Attenuation of acoustic waves in glacial ice and salt domes

Two classes of natural solid media (glacial ice and salt domes) are under consideration as media in which to deploy instruments for detection of neutrinos with energy >1e18 eV. Though insensitive to 1e11 to 1e16 eV neutrinos for which observatories (e.g., AMANDA and IceCube) that utilize optical Cherenkov radiation detectors are designed, radio and acoustic methods are suited for searches for the very low fluxes of neutrinos with energies >1017 eV. This is because, due to the very long attenuation lengths of radio and acoustic waves in ice and salt, detection modules can be spaced very far apart. In this paper, I calculate the absorption and scattering coefficients as a function of frequency and grain size for acoustic waves in glacial ice and salt domes and show that experimental measurements on laboratory samples and in glacial ice and salt domes are consistent with theory. For South Pole ice with grain size 0.2 cm at -51 degrees C, scattering lengths are calculated to be 2000 km and 25 km at 10 kHz and 30 kHz, respectively, and the absorption length is calculated to be 9 km at frequencies above 100 Hz. For NaCl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 km and 1.4 km at 10 kHz and 30 kHz, and absorption lengths are calculated to be 30,000 km and 3300 km at 10 kHz and 30 kHz. Existing measurements are consistent with theory. For ice, absorption is the limiting factor; for salt, scattering is the limiting factor.Comment: 16 pages, 7 figures, submitted to Journal of Geophysical Research - Solid Eart

Thermoelastic Sound Source: Waveforms in a Sensing Application

Photoacoustically generated sound pulses are widely used in various NDT, NDE and sensing applications when a non-touching method is preferred. The generation mechanisms are relatively well known, including types of waves generated, directional patterns, sound pressures and damage thresholds for the laser intensity [1]. The so-called thermoelastic regime is attractive to many applications despite of its low efficiency (usually about sub 0.1%). It is because that the process is nondestructive to samples and the theory is well established [2,3,4]. The current study addresses the prediction of the temporal ultrasound pulse shape of an optimum sound generation scheme using a low power diode pumped high repetition rate Nd:YAG pulse laser [5]. A model is proposed in which the radiation from the thermoelastic sound source is treated as an instantaneous piston source at the solid-fluid interface

Optimization of Sound Pulse Generation for Photoacoustic Sensing Applications

Photoacoustically generated sound pulses are currently used in various NDT, NDE and sensing applications, often because this method generates ultrasound without touching the sample. The generation mechanisms are relatively well known, including directional patterns, sound pressures and damage thresholds for the laser intensity. Our study addresses the optimal conditions for sound generation for sensing purposes in a liquid using a low power diode pumped Nd:YAG pulse laser.</p

On the acoustic diffraction by the edges of benthic shells

Author Posting. © Acoustical Society of America, 2004. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 116 (2004): 239-244, doi:10.1121/1.1675813.Recent laboratory measurements of acoustic backscattering by individual benthic shells have isolated the edge-diffracted echo from echoes due to the surface of the main body of the shell. The data indicate that the echo near broadside incidence is generally the strongest for all orientations and is due principally to the surface of the main body. At angles well away from broadside, the echo levels are lower and are due primarily to the diffraction from the edge of the shell. The decrease in echo levels from broadside incidence to well off broadside is shown to be reasonably consistent with the decrease in acoustic backscattering from normal incidence to well off normal incidence by a shell-covered seafloor. The results suggest the importance of the edge of the shell in off-normal-incidence backscattering by a shell-covered seafloor. Furthermore, when considering bistatic diffraction by edges, there are implications that the edge of the shell (lying on the seafloor) can cause significant scattering in many directions, including at subcritical angles.This research was supported by the U.S. Office of Naval Research (Grant No. N00014-02-1-0095) and the Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA

RADIATION ACOUSTICS

Acoustique de radiation est une nouvelle branche de l'acoustique. L'etude des effets de l'acoustique de radiation est a sa base. Ces effets sont le résultat de l'interaction du rayonnement pénétrante avec une matière. On examine l'excitation du son par le rayonnement pénétrant module ou impulsif (faisceaux de électrons, des protones, des ions etc., γ-rayonnement) et par des particules fondamentales de haute énérgetique. On discute les applications possibles des effets de l'acoustique de radiation en contrôle non destructif et pour la détection des particules fondamentales de haute énérgetique.Radiation acoustics is a new branch of acoustics. Its' fundamentals are lying in the research of acoustical effects due to the interaction of a radiation with matter. The sound excitation in liquids and solids by modulated or pulsed particle beams (electron, proton, ion beams, γ-radiation and single high-energy elementary particles) and some practical applications are discussed

Nonspecular reflection, resonance scattering and radiation of sound by elastic bodies in water

Results of studies of sound reflection by plates and shells immersed in water are given. The are incidence angles of sound waves upon plates or shells, under which strong reflection backwards, i.e. nonspecular reflection, is observed. Physical nature of nonspecular reflection is discussed and its theory is given. It is demonstrated that nonspecular reflection is accompanied by the effect of spatial-frequency resonance. It is revealed that resonance scattering and radiation of sound by shells immersed in water is connected with the effect of spatial frequency resonance. The discussed effects can play the dominant role in formation of underwater acoustic fields

Laser photoacoustic monitoring of piezoelectric elements of hydroacoustic transducers

Excitation of flexural vibrations of a bounded thin plate by laser radiation is considered. The relations connecting the parameters of the laser radiation and the plate are obtained. Opportunities for remote laser photoacoustic monitoring and identification of piezoelectric elements of hydroacoustic transducers (arrays) are discussed