Perhaps because we are constantly bombarded by sound, it is easy to forget that sound waves actually represent quite small pressure variations. The sound of a jet engine a few meters away measures only about 20 Pa (about 0.0002 atmospheres). As one increases the energy going into a sound wave, nonlinear processes in the gas in which the wave propagates direct more and more energy into harmonics of the drive frequency. The harmonics distort the sound wave and ultimately form shock waves. It is these shocks that limit the amplitudes attainable. Soundwaves’ low energy levels and compression ratios (defined as the ratio of the waveform's peak and minimum pressures) have limited their usefulness in high‐power applications such as compressors and pumps. Accordingly, many researchers have wondered whether the acoustic saturation imposed by shock formation can be circumvented in some special circumstances.

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