Evaluation of the influence of a finitely long circular cylindrical shield on the electromagnetic field

The authors present a semianalytical approach for calculating the electromagnetic field due to a time-varying, three-dimensional incident field which is caused by a line current situated in the cavity of a finitely long circular cylindrical conducting and permeable shell of finite thickness. The 3D Helmholtz equations are solved using the Fourier coefficients of the longitudinal field components. The Fourier coefficients of the transversal coefficients are expressed in terms of the Fourier coefficients of the longitudinal components. To deal with the complicated incident field and the finite length of the shell, a Fourier expansion of the field is made in the azimuthal and in the axial direction