Difference In Sound Velocity Research Articles

Thinned array ultrasonic imaging of debonding defects in discontinuous impedance bonded structures

Ballastless track is a typical bonding structure with discontinuous impedance. Under the influence of heavy load, deteriorating environment and other situations, the circumstance of debonding occurs frequently and seriously affects the safety of train operation. In this work, a high-precision array ultrasound fast imaging method is proposed. Based on the propagation path and time of sound wave in the medium obtained by ray tracing method, a theoretical model of sound velocity of discontinuous impedance bonding structure is established when the difference in sound velocity among dielectric layers is taken into account. High degree of freedom sparse array based on real number coding as well as synthetic aperture focusing technology (SAFT) imaging method is used to improve detection efficiency. The results of the experiments carried out on ballast less track structure are shown below. The ray tracing method can accurately calculate the propagation path and propagation time of ultrasonic wave and improve the detection accuracy. The optimized thinned array pattern has narrowed the main lobe width and low side lobe gain, which improves the detection efficiency and sound field directivity. The efficiency of thinned array SAFT imaging method is improved by 30.9% when the imaging error of debonding defects is within ±5%, which provides a theoretical support fordetecting such debonding defects.

Investigation of the microsecond-pulse acoustic wave generated by a single nanosecond-pulse discharge

A single nanosecond-pulse discharge can produce a high-intensity pulsed acoustic wave. The pulse width of the acoustic wave is much wider than that of the current, more than 20 μs at 30 cm from the source, which is the basis of synthesizing low-frequency sound by repetitively nanosecond-pulse discharges. The investigations of electroacoustic characteristics and the sound formation process of the single nanosecond-pulse discharge are vital to advance this technology. In this paper, an experimental platform for the single nanosecond-pulse discharge was built, and time-domain waveforms of the voltage, the current, and the sound pressure were measured. The effects of electrode shape, current limiting resistors, and current pulse width on the acoustic wave were discussed. To analyze the formation process of the acoustic wave, the gas densities near the electrodes at different moments after the discharge were diagnosed by laser Schlieren photography. The result shows that the formation of the acoustic wave is much slower than the discharge. A two-stage model was developed to qualitatively describe the formation process of the acoustic wave, and numerical calculations were carried out using thermodynamic and hydrodynamic equations. At the end of the discharge, a huge pressure difference is formed inside and outside the gas channel due to the Joule heating, which can be considered as a shock wave. During the outward propagation, the wave tail is elongated by the difference in sound velocity at each point, and the thickness of the shock wave increases due to the dissipation. This eventually leads to the half-duration of more than 20 μs.

Fabry–Pérot interference principle-based non-contact thermoacoustic imaging system for breast tumor screening

Microwave-induced thermoacoustic imaging (MTAI) is a potential nonionizing candidate for breast tumor detection due to its high contrast of tissue dielectric absorption and high resolution of ultrasonography. However, conventional MTAI systems need to contact the imaging targets through the ultrasound-coupling medium for the efficient transmission of thermoacoustic signals. This is a major drawback for potential applications such as navigation of open surgeries, burns, and ulcer testing. In this paper, we report a Fabry–Pérot (FP) interference principle-based non-contact thermoacoustic imaging system (NCTAIS). The system can infer the ultrasonic intensity by detecting the changes of the acoustically induced refractive index in the FP cavity. The miniaturized FP interferometer with a diameter of 5 mm achieves outstanding imaging sensitivity with a frequency response up to 1 MHz. An adaptive Stolt migration-based imaging reconstruction algorithm is proposed to solve the MTAI image distortion caused by the significant difference in sound velocity between air and a biological tissue. The NCTAIS is capable of achieving an axial resolution of 0.95 mm and a lateral resolution of 1.91 mm. The technical feasibility for breast tumor screening is validated with an in vitro simulated breast tumor model. The results demonstrate that the proposed NCTAIS offers high imaging sensitivity, high contrast, and deep imaging depth and will have more application scenarios than the conventional MTAI system, requiring the ultrasonic coupling medium to contact ultrasonic transducers.

