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Electromagnetic compatibility is achieved by reducing the interference below the level that disrupts the proper operation of the electronic system or subsystem. This compatibility is generally accomplished by means of electronic filters, and component or equipment shielding. Shielding an electromagnetic field is a complex and sometimes formidable task. The reasons are many, since the effectiveness of any strategy or technique aimed at the reduction of the electromagnetic field levels in a prescribed region depends largely upon the source (s) characteristics, the shield topology, and materials. In this paper, the effect of an incident plane wave with linear polarization on aluminum shield in UHF frequency is investigated, then, the type of shield material is changed and shielding effectiveness caused by it is investigated. Also, the linear polarization of incident wave is converted to circular polarization and shielding effectiveness variation is obtained in this stage. Slots and apertures are very important parameters to determine suitable shielding effectiveness. In following paper, slot is placed on shield, and its shielding effectiveness is evaluated. The effects of slot width variation, slot length variation and slot displacement, on shielding effectiveness are investigated. Finally, the effect of different aperture structure is evaluated and shielding factor is obtained in any stage. The whole of simulations in this paper, are done with CADFEKO.

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Abstract-Since the early days of radio and telegraph communications, it has been known that a spark gap generates electromagnetic waves rich in spectral content (frequency components) and that these waves can cause interference or noise in various electronic and electrical devices such as radio receivers and telephone communications. Electromagnetic pulses are fields of energy that they can damage electrical and electronic circuits at once. New technology of microelectronic circuits is sensitive to interference power. An intentional or inadvertent risk and unforeseen create irreparable damages, so that it is important to investigate electromagnetic interference from viewpoint: generation source, the effectiveness on electronic components and safekeeping methods. One of the prevalent methods for safekeeping against these pulses is shielding. In this paper, at first, the effect of magnetic field intensity is investigated in frequency selected (0-545Hz) for various shields such as: paramagnetic materials, diamagnetic materials and ferromagnetic materials and shielding effectiveness is calculated for various low frequencies in one point in shield and shielding effectiveness variation with increase in frequency for any material is obtained. In The following of paper, the effect of magnetic field intensity is investigated on shield's two apertures and six apertures. Then, the apertures are displaced on shield surface and shielding effectiveness variation is obtained. This apertures displacement has done for various shield materials. Finally, the effects of composite shields are studied to shielding effectiveness. These shields have combined to two materials. We obtained interesting results from composite shields. In this paper, solution method has chosen 2DFEM and the whole of simulations have done Cosmos/M. Index Terms-Shielding effectiveness, Helmholtz coil, paramagnetic material, diamagnetic material, ferromagnetic material, low frequency.

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