The attenuation and phase velocity of ultrasonic third sound for optically smooth and roughened substrates

The attenuation and phase velocity of third sound have been measured for propagation on optically smooth and roughened substrates and for ultrasonic frequencies in the 20–200 kHz range. The attenuation for both kinds of substrates is found to be proportional to the frequency and have a magnitude that increases with the amount of roughening. The data are found to be inconsistent with a number of proposed attenuation mechanisms. The phase velocity is nearly independent of the frequency. Pulse wave shapes change substantially as the third sound propagates along a substrate surface.     

Temperature dependences of longitudinal ultrasonic wave propagation velocity in gallium arsenide and indium phosphide single crystals

Results are considered for experimental studies of the longitudinal ultrasonic wave propagation velocity in gallium arsenide <001> and indium phosphide <100> single crystals in the temperature range 200–355 K with measurements made through each 0.5–1 K. Measurements were made by the ultrasonic echo-pulse procedure using calibration marks of time. The frequency of the sounding signal is 10 MHz.Translated from Problemy Prochnosti, No. 11, pp. 48–49, November, 1991.     

Phase transformations during the cure of unsaturated polyester resins

The phase transformations occurring during the cure of an unsaturated polyester resin have been investigated by different techniques, including high frequency dynamic–mechanical analysis by ultrasonic wave propagation. The increase of longitudinal sound velocity can be attributed to the increase of longitudinal modulus L′ while irreversible viscous losses are responsible for the increase of sound attenuation. A correspondence between the changes in the velocity and attenuation and the phase transformations (gelation and vitrification) can be observed. The ultrasonic properties have been compared with the gel time values obtained from parallel-plate rheological measurements. Finally, a DSC analysis has been carried out to compare the evolution of degree of reaction with that of the ultrasonic modulus.     

Ultrasonic attenuation in normal and superconducting indium

Measurements have been made of the ultrasonic attenuation in the normal and superconducting states of pure In single crystals. The measurements spanned the frequency range of 6–66 MHz. The data, taken in the amplitude-independent regime, displayed the expected deviations from the BCS-type attenuation which are generally attributed to dislocation attenuation as described by Granato and Lücke. Earlier attempts to use this theory to study the amplitude-independent dislocation attenuation of ultrasound in superconductors (e.g., Mason) were generally limited to very narrow frequency ranges. These earlier results were in general agreement with the Granato and Lücke theory. However, the present multiple-frequency measurements are shown to be inconsistent with the Granato and Lücke theory.Supported by the Applied Research Laboratory of The Pennsylvania State University, under contract with the U.S. Naval Sea Systems Command.     

超声波在水中衰减的频率效应及其对脉冲回波的影响

超声波在传播中会发生幅值衰减,该衰减不仅与超声波传播的距离有关,还与超声波的频率有关。为了研究高频超声波衰减的频率效应,本文通过脉冲回波法分析脉冲超声波在水中传播反射回波的幅值和频谱变化,研究了超声波在水中传播时幅值衰减与传播距离及其与超声频率之间的关系,通过测量脉冲超声波在水中传播不同距离时的反射回波,并对其进行傅里叶变换,分析了超声波传播衰减的距离效应和频率效应。研究发现:超声波在水中的传播衰减随距离呈指数规律,且不同频率超声波的衰减系数不相同,频率越高,衰减越大,衰减的频率效应可有效解释反射法高频脉冲超声检测中回波脉冲信号的中心频率远低于换能器标称中心频率的现象。     

Experimental validation for the diffraction effect in the ultrasonic field of piston transducers and its influence on absorption and dispersion measurements

The aim of this work was to study the diffraction effects in the ultrasonic field of piston source transducers and their importance for accurate measurements of attenuation and dispersion in viscoelastic materials. In laboratory measurements, the diffraction phenomena are mainly due to the beam spread of the ultrasonic wave propagating in viscoelastic materials. This effect is essentially related to the estimated attenuation and dispersion in the material. In this work, a frequency domain system identification approach, using the maximum likelihood estimator (MLE), was applied to the measured data in order to determine a function for correcting the diffraction losses in both normal and oblique incidences for a large frequency band (300 kHz to 3 MHz). The effective radius of the used transmitter was determined by the inverse problem when ultrasonic beam propagation was investigated in a water medium. Using the estimated radius, the propagation through viscoelastic materials was established, and the acoustic parameters of these materials were estimated. Attention was paid to the determination of the attenuation and dispersion in the materials. These quantities were compared to those obtained without diffraction correction in order to see the influence of introducing the diffraction correction into the propagation model     

