RADIOENGINEERING, VOL. 18, NO. 1, APRIL 2009 29 Homogeneous Dielectric Equivalents of Composite Material Shields Tomáš ZVOLENSKÝ 1 , Zbyněk RAIDA 1 , Pavel TOBOLA 2 Dept. of Radio Electronics, Brno University of Technology, Purkyňova 118, 612 00 Brno, Czech Republic 2 Evektor Ltd., Letecká 1008, 68604 Kunovice, Czech Republic raida@feec.vutbr.cz Abstract. The paper deals with the methodology of re- placing complicated parts of an airplane skin by simple homogeneous equivalents, which can exhibit similar shielding efficiency. On one hand, the airplane built from the virtual homogeneous equivalents can be analyzed with significantly reduced CPU-time demands and memory requirements. On the other hand, the equivalent model can estimate the internal fields satisfactory enough to evaluate the electromagnetic immunity of the airplane. Keywords Composite material, dielectric layers, electromagnetic immunity, shielding. 1. Introduction Requirements of the electromagnetic immunity of small airplanes are higher and higher on one hand, and more and more difficult to be fulfilled on the other hand. Several metallic parts of the airplane skin are going to be replaced by composite ones in order to reduce the weight of the airplane, and consequently the jet fuel consumption in order to decrease the operation costs. Unfortunately, the shielding efficiency of composite parts is lower compared to fully metallic parts, which can negatively influence the electromagnetic immunity of the airplane towards the high intensity external fields. For those reasons, small airplanes have to be carefully tested from the viewpoint of electro- magnetic aspects. Numerical analysis of a realistic model of an airplane is extremely complicated, and CPU-time requirements and memory demands are enormous since the electrically large airplane contains very small significant details (a metallic network inside composite parts, several gaps and slots increasing the internal electromagnetic field in the airplane, etc.). Whereas these details have to be covered by a very fine mesh, the continuous parts require a quite rough mesh. In the paper, the described problem is solved by in- troducing homogeneous equivalent layers, which exhibit a similar behavior like the realistic structures, but thanks to their homogeneity, can be covered by the usual rough enough mesh. Shielding efficiency of composite materials belongs to the hot research topics these days. In the last decade, over 100 papers related to this topic were published in IEEE periodicals. On the other hand, papers discussing a proper and efficient numerical modeling of composite layers are quite rare: • In [1], a model allowing simulation of thin composite multilayered panels in finite-difference time-domain (FDTD) procedure was proposed. The model enabled to overcome the limitations of sub-gridding algo- rithms, hybrid approaches, and surface impedance boundaries. Each layer of the composite was modeled as a homogeneous medium, characterized by constant effective conductivity and permittivity. • In [2], an analysis of the lossy periodic multilayer structures consisting of conducting fibers situated in a dielectric matrix was described. In order to discuss the combined effect of fibers and the dielectric ma- trix, reflection and transmission matrices at the air- matrix, and grating interfaces together with suitable phase correction were incorporated in the model in which the fiber grating was regarded as a thin Floquet layer. In order to reduce the CPU time, an extended filament-current model was examined. • In [3], a combined magnetic field integral equation and FDTD procedure was developed for the efficient analysis of the transient plane wave penetration inside a metallic-composite box. Suitable boundary condi- tions were enforced on the composite walls of the en- closure in order to link the methods. • In [4], a carbon fiber reinforced layer of the compos- ite panel constituted by a braided carbon tissue with weave angle of 90° was analyzed by FDTD. In order to obtain an effective equivalent layer model, effec- tive tensors of conductivity and permittivity were de- rived in order to represent the composite as a homo- geneous anisotropic material. • In [5], an equivalent circuit of a single-layer homoge- neous and anisotropic composite material was calcu- lated considering the diffusion equation. • In [6], an analytical study in the spectral domain of inhomogeneous layers, which were characterized in terms of transmission matrices, led to an equivalent