A new pulse-interferometric system which introduces the Maximum Entropy Method (MEM) has been constructed to measure sound velocity in liquids. With this system, a measurement accuracy better than 0.1% with a sample volume of 3 cc at a frequency of 5 MHz has been attained.

A new system of measuring the thickness of thin filn or paper using 40 kHz ultrasonic wave in air is described. The thickness of samples measured is smaller by a factor of sevreal hundreds than the wavelength of sound. Experinents with polymer and metal films and paper are described to demonstrate the measurement possibilities.

Measurement of the viscosity of liquid using a piezoelectric disk is described. Experiments with a radial expansion mode of a piezoceramic disk were carried out for water-glycerin mixture samples. Resonant resistance has linearity to the square root of the product of density and viscosity of a liquid around 113 kHz.

A new system for measuring sound velocity change in liquid is described. The experiment with water as a function of temperature has been demonstrated to clarify the effectiveness of the system. As a result, resolution of sound velocity change better than 10-4 has been established with the system.