Phase Velocity Of Ultrasonic Waves Research Articles

A broadband spectroscopy method for ultrasonic wave velocity measurement under high pressure

A broadband spectroscopy method is proposed to measure the ultrasonic wave phase velocity of Z-cut quartz under high pressure up to 4.7 GPa. The sample is in a hydrostatic circumstance under high pressure, and we can get longitudinal wave and shear wave signals simultaneously in our work. By fast Fourier transform of received signals, the spectrum and phase of the received signals could be obtained. After unwrapping the phase of the received signals, the travel time of ultrasonic wave in the sample could be obtained, and the ultrasonic wave phase velocity could also be resolved after data processing. The elastic constant of measurement under high pressure is also compared with previous studies. This broadband spectroscopy method is a valid method to get ultrasonic wave travel parameters, and it could be applied for elasticity study of materials under high pressure.

1499: Assessment of Acoustical and Mechanical Properties of PVA-Shelled Ultrasound Contrast Agents

The objective of this work is the investigation of linear acoustic response of three types of ultrasound contrast agents (UCAs) made from poly (vinyl alcohol) (PVA) shelled microbubbles synthesized under varied pH and temperature conditions. Backscattered power, attenuation coefficient and phase velocity of ultrasonic waves propagating through suspensions of UCAs were measured in a frequency range from 3 MHz to 13 MHz and temperature range between 24°C and 37°C. The backscattered power was enhanced up to 20 dB and displayed a weak dependence on temperature.

Characterization of Acoustic Properties of PVA-Shelled Ultrasound Contrast Agents: Linear Properties (Part I)

This work examines the linear acoustic behavior of ultrasound contrast agents made of three types of poly (vinyl alcohol) (PVA) shelled microbubbles manufactured at different pH and temperature conditions. Backscattered power, attenuation coefficient and phase velocity of ultrasonic waves propagating through suspensions of PVA contrast agents were measured at temperature values ranging between 24°C and 37°C in a frequency range from 3 MHz to 13 MHz. Enhancement of the backscattered power higher than 20 dB and displaying a weak dependence on temperature was observed. Attenuation and phase velocity, on the other hand, showed higher sensitivity to temperature variations. A modified version of the Church model, which accounts for the dispersion of the dynamic modulus of the PVA shells, was developed to simultaneously fit the attenuation and phase velocity data at 24°C. The frequency dependence of the storage modulus was found to be that of semiflexible polymeric networks. On the other hand, the frequency dependence of the dynamic loss modulus suggests that additional mechanisms, which may be related to the finite dimensions of the shell and/or to its inhomogeneity, may play a significant role in the dissipation of the acoustic energy. For the microbubbles of interest, this model predicts frequency dependent resonance frequency higher than 100 MHz. (E-mail: dmitryg@kth.se)

Cancellous bone as a poroelastic medium: Extracting underlying material properties from improved ultrasonic measurements of frequency dependent attenuation and phase velocity.

Cancellous bone can be modeled as a poroelastic medium consisting of a viscous fluid (marrow) and a stiff framework (trabeculae). Transmission of ultrasound through bone can result in fast and slow waves as well as mode conversion and multiple scattering, all of which can mask the underlying material properties of bone that determine fracture risk. Phase cancellation at the receiving transducer and interference effects in the field can further compromise the potential of bone sonometry for assessing bone quality. The attenuation coefficient is observed to increase approximately linearly with frequency, a fact that accounts for the use of broadband ultrasound attenuation (BUA) to characterize bone. Many laboratories report that the phase velocity of ultrasonic waves propagating through cancellous bone decreases with increasing frequency (negative dispersion). However, an increase in phase velocity with frequency (positive dispersion) would be expected based on the causality-imposed Kramers–Kronig relations. This apparent negative dispersion in bone can arise from interference between fast wave and slow wave longitudinal modes. Interference and phase cancellation at the receiver can also be sources of artifactual alterations in the attenuation and phase velocity. [Work supported in part by NIH R37HL40302 R01AR057433, NSF CBET-0717830].

