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We present a study on the acoustic radiation forces exerted on a cylindrical particle near the surface of a periodically structured brass plate. When resonance of the structured plate occurs, this configuration shows an interesting trapping effect, which essentially arises from the gradient force induced by gradient vortex velocity field near the surface. This artificial structure for providing a geometrically modulated trapping force may be of interest for acoustic manipulation and sorting in various complex mechanical systems. [ABSTRACT FROM AUTHOR]

Periodic solid state structures exhibit transmission stop bands for waves of certain frequencies. We report the realization and direct measurement of acoustic band gaps in porous silicon multilayer structures which exhibit ∼50 dB stop bands for longitudinal acoustic waves in the gigahertz range. Furthermore, realization of an acoustic microcavity structure in porous silicon is demonstrated. [ABSTRACT FROM AUTHOR]

This letter aims at showing the interest in using an integration path in the complex plane in order to calculate Fourier integrals, instead of using a real path, as needed for the fast Fourier transform algorithm as follows: fastness, accuracy, avoiding of singularities, or even aliasing phenomenon. The method is applied to the calculation of the acoustic field emitted by a transducer or a loudspeaker; for the same number of sampling points, the calculation of the spatial Fourier integrals is more accurate using a complex path than using a real path. [ABSTRACT FROM AUTHOR]

The authors report a design of a highly magnified directional acoustic source based on the planar resonant cavity of two-dimensional phononic crystals. The authors demonstrate that the order of the resonant mode and the reflective ratio of the double phononic crystal slab are the key factors to the magnified ratio of the directional acoustic amplifier. With properly designed mode and cavity width of the asymmetric phononic structure, the optimal magnified amplitude can be achieved by more than 86.5 times in comparison with the amplitude of the original line source freely radiating in water. [ABSTRACT FROM AUTHOR]

We present a simple method for fluid velocimetry based on the velocity of the heterodyne speckles generated by tracking particles illuminated with coherent light. It works in real time and provides instantaneous two-dimensional velocity mappings in the direction orthogonal to the optical axis, independently of the particle concentration and size, also for subwavelength particles. It also provides the velocity distribution of the fluid over the entire sample thickness. The method has been quantitatively tested by using the motions of rigid diffusers and applied for mapping the flow of a confined fluid. [ABSTRACT FROM AUTHOR]

The emergence of the area of nanophononics requires the development of terahertz (THz) acoustic devices with tailored properties. We describe nonperiodic planar nanostructures with specific THz phononic response and superior performance. We show that improved devices based on GaAs and AlAs layers can be designed using an optimization Nelder-Mead simplex method, and grown with state-of-the-art molecular beam epitaxy. We also demonstrate that high-resolution Raman scattering provides a powerful tool to characterize these devices. We illustrate the concept with results on acoustic THz edge and color filters. [ABSTRACT FROM AUTHOR]

First-principles calculations show that AB defects substituting on an O site in ZnO where A, B=N, O, or C are an important class of defects whose physical properties cannot be described by the usual split interstitials but rather by substitutional diatomic molecules. The molecular natures of the (AB)O defects are reflected in their vibrational frequencies which are redshifted from those of the corresponding free molecules but only by about 10%. These calculated results agree with the frequency range recently observed by IR measurement on N-doped ZnO. Moreover, most (AB)O defects are donors in p-type samples. The (NC)O and (N2)O defects have sufficiently low energies to convert substituional NO acceptors into donors, thereby hindering the efforts of doping ZnO p type. [ABSTRACT FROM AUTHOR]

We utilize a real-time acoustic technique, based on pulse-echo measurements to detect formation of microbubbles in an aqueous solution of a silver/dendrimer nanocomposite (DNC). Wave-field plots of successive recordings illustrate the generation and behavior of bubbles created by the optical breakdown process. A significant threshold reduction is achieved with DNC particles compared to its host dendrimer, enabling a diverse field of low-threshold breakdown applications. [ABSTRACT FROM AUTHOR]