MECHANISM OF ACOUSTIC WAVE PROPAGATION: A REAL ROLE OF VIRTUAL SOURCES

The Huygens problem of self-regeneration of the acoustic wave crossing a liquid medium is discussed in the paper. Equal weight of both elastic and kinetic aspects of mechanical waves in fluids is stressed. Two types of virtual surface sources are defined, reflecting local action of the pressure and particle velocity, respectively. They are applied by the author in calculations of secondary radiation from the wave front of the plane wave. The Dirac delta impulse has been used as a waveform, the wave thus being reduced to its own front. The results have been obtained analytically, thanks to some particularly "friendly" features of the operation of convolution with the delta distribution. The paper gives formal proof to Fresnel's intuitive explanation of the mechanism of the forward-only propagation of the wave with no backward effects.