Toward bone quality assessment: Interference of fast and slow wave modes with positive dispersion can account for the apparent negative dispersion

The goal of this work was to show that apparently negative dispersion in bone can arise from interference between fast wave and slow wave longitudinal modes, each of positive dispersion. Simulations were carried out using two approaches, one based on the Biot-Johnson model and the second independent of that model. The resulting propagating fast wave and slow wave modes accumulated phase and suffered loss with distance traveled. Results of both types of simulation served as the input into a phase and magnitude spectroscopy algorithm (previously validated with experimental data) in order to determine the phase velocity as a function of frequency. Results based on both methods of simulation were mutually consistent. Depending upon the relative magnitudes and time relationships between the fast and slow wave modes, the apparent phase velocities as functions of frequency demonstrated either negative or positive dispersions. These results appear to account for measurements from many laboratories that report that the phase velocity of ultrasonic waves propagating in cancellous bone decreases with increasing frequency (negative dispersion) in about 90% of specimens but increases with frequency in about 10%. [Work supported in part by Grant NIH R37HL40302.]

Anomalous negative dispersion in bone can result from the interference of fast and slow waves

The goal of this work was to show that the apparent negative dispersion of ultrasonic waves propagating in bone can arise from interference between fast and slow longitudinal modes, each exhibiting positive dispersion. Simulations were carried out using two approaches: one based on the Biot-Johnson model and one independent of that model. Results of the simulations are mutually consistent and appear to account for measurements from many laboratories that report that the phase velocity of ultrasonic waves propagating in cancellous bone decreases with increasing frequency (negative dispersion) in about 90% of specimens but increases with frequency in about 10%.

Determination of Residual Stress in Z8CDWV12 Steel Using Critically Refracted Longitudinal Waves.

Acoustoelasticity, i.e. the stress dependence of the phase velocity of ultrasonic waves in deformed elastic media, provides a method for determining the stress level. A primary motivation for using the ultrasonic technique is that it allowed to obtain information about stresses in the material. In fact, the velocity shift is proportional to the average stress in the region through which the waves are propagated. This leads to an ultrasonic technique of measure which may be used to determine residual stresses induced by welding processes. In this work, the experiment procedure for the determination of the residual stresses based on the critically refracted longitudinal (L er ) wave is developed. Different steps of the experiment are presented namely the travel time measurement, the calibration of the acoustoelastic effect and the residual stress determination. The application of this experimental methodology has been performed on the welded stainless steel plates, for which the residual stresses are determined in different zones and depths using the L er waves. The obtained results show that the ultrasonic technique is rather efficient for the evaluation of residual stresses and permit to control the state of the material after thermal and mechanical treatments.

Experimental Study on Phase Velocity of Ultrasonic Waves Decaying in Space and in Time

Modified system of high-resolution Bragg reflection was used to observe both the spatial and temporal sound waves simultaneously in the relaxation region of liquid furan (${\mathrm{C}}_{4}$${\mathrm{H}}_{4}$O). The spatial phase velocity at 100 MHz was shown to be higher than the temporal velocity by 7 m/s at 20\ifmmode^\circ\else\textdegree\fi{}C. The result is in good agreement with the theoretical prediction, providing an experimental evidence of the difference between them.

Ultrasonic velocity measurement of elastic constants of Al-CuAl2 eutectic composite

Ultrasonic velocity measurements were performed to determine the dynamic elastic stiffness constants of the Al-CuAl2 unidirectionally solidified eutectic, which consists of unidirectional CuAl2 platelets in an Al matrix. The phase velocity of ultrasonic waves in the eutectic was measured by the echo-overlap technique. The material was assumed to be transversely isotropic and its elastic constants, in units of 1010 dyn cm−2, are found to be: c33=c11=c22=122.8, c44=c55=29.7, c12=c13=c23=59.5, where the subscript 3 indicates the fibre direction. These results indicate that the Al-CuAl2 eutectic is almost elastically isotropic or more precisely, has cubic symmetry. The elastic moduli are used to evaluate the engineering constants of this material. The value of Young's modulus is found to be in close agreement with that measured by others in quasi-static tests.