Why do electromagnetic fields need magnetic shielding?
EMI, or electromagnetic interference can be a problem to designers of many products. Personal Computer manufacturers must design to meet the FCC Part 15 regulations to prevent PCs from interfering with other office equipment. Cell phone designers have to incorporate RFI shielding to stop unwanted RF emissions, as well as to prevent other electrical equipment from interfering with the cellular telephone's operation. Designers may find that densely packed electronic assemblies may have internal components that interfere with each other, requiring electromagnetic shielding. When the electromagnetic interference includes low frequency radiation, magnetic shielding is essential to assure proper operation of the electronic equipment.

What blocks magnetic fields?
There is no known material that blocks magnetic fields without itself being attracted to the magnetic force. Magnetic fields can only be redirected, not created or removed. To do this, high-permeability shielding alloys are used. The magnetic field lines are strongly attracted into the shielding material.

What is MUMETAL®?
MUMETAL® offers important electromagnetic field shielding characteristics, including very high magnetic permeability - its ability to absorb magnetic energy. The unique properties of this family of alloys results in the highest possible attenuation, making these shielding alloys the materials of choice for reducing low-frequency electromagnetic interference (EMI).

What do we mean by "magnetically 'soft'"?
Alloys useful for magnetic shielding are said to be magnetically "soft" because they can absorb magnetic energy without retaining it. Magnetically "hard" materials, on the other hand, make good magnets because they can retain a strong magnetic field even after the source of the magnetic energy has been removed. When a magnetic field is removed from a magnetic shield alloy, there is no remaining (residual) magnetic field. The measure of this property is called coercive force. For a magnetic shield, the lower the coercive force, the better.

Why is MUMETAL® offered?
MUMETAL® is an industry reference material, with different characteristics than proprietary alloys. MUMETAL® meets MILSPEC 14411C, composition 1. When the specification or the application calls for a magnetically soft or high permeability material, MUMETAL® can frequently be successfully applied.

How does magnetic shielding work?
Magnetic fields can only be redirected. They cannot be blocked or reflected. Even to do this requires special shielding alloys with high permeability. All shielding materials work by diverting the magnetic flux to themselves, so although the field from a magnet will be greatly reduced by a shield plate, the shield plate will itself be attracted to the magnet. Closed shapes are the most efficient for magnetic shielding - cylinders with caps, boxes with covers, and similar shapes are the most effective. Magnetic shielding materials offer a very high permeability path for magnetic field lines, directing the electromagnetic energy through the thickness of the alloy, and keeping the electromagnetic field from going where it is not wanted. It is important that the shield offers a