Long-range nonspreading propagation of sound beam through periodic layered structure

Abstract

Linear spreading of a wave packet or a Gaussian beam is a fundamental effect known in evolution of quantum state and propagation of optical/acoustic beams. The rate of spreading is determined by the diffraction coefficient D which is proportional to the curvature of the isofrequency surface. Here, we analyzed dispersion of sound in a solid-fluid layered structure and found a flex point on the isofrequency curve where D vanishes for given direction of propagation and frequency. Nonspreading propagation is experimentally observed in a water steel lattice of 75 periods (~1 meter long) and occurs in the regime of anomalous dispersion and strong acoustic anisotropy when the effective mass along periodicity is close to zero. Under these conditions the incoming beam experiences negative refraction of phase velocity leading to backward wave propagation. The observed effect is explained using a complete set of dynamical equations and our effective medium theory.

Longitudinal Monostatic Acoustic Effective Bulk Modulus and Effective Density Evaluation of Underground Soil Quality: A Numerical Approach

“…Instead of using a long-wavelength sound wave to detect the comparable size of soil void, the EBME technique uses a relatively scaled effective bulk modulus and effective density to estimate the volume fraction of the void inside the soil by using a rapid non-contact raster scan. Once the porous soil's target area was determined, a higher frequency sound wave detector [22], acoustic lens/collimator [23][24][25][26], or electromagnetic radar could be applied in the region to find detailed information of the specific voids for further interest. This work showed the initial feasibility of underground acoustic detection.…”

MetaMembranes for the Sensitivity Enhancement of Wearable Piezoelectric MetaSensors

“…Metamaterials are artificial structures which provide unusual mechanical properties with regard to energy absorption, mass, density, deformation, static modulus, smart functionality, and negative Poisson's ratio (NPR) [6]. During the past decade, there has been a tremendous interest in the use of metamaterial in 1D, 2D, and 3D structures such as: lenses, photonic crystals for light, phononic crystals for sound, and soft acoustic metamaterials [7][8][9]. Poisson's ratio defines the ratio between two characteristics of the transverse and longitudinal strain of a structure, and NPR behavior has been discovered in auxetic materials that expand (contract) in the transverse direction when stretched (compressed), instead of usual materials (Figure 1) [10][11][12][13][14].…”

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

“…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 monostatic [ 16 , 17 ] and bistatic [ 18 , 19 , 20 ] lenses, which showed great improvement in acoustic detection [ 21 ] and ultrasonic imaging [ 22 , 23 , 24 ] and elastography [ 25 , 26 , 27 ].…”

“…This study proposes a numerical and experimental realization of the spectral and spatial deconvolution of an acoustic broadband pulse into frequency components using an acoustic metamaterial superlattice. The superlattice design was introduced in our previous work on non-spreading propagation of acoustic beam [ 8 ]. Here, we focus on the decomposition behavior of the superlattice.…”