Propagation of elastic vibrations in snow

At rather low temperatures snow is characterized by three velocities of sound, two of which are related to propagation of longitudinal and transverse waves through a solid skeleton formed by ice crystals and the third of which is related to propagation of longitudinal waves through air in snow pores. The main laws governing propagation and absorption of these waves are determined. Analytical formulas that express the dependence of the coefficient of attenuation of waves on frequency are obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 77, No. 6, pp. 124–130, November–December, 2004.     

Absorption of ultrasound in the intermediate state of indium

The attenuation of longitudinal ultrasonic waves has been measured in spectroscopically pure single crystals of indium in the intermediate state over the frequency range of 10–30 MHz. It is shown that the total attenuation in the intermediate state can be divided into two parts. The superconducting layers give rise to the oscillatory temperature-dependent attenuation, while the normal layers and the boundary effect between the normal and superconducting layers produce a temperature-independent constant attenuation. A plausible explanation of the observed experimental results is discussed.     

Ultrasonic attenuation and velocity in AS/3501-6 graphite fiber composite

The ultrasonic group velocity and attenuation were measured as a function of frequency for longitudinal and shear waves in the Hercules epoxy matrix (3501-6) and in the principal directions of the unidirectional Hercules graphite fiber epoxy composite (AS/3501-6). Tests were conducted in the frequency ranges 0.25–14 MHz and 0.5–3 MHz for longitudinal and shear wave modes, respectively. While the attenuation increased with frequency for all wave modes, the group velocity was independent of frequency for all wave modes. In studying the effects of transducer-specimen interface couplant and pressure, it was found that for each transducer, there exists a frequency-dependent saturation pressure corresponding to the maximum output amplitude of the signal.     

Ultrasonic attenuation calculations for magnesium,zinc, and cadmium. II. Shear waves

The normal-state shear-wave attenuation has been calculated for propagation along the three principal symmetry directions in magnesium, zinc, and cadmium. The real metal theory of Pippard employing Fermi surfaces of these metals based on band structure calculations was used to calculate the attenuation. The attenuation was calculated for five shear modes for ql values between 0.1 and 60. The shear deformation parameter was assumed to equal zero in these calculations. The calculations are compared with experimental data for the fast shear modes for propagation along the [11–20] and [10–10] directions.Supported in part by the NSF.     

Ultrasonic attenuation in the superconducting and intermediate states of pure and doped type I superconductors

The attenuation of longitudinal ultrasonic waves has been measured in single crystals of indium (99.999%), indium doped with 0.003 at % of tin, and indium doped with 0.002 at % of bismuth in the intermediate and superconducting states over the frequency range 10–30 MHz. For the bismuth-doped indium specimen, measurements were taken for three different physical states, i.e., for three different dislocation densities, and for the indium and the tin-doped indium specimens, measurements were for one physical state. For a particular measurement, the same physical state was maintained both in the intermediate and superconducting states. A temperature-dependent oscillatory behavior of the ultrasonic attenuation was observed in the intermediate state in all the three specimens, but in the superconducting state the oscillatory behavior was observed only in the bismuth-doped specimen. Two phases have been identified in the superconducting layers of the intermediate state and there is only one phase in the superconducting state of the bismuth-doped sample. The origin of the two phases in the intermediate state and that of the single phase in the superconducting state of the bismuth-doped sample are discussed. A qualitative explanation is presented for the occurrence of oscillatory attenuation in the intermediate state irrespective of the nature of the dopant and the selective occurrence of oscillatory attenuation in the superconducting state due to the nature of the dopant.     

