This paper presents an efficient time-domain approach to evaluate the effect of the metallic shield on enclosed multilayered structures. In the proposed method, using the surface equivalence theorem, the multilayered structure is divided into separate layers, which are coupled together by the assumed unknown magnetic currents on the nonmetallic interfaces (apertures) between the layers. As a result, the problem is converted to a cascade of coupled rectangular cavities whose Green's functions in time-domain are available. To eliminate the late time instabilities, the marching-on-in-degree method is used to solve the produced integral equations. Then, the impressed current source model is utilized to extract the scattering parameters at the ports of the multilayered structure. In addition, a new accelerating algorithm that is based on the separation of time and space variables in the Green's function of the rectangular box is applied to the presented method. The proposed acceleration technique reduces the order of computational process and memory usage as O(MNsNmod) and O(Nmod(M + Ns)), respectively, where M, Ns, and Nmod denote the maximum temporal degree, the number of spatial unknowns and the total number of the Green's function modes. It is shown that the presented technique is more efficient than the commercial software, CST-MWS, for the considered problem.
