Search

In acoustics, it is known that, for a given response signal at an arbitrary location, reciprocity and time reversal (TR) can be used to focus high levels of acoustic energy at that position. In solid media, elastic waves generally induce different disturbances in three directions. In this paper, both experimental and numerical wave propagation results for solid materials demonstrate the ability to use a scalar source, a three component detector and the reciprocal TR process to selectively focus each of the different vector components, either individually or collectively. The principle is explained from an analytical point of view. The numerical and experimental study demonstrates excellent temporal and spatial focalization. Applications of the selective vector component focusing can be found in damage imaging techniques using both linear or nonlinear ultrasonic waves. [ABSTRACT FROM AUTHOR]

We measured acoustic transmissions through subwavelength hole arrays fabricated on brass plates at normal and oblique incidence. It is found experimentally that the transmission phenomena for the hole array in thin plate case are analogous to the previously observed enhanced transmission of electromagnetic waves [Ebbesen et al., Nature (London) 391, 667 (1998)]. While for the hole array in thick plate case, the transmission peaks of acoustic wave occur well below Wood’s anomalies, and the spectrum characteristics reveal a Fabry–Pérot-like resonance. An effective fluid approach is conceived and it can well describe the transmission properties of the hole array in thick plates within a range of incidence angle. [ABSTRACT FROM AUTHOR]

This paper presents the propagation of waves along a one-dimensional “diatomic” chain made up to welded spheres, i.e., with two steel spheres of different diameters alternating. First, a theoretical analysis is presented, which gives the vibration modes of an infinite chain, leading to two low-frequency branches, separated by a band gap. A theoretical analysis is then performed on a finite chain, containing an even or an odd number of spheres. Depending on the parity of the number of spheres in the finite chain and on the ratio between the masses of the spheres, it points out that localized modes may appear in the band gap. The theoretical results have been validated by a comparison between numerical and experimental results. Many applications of such systems can therefore be found: acoustic filters, noise and vibration isolation, acoustic wave guiding, etc. [ABSTRACT FROM AUTHOR]

We report on the interaction between photogenerated electron-hole pairs and surface acoustic waves (SAW) in GaN films grown on sapphire substrates. The spatial separation of photogenerated carriers by the piezoelectric field of the SAW is evidenced by the quenching of the photoluminescence (PL) intensity. The quenching levels in GaN are significantly smaller than those measured in GaAs under similar conditions. The latter is attributed to the lower exciton ionization efficiency and carrier separation probabilities mediated by the piezoelectric effect. The PL spectra also evidence energy shifts and broadenings of the electronic transitions, which are attributed to the band gap modulation by the SAW strain field. [ABSTRACT FROM AUTHOR]

Analyzes the dynamic behavior of anisotropic open porous materials using a general mixed displacement-pressure formulation. Use of Coussy's description of porous materials; Reduction to a set of equations of motion used in acoustics.

Deals with a study which applied the photoacoustic resonance method to study molecular relaxation in a cylindrical cavity. Background to the study; Theoretical framework; Experimental results and discussion.

Provides information on a study which investigated the acoustic quality factor and relative shear modulus of polycrystalline samples of niobium and vanadium. Methods; Results; Conclusion.

Focuses on a study which developed a computer program designed to examine the generation mechanism and acoustic response of insulating substrate. Determination of the delamination in matallized films on insulating substrates; Computation of the deformation of model resonance; Results and discussion.

We investigate theoretically subwavelength imaging by acoustic metamaterial slabs immersed in the liquid matrix. A near-field subwavelength image formed by evanescent waves is achieved by a designed metamaterial slab with negative mass density and positive modulus. A subwavelength real image is achieved by a designed metamaterial slab with simultaneously negative mass density and modulus. These results are expected to shed some light on designing novel devices of acoustic metamaterials. [ABSTRACT FROM AUTHOR]