Dynamic mechanical and ultrasonic properties of polyurea

Dynamic mechanical analysis (DMA) and ultrasonic measurements were carried out to study the temperature and frequency dependences of viscoelastic properties of polyurea. Master curves of Young’s storage and loss moduli were developed from the DMA data. Relaxation spectra were subsequently calculated by means of two approximate models, and the apparent activation energy of molecular rearrangements was also determined based on the temperature dependence of the time-temperature shift factor. Velocity and attenuation of longitudinal and shear ultrasonic waves in polyurea were measured in the 0.5-2 MHz frequency range between −60 and 30 °C temperatures. The complex longitudinal and shear moduli were computed from these measurements. Combining these results provided an estimate of the complex bulk and Young’s moduli at high frequencies. The results of the DMA and temperature and frequency shifted ultrasonic measurements are compared and similarities and deviations are discussed.     

Additional frequency errors due to the transmission of electrical oscillations

Conclusions Existing data shows that all the elements of the circuit, whether propagating or transforming oscillations, introduce frequency errors in the transmitted signals. The relative errors due to the frequency divider is 10^–8 to 10^–10 and frequency multipliers 10^–12 to 10^–13[5]. Wire lines introduce an error of 1 · 10^–8 to 1 · 10^–9, depending on their type and the frequency transmitted.Radio transmitted signals acquire additional frequency errors depending on the frequency transmitted and the distance of propagation. Thus low frequency transmissions are accompanied by relative errors of the order of 1 to 5 · 10^–9 and high frequency ones by errors varying from 1 · 10^–8 (if the transmitting and receiving ends are not separated by the rising or setting sun) to 10 · 10^–8 (if the transmitting and receiving ends are separated by the rising or setting sun).The existing accuracy of the standard frequency oscillations and the prospects of its further improvement by using resonance absorption frequencies of various atoms and molecules make it imperative to investigate on a wide scale the circuits and propagation media used in conveying the signals to their users.     

Dynamic-scaling theory of critical ultrasonic attenuation in binary liquids

The critical slowing down that sets in near the critical point of a second-order phase transition is manifested in fluids by a diverging relaxation time for the long-wavelength order-parameter fluctuations. This divergence has a profound effect on all of the transport properties. In sound propagation, the adiabatic compressions and dilations produce temperature swings which the order-parameter fluctuations can follow fully only if the sound frequency is smaller than the relaxation rates in the fluid. As the critical point is approached this condition is violated and a lagging, or hysteretic, response results. As demonstrated by Clerkeet al., the known amplitude of the temperature swings leads to a prediction of ultrasonic attenuation at the critical point that agrees, in magnitude, exactly with that found by Harada et al. The theoretically predicted scaling function that describes how the attenuation and dispersion vary as the critical point is approached is in good agreement with the experimental findings of Garland and Sanchez.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Attenuation coefficient and propagation speed estimates of intercostal tissue as a function of pig age

Attention coefficient and propagation speed of intercostal tissues were estimated from chest walls removed postmortem (pm) from 15 5.3 /spl plusmn/ 2.3-day-old, 19 31 /spl plusmn/ 6-day-old, and 15 61 /spl plusmn/ 3-day-old crossbred pigs. These ultrasonic propagation properties were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. The chest walls were placed in a 0.9% sodium chloride solution, sealed in freezer bags, and stored at -15/spl deg/C prior to measurements. When evaluated, chest-wall storage time ranged between 1 and 477 days pm. All chest walls were allowed to equilibrate to 22/spl deg/C in a water bath prior to evaluation. There was an age dependency of the intercostal tissue propagation speed, with the speed increasing with increasing age. The attenuation coefficient of intercostal tissue was shown to be independent of the age of the pig at the discrete frequencies of 3.1 and 6.2 MHz. For pig intercostal tissues, the estimated attenuation coefficient over the 3.1-9.2 MHz frequency range was A = 1.94f/sup 0.90/ where A is in decibels per centimeter (dB/cm) and f is the ultrasonic frequency in megahertz. In order to determine if there was an effect of storage time pm on estimates of attenuation coefficient, a second experiment was conducted. Five of the youngest pig chest walls measured on day 1 pm in the first experiment were stored at 4/spl deg/C prior to the first evaluation then stored at -15/spl deg/C before being measured again at 108 days pm. There was no difference in the estimated intercostal tissue attenuation coefficient as a function of storage time pm.     

