Changes In Ultrasonic Velocity Research Articles

Frequency modulation (continuous wave) technique for the measurement of very small changes in ultrasonic velocity: Melcher, R.L., Bolef, D.I., Merry, J.B. The Review of Scientific Instruments, Vol 39, No 11 (November 1968) pp 1618–1620 (1069)

Frequency modulation (continuous wave) technique for the measurement of very small changes in ultrasonic velocity: Melcher, R.L., Bolef, D.I., Merry, J.B. The Review of Scientific Instruments, Vol 39, No 11 (November 1968) pp 1618–1620 (1069)

Frequency Modulation CW Technique for the Measurement of Very Small Changes in Ultrasonic Velocity

An improved continuous wave technique capable of measuring changes in ultrasonic velocity of 1 part in 107 or better is described. The technique utilizes frequency modulation of the cw carrier signal and subsequent lock-in amplification.

Variation of Sound Velocity with Magnetic Field in Mn-Doped YIG

The variation of the sound velocity with magnetic field in Mn-doped YIG has been studied in both rods and spheres. The samples were single crystals containing 2.3 wt % Mn. With the rods, which were approximately 0.3×0.3×2.0 cm, the sound velocity was measured directly while with the spheres (about 0.3 cm in diameter) the resonant frequency was measured. For a rod with the sound propagation in the 〈111〉 direction, the change in ultrasonic shear velocity for a field change from 200 G (required for saturation) to 2 kG was 13% at 87°K, 13% at 106°K; 9.5% at 140°K, 8% at 213°K, and 3.4% at 290°K. For rods with the sound propagation in the 〈100〉 direction, the change in velocity with magnetic field at any temperature was greatly reduced compared to that observed for the 〈111〉 direction. Furthermore, the velocity of longitudinal waves did not show any appreciable field dependence. With spheres magnetized along 〈111〉, the resonant frequency of the lowest shear mode changed by 30% at 77°K for a field change from 0.8 kG (sufficient to saturate the sample) to 6.0 kG. Some of the experimental observations can be interpreted on the basis of the simple theory of magnetostrictively coupled phonon and spin waves. However, this picture fails in some important aspects, indicating that the interaction of the acoustic waves with the magnetization in Mn-doped YIG is more complex.

Artefacts in ultrasonic echoscopic visualization

Two-dimensional ultrasonic visualization uses information derived from the direction and delay of echoes. It is prone to artefacts due to multiple reflection, width of the ultrasonic beam, transducer design, shadowing, velocity changes and signal processing. These are described in detail, both in contact and water delay scanning. In many cases the artefacts are inherent in the ultrasonic visualization technique and must be recognized to avoid mis-interpretation

A CW Phase System for Measurement of Small Changes of Ultrasonic Velocity in Liquids and Gases

A continuous radio-frequency signal is applied to a sending transducer located at one end of a pipe containing the sample fluid. The frequency and the pipe length are chosen to result in an attenuation of at least 60% so that reflected waves are reduced to negligible proportions. The phase angle between the voltage driving the sender and the voltage produced by a receiver transducer located at the other end of the pipe is measured by means of a phasemeter having a full-scale sensitivity of 1.8°. A system presently in use operates at 20 MHz, with a pathlength of 1 in. in water. The resolution at twice noise level is 0.4-cm/sec change in sound velocity. As a result of the “foldover” characteristic of the phasemeter, it is possible to measure phase changes of thousands of degrees without ambiguity and without sacrifice in resolution.

Effects of mechanical properties of materials on the cutting rate and specific energy consumption in ultrasonic machining: Kurochkin, N.V. Soviet Physics-Doklady, 9, No. 7, 599 (1965)

Two-dimensional ultrasonic visualization uses information derived from the direction and delay of echoes. It is prone to artefacts due to multiple reflection, width of the ultrasonic beam, transducer design, shadowing, velocity changes and signal processing. These are described in detail, both in contact and water delay scanning. In many cases the artefacts are inherent in the ultrasonic visualization technique and must be recognized to avoid mis-interpretation

Dislocation Damping due to Kink Motion

The ultrasonic attenuation and velocity change that result from the damping due to motion of dislocation kinks have been calculated on the following assumptions: (1) the frequency of thermal creation of kinks is smaller than the frequency of the applied stress; (2) the frequency of thermal motion of the kinks is larger than the frequency of the applied stress. The characteristics of the attenuation calculated from the above assumptions differ from those of the string model for dislocation damping as follows. First, the resonance frequency depends on kink spacings and on the distance between pinning points on the dislocation. Second, for strain amplitude in excess of a critical value given in terms of kink spacings and the distance between pinning points, the attenuation decreases with increasing strain amplitude.

