EXPERIMENTAL STUDY OF NONLINEARITY IN FREE

Abstract.- This paper describes an experimental investigation of the propagation of periodic waves of finite amplitude in air at 20 kHz. The acoustic source used in our experimental work is a new high-power ultrasonic transducer for use in air. This transducer, which emits a directive radiation, is able to generate a nearly pure sinusoTdal wave up to sound pressure levels over 160 dB. The experiments were done in a 7.4 m long, 5.5 m wide and 5.5 m high anechoic chamber, using cw mode. They consisted essentially of measuring the amplitude of the fundamental component of the wave and its first three harmonics for different source pressure levels and at different distances in the farfield. In addition, oscillograms and directivity patterns were recorded. The obtained results confirm the strong limitations in the transmission of intense waves due to nonlinear distortion. The phenomenon of acoustic saturation at high source levels is clearly observed. Also the evolution of waveforms and the changes in the radiation patterns show the effect of nonlinear behaviour. 1. Introduction.- Th