Dislocation damping and the ultrasonic attenuation in the normal and superconducting states of pure tin

Ultrasonic attenuation studies have been carried out both in the normal and superconducting states in pure (99.9999%) single crystals of tin containing various amounts of dislocations. At low pulse amplitude the normal state attenuation is effectively independent of the dislocation density. The dislocations have been found to introduce significant deviations in the superconducting state attenuations from the BCS values. The extra attenuation Δα_s in the superconducting state due to dislocations has been found to show an inverse fourth power dependence on the temperature. Δα_s has also been shown to exhibit resonance type of behaviour over the frequency range 3 to 50 MHz. This resonance frequency depends on the dislocation density with different power laws in different ranges of the dislocation density.     

Damping of dislocation and the ultrasonic attenuation in normal and superconducting tin

Ultrasonic attenuation measurements at liquid helium temperatures, 77 K, and 300 K in single crystals of pure tin with frequencies varying from 3 to 50 MHz reveal in a qualitative way the temperature dependence of the electronic damping parameter B _en. An approximate estimate of B _en at 300 K has been made.     

Amplitude-dependent ultrasonic attenuation in the normal and superconducting states of indium-doped tin

The amplitude-dependent ultrasonic attenuation was studied at 3.6 and 10 MHz in three annealed single crystals of tin doped with 0.0016, 0.0031, and 0.00928 at% indium. The amplitude of the pulse in each case was varied from 30 to 300 V peak to peak. The results show that the dynamic loss is amplitude dependent, as predicted theoretically by Rogers. The attenuation peaks due to the breakaway of the dislocation from minor pinning points were observed and were used to calculate the electronic damping parameter and the dislocation resonance frequency. The former parameter was calculated from Holstein's theoretical expression and was found to be in agreement with the value determined experimentally.     

Dislocation resonance in superconducting tin

Ultrasonic attenuation in the superconducting state of strained samples of single crystals of tin shows a strong dependence on the dislocation density. The dislocation density is estimated with the help of a suitable etch pit method. The etch pits are square in shape and exhibit symmetric dislocation lines normal to the (100) planes. The number of etch pits reveals a direct dependence on the physical state of the specimen. The dislocation density estimated by this etch pit method can be related to the extra attenuation Δα_s shows a resonant behaviour and the resonance frequency is dependent on the dislocation density. It is also observed that the functional relationship between the resonance frequency and the dislocation density is different in different regions of the dislocation density.     

Ultrasonic attenuation in the intermediate state of tin

Attenuation of ultrasound has been measured in the intermediate state of single crystals of tin at 3.3 MHz in the temperature range 1.5–3.7 K. A small measurable change of the frequency v_O of the collective modes of excitations has been observed very near the critical magnetic field.     

Electron-electron scattering and ultrasonic attenuation in potassium

The electron-electron scattering contribution to the ultrasonic attenuation in potassium at low temperatures is evaluated using the Landau Fermi liquid theory. The scattering function is evaluated using the approximation suggested by MacDonald and Geldart. The results are compared with theoretically evaluated electron-phonon scattering contributions. The results show that the electron-electron scattering contribution is of the same order as the electron-phonon scattering contribution in the 2–5 K range. Below 2 K the electron-electron scattering predominates.     

Three-dimensional ultrasonic reflection and attenuation imaging

A three-dimensional, volumetric, data acquisition and reconstruction system for ultrasonic imaging is described. The method entails storing the digitized waveforms from each element of a multielement annular array, with bidirectional mechanical scanning. The system was implemented through digitization of the RF signals from each of the rings of an annular-array transducer, storage of the signals in computer memory, and offline image reconstruction. Initial reflection and reflex transmission images acquired with this system are presented. The results of different image reconstruction algorithms are demonstrated.     

Dislocation generation at surfaces of tin single crystals

Single crystals of 99.999% purity-tin grown from the melt were shown by X-ray topography to contain dislocations with Burgers vectors of [001] type and of 1/2111 type. Specimen plates cut roughly parallel to (311) were chemically thinned from 1.25 mm to 100m thickness and in two cases characteristic dislocation structures were generated at their surfaces. A specimen thinned in concentrated HCl possessed stress-producing centres distributed on its surfaces with a density of about 75 mm^–2 from which regular helices and coaxial prismatic loops with [001] Burgers vector were generated together with irregular loops of 1/2111 Burgers vector dislocations. In one specimen thinned in a H₃PO₄, CH₃COOH, HF and HNO₃ mixture large arrays of pure edge dislocations grew parallel to the surface at a depth of 2 to 4m below it, the individual dislocations extending at about 1m h^–1 during several weeks. These edge arrays all had that one of the four 1/2111-type Burgers vectors which made the smallest angle (5°) with the surface. The Burgers vector sense, determined by X-ray diffraction contrast, corresponded to a sheet of vacancies lying between the dislocation line and the surface.Visitor to H. H. Wills Physics Laboratory under Royal Society-SSR Cultural Agreement.     

