Acoustical absorption spectroscopy of liquids between 0.15 and 3000 MHz: III. Hypersonic comparator technique

Abstract

A method has been developed to measure the absolute hypersonic absorption of liquids in the frequency range from 0.3 to 3 GHz with 1% accuracy using a pulse transmission technique. Excitation of surface vibrations on small rod-shaped piezoelectric LiNbO3 crystals at variable transducer spacing is combined with a direct parallel RF substitution technique in which a below-cut-off piston attenuator is used as reference. Sensitive superheterodyne detection followed by signal averaging and multiple data recording allow for a low input power level so that heating of the small sample volume (<1 ml) is avoided. The measurements are automatically driven by a process control control.