Determination of Phase Jumps in the Measurement of Phase Velocity of Samples Obeying a Frequency Power-Law Attenuation Coefficient Using Kramers-Kronig Relations.

Ultrasonic phase velocity spectroscopy is a very sensitive technique used in the measurement of material properties. In a phase velocity calculation, ambiguities can arise in the spectral phases, in the form of integer multiples of 2π rad, which, if not corrected, results in large errors. In this work, we propose a method for determining these ambiguities, more specifically, the number of 2π rad phase jumps, using the Kramers-Kronig relations, for samples exhibiting a frequency power-law attenuation coefficient. The method is based on a first estimate of the phase velocity from group velocity and attenuation coefficient that are not affected by phase jumps. This estimated phase velocity is used to obtain the number of 2π rad phase jumps, which in turn is used to calculate the corrected phase velocity. The method was tested with samples of liquids with a frequency power-law attenuation coefficient (exponent y varying from 1.5 to 2) and a solid [polymethyl methacrylate (PMMA)] with y  âˆ¼  1 , and velocity dispersions ranging from 0 to 34 (cm/s)/MHz.

Versatile Ultrasonic Spectrometer for Liquids With Practical Sample Handling by Using Standard Cuvettes.

This work describes the development and tests of a new ultrasonic spectrometer for liquids based on the use of commercial cuvettes for sample handling. The spectrometer operates in the frequency range from 20 to 80 MHz and gathers some important characteristics, which are its high thermal stability (better than 0.01 °C), by the use of Peltier cells, and practical sample handling with small volume (≤3 ml) samples placed inside cuvettes which can be easily removed from the spectrometer, cleaned/sterilized, or simply discarded. Through-transmission operation is used to measure propagation velocity and attenuation coefficient, and the spectrometer was tested with mixtures of water and NaCl, which have attenuations smaller than that of distilled water, and higher attenuation samples of silicone and castor oil. Backscattering studies of polystyrene particles of 10- and 15- [Formula: see text] diameters were also conducted, showing the versatility of the instrument.