Attenuation Of Sound Waves Research Articles

Investigation of Warping of the Electron Fermi Surface of Antimony by Giant Quantum Attenuation of Sound Waves

Warping of the Fermi surface of the electrons in antimony was investigated by using the giant quantum attenuation of sound waves. The magnetic field directions which give rise to two or three extremal cross-sections of the surface were determined and the data were used to construct the Fermi surface shape. The model of the warped surface presented here is partly in agreement with existing models derived from caliper data such as the geometric resonance and R. F. size effect and from area data such as the de Haas-van Alphen effect, but the fine detail is different in several points.

On the excess attenuation of sound in the atmosphere

The attenuation suffered by a sound wave propagating from an elevated source to the ground, in excess of spherical spreading losses and classical and molecular absorption effects, is studied. Reported discrepancies between attenuation measurements made in the field and the predictions of theories based only on absorption effects are discussed. It is concluded that atmospheric dynamics (turbulence) is a major contributor to the attenuation of sound waves propagating vertically in the atmosphere. Earlier theories on the attenuation of sound due to scattering have led to predictions of a strong (square-law) frequency dependence and relatively large magnitudes which are not supported by the available field data. The present theory predicts a square-law frequency dependence only for the special case of a homogeneous, isotropic medium. For a medium such as the atmosphere, with an inhomogeneous, anisotropic outer scale, a much milder frequency dependence is predicted which approaches a cube-root dependence for the case of an outer scale of turbulence large compared to half an acoustic wavelength (the general case for audio frequencies in the atmosphere). This result is supported by field data, as are the excess attenuation magnitudes predicted by the present theory.

Sound attenuation over homogeneous ground cover

The attenuation of 25- to 250-Hz sound waves has been measured over a homogeneous ground cover. One-third-octave bands of pink noise were transmitted across a field of soy beans and sound-pressure levels were recorded as a function of frequency, distance of absorber, and height and density of the absorber. The total absorption was compared to theoretical predictions of attenuation of sound waves layered boundaries. [Work supported by the Army Research Office, Durham, North Carolina.]

Effects of evaporation and diffusion on an oscillating bubble

The effects of the diffusion process, due to the dissolved gas in liquid, and the evaporation process, due to the liquid-vapor phase transformation, on the motion of an oscillating bubble are studied. It is found that while the effect of gas diffusion alone is significant only when the diffusion length is large compared with the size of the bubble, evaporation effects can produce some interesting features. In particular, a second resonance is found for bubbles in superheated liquid. The stability of the linear motion of the bubble is also better understood with the inclusion of evaporation and diffusion effects. Attenuation of sound waves in an incompressible liquid due to the presence of a single bubble is also calculated.

Theoretical Performance of a Parametric Array with Phase-Reversed Primary Radiation

Finite-amplitude attenuation of an intense sound wave may be diminished by reflection from a pressure release surface. Muir has suggested that this effect might be utilized to lengthen the region of interaction of a high-intensity parametric array and, hence, improve its performance. A theoretical analysis of a reflected parametric array has been performed. In this analysis a modification of the Mellen-Moffet model for parametric array performance has been utilized. The modifications consist of introducing the appropriate finite-amplitude taper function for reflected primary radiation into the model and of performing vector summations of difference frequency components generated with different phases. The results of the investigation indicate that the far-field difference frequency source level may, in some cases, be increased by more than 3 dB by reflecting the primary radiation from a pressure release reflector placed near the point of initial shock formation. Theretical data have been obtained for comparison with the experimental results presented at this meeting by Muir and Mellenbruch.

Nonlinear ultrasonic attenuation in glasses

Measurements of the attenuation of longitudinal sound waves of frequencies between 730 MHz and 1400 MHz were made on a borosilicate glass at temperatures from 0.4 K to 2 K. For high acoustic intensity J the absorption decreases with decreasing temperature. At low temperatures the attenuation is strongly dependent on the acoustic input power and was found to be proportional to J − 1 2 indicating a saturation of the absorption. For low acoustic intensities ( J ⪅ 2 × 10 −7 W/cm 2) an increase of the attenuation with decreasing temperature below T < 0.6 K was observed. The experimental results are compared with recent data in vitreous silica and can qualitatively be described by current theories based on a tunneling model.

Pressure dependence of the acoustic relaxation frequency associated with MgSO4 in the ocean

Utilizing horizontal transmission paths located at various depths in the ocean, the attenuation of sound waves has been measured at nominal frequencies of 30, 45, 60, 75, 90, and 145 kHz. Analysis of the data indicates that both the relaxation frequency at 50 kHz, which is usually attributed to the presence of MgSO4 in the sea, and the associated compressibility are functions of pressure. As pressure increases, the relaxation frequency shifts upward with a corresponding downward shift in the chemical compressibility. Results are also given for the pressure coefficient of attenuation which permit more precise predictions of acoustic attenuation at frequencies within the range of this experiment.

Anomalous ultrasonic attenuation in vitreous silica at low temperatures

The attenuation of longitudinal sound waves of 750 and 970 MHz has been determined in vitreous silica down to 0.4 K. The unsaturated attenuation observed at the smallest incident acoustic intensities allows a quantitative comparison with the “tunneling model” for glasses.

Further Study of the Occurrence of the Excitonic Phase Transition in Bismuth under Strong Magnetic Fields by Ultrasonic Attenuation

A previous measurement of the anomalous temperature dependence of the giant quantum attenuation of longitudinal sound waves in bismuth under strong magnetic fields was extended down to 1.06 K, and further evidence for the occurrence of the excitonic phase transition was obtained. The plot of sound attenuation versus temperature in the anomalous case showed a roundish convex curve near a maximum located at a point a little below T c , a temperature parameter to be identified with the phase transition point. This temperature dependence of the attenuation is well explained in terms of the critical fluctuation and a modified form of Maki-Nakanishi's formula of the attenuation of the excitonic state in the absence of field. The transition temperature, the critical exponent and other parameters to specify the anomalous attenuation curve near T c are evaluated for several cases of a parameter related to the energy difference between the hole and electron Landau levels in the normal state.

Attenuation and Redistribution of Sound Energy in Lined Annular Ducts with Shear Flow

The effects of shear flow and duct lining on the attenuation and energy distribution of complex sound waves in annular ducts are theoretically investigated. Detailed quantitative results show that the extent of redistribution of modal energy due to shear flow effects increases with boundary-layer thickness, flow Mach number, and importantly with the difference between the sound frequency and the mode cutoff frequency. For the frequency range and liner impedances considered in this study, the attenuation of sound propagating with the flow increases with boundary-layer thickness and Mach number. This trend is reversed for sound propagation in the upstream direction. The effects of liner impedance on sound attenuation and mode shapes are also investigated in detail. The information presented in this paper leads to a better design of annular duct liners and accurate prediction of the directivity patterns of sound radiated from duct ends. [Research supported by National Research Council of Canada.]

Ultrasonic attenuation due to polarization domain relaxation processes in the transverse spin density wave phase of antiferromagnetic chromium

Measurements of the field dependence of the ultrasonic attenuation of longitudinal sound waves in the frequency range 10 MHz to 300 MHz propagating in the transverse spin density wave phase of a single Q single crystal of chromium interpreted in terms of a relaxation model for thermally activated polarization domains and provide an independent indication that their volume in this sample is of the order of 10-15 to 10-16 cm3.

Sound velocity and internal friction in vacuum-deposited gold films

The velocity and attenuation of ultrasonic sound waves propagating through self-supporting vacuum-deposited gold films were measured by the pulse-echo method. The velocity of longitudinal and transverse waves of 5 MHz at room temperature were determined to be 2.21 x 105 cm/s and 1.17 x 105 cm/s respectively. These values are both a little smaller than the bulk values. The temperature dependence of the total attenuation was measured for two lengths of the film. Hence the internal friction could be determined. A sharp peak observed near 73 K in the attenuation coefficient versus temperature graph may be due to liquid air condensed on the film surface. No other relaxation peak, such as the Bordoni peak seen in cold-worked bulk gold, was observed.

A Useful Analytical Model for the Parametric Acoustic Array

In 1963, Westervelt presented a simple analytical model for the parametric acoustic array. Making a number of simplifying assumptions, among them that nonlinear attenuation is negligible, Westervelt arrives at the following: (1) quadratic dependence of secondary level on primary level and (2) Rutherford scattering angle dependence, independent of primary level. Now, experiments show that: (1) the quadratic level dependence goes over to a linear dependence at high levels and (2) the difference frequency beamwidth broadens with increasing level. These effects are not predicted by Westervelt's model. In this letter, it is shown that it is easy to substitute the attenuation of a shocked sound wave in place of the simple linear attenuation used by Westervelt. The resulting Green's function integral is no longer elementary, but has a simply expressed hypergeometric series solution. On axis, the series sums to a simple closed form solution, correctly predicting the transfer from the quadratic to linear level dependence. Off axis, the series apparently does not sum to closed form, but is readily evaluated with a digital computer. The results agree rather well with experiment.

Mechanical properties ofChlorella cell walls as determined by the suspension method

The so-called suspension method was employed to measure the mechanical properties ofChlorella cell walls. This method worked well for the present sample. The ratio of compressibility of the cell wall to that of water was 0.62 at room temperature at frequencies of 1.5 and 2.0 MHz. Temperature dependence of compressibility was similar to that of many polymer samples. A difference of compressibility was observed at two different stages of the cell cycle ofChlorella, but any difference of volume viscosity was not as obvious. The more extensive the enlargement growth of the cell, the larger was the compressibility. The existence of a relaxation mechanism in the order of microseconds was postulated from measurements of the frequency dependence of the attenuation of sound waves.

Attenuation of low-frequency sound waves in sediments : Anderson, R.S., Blackman, A., Vol 49, No 3, Part 2 (March 1971) pp 786–791

Attenuation of low-frequency sound waves in sediments : Anderson, R.S., Blackman, A., Vol 49, No 3, Part 2 (March 1971) pp 786–791

Giant Quantum Attenuation of Sound Waves in Antimony. I. Deformation Potential Constants and Spin Splitting Factors of Electrons

The giant quantum attenuation of longitudinal sound waves in antimony was investigated in pulsed magnetic fields up to 170 kG, at temperatures of about 1.6 K and at sound wave frequencies of 60 and 100 Mc/s. The values of the deformation potential tensor components for the electrons in the principal pocket obtained from an amplitude analysis are as follows: | D x x (e) |=6.1 eV, | D y y (e) |=7.9 eV, | D z z (e) |=0.44 eV, and D x x (e) / D y y (e) =-0.77, where x -, y - and z -axis refer to a binary, a bisectrix and the trigonal axis respectively. A determination of the anisotropy of spin splitting factors (spin splitting/Landau splitting) of the electrons is made for two cases of H ∥ x y -plane and H ∥ y z -plane.

High frequency sound wave attenuation in β-brass around T c

High frequency (20 MHz) sound wave attenuation in β-brass around its order-disorder critical temperature has been measured. The attenuation maximum appears above T c . Longitudinal wave attenuation is linearly dependent on frequency and is much less than shear

Ultrasonic Velocity and Attenuation in Liquid Neon

The velocity and attenuation of 30-MHz sound waves were measured in liquid neon from 25 to 37°K at pressures to 28 kg/cm2. The values of the velocity, extrapolated to the vapor pressure curve, are from 1.5% higher at 25°K to 0.4% higher at 32°K than corresponding values reported for 2-GHz sound waves. This negative dispersion is in agreement with recent predictions by Fleury and Boon. Values of the attenuation exceed the classical values calculated from the Navier–Stokes equation. This excess attenuation is attributed to a volume viscosity of the same magnitude as the shear viscosity. No anomaly in the temperature dependence of either velocity or attenuation was observed near the temperature where an anomaly has been reported for thermal conductivity, shear viscosity, and hypersonic velocity.

Analog Method of Optimizing Duct-Lining Design

The analytical results by Cremer and Morse on the attenuation of sound waves in rectangular ducts were used in the development of an electrical analog for the study of different lining designs for a jet engine fan duct. The analog was designed to give the optimum attenuation of a certain lining to sound waves grazing at the surface. The variables in the analog allow the variation of such parameters as the resistance and reactance of the lining material, the number of layers of lining, and the back spacing behind each layer, as well as the frequencies at which maximum attenuation is desired.

Relations Between Atomic Transport Coefficients in Simple Liquids and Moments of Neutron Scattering Functions

Abstract A possible alternative to Kubo theory is discussed for relating atomic transport coefficients in simple liquids. The arguments used result in a new expansion, in which the density-density response function x is expanded in a power series in the self response function Xs. The coefficients of this expansion can be determined, in principle, to all orders, from the moments of the neutron scattering functions S(qω) and S s(qω). It is then proposed, by appeal to the hydrodynamic equations, that the radius of convergence of this series can be used to relate diffusion to the sound wave attenuation coefficient. Finally, this x-xs expansion allows a direct comparison of the exact theory presented in this paper with earlier approximate theories relating incoherent and coherent neutron scattering from liquids.