Propagation of sound beams behind sonic crystals (original) (raw)

Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals

Physical review. E, Statistical, nonlinear, and soft matter physics, 2003

Motivated by a recent experiment on acoustic lenses, we perform numerical calculations based on a multiple scattering technique to investigate the focusing of acoustic waves with sonic crystals formed by rigid cylinders in air. The focusing effects for crystals of various shapes are examined. The dependence of the focusing length on the filling factor is also studied. It is observed that both the shape and filling factor play a crucial role in controlling the focusing. Furthermore, the robustness of the focusing against disorders is studied. The results show that the sensitivity of the focusing behavior depends on the strength of positional disorders. The theoretical results compare favorably with the experimental observations, reported by Cervera, et al. [Phys. Rev. Lett. 88, 023902 (2002)].

Formation of collimated sound beams by three-dimensional sonic crystals

Journal of Applied Physics, 2012

A theoretical and experimental study of the propagation of sound beams in-and behind three-dimensional sonic crystals at frequencies close to the band edges is presented. An efficient collimation of the beam behind the crystal is predicted and experimentally demonstrated. This effect could allow the design of sources of high spatial quality sound beams.

Subdiffractive propagation of ultrasound in sonic crystals

Physical Review B, 2007

We present an experimental demonstration of the subdiffractive propagation Í‘self-collimationÍ’ of an ultrasound beam in a two-dimensional sonic crystal formed by a square array of steel cylinders inmersed in water. Measurements show that the diffractive spreading of a narrow beam is strongly reduced along the spatially modulated direction of the crystal. The effect of the finite crystal length is theoretically analyzed, resulting in a frequency shift of the subdiffractive point in good correspondence with the experimental results.

Nondiffractive propagation of sound in sonic crystals

Journal of The Acoustical Society of America, 2008

We report the nondiffractive propagation of acoustic waved in sonic crystals, e.g., acoustic media with periodic modulation of the material parameters (density and bulk modulus). Such novel materials 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. In particular we consider the case of two-dimensional sonic crystals, consisting, e.g. in an array of steel cylinders in water. 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 occurs at frequencies and wavevectors for which dispersion curves (isofrequency lines) have zero curvature, i.e, are locally flat. 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 the FDTD technique. We present experimental evidence of the nondiffractive propagation in a periodic array of steel cylinders in water.

Spatial filtering of sound beams by sonic crystals

Applied Acoustics, 2012

We propose and numerically demonstrate an efficient cleaning of spatial structure (spatial filtering) of sound beams by propagating them through at least twodimensional sonic crystals, i.e. through acoustic structures periodically modulated in longitudinal and in transversal direction with respect to the sound propagation direction. We show the spatial filtering in two configurations: with-and without the angular band-gap. We also show that besides the spatial filtering the beams can be additionally focalized at a particular distance behind the sonic crystal in both configurations.

Acoustic wave focusing by two-dimensional lattice of cylinders in air

Physics of Wave Phenomena, 2007

A sound source (3 cm in diameter) image in air, formed in the far wave zone behind a two-dimensional periodic lattice, was experimentally obtained. The lattice consisted of plane parallel rows of steel cylinders with a diameter of 1.58 cm, forming an acoustic crystal with hexagonal structure, The crystal lattice constant (a = 2.14 cm) is smaller than the emission wavelength in air (~ 3.4 cm). The relations between the emission wavelength and lattice parameters were selected according to model calculation in the second transmission band of the crystal at its negative refractive index n = -0.7. The lateral size of the focused (over the sound pressure distribution) image of the sound source is close to the emission wavelength. A distinctive feature of the experiment is the formation of such a sharply focused image under conditions of an extremely small output aperture (the beam diameter at the acoustic crystal output did not exceed 2.5 acoustic wavelengths in air). It can be considered that the flat acoustic lens is realized. Possible explanations of the observed effect are discussed.

Nondiffractive propagation in sonic crystals

The Journal of the Acoustical Society of America, 2006

We report the nondiffractive propagation of acoustic waved in sonic crystals, e.g., acoustic media with periodic modulation of the material parameters (density and bulk modulus). Such novel materials 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. In particular we consider the case of two-dimensional sonic crystals, consisting, e.g. in an array of steel cylinders in water. 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 occurs at frequencies and wavevectors for which dispersion curves (isofrequency lines) have zero curvature, i.e, are locally flat. 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 the FDTD technique. We present experimental evidence of the nondiffractive propagation in a periodic array of steel cylinders in water.

Subdiffractive propagation in a bidimansional sonic crystal

Hydroacoustics, 2007

Sonic crystals are media with a periodic modulation of the acoustic parameters, 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 wavevectors 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 the FDTD technique with very good agreement with the preliminary experimental results. Support from Spanish MEC, project FIS2005-07931-C03-01, is acknowledged.

Nonlinear self-collimated sound beams in sonic crystals

Physical Review B, 2015

We report the propagation of high-intensity sound beams in a sonic crystal, under self-collimation or reduced-divergence conditions. The medium is a fluid with elastic quadratic nonlinearity, where the dominating nonlinear effect is harmonic generation. The conditions for the efficient generation of narrow, non-diverging beam of second harmonic are discussed. Numerical simulations are in agreement with the analytical predictions made, based on the linear dispersion characteristics in modulated media and the nonlinear interaction in a quadratic medium under phase matching conditions.

Self collimation of ultrasound in a three-dimensional sonic crystal

Applied Physics Letters, 2009

We present the experimental demonstration of self-collimation (subdiffractive propagation) of an ultrasonic beam inside a three-dimensional sonic crystal. The crystal is formed by two crossed steel cylinders structures in a woodpile-like geometry disposed in water. Measurements of the 3D field distribution show that a narrow beam which diffractively spreads in the absence of the sonic crystal is strongly collimated in propagation inside the crystal, demonstrating the 3D self-collimation effect.