Directional characteristics of a planar annular plate for axially-symmetric free vibrations

There is solved a coastal problem of the acoustic wave
radiation at Fraunhofer zone for a planar annular plate vibrating harmonically.
It is assumed that a plate is clamped with both its banks, inner and outer, into
a planar rigid baffle. There is an analysis of axially-symmetric free
vibrations. There are directional-frequency characteristics for both kinds of
sources - annular plate and annular membrane.