Ultrasonic examination of reaction bonded silicon nitride

An ultrasonic examination has been made of a series of partially nitrided reaction-bonded silicon nitride (RBSN) ceramics whose weight gains varied from 22% to nearly 64% representing full nitridation. A pulse echo overlap technique was used which enabled both the longitudinal and shear velocities of propagation to be measured at 15 MHz; from these measurements values of Young's modulus (E) and the bulk modulus (K) at room temperature were derived. For fully nitrided RBSN the values obtained wereE=160 GN m^–2,K=90 GN m^–2 in good agreement with published values obtained by ultrasonic methods. Both Young's modulus and the bulk modulus were found to be markedly sensitive to the changes in fractional porosity due to changes in weight gain (and green density) each decreasing by over 50% as the fractional porosity increased from 0.16 for a fully nitrided ceramic to 0.26 for 60% weight gain material.     

Ultrasonic detection of fatigue damage

Results are reported of recent experiments which used change in ultrasonic attenuation measurements as a continuous monitor of fatigue damage during cyclic testing of polycrystalline aluminum and steel specimens. Ultrasonic pulses were generated by an x-cut quartz transducer firmly attached to the clamped end of a specimen rod using Eastman 910 cement. The frequencies of these ultrasonic pulses were 10 MHz for polycrystalline aluminum and 5 MHz for cold rolled steel. The specimen shape, transducer size, and frequency used insured that the entire specimen was completely filled with ultrasound in a guided wave mode. The specimen was fatigued as a cantilever beam in reverse bending at 1800 cycles per minute with vertical amplitude peak-to-peak set at a fixed value in the range 7·5–15 mm. In a typical test the ultrasonic attenuation initially remained constant, increased slowly, and then increased catastropically just prior to fracture of the test specimen. All experiments performed on both aluminum and steel specimens at various vibrational amplitudes yielded similar results in that ultrasonic attenuation served as a very sensitive indicator of fatigue damage and in every case indicated that failure was eminent several hours before conventional ultrasonic testing could detect an additional echo caused by energy reflected from a crack. These results strongly suggest that ultrasonic attenuation measurements can be exploited successfully to predict earlier fatigue damage and perhaps fatigue life in practical applications.     

Sound velocity and sound attenuation measurements by dynamic light scattering

Dynamic light scattering (photon correlation spectroscopy) has been applied to the determination of sound velocity and sound attenuation from the Brillouin component of the frequency spectrum scattered from a fluid sample transversed by a laser beam. In this paper the time-resolved determination of the Brillouin component is described. The measurement of the linewidth allows an accurate determination of the sound attenuation, while the central frequency is connected to the adiabatic sound velocity. Sound attenuation and sound velocity measurements are presented for the new refrigerant pentafluorethane (R125). The accuracy and possible systematic errors of this technique are discussed and compared to those obtained from other spectroscopic and acoustic techniques.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado. U.S.A.     

Experimental study of construction mechanism of V(z) curves obtained by line-focus-beam acoustic microscopy

The propagation characteristics, viz., phase velocity and attenuation, of leaky surface acoustic waves (LSAWs), excited on the water/sample boundary are obtained through analyzing the V(z) curves measured by line-focus-beam acoustic microscopy. However, different values of these characteristics are obtained, depending upon different ultrasonic devices and operating frequencies employed. The construction mechanism of V(z) curves was investigated experimentally by measuring the amplitude and phase for Teflon to provide an understanding of the device performance for velocity measurements. A V(z) curve measured for Teflon, on which no leaky waves are excited when water is the coupling medium, can be used for the characteristic device response, depending only upon the device parameters and the operating frequencies. From the investigation of the ultrasonic device and the frequency dependences of the characteristic device responses, the phase gradient was found to be directly related to values of measured LSAW velocities. From this result, apparent frequency dependences in LSAW velocity measurements are explained quantitatively for a specimen of gadolinium gallium garnet.     

The effect of deuteration on the ultrasonic properties of poly(methyl methacrylate)

Room-temperature ultrasonic compressional wave velocity and attenuation measurements have been carried out on commercial poly-methyl methacrylate (PMMA) and fully deuterated PMMA. Deuteration was found to reduce the velocity by 4.4 ± 1.2% which can be completely accounted for by the density change of 8.0%, assuming no changes in atomic force constants or molar volume. The attenuation was 17% higher in the deuterated sample. Making reasonable assumptions about the distribution function for the relaxation times of molecular groupings moving in two-well potentials, the attenuation increase is attributed to a reduction in the attempt frequency for barrier hopping of main chain and/or ester methyl groups.