Absorbing boundary conditions for solid waveguides

We present two simple and effective schemes to formulate absorbing boundary conditions for time harmonic finite element analyses of waveguide structures. An impedance matching condition, applicable to single mode waveguides, is derived as well as an enhanced method for multi-modal wave propagation, making use of guided wave mode orthogonality.Both types are implemented in models generated with standard finite element software. Two examples of ultrasonic transducers attached to cylindrical waveguides are presented.