reverberation room underscores the exceptional sound absorption capabilities of the panel at desired operational frequencies – showcasing results close to ideal values. Overall,this work not only proposes an innovative design methodology for noise-mitigation panels but also offers empirical evidence supporting the versatility and efficacy of labyrinthine metamaterials in achieving tunable mid- to low-frequency sound attenuation – marking significant strides in advancing acoustic engineering solutions for enhanced noise control applications.