A Radiation Pressure Balance for the Absolute Measurement of Ultrasonic Power

Abstract

A balance for measuring ultrasonic radiation pressure has been built, employing the parallelogram principle of Roberval''s Enigme Statique to provide a measuring surface above the balance beam. This renders measurements independent of the position and uniformity of the sound beam. A suspension system of 4 horizontal torsion wires eliminates friction, and sensitivity can be varied in steps over a wide range. A 45[degree] reflector acts as a perfect absorber independent of the reflection coefficient of its surface. This balance gives an absolute measure of the total acoustic power in a sound beam.