The Quasi Parallel-Sided Sound Focusing Lens
is much smaller compared with fl, f and the aperture of the lens, and that some of the sound beams projected by the source pass discussion about the computing method of through the medium surrounding the lens and the lens in the cases of the point source finally reach the lens surface which faces (caee 1) and the parallel sound beme (caee the source* discuss the O-th and 2) incident on its step aide, and derived the n-th sound beams only, and the rest thout the calculating formulas of the lens en can be deduced in the same way.