مقدمه:

شیلدینگ امواج الکترومغناطیسی در واقع کاهش شدت میدان الکترومغناطیسی در فضا است.

کاهش اثر امواج الکترو مغناطیسی از طریق مسدود کردن امواج با استفاده از موانع رسانا یا مواد مغناطیسی صورت میگیرد.

شیلدینگ امواج الکترومغناطیسی اغلب در راستای ایزوله سازی سیستم ها و ساختار های خاص و حیاتی صورت میگیرد.

استفاده از سیستم شیلدینگ در مکانهای زیر از اهمیت خاصی برخوردار است:

سایت های نظامی

بیمارستان ها

نیروگاه های برق

مراکز داده(دیتا سنترز)

فرستنده ها و گیرنده‌های رادیو و تلویزیون

سیستم های مخابراتی

سایت‌ های پتروشیمی و پالایشگاه

What is Passive Magnetic Shielding

Rigid (passive) magnetic shielding is divided into two fundamental types based upon the magnetic and conductive properties of the shielding materials: flux-entrapment shields and lossy shields

A flux-entrapment or flux ducting shield is constructed with a permeable (μ) ferromagnetic material such as low-carbon steel, silicon-iron steel (oriented and non-oriented) and nickel-iron alloy which either surrounds (cylinder or rectangular box) or separates (“U” shaped or flat-plate) the victim (i.e., people or equipment) from the magnetic field source.  Ideally, magnetic flux lines incident upon the flux entrapment shield prefer to enter the permeable (μ) material via the path of least magnetic reluctance ℜ, rather than pass into the protected (shielded) space. The higher the permeability the more magnetic flux lines will prefer to travel within the material rather than a lower permeable material including air (or vacuum) which has the lowest mu (μ) of 1

Lossy shielding depends on the eddy-current losses that occur within highly conductive copper and aluminum materials, and higher permeable (μ) ferromagnetic materials that are also less conductive.  When a highly conductive materials are subjected to a time-varying (60Hz) magnetic fields, currents are induced within the material that flow in closed circular paths, perpendicular to the inducing field.  According to Lenz’s Law, these eddy-currents oppose changes in the inducing field, therefore the magnetic fields produced by the circulating eddy-currents attempt to cancel the larger external fields near the conductive surface, thereby generating a very effective shielding effect

What’s Your Shielding Factor

Shielding Factor (SF) is the ratio between the unperturbed magnetic field Bo and the shielded magnetic field Bi as expressed in: SF = Bi/Bo The final shielding design depends on several critical factors: maximum predicted worst-case 60-Hz magnetic field intensity (magnitude and polarization) and the geomagnetic (DC static) field at that location- whichever is greater; shield geometry and volumetric area; type of materials, permeability, induction & saturation; and, number of shield layers