Spatial Decomposition of a Broadband Pulse Caused by Strong Frequency Dispersion of Sound in Acoustic Metamaterial Superlattice.

Yuqi Jin,Teng Yang,Tae-Youl Choi,Yurii Zubov,Arup Neogi,Arkadii Krokhin

doi:10.3390/ma14010125

Abstract

An acoustic metamaterial superlattice is used for the spatial and spectral deconvolution of a broadband acoustic pulse into narrowband signals with different central frequencies. The operating frequency range is located on the second transmission band of the superlattice. The decomposition of the broadband pulse was achieved by the frequency-dependent refraction angle in the superlattice. The refracted angle within the acoustic superlattice was larger at higher operating frequency and verified by numerical calculated and experimental mapped sound fields between the layers. The spatial dispersion and the spectral decomposition of a broadband pulse were studied using lateral position-dependent frequency spectra experimentally with and without the superlattice structure along the direction of the propagating acoustic wave. In the absence of the superlattice, the acoustic propagation was influenced by the usual divergence of the beam, and the frequency spectrum was unaffected. The decomposition of the broadband wave in the superlattice’s presence was measured by two-dimensional spatial mapping of the acoustic spectra along the superlattice’s in-plane direction to characterize the propagation of the beam through the crystal. About 80% of the frequency range of the second transmission band showed exceptional performance on decomposition.

Highlights

Artificial phononic periodic structures have been studied for decades and are generally termed phononic crystals [1]
The nature of the physical decomposition of the acoustic pulse by superlattice is the same as splitting white light by a spectrum of different colors when passing through a prism, namely the refraction coefficient’s frequency dispersion
Fundamental studies of periodic structures of acoustic metamaterials have been of high interest for decades

Summary

Introduction

Artificial phononic periodic structures have been studied for decades and are generally termed phononic crystals [1]. Once the operating wavelength approaches the periodicity or smaller, the eigenmodes’ dispersion relation becomes highly nonlinear and may exhibit anomalous group velocity [6] In this region, the phononic crystals behave as metamaterials [7,8,9,10]. The potential wave steering functionalities of elastic [11], acoustic [12], and thermal waves [13] using 1D, 2D, or 3D phononic periodic structures have been demonstrated along with the fundamental principles in the existing studies In those transmission bands, the abnormal behavior includes negative refraction [14] and flat regions of the equifrequency surface [9,15]. These unique properties provide opportunities to realize long-distance acoustic collimator [8] and super-resolution

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Results

Conclusion