Supersonic Interferometers

Abstract

The methods of applying high frequency sounds to small scale measurements are discussed. An interferometer was constructed and used to measure the velocity of sound in gases, liquids, and solids at frequencies ranging from about 10 to 700 kc. Three types of sources were tried, viz: quartz and Rochelle-salt crystals and magnetostrictive rods. The determination of the velocity of sound in solids is based upon: (1) optimum transmission of sound through a partition whose thickness is an integral number of half wave-lengths; (2) relative displacement of the nodal planes in a given liquid due to the immersion of a solid slab in the acoustical path. In the same manner, a small quantity of an unknown liquid is placed in a parallel walled cell and the latter is immersed in a liquid of known acoustic properties. Reactance and effective resistance of the interferometer (with a liquid medium) as a function of the reflector distance from the sound source were investigated. Approximate values of the impedance, power factor and watts dissipated in the instrument were thus computed. An improved circuit for use in absorption measurements in gases is described as well as the extended use of the interferometer employing two identical sound generators.