@article{cockrell2011jasa,
title = {A Modal Wentzel-Kramers-Brillouin Approach to Calculating the Waveguide
Invariant for Non-ideal Waveguides},
author = {Kevin L. Cockrell and Henrik Schmidt},
journal = {The Journal of the Acoustical Society of America},
pages = {72-83},
number = {1},
volume = {130},
month = {Jyly},
year = {2011}}