1 Modeling of the Reverberation Chamber Method for the Wire-mesh Shielding Performance Evaluation Valter Mariani Primiani, Member, IEEE, Franco Moglie, Member, IEEE, Anna Pia Pastore, Sara Pistolesi Abstract— The problem of the field penetration into a metallic enclosure with a large aperture protected by a wire-mesh screen is approached in this work, using our home made Finite Difference - Time Domain (FDTD) code. This code with a thin wire approximation accurately accounts the cross between wires of the mesh. All results are experimentally validated using a Reverberation Chamber (RC). Index Terms— FDTD methods, reverberation chambers, wire- mesh screen, shielding effectiveness I. I NTRODUCTION I T is well known that apertures are responsible for shielding degradation of metallic enclosures, enhancing the electro- magnetic interference (EMI) problem especially in presence of a high speed digital circuit inside [1]. A particular threat is represented by intended apertures whose radiation cannot be mitigated by electromagnetic gasketing. In particular, heat dissipation requirements fix a lower bound on aperture size. Considerable work has been done in the past to calculate the field penetration through apertures of different shapes, and a comprehensive list of references can be found in [2]. On the other hand, the use of arrays of small apertures represents an efficient compromise between the heat dissipation and the shielding degradation. The benefit obtained is numerically evaluated applying the Method of Moments (MoM) in both frequency [3] and time domain [4] including transient excita- tions. The FDTD method has also been successfully applied to model airflow aperture array in shielding enclosures [5]: the combined application of the MoM allowed the radiation estimation and the mutual coupling among the apertures of the array. A particular type of aperture array is represented by wire-mesh screens; they are simple to realize, and they has the advantage that they can be inserted over a large aperture after the enclosure construction. The screening performance of wire-mesh has been analytically treated introducing an equivalent sheet impedance operator [6] giving results for plane wave, electric and magnetic dipoles. In the present paper, the problem of the field penetration into a metallic enclosure, whose large aperture is protected by a wire-mesh screen, is addressed. The solution is achieved by applying our home made FDTD code with a thin wire approximation that accurately accounts for the junction between the crossing wires of the mesh. Results are compared to those obtained removing this approximation [7]. Moreover, all results are experimen- tally validated using a reverberation chamber. This way to Authors are with the Dipartimento di Elettromagnetismo e Bioingegneria, Universit` a Politecnica delle Marche, via Brecce Bianche 12, 60131 Ancona, Italy. y z x L x L y L z L xap L zap Δs Fig. 1. Geometry of the box with the aperture. Its dimensions are Lx = 0.5 m, Ly =0.3 m, Lz =0.2 m, Lxap =0.135 m, Lzap =0.085 m, Δs =0.04 m characterize shielding effectiveness exhibits some advantages with respect to traditional methods (anechoic chamber for example) and it is a better representation of real world because the disturbance comes from any direction with an arbitrary polarization. Therefore, the FDTD code was also used to represent the field inside the reverberation chamber in order to directly compare numerical and experimental results [8]. II. GEOMETRY OF THE PROBLEM Fig. 1 reports the analyzed enclosure with an aperture. It consists of a copper box where the front face is connected by a screw system and can be removed to allow the analysis of different aperture types. In the present case, there is an aperture of dimensions L xap =0.135 m, L zap =0.085 m, and a metallic grid on the aperture with a square mesh with a size Δg = 12 mm and a diameter of the metallic wire of d w =1.2 mm. The thickness of the copper panels is about 1.5 mm. Inside the box there is a square loop with side Δs = 0.04 m which couples to the internal field. III. DESCRIPTION OF THE NUMERICAL PROCEDURE Inside a well operating reverberation chamber the field is statistically uniform, isotropic and depolarized. This type of electromagnetic field is representable by a superposition of infinite plane waves coming from arbitrary directions. The plane wave integral representation of the field is therefore [9]. ¯ E(P )= ¯ E(¯ r)=  4π ¯ F (Ω)e j ¯ β· ¯ r dΩ (1) where Ω is the solid angle and dΩ = sin ϑ dϑdϕ, being ϑ and ϕ the elevation and azimuth angles, respectively. The angular