On the ultrasonic attenuation in glasses at low temperatures

The ultrasonic attenuation in glasses at low temperatures is calculated using the model proposed by Anderson, Halperin, and Varma. It is found that the resonant absorption of sound by the localized two-level systems saturates and can be observed only if the sound amplitude is extremely small. A second contribution to the sound absorption is derived which arises from the relaxation of the localized excitations and does not saturate. Qualitative agreement with recent measurements of the ultrasonic attenuation in fused silica is obtained.     

Ultrasonic attenuation in dirty two-band superconductors with persistent currents

The ultrasonic attenuation in two-band superconductors with non-magnetic and paramagnetic impurities in the presence of persistent currents is studied. The case of high impurity concentrations is considered. Assuming space-independent sound waves, the absorption energy in the case of relatively low frequencies at low and zero temperatures is calculated.     

Ultrasonic attenuation in copper at low temperatures

Ultrasonic attenuation in copper at low temperatures has been analysed in terms of electron-electron and electron-phonon interactions. The contribution due to electron-electron interactions has been evaluated using a simplified spherical Fermi-surface model with an isotropic Umklapp transition probability. We observe that the contribution to the attenuation constant (α) due to electron-electron scattering in copper at 3 K is about 10% of the electron-phonon contribution. We have also considered the viscous attenuation and the induction attenuation mechanisms simultaneously in copper as suggested by Orlov and find that our results improve the existing theoretical data considerably.     

Effect of thermal conductivity on ultrasonic attenuation in praseodymium monochalcogenides

The ultrasonic attenuation in intermetallic praseodymium monochalcogenides are evaluated in the temperature interval 100–500 K along the crystallographic directions 〈100〉, 〈110〉, and 〈111〉 for longitudinal and shear waves. A comparison has been made with lanthanum monochalcogenides and other similar materials. Ultrasonic attenuation at different temperatures is mainly affected by the lattice thermal conductivity values of the materials at these temperatures. Thermoelastic loss is very small in comparison to the attenuation due to phonon-phonon interaction mechanism at higher temperatures.     

Temperature dependent ultrasonic properties of aluminium nitride

Hexagonal wurtzite structured aluminium nitride has been characterized by the theoretical calculation of ultrasonic attenuation, ultrasonic velocity, higher order elastic constants, thermal relaxation time, acoustic coupling constants and other related parameters in temperature range 200-800 K for wave propagation along the unique axis of the crystal. Higher order elastic constants of AlN at different temperatures are calculated using Lennard-Jones potential for the determination of ultrasonic attenuation. A decrease in ultrasonic velocity with temperature has been predicted, which is caused by reduction in higher order elastic constants with temperature. The temperature dependent ultrasonic properties have been discussed in correlation with higher order elastic constants, thermal relaxation time, thermal conductivity, acoustic coupling constants and thermal energy density. Anomalous behaviour of the attenuation is found at 400 K. On the basis of attenuation, the ductility and performance of AlN have been studied.     

Ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with dipolar interactions

The ultrasonic attenuation and kinetic coefficients in pure and random uniaxial ferromagnets with both short range exchange and long range dipolar interactions are calculated near the critical point using renormalization group theory. The dispersion and temperature dependences found differ logarithmically from classical theory and suggest new experiments. In the pure system a recent phenomenological calculation of the ultrasonic attenuation in the low frequency limit is confirmed.Project of the Sonderforschungsbereich Frankfurt/Darmstadt financed by special funds of the Deutsche Forschungsgemeinschaft     

An acoustic study of the mixed-alkali-mixed phase β-aluminas. Part 1: Naβ″/βAl2O3, Kβ″/βAl2O3 and (Na0.6K0.4)β″/βAl2O3

The relative attenuation of compressional sound waves of frequencies 10–60 MHz in mixed alkali (Na/K) mixed phase (β″/β)-aluminas is reported for temperatures 80–550 K. The internal friction peaks shift to higher frequencies at higher temperatures and are attributed to Na⁺ interactions in Naβ″/β alumina and Na⁺ and K⁺ in NaK β″/β alumina. The broad attenuation peaks occuring at low temperatures (< 300 K) and at higher temperatures (> 400 K) suggest multi-relaxation processes giving a distribution of activation energies. The estimated average activation energy for Na⁺ diffusion in Naβ″/βAl₂ O₃ at low temperatures and high temperatures is 0.183 eV and 0.387 eV respectively. In the NaK β″/βAl₂o₃ samples, the Na ⁺ values were 0.239 eV and 0.386 eV, respectively. The estimated average activation energies for K⁺ diffusion at low and high temperatures in the Kβ″/β-alumina samples were 0.269 eV and 0.371 eV and for K⁺ in the NaK β″/β samples, 0252 eV and 0.339 eV, respectively. The low temperature attenuation peaks were interpreted in terms of ionic interaction in the bulk and the high temperature peaks were related to interactions in the grain boundaries. The measured activation energies confirmed these interpretations. A reversal of the temperature appearance of the Na⁺ and K⁺ high temperature peaks in the NaKβ″/βAl₂ O₃ is explained by the disorder at the grain boundaries.     

