Extension of the mode method for viscoelastic media and focused ultrasonicbeams

In the present study viscoelasticity is introduced in the mode model and th e orthogonality condition is adapted for viscous media. The expansion of co nvergent acoustic Gaussian beams in terms of radiation modes for viscoelast ic media is studied as well. The effects on the reflected and transmitted p rofiles of acoustic beams incident from an ideal liquid onto a viscoelastic plate are shown and physically explained. It is shown that focusing the in cident beam can suppress divergence effects and gives the possibility to me asure shear wave attenuation coefficients. (C) 2000 Acoustical Society of A merica. [S0001-4966(00)01907-X].