Design and Preliminary Results of an Acoustic Parametric Source in Air

Abstract

An acoustic parametric source for use in air was constructed and tested. The source uses a modified St. Clair resonator (a solid aluminum cylinder driven by a ceramic disk at one end) to generate the two high-frequency primary signals. The resonator is excited simultaneously in two resonant modes at frequencies from 20 to 40 kHz and radiates primary signals at levels that typically exceed 130 dB re 0.0002 dyn/cm2 in the nearfield. The two high-frequency primaries mix within the air to generate narrow-beam waves at the difference frequency, ranging typically from 3 to 10 kHz. This paper describes the radiation properties of the modified St. Clair resonator and presents measurements of the beam width and source level of the difference-frequency signal for a variety of primary wave combinations.