Studies of N Waves from Weak Sparks in Air.
KALAMAZOO COLL MICH DEPT OF PHYSICS
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The report summarizes work performed at Kalamazoo College during the period 1962-1970 on the study of acoustic transients in air. The major portion of this research was a many faceted study of the acoustic transients produced in air by weak sparks. The spark energies were in the range 0.0016 - 0.56 J, and the acoustic waveforms resembled N waves with durations of 10 - 40 microseconds and amplitudes of the order of 0.01 atmosphere. These waveforms were observed by means of wide-band condenser microphones. It was possible to reproduce a weak shock with a rise time as short as 12 microseconds. Topics investigated include the dependence of acoustic waveform upon propagation direction, spark length, and discharge energy the distortion of the wave profile with propagation distance and the diffraction and scattering of N waves from rectangular plates, circular discs, and cylindrical rods. Author