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. I. INTRODUCTION With the increase applications of electronic equipment, the electromagnetic interfering problem becomes more and more serious. Also, increasing use of electrical power, high magnetic fields of power frequency are often encountered in our environment. These high field strengths may cause disturbances on video display units. The interference occurs mainly as frame disturbances when the magnetic flux density is above 0.5-1 µT [1]. One of ways to limit the penetration electromagnetic fields into systems is shielding. Electromagnetic shielding is the process of limiting the penetration of electromagnetic fields into a space, by Manuscript received March 11, 2011; revised July 11, 2011. A. Keshtkar is with the Faculty of Engineering and Technology, Imam Khomeini International University, Ghazvin (akeshtkar@gmail.com). A. Maghoul is currently a researcher with EMC department in space research center of Iran, Tehran, Iran. (amir.maghoul@yahoo.com). A. Kalantarnia is currently a Faculty member of Applied and Science Technology, Hamedan, Iran (ali.kalantarnia@gmail.com). blocking them with a barrier made of conductive material. Typically it is applied to enclosures, separating electrical devices from the 'outside world', and to cables, separating wires from the environment the cable runs through. The shape of the shield is in many cases restricted by practical limitations, and only partial shielding may be possible to use. In electromagnetic, shielding effectiveness (SE) is a concise parameter generally applied to quantify shielding performance [2]? The shielding effectiveness (SE) is equal to ratio quantities at the receptor without the enclosure and with enclosure: 0 dB 0 dB E for E - field : SE = 20log( ) (1) E H for H - field : SE = 20log( ) (2) H s s where, E 0 and H 0 represent quantities at the receptor without shielding body, E s and H s denote quantities at the receptor with a shielding barrier between the emitter and receptor. Owing to some special demands, the lower frequency need shielding is 50 Hz or even 0.01Hz sometimes. This special shielding is used for the protection against the electromagnetic radiation field generated by generator or large-scale voltage transformer, the experiment of measuring and regulating, and the laboratory of the electron microscope test [3]. The shielding of low frequency, low Impedance and high intensity electromagnetic waves is a complex task. Indeed, as is known from the Schekunoff's theory [4]. Reflection losses are significantly reduced for low impedance waves, i.e. when the wave impedance value is close to that of the intrinsic impedance of the shield, and absorption losses diminish for low frequency operation. The use of materials that exhibit a magnetic structure with not vanishing macroscopic magnetic moment, i.e. ferromagnetic bodies, usually increases the shielding of magnetic fields. Essentially, this is because of the shielding of the result of two synchronously occurring physical mechanism: the flux shunting through the high permeability of the materials and redirection of flux due to induced eddy current [5]. In this paper, the effect of magnetic field intensity is studied in low frequency for shields with various materials. Also, the effect of magnetic field intensity is investigated on shield with aperture, by frequency variation and could see the diversion of field lines on shield. Then, the effect of increase in apertures number on shielding effectiveness has obtained. In following paper, the apertures are displaced on shield surface and shielding effectiveness variation is obtained. Finally, the effects of composite shields were investigated to shielding effectiveness. Also, it is necessary to know, in this paper, shielding effectiveness in magnetic field is investigated. Magnetic Shield Effectiveness in Low Frequency A. Keshtkar, A. Maghoul and A. Kalantarnia 507 International Journal of Computer and Electrical Engineering, Vol. 3, No. 4, August 2011