Control Of Sound Propagation Research Articles

Controlling terahertz sound propagation: some preliminary Inelastic X-Ray Scattering result

The control of sound propagation in materials via the design of their elastic properties is an exciting task at the forefront of Condensed Matter. It becomes especially compelling at terahertz frequencies, where phonons are the primary conveyors of heat flow. Despite the increasing focus on this goal, this field of research is still in its infancy; To achieve a few advances in this field, we performed several Inelastic X-Ray Scattering (IXS) measurements on elementary systems as dilute suspensions of nanoparticles (NPs) in liquids. We found that nanoparticles can effectively impact the sound propagation of the hosting liquid. We also explored the possibility of shaping terahertz sound propagation in a liquid upon confinement on quasi-unidimensional cavities. These results are here reviewed and discussed, and future research directions are finally outlined.

Extreme anisotropy and dispersion engineering in locally resonant acoustic metamaterials.

In the last few years, highly anisotropic metamaterials have been explored in various geometries, showcasing interesting routes to achieve better control of sound propagation. As an extreme example, hyperbolic metasurfaces have been shown to offer broadband enhanced sound-matter interactions and diffraction-less propagation of acoustic waves, providing opportunities for sub-diffraction imaging and enhanced sound emission. In this study, we show that structure design of a locally resonant metamaterial enables extreme anisotropic responses, ranging from elliptic to hyperbolic propagation of acoustic surface waves, offering interesting opportunities for extreme sound guiding and steering at the subwavelength scale well compatible with a wide range of additive manufacturing techniques.

Three-dimensional broadband omnidirectional acoustic ground cloak

The control of sound propagation and reflection has always been the goal of engineers involved in the design of acoustic systems. A recent design approach based on coordinate transformations, which is applicable to many physical systems, together with the development of a new class of engineered materials called metamaterials, has opened the road to the unconstrained control of sound. However, the ideal material parameters prescribed by this methodology are complex and challenging to obtain experimentally, even using metamaterial design approaches. Not surprisingly, experimental demonstration of devices obtained using transformation acoustics is difficult, and has been implemented only in two-dimensional configurations. Here, we demonstrate the design and experimental characterization of an almost perfect three-dimensional, broadband, and, most importantly, omnidirectional acoustic device that renders a region of space three wavelengths in diameter invisible to sound.

Numerical analysis of a blocking mass attenuating wave propagation

Based on wave theory, blocking mass impeding propagation of flexural waves was analyzed with force excitation applied on a ship pedestal. The analysis model of a complex structure was developed by combining statistical energy analysis and the finite element method. Based on the hybrid FE-SEA method, the vibro-acoustic response of a complex structure was solved. Then, the sound radiation of a cylindrical shell model influenced by blocking mass was calculated in mid/high frequency. The result shows that blocking mass has an obvious effect on impeding propagation. The study provides a theoretical and experimental basis for application of the blocking mass to structure-borne sound propagation control.

Nondiffractive propagation in sonic crystals

Sonic crystals are media with a periodic modulation of the acoustic parameters, such as the density and the bulk modulus. They have recently attracted a great interest, because of their potential applications in the control of sound propagation, used as reflectors, focusers, or waveguides. All these properties are related with the dispersion introduced by the crystal anisotropy. We report on the nondiffractive propagation of sound in two‐dimensional sonic crystals. It is shown that, for given frequencies and directions of incidence, a narrow sonic beam can propagate without diffractive broadening. Such nondiffractive sonic beams exist in crystals with perfect symmetry and do not require the presence of defects, differently from other waveguiding phenomena reported previously. The cancellation of diffraction has been predicted using the plane‐wave expansion method to evaluate the dispersion surfaces of the crystal and the spatial dispersion (isofrequency) curves. It occurs for frequencies and wave vectors for which dispersion curves have zero curvature, denoting a transition between focusing and defocusing regimes. By means of perturbative techniques, a simple analytical expression for the nondiffractive conditions has been obtained. The phenomenon is also demonstrated by numerical integration of the acoustic equations using FDTD techniques. [Support from Spanish MEC, Project FIS2005‐07931‐C03‐01/03, is acknowledged.]