On the application of the reciprocity principle to coupled-mode propagation

The reciprocity principle is applied to the derivation of coefficients describing the coupling of acoustic normal modes in waveguides characterized by range-dependent density gradients and discontinuities. The requirement of reciprocity alone is found insufficient to determine the mode-coupling coefficients. The stronger requirement of continuity of pressure and particle velocity at horizontal discontinuities of the waveguide is shown to provide coupling coefficients in agreement with those of Fawcett [J. Acoust. Soc. Am. 92, 290-295 (1992)]. (C) 2003 Acoustical Society of America.