Acoustic interferometer

About: Acoustic interferometer is a research topic. Over the lifetime, 1493 publications have been published within this topic receiving 19355 citations.

Electromagnetic generation of acoustic waves in metals : applications to ultrasonic measurements. -

Abstract: The generation ot radlo-frequency acoustic waves within the skin layer of a metal In the presence of a statlc magnetic field has been studied in single-crystal plates of puve gallium. Acoustic resonances generated in this manner were detected as sangularities in the surface impedance at those fsequencies which satisfy the boundary conditions for the existence of standing sound waves In the plate. The amplitude, line-shape, and magnetic field dependence of these singularities are in quantitative agreement with the predictions of the phenomenological model of Turner, Lyall, and Cochran. This theory is applicable to all real metals, under certain conditions of frequency and magnetic field, and its results are discussed in relation to those detailed calculations which assume that the metal consists of a free-electron gas in an isotropic, positively-charged background. The measurements were obtained using a radio-frequency bridge which is capable of measuring changes in the phase and amplitude of the surface impedance of a metal plate, with an amplitude uncertainty of + 3 % , and a phase-angle uncertainty of 1.5 degrees. This apparatus was calibrated at helium temperatures, and at frequencies between 5 MHz and 10 MHz. Using the continuous-wave resonance technique, the velocities of ultrasound in single crystals of gallium were measured at 4.20KI 77OK, and 273'K. From these measurements, the nine elastic constants of gallium were calculated. The Debye temperature calculated from the 4.2OK elastic constants, 328 k 3.3"K, is in agreement with the value of 324.7 + 2OK previously obtained from low-temperature specific heat data by

Excitation and detection of acoustic waves in plasmas

Abstract: : This report contains initial results of an experimental study of acoustic disturbances in weakly ionized gaseous plasmas which exist in the positive column of dc discharges. One phase of the research concerns itself with the effects of externally perturbing such a medium with acoustic waves emanating from transducers that operate in the audio and ultrasonic frequency ranges. The balance of the effort is devoted to the observation of sound waves generated by natural and uncontrolled low-frequency oscillations which commonly occur in laboratory discharges. Compact transducers incorporated into cylindrical discharge tubes provide the source of acoustic signals and serve as microphones in detecting sound waves. Modulation of electromagnetic waves by the intentionally disturbed plasma was measured in a novel rectangular cavity whose output was detected and fed to a wave analyzer. Resultant wave-analyzer responses indicate that the electron collision frequency was modulated in addition to the electron plasma frequency, and that the variations in both were proportional to the magnitude of loudspeakerdiaphragm deflection, as predicted by simple acoustic theory.

Scattering of plane acoustic waves at elastic particles with rough surfaces

Abstract: A comprehensive theoretical and numerical study of the influence of surface roughness of elastic particles in water on the scattering of ultrasonic waves has been carried out. For near spherical shape of the particles and with small rms-roughness heights, a perturbation method has been developed. In this method, the first-order perturbation contribution predicts the contribution to the incoherently scattered acoustic field due to surface roughness, and the second-order perturbation contribution predicts the change in the coherent field and will satisfy the requirement of energy conservation. The second-order perturbation contribution is evaluated by use of the form function concept, while the first-order perturbation to the total scattered acoustic field is evaluated by use of the scattering cross-section. As a function of the ka-value and for different rms-roughness heights a numerical study of the forward and backward scattering from rough, elastic particles has been carried out and a substantial roughness influence on the scattered field has been verified. Some experimental results from measurements of scattering from glass and cast iron spheres have given evidence to the numerical predictions.

The energy transport by the propagation of sound waves in wave guides with a moving medium

Abstract: The problem of the propagation of sound waves radiated by a source in a fluid moving with subsonic velocity between two parallel walls or inside a cylindrical tube is considered in [2], The most interesting thing of this problem is that waves may occur with constant amplitude coming from infinity. This article gives the calculation of the energy transport in the wave guides. It is shown that it is not possible to gain energy from infinity.

Remote Measurement Method of Acoustic Velocity in Liquids by a Pair of Leaky Acoustic Waveguides

Abstract: We propose a new method to measure the elastic characteristics (the acoustic velocity) of liquids by a pair of leaky acoustic waveguides as probes. Transducers are not immersed or inserted into liquids to be measured in this method, s o that it is suitable for remote measurement of the acoustic properties of liquids at high temperatures or in chemically active conditions. In this paper, long steel plates have been investigated as the waveguides. An L1-mode Lamb wave and a Rayleigh wave have been studied experimentally as guided waves. The principle of measurement method, the experimental equipments and the experimental results are described in detail.