Numerical Analysis on Target Strength of the Filled Spherical Elastic Shell

In this paper, the acoustic target strength of spherical shells in water with internal fillers is calculated by using the normal series expansion method, and the effects of metal and non-spherical shell materials, size factors and different fillers on the target strength of spherical shells are analyzed. The results show that for different elastic shell parameters, the influence of the acoustic characteristics of the internal filler on the target strength is quite different. For non-metallic sound transmission spherical shells filled with fluid, only when the sound velocity difference between the filler and the water medium is large, the target strength is greatly improved compared with the corresponding rigid sphere, and the shell size parameters have little effect on the target strength. However, for metal spherical shells with internal fillers, the material and size factors of the shell have a greater impact on its target strength, and the sensitivity to sound velocity mismatch inside and outside the shell is relatively small.

Sound Velocities for Dissolving AgI + LiCl Melts

The ultrasonic velocities of a molten stratified mixture at a molar ratio of 0.3AgI and 0.7LiCl (the composition corresponding to the top of the miscibility gap) were measured along the saturation line over a wide temperature range using the pulse method to establish the characteristics of mixing salts comprising different chemical bonds. It is shown that the coefficients of the temperature dependences for the sound velocities in the coexisting phases have opposite signs as a result of the superposition of the temperature and concentration factors. It is found that the difference, Δu, between the magnitudes of the sound velocities for the coexisting phases decreases with increasing temperature and becomes zero at 1250 K. This temperature corresponds to the critical phase transition point, Tc. The temperature dependence of the sound velocity difference, Δu, for the system studied is described by the equation Δu ≈ (Tc – T)β, where β = 0.900, which is close to the value 0.896 obtained for the previously investigated AgI+NaCl melt but is less than the value found for alkali halide melts (β = 1.02), in which long-range Coulomb forces between ions prevail. The results are discussed in terms of the peculiarity of the chemical bond in silver iodide.

Ultrasonic velocity for an equimolar mixture of molten AgI and NaCl in the biphasic region

The ultrasonic velocities of a molten stratifying mixture composed of 0.5 AgI and 0.5 NaCl (the composition corresponding to the top of the miscibility gap) were measured along the saturation line for a wide temperature range via the pulse method to establish the characteristics of mixing salts with different chemical bonds. We show that the difference, Δu, between the magnitudes of the sound velocities for the coexisting phases decreases with increasing temperature and becomes zero at 1064K. This temperature corresponds to the critical phase transition point, Tc. The temperature dependence of the sound velocity difference, Δu, is described by the equation Δu≈(Tc−T)Θ, where Θ=0.896, which is less than that found for alkali halide melts (Θ=1.02), in which long-range Coulomb forces between ions prevail. The results are discussed in terms of the peculiarity of the chemical bond in silver iodide.

The finite-difference lattice Boltzmann method and its application in computational aero-acoustics

The application of the finite-difference lattice Boltzmann method in computational aero-acoustics is reviewed, mainly on the basis of the work of the author and his colleagues. Some models of thermal and isothermal fluids are described and the constraints for recovering the Euler equations and the Navier–Stokes equations are described. The arbitrary Lagrangian Eulerian technique is used for high Mach number flows and for simulations of moving bodies. A model of gas–liquid two-phase fluid is introduced in which the density difference is 800 times and the sound velocity difference is 4 times. Some applications of aero-acoustic problems are briefly described and the simultaneous simulation of underwater sound and sound propagating in air is also presented. The difference between the thermal model and the isothermal model is shown in the aero-acoustic problems.

Wave equation-based imaging of mode converted waves in ultrasonic NDI, with suppressed leakage from nonmode converted waves

The value of imaging techniques in ultrasonic nondestructive inspection (NDI) to find and characterize defects in steel components has already been demonstrated. The imaging techniques based on the integral representation of the wave equation, the Rayleigh integrals for wave field extrapolation, are becoming feasible and attractive due to advances in array technology and due to faster computers. Known implementations are the total focusing method (TFM), the synthetic aperture focusing method (SAFT), and the inverse wave field extrapolation method (IWEX). In principle, these techniques compensate propagation effects from sources to a scatterer such as a defect and propagation effects from the scatterer to receivers. Currently, this approach is applied to wave fronts of single modes (pure longitudinal or pure transversal). In practice, multiple wave fronts from the scatterer will be received as a result of mode conversion. These arrivals will not have the same arrival time because of the difference in sound velocity between longitudinal and transversal waves. Images of mode converted waves are obtained by choosing the appropriate sound velocity that corresponds with the mode-converted scattered wave in the imaging process. Therefore, the nonmode converted waves will image as leakage artifacts in the mode-converted images, and vice versa. This may lead to false interpretations. In this paper, such artifacts will be identified and explained with the help of an analytical example. Measurements from steel test pieces with a 4 MHz linear array transducer with 64 elements will be used to demonstrate the artifacts. Furthermore, a procedure to predict the artifacts and the subsequent suppression from the input measurements will be presented and demonstrated.

