Orthogonality of 3D guided waves in viscoelastic laminates and far field evaluation to a local acoustic source

The fundamental properties of guided waves in a laminate with any homogeneous boundary conditions on its faces are considered. As shown, the waves satisfy orthogonality relations whose physical meaning is related to the additivity of the average power flow. The applications of this orthogonality for solving some particular boundary value problems are discussed. A method for exact calculation of the far field caused by an acoustic source of a finite size is suggested. The only restriction is that the distance required must exceed the longitudinal radius of the source. The obtained results can be used for evaluating the fields radiated by ultrasonic transducers of arbitrary aperture and by other realistic sources.