Shielding Analysis of Enclosures Made of Arbitrary Simple Material Using a Novel Combination of Open Surface Integral Equations

A new set of surface integral equations for computing the shielding effectiveness of an enclosure made of any simple (linear, homogeneous, and isotropic) material is presented and discussed. First, the assumption of a thin slab is used to ignore the equivalent currents on the side surfaces of the slab. Then, four equations are derived from the electric and magnetic field integral equations for the outside and inside regions of the slab. The total number of equations is then reduced to two independent equations by applying the approximate surface impedance relationships for a thin material slab. The established formulation is discretized through the method of moments by rooftop basis functions over flat quadrilaterals represented as bilinear surfaces, with razor-blade functions used for the testing procedure. It is shown that the electromagnetic response of a very thin material plate can be represented by the sum of the responses of a perturbed perfect electric conductor and a perturbed perfect magnetic conductor. The accuracy of the method is first evaluated for several frequencies and various types of materials, using available numerical methods and measurements. Then, a practical example of the magnetic shielding effectiveness of a rectangular enclosure made of a Mu-metal material is analyzed for frequencies up to 1 MHz.