Study of ultrasonic contrast agents using a dual-frequency band technique

We have developed a dual-frequency band technique to study frequency-dependent phenomena associated with ultrasonic contrast agents. Our technique uses a superimposed high-frequency (10 MHz) broad-band ultrasound (US) pulse to investigate contrast agent interaction with a low-frequency ( e.g., 0.5 MHz) ultrasonic field. Our digitally controlled system has the ability to produce two colinear, confocal US pulses at different center frequencies, to adjust the relative phasing and pulse repetition frequency of each pulse, and to acquire digital backscatter data. A series of experimental studies demonstrated that the high-frequency backscatter signal responded to several phenomena induced in contrast agent particles by the low-frequency beam. These phenomena included radial pulsations, nonlinear oscillations and depletion. Initial results also demonstrated a relative phase shift between the high- and low-frequency signals; this shift is due to a difference in sound velocity at these frequencies, and it may convey information about the contrast agent concentration.

Temporal averaging for quantification of lumen dimensions in intravascular ultrasound images

Quantitative analysis of arterial dimensions from high frequency intravascular ultrasound images (30 MHz) may be hampered by strong blood scattering. Replacement of blood by saline is one method to provide a clear view of the arterial lumen; another method is that of temporal averaging of successive ultrasound images. The accuracy of this latter method was tested by comparing the lumen area measurements on the temporal-averaged image, with the data of the same cross-section obtained from the single-frame and saline-filled images. The mean lumen area measured on the temporal-averaged images was similar to that measured on the single-frame images (mean difference: −0.02 ± 1.16 mm 2; p = ns). The mean lumen area of the saline-filled images was 8% larger than the values obtained from the temporal-averaged and single-frame images (mean difference: −1.14 ± 0.85 mm 2, p < 0.05), probably due to the difference in sound velocity between saline and blood. Intraobserver variation in the averaging method were 2.4 times smaller than the measurements of the single-frame images and close to the data obtained by saline injection (variation coefficient: single-frame: 8.8%; temporal-averaged: 3.6%; saline-filled: 2.9%). It is concluded that analysis from temporal-averaged images is more efficient, enabling accurate and reproducible measurement of the luminal dimensions from images containing blood scattering echoes. This technique is suitable to replace the laborious saline injection method and facilitates off-line quantitative analysis.

The acidic molten globule state of .alpha.-lactalbumin probed by sound velocity

We have investigated the structure and the chemical and conformational relaxation in the acidic molten globule state of α-lactalbumin (A-state) by using ultrasonic velocimetry. The A-state of the α-lactalbumin at pH 2 exhibits an 11% lower sound-velocity increment than that of the native state at neutral pH and 2-MHz sound frequency. An excess of calcium decreases this effect. For lysozyme, the difference in sound velocity between pH 7 and 2 is significantly smaller. Lysozyme has a large sequence homology and structure similarity to the native α-lactalbumin, but no molten globule state in aqueous solution has been described. The destabilized apo-state of α-lactalbumin at neutral pH exhibits a small decrease of roughly 4% in its sound-velocity increment relative to the native state

An acoustic method of measuring particle mass concentrations in gases

An instrument is described that measures particle mass concentration in specific size ranges. The basic principle used is the difference in sound velocity experienced when two sound waves of different frequencies travel through an aerosol. Particles oscillate in a sound field due to their size and the sound frequency. The most important parameters that determine the velocity difference of the sound are the mass concentration and ωτ, where ω is the angular velocity of the wave, and τ the relaxation time of the particle. As τ is uniquely dependent on the aerodynamic size of the particle, the instrument responds to a certain aerodynamic size fraction. The instrument has been used to detect concentrations of particles less than 7 μm from a few mg m −3 to several g m −3.

Measurement of the sound velocity difference in two liquids by using interdigital transducers

The theory and experimental results for a method of measuring the sound velocity difference in two liquids are described. The compressional wave is radiated into a liquid from an interdigital transducer. The substrate surface without the interdigital electrodes is not in contact with the liquid. The phase difference between two delayed signals passed through two liquid cavities, which is converted to a dc voltage via a phase comparating circuit, corresponds to the sound velocity difference. An experimental confirmation of the propriety of the values obtained by the method is given in water with different temperatures.

