Why do we need Magnetic Shielding?

Our Magnetic Shielding products protect electronic circuitry from "EMI", or  Electro-Magnetic Interference. There are many sources of this interference.

Magnetic Shielding Theory

Shielding components can be accomplished in different ways.

Flux Density Calculation & Shielding Effectiveness

It is a common question to ask, how much shielding can I expect?

First it must be understood that a Shield functioning within a measured field (Hd) will not operate at that level. It will be at a considerably higher level which is determined by:

Definitions

Gauss = A measure of magnetic intensity equal to one line of magnetic force per square centimeter.

B = The flux density in the shield, in gauss

Hd = External field in gauss (oersted).

Flux = The rate of flow of magnetic field.

Saturation Field = The field generated within the magnetic shield causing the permeability to asymptotically approach unity.

d = Shield diameter, or largest dimension of rectangle shapes.

b = Radius of shield

µ = Permeability of material.

t = Thickness of shield material . 

A = Attenuation of field (ratio).

Formulas

Magnetic Field:

Use this formula to determine the approximate magnetic field in the shield.

Example: 

Using a simple 4" Diameter cylinder, .040" thick material, and in a 2.0 Oerstead Field, the approach is as follows.

Shield Effectiveness:

Using the B-H Curves of Alloy, move vertically on the "B" scale, in this case to 250, then horizontally to Alloy selected intersection, then at angle to permeability. This will read 100,000, being conservative lets use 95,000.

Shielding Effectiveness (SE) = 20 Log (A) = 20 Log 950

                                                SE = 60 Db

Generally speaking, the same shield will provide better attenuation to DC fields than it does to AC Fields.

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Send mail to RJaggers@EagleMagnetic.com with questions or comments about this web site.
Last modified: January 23, 2008