RADIATION FROM PARTIALLY EXCITED PLATES

The problem studied here deals with the sound radiation from a finite area of a large plate carrying bending waves. Results for square and r ectangular areas are given for free vibrations as well as vibrations f orced by airborne sound fields; in the latter case, the radiation effi ciency is presented for plates excited by plane waves as well as diffu se fields. The results for free vibrations show, as expected, that the radiation efficiency is close to unity for high frequencies. Furtherm ore, in the case of comparatively large plates, a maximum value is rea ched in the region of the critical frequency. This maximum does not, h owever, occur at exactly the critical frequency, but at a somewhat hig her frequency. For smaller plates, where the Helmholtz number (with re spect to the wave number at the critical frequency and a typical side length) is less than approximately 4, no pronounced maximum appears. I nstead, the radiation efficiency increases asymptotically with the fre quency towards unity. For free bending waves, the maximum value in the region of the critical frequency is found to be somewhat smaller than that given by Maidanik's well-known theory. It is also shown, that th e radiation efficiency of forced vibrations at low frequencies can be expressed as a single function of a suitably defined Helmholtz number.