CW Measurement of Sound Velocity Difference in Two Liquids

A technique for measuring the sound velocity difference in two liquids which makes use of interdigital transducers is developed. There exists a linear relationship between the sound velocity difference in two liquids and the phase difference of two delayed output signals, which is converted to a dc voltage by using a phase comparation technique. A prototype with an 10.0 MHz input signal and three times reflections at the liquid cavity surface is fabricated and tested successfully.

A technique for measuring the sound velocity difference in two liquids

A new technique for measuring the sound velocity difference in two liquids is presented by using interdigital transducers in contact with the liquids. The phase difference between two delayed signals obtained at the output transducers, corresponding to the sound velocity difference, is converted to a dc voltage via a circuit with a function of phase comparation. As an example, the difference between the sound velocity in solutions of NaCl and that in water is given as a function of concentration. Basic design considerations for the device and experimental performance are given.

High-accuracy differential measurement of ultrasonic velocity in liquids

An improved technique for measuring very accurately the difference in sound velocity between two liquids is described. The technique, which can be used over a frequency range from 1 to 100 MHz, uses a differential cell that is completely submerged in a thermostatically controlled fluid and a phase-sensitive detection scheme accurate to 2x10(-4) signal periods. Measurements of the velocity difference between water and dilute NaCl solutions (3x10(-5) to 6.6x10(-4) M), accurate to +/-0.02 cm s(-1) (relative accuracy 1 part in 10(7)), are presented.

Design of broad-band transducer for high-temperature application to nuclear reactors

Ultrasonic transducers are usually damped with metal powder-loaded plastic or lossy rubber materials, which are effective only over a narrow temperature region. A shear-wave transducer was designed using only materials capable of withstanding high temperature (650 °C, 1200 °F). The design employs a laminated stainless steel coupling block, a piezoelectric X-cut lithium niobate crystal, a laminated backing plate, and a clamp to force intimate mechanical contact between the crystal and the coupling block. Transmission of ultrasonic energy in the desired direction parallel to the interfaces of the coupling laminac is not affected by the laminated structure. However, subsequent reverberation in the coupling block is damped by Coulomb friction between interfaces after reflection at the third oblique surface of the coupling block. Radiation into the pressure pad forcing the crystal into contact with the coupling is strongly attenuated by laminating the pressure pad normal to the propagation direction. Uniformity of pressure is assured by applying pressure via a single ball bearing and thick solid blocks. The transducers were used to monitor flow in pipes by measuring sound velocity difference in the upstream and downstream directions. A time interval difference of 110 nsec for pulses transmitted simultaneously in both directions across a 4-in. Schedule 10 stainless steel pipe (108.2 mm ID) was readily measured to four significant figures, using a HP model 5345 Time Interval Averager for water flow at 500 gpm (31.5 l/sec).

Resonance phenomena accompanying wave scattering by an uneven separation boundary between media with a small sound-velocity difference: Akusticheskii Zhurnal, Vol 14 No 3 (1968) pp 413–415

In this work, presented is a novel and facile strategy to enhance Pb(II) adsorption capacity of graphene oxide (GO) hydrosols via the modified Hummers’ method, using the smaller-sized natural flake graphite as starting materials. The as-prepared micron GO (MGO) and submicron GO (SMGO) hydrosols were sealed in dialysis bags for adsorptive separation of Pb(II) from water to avoid secondary pollution. The effects of pH and contact duration on Pb(II) adsorption on MGO and SMGO as well as their thermodynamics and kinetics were investigated comparatively. Their performances for recycling and regeneration were also evaluated. The results indicated that SMGO exhibited an enhanced maximum sorption capacity for Pb(II) up to 1162.60 mg·g−1 higher than MGO by 25.75% and achieved adsorption equilibrium faster, which can be attributed to the fact that SMGO has more oxygen-containing functional groups on the sheet basal planes and especially at the sheet edges than SMGO. The adsorption of Pb(II) on MGO and SMGO was a spontaneous and endothermic process and well fitted the pseudo-second-order kinetics and the Langmuir sorption model. Significantly, MGO and SMGO nanosheets still kept the high sorption capacities of 514.26 mg·g−1 and 700.35 mg·g−1 after the 5 cycles, respectively, promising of enormous potential applications.