The Propagation of a Spherical N Wave in an Absorbing Medium and Its Diffraction by a Circular Aperture.
TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
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The report investigates the effects of finite amplitude on the diffraction of a spherical N wave by a circular aperture. The investigation was to be carried out in the farfield of the aperture, i.e., where the incident and diffracted signals were not completely resolved. An experiment was done in which an N wave was produced by an electric spark. A condenser microphone received the acoustic signal, and an aperture in a rigid baffle was placed between the spark and the microphone. The preliminary investigations revealed that, in the farfield, absorptions as well as nonlinear distortion is important. A computer algorithm was developed in which the effects of nonlinear distortion and absorption are combined in a stepwise manner. To test the algorithm, it was used to predict the waveform of a propagating N wave. The predicted waveforms agree very favorably with experiment. Modified author abstract