Theory of ultrasonic attenuation in magnetic fluids

Recent ultrasonic measurements have yielded anomalous results for the velocity and attenuation in magnetic fluids as a function of the applied field. Thus far, the experimental results have not been satisfactorily explained by a theoretical model. In the present paper, starting with Tarapov's ferrohydro-dynamical equations, we attempt to derive an expression for the ultrasonic attenuation. Numerical calculations, with adjustable parameters, give fairly good agreement between theory and experiment for attenuation versus field angle.     

Apparent screening breakdown mechanism in ultrasonic attenuation

Robinson and Levy have suggested that the mechanism of apparent screening breakdown may be responsible for an anomalous peak observed in the attenuation of transverse ultrasonic waves in metals. We show that this mechanism is consistent with Pippard's real metal theory despite a recent claim of Almond and Rayne to the contrary. Numerical calculations within a two-band model suggest that apparent screening breakdown effects may be important in compensated metals. This is in agreement with experimental data.Research sponsored by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant No. AFOSR-76-3082. The United States Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation hereon.     

Field and excitation dependent ultrasonic attenuation in3He-B

Sound absorption of³He-B at 0 bar was studied at a frequency of 10 MHz. We performed pulsed experiments with different pulse lengths (4 to 15 s) and pulse powers (0.1 to 160 W) in the temperature range 0.2 < T/T_C < 2. For pulse power less than pth 50 W, and in the temperature range 0.4 to 0.8 T_c and zero field, the attenuation coefficient a decreases monotonically at about 0.2 cm^–1 per decade of power. Above pth. increases up to values of 3.5 cm^–1 and 1.9 cm^–1 at highest power for temperatures of 0.8 T_c and 0.4 T_c, respectively. At pulse power around 100 W and at the lowest temperatures, the attenuation changes within the first 200 s after the application of the pulse; also increases with increasing field. In the normal fluid decreases with increasing power. All of our observations are lacking a rigorous theoretical understanding.     

Deformation attenuation of ultrasonic shear waves in aluminum

The deformation contribution to the electronic attenuation of ultrasonic shear waves in aluminum is measured to be of the same order of magnitude as for longitudinal waves. This real metal effect is found highly anisotropic, depending both on the directionq/q and the polarization ε of the ultrasound. An anisotropic deformation parameterK _y is therefore suggested as being large whenever ε is close to the edgeWK of the Fermi surface.     

Stress-wave attenuation in thin structures by ultrasonic through-transmission

The steady-state amplitude of the output of an ultrasonic through-transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios, the specimen-transducer reflection coefficient, the specimen-transducer phase-shift parameter, and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress-wave reflections are taken into account, and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). Thus, the technique provides a direct method for continuous or intermittent monitoring of through-thickness attenuation of plate structures which may be subject to service structural degradation.     

颗粒阻尼技术在制动鼓减振方面的应用研究

颗粒阻尼器具有不改变结构形状、附加质量小等特点,在其他被动阻尼常失效的恶劣环境下仍具有良好的减振效果。然而,传统的颗粒阻尼器设计通常依靠试验的方法。研究了颗粒阻尼技术在汽车制动鼓减振降噪领域的应用,基于离散元和有限元的耦合方法分析颗粒阻尼在汽车制动鼓上的应用,使颗粒阻尼减振器在旋转结构上的研究成为可能。结果表明:颗粒阻尼技术在汽车制动鼓减振降噪领域的应用是可行的,仿真结果与试验结果具有很好的一致性。     

Electron-phonon interaction in aluminum from ultrasonic attenuation measurements

The attenuation of longitudinal soundwaves in normal and superconducting aluminum has been measured, yielding the electronic contribution to the normal state attenuation. The electron-phonon interaction constant is found to be in good agreement with the calculated constant based on Pippard's theory. The experiments support our assumption of an isotropic deformation parameterK _x , using Segall's and Ashcroft's modifications of the Harrison model of the Fermi surface.     

Errors and uncertainties in the measurement of ultrasonic wave attenuation and phase velocity

This paper presents an analysis of the error generation mechanisms that affect the accuracy of measurements of ultrasonic wave attenuation coefficient and phase velocity as functions of frequency. In the first stage of the analysis we show that electronic system noise, expressed in the frequency domain, maps into errors in the attenuation and the phase velocity spectra in a highly nonlinear way; the condition for minimum error is when the total measured attenuation is around 1 Neper. The maximum measurable total attenuation has a practical limit of around 6 Nepers and the minimum measurable value is around 0.1 Neper. In the second part of the paper we consider electronic noise as the primary source of measurement error; errors in attenuation result from additive noise whereas errors in phase velocity result from both additive noise and system timing jitter. Quantization noise can be neglected if the amplitude of the additive noise is comparable with the quantization step, and coherent averaging is employed. Experimental results are presented which confirm the relationship between electronic noise and measurement errors. The analytical technique is applicable to the design of ultrasonic spectrometers, formal assessment of the accuracy of ultrasonic measurements, and the optimization of signal processing procedures to achieve a specified accuracy.