Ultrasonic Propagation in Nickel and Mn-Ferrite at High Magnetic Fields

The velocity and attenuation of ultrasonic waves at magnetic fields, sufficiently high to produce magnetic saturation in nickel and Mn-ferrite, have been measured as a function of orientation, intensity of magnetic field, and ultrasonic frequency at room temperature. In the case of nickel, the change in ultrasonic velocity was inversely proporational to the applied magnetic field in the range from 5 to 20 kG; the ultrasonic attenuation coefficient also changed and showed a frequency dependence of the relaxation type \(\frac{\omega/\omega_{0}}{1+\omega^{2}/{\omega_{0}}^{2}}\) in the range from 5 to 65 Mc/s. In the case of Mn-ferrite, it was found that the magnitude of the changes in ultrasonic velocity was almost the same as that in the case of nickel, but no attenuation change was observed within experimental error. All the observations can be explained by the theory based upon magneto-elastic coupling and eddy current loss.

Sensitivity of Ultrasonic Attenuation and Velocity Changes to Plastic Deformation and Recovery in Aluminum

Measurements of changes in ultrasonic attenuation together with changes in ultrasonic velocity have been made concurrently with load strain measurements in tensile tests on the same specimen of aluminum. The results of such measurements taken during loading of the specimen, during relaxation or recovery at constant strain, and during unloading show a number of interesting effects. These observed effects are interpreted in terms of dislocation behavior for the various stages of the experiment. The experimental results for attenuation α and velocity change Δv/v permit the calculation of changes in dislocation density and loop length based on a dislocation damping theory developed in this laboratory to include both megacycle and kilocycle frequencies. The strain due to dislocation motion was calculated with a simple model and with dislocation loop lengths and densities obtained from the data and the theory just mentioned. The comparison of the calculated strain and the measured strain lends support to the use of this model, and while this dislocation damping model may not be entirely correct it does seem to be possible to obtain information about stress-strain behavior at low strains from sound propagation data alone.

Magnetically Induced Ultrasonic Velocity Changes in Polycrystalline Nickel

Measurements of magnetically induced velocity changes in polycrystalline nickel rods are discussed. Shear and compressional ultrasonic propagation modes are used throughout the frequency range of 1–10 megacycles. The polycrystalline measurements are compared to recently published single nickel crystal values. The ΔE effect is found to decrease with increasing frequency throughout the megacycle region, showing general agreement with low frequency measurements.

A Pulse Method for Measuring Small Changes in Ultrasonic Velocity in Solids with Temperature

A pulse-modulated, 10- to 30-mc oscillator is used to apply pulses of r-f voltage to piezoelectric crystals attached to solid samples. The transmitted pulse is amplified, detected, and returned to the pulsed oscillator as a trigger voltage. The number of pulses occurring per second is then a function of the electrical and acoustic delay. Since the latter is a function of temperature, small changes in sound velocity can be determined from observed differences in the repetition frequency of the pulsed oscillator after correcting for changes in acoustic path length caused by linear expansion. Repetition frequencies in the region 50,000 to 100,000 per second are used.

Temperature Effect on Ultra-sonic Velocity in Water

VERY few systematic data exist so far relating to the effect of temperature on ultrasonic velocity in liquids, especially water. Loomis and Hubbard's results1 for the change of ultra-sonic velocity in water and other liquids with rising temperature may be cited as perhaps the only systematic investigations, because earlier experiments2 were carried out under rather unstandard conditions and in a very low region of sonic frequencies and therefore are not reliable. Even Hubbard's data for water are reported for a very limited range of temperature, 0°–40° C., using a sonic interferometer at a frequency of 500 kc. only. The present work extends the knowledge of ultrasonic velocity in water up to a temperature of 70° C., using the method of diffraction of light by ultrasonics at a frequency of 5·7 mc./sec.