Ultrasonic attenuation due to the neutral acceptor Mn in GaAs

We report on measurements of the ultrasonic attenuation in GaAs:Mn at frequencies between 400 and 2000 MHz and at temperatures between 1 and 35K. The results indicate that there is a level 3 meV above the acceptor ground state.     

In-line ultrasonic monitoring of semi-solid magnesium die casting process

Ultrasonic velocity and attenuation measurements in AZ91D magnesium (Mg) alloy with dendritic, rosette and globular microstructures were performed at elevated temperatures using a non-contact laser-ultrasonic technique. It was found that the ultrasonic velocity in the globular microstructure and the ultrasonic attenuation in the dendritic microstructure are the highest among the three microstructures. An ultrasonic clad steel buffer rod sensor embedded in the die has been used to monitor the semi-solid die casting process in-line for the AZ91D Mg alloy. This probe monitored the completion of the die filling, the release of the pressure, the opening of the die, part detachment, solidification of the part, the averaged temperature of the die and the part.     

Application of low intensity ultrasonics to cheese manufacturing processes

Ultrasound has been used to non-destructively assess the quality of many foods such as meat, fish, vegetables and dairy products. This paper addresses the applications of low intensity ultrasonics in the cheese manufacturing processes and highlights the areas where ultrasonics could be successfully implemented in the future. The decrease of ultrasonic attenuation during the renneting process can be used to determine the optimum cut time for cheese making. The ultrasonic velocity increases during maturation for those types of cheese that become harder during this manufacturing stage, thus being an indicator of the maturity degree. Moreover, ultrasonic measurements could be linked to sensory parameters. From the ultrasonic velocity measurements at two different temperatures, it is possible to assess cheese composition, thus allowing an improvement in the quality and uniformity of cheese commercialization. In addition, in pulse-echo mode it is possible to detect cracked pieces due to abnormal fermentations and also to assess the distance of the crack from the surface.     

超离子玻璃中的超声吸收理论

本文依据红外发散理论讨论超离子玻璃中无序引起的多体相互作用所导致的红外发散响应。在研究新的弛豫机制的基础上,修正了滞弹性应变的速率方程,并利用玻耳兹曼叠加原理,导得具有红外发散的超声吸收公式。由此导出超声吸收与频率的ωⁿ关系和表观激活能。这些都与超离子玻璃(AgI)_x(Ag₂O·nB₂O₃)_1-x的实验数据符合。 关键词：     

Temperature dependence of electron mean free path in molybdenum from ultrasonic measurements

The temperature dependence of the electronic mean free path in molybdenum has been obtained from ultrasonic attenuation measurements. For temperatures up to 30 K a T^?2 law is followed suggesting the importance of electron-electron scattering in the attenuation mechanism.     

Theory of the contribution of the electron-phonon interaction to the anisotropic electronic lifetime and transport properties of zine

Using pseudopotential theory for the phonons, electrons, and electron-phonon interaction of zine, we have calculated several electronic properties of this metal. Among these are the electron lifetime at three positions on the Fermi surface, the anisotropic electrical resistivity, the anisotropic thermal conductivity, and the ultrasonic attenuation, all due to the electron-phonon interaction, and all as a function of temperature. For the electrical resistivity, two solutions of the Boltzmann equation were obtained, one consisting of a single spherical harmonic, and the other made up of six spherical harmonics. The single spherical harmonic is not adequate at low temperatures.     

Acoustic properties of multiferroic BiFeO<Subscript>3</Subscript> over the temperature range 4.2–830 K

The longitudinal acoustic wave velocity and attenuation in BiFeO₃ ceramics have been measured by ultrasonic pulse-echo technique at a frequency of 10 MHz in the temperature range from 4.2 K to 830 K. The anomalies observed in the sound velocity and attenuation behavior versus temperature are attributed to the assumed relaxation in the temperature range 200–500 K and antiferromagnetic phase transition at higher temperatures. Order parameter fluctuations along with magnetostriction are discussed as the factors determining the acoustic wave velocity anomaly in the vicinity of the antiferromagnetic phase transition point.     

Structural studies of nano silica employing on-line ultrasonic studies

Monodispersed, nano silica particles have been prepared by sol-gel hydrolysis and condensation of the metal alkoxide using pH buffer. The prepared particles are characterised by XRD, FTIR, BET, SEM, TEM measurements. The measurements reveal that the size and shape of silica particles depend on concentration of water. In addition, the ultrasonic longitudinal velocity and attenuation of the nano silica particles have been measured at a frequency of 5?MHz over a wide range of temperatures from 300?K to 1150?K in nano silica. The different structural transitions, such as monoclinic, orthorhombic, orthorhombic with a non-integral super lattice, stable orthorhombic and hexagonal, which exist in silica are explained based on on-line high-temperature ultrasonic velocity and attenuation measurements.     

Measurement of the acoustic properties of a nerve-muscle preparation as a function of physiologic state

Nerve-muscle preparations of Sprague Dawley rats were exposed to low dosage ultrasound. The objectives were to measure the velocity of propagation and attenuation of ultrasonic energy in both the relaxed and contracted states. A tension-measuring system and associated ultrasonic instrumentation were designed to measure the tension developed in stimulated muscle and its corresponding acoustic parameters, ie the attenuation coefficient, (db cm^-1) and the velocity of propagation, c (ms^-1). Each test was performed at ultrasonic frequencies 3.1, 5.35, and 7.68 MHz and with the preparation maintained at 23 ± 0.5° C. Attenuation of ultrasonic energy was observed to increase by 10 ± 0.5% in the active state from its value in the relaxed state. The relation between the attenuation and the acoustic frequency was found to be approximately linear over the frequency range tested. The velocity of propagation in the active state did not change appreciably from its value in the relaxed state and was observed to be independent of the acoustic frequency in the range used.     

Dynamic scaling of the critical ultrasonic attenuation in binary liquids: evidence from broadband spectrometry

Between 200 kHz and 500 MHz, the ultrasonic attenuation spectrum of the ethanol/dodecane mixture of critical composition has been measured at various temperatures near the critical one. The measured broadband spectra are evaluated in light of the Ferrell-Bhattacharjee dynamic scaling theory. The experimental findings largely fit the theoretical spectral function if suitable crossover corrections are made using dynamic light-scattering data. The measured scaling function follows the predictions of the recent Folk-Moser renormalization-group theory even better. Combining our ultrasonic attenuation coefficient data with density data from the literature, the asymptotic critical behavior of the thermal expansion coefficient and of the specific heat has been determined and found consistent with the two-scale factor universality. The sonic attenuation data have also been evaluated to yield the adiabatic coupling constant g of the dynamic scaling theory. The unusually small absolute value |g|=0.1 resulted, in fairly good agreement with |g|=0.13 as following from thermodynamic data.     

Non-contact sound velocities and attenuation measurements of several ceramics at elevated temperatures

Laser ultrasonic technique has been employed to carry out the sound velocities and attenuation measurements as a function of temperature in alumina, two kinds of silicon nitride and partially stabilized zirconia (PSZ) samples. Accuracy of the laser technique used has been checked in terms of the diffraction effect and reproducibility of the results. Results of attenuation at room temperature have been compared with quartz transducer technique. In PSZ, velocity behavior has become non-linear and also, a peak in attenuation has been observed around 500 degrees C. In one of the silicon nitride sample, which uses glassy sintering agent, attenuation has shown a sharp peak around 950 degrees C. Interestingly, when the experiment was repeated from 800 to 1000 degrees C, this anomalous attenuation peak has disappeared, leaving a background increasing towards higher temperatures.     

Features of high-frequency ultrasound propagation in the temperature range of structural and magnetic phase transitions in La1−x SrxMnO3 (x=0.175) manganite

The propagation of ultrasonic waves at a frequency of 770 MHz in a La_0.825Sr_0.175MnO₃ single crystal is investigated in the temperature range 350–150 K. It is found that the velocity, attenuation, and mode composition of ultrasonic waves change at temperatures of 315–280 and 220 K. These changes correlate with the structural and magnetic phase transitions and can be explained in terms of the Jahn-Teller distortions of the crystal lattice.     

Pr1/3Sr2/3FeO3中电荷有序现象的超声研究

系统研究了Pr1/3Sr2/3FeO3单相多晶样品在低温下的电荷输运性质和超声特性.电阻测量表明,Pr1/3Sr2/3FeO3在162K发生了电荷有序相变.而超声声速从室温开始就出现了明显的软化,在电荷有序温度附近达到最小值,随后又急剧硬化,同时伴随着一个巨大的衰减峰.分析指出这是由于电-声子相互作用导致的结果,该电-声子耦合可能起源于Fe4 的Jahn-Teller效应.