This paper presents an innovative method, called the mode-exciting method, to solve Lamb wave-scattering problems in an infinite plate. In this method, a set of Lamb wave modes is excited by appropriate boundary conditions given on the virtual edges of a finite plate. After solving numerically the elastodynamic problem defined in the finite domain, the numerical solution is decomposed into Lamb wave modes. The Lamb wave modes constitute a system of equations, which can be used to determine the scattering coefficients of Lamb waves for the original problem in an infinite plate. The advantage of the mode-exciting method is that a well-developed numerical method such as finite-element (FEM) or boundary element (BEM) can be used in the elastodynamic analysis for the finite region without any modification like coupling with other numerical techniques. In numerical examples, first the error estimation of the mode-exciting method is discussed by considering three types of error indicators. It is shown that among them, the power ratio of nonpropagating modes to propagating modes is the most suitable for the error estimation. Numerical results are then shown for scattering coefficients as a function of nondimensional frequency for edge reflection and crack scattering problems.

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