4 Things You Must Know about Magnetic Shielding Material

Author: Elvis Moore

When you use magnetic shielding material, you can't block an electromagnetic field, but can redirect it. Designers use conductive material for the purpose, and shielding is typically applicable to electrical devices to lessen the coupling of electromagnetic fields, radio waves and electrostatic fields. Read on to learn about four of the most important things about magnetic shielding materials.

1. Thickness of Shielding Material

What material thickness you'll consider depends on a host of factors. They are:

  • The size and type of the magnetic field
  • What you are shielding — the magnet or the device
  • The shape of the shield – a closed cylinder, a circular object or any other shape

    • 2. Material Types to Use

    You can use ferromagnetic metals like nickel, iron and cobalt for shielding purposes. Steel is a good ferromagnetic material, and works pretty well for redirecting the lines of flux moving from a magnetic north pole to the south pole. EMI shielding designers often prefer steel because it is easily available and is cost-effective. However, some of the stainless steel varieties, particularly the 300 series, are not good for shielding as they lack ferromagnetic properties.

    The material thickness matters to a certain point. When your shield is too thin, it is easily saturated and cannot support more flux. Use a thick shielding material so that it can hold more lines of flux. However, when reaching a certain limit, adding thickness to steel will not enhance EMI shielding effectiveness. When saturation is the problem, use several layers of an EMI shielding material.

    3. Special Materials for Magnetic Shielding

    Use MuMetal for effective EMI shielding. Suppliers dealing with shielding products use industry-specific materials defined in Milspec 14411C, and offer the best quality MuMetal together with some proprietary alloys. Most of these material types contain more nickel (about 50 to 80 percent of the metal in the mix). The high relative permeability of this special magnetic shielding material is its unique quality. However, it does have a low saturation point. Permeability is the level of magnetization of any material responding progressively to an applied magnetic field. A shielding material having higher permeability has the ability to absorb more magnetic flux. The higher the permeability, more effective is the shielding.

    4. Permeability and Saturation Point

    When it comes to low carbon steels, they have a permeability of 1000 to 3000. MuMetal, on the other hand, has a permeability range from 300,000 to 400,000. The saturation point of a material is the flux density at which it is unable to hold any more flux. Steel will saturate at about 22,000 Gauss and MuMetal at 8,000 Gauss approximately. MuMetal will lose its shielding effectiveness when saturated or when used in higher field densities. Use steel in such scenarios because the metal offers better attenuation, and a relatively higher saturation limit.

    Use the right magnetic shielding material to address your specific EMI problems. Use MuMetal for sensitive electrical appliances and low field strength. That's because the material offers enhanced shielding effectiveness than steel. However, for applications like huge, robust neodymium magnets, steel is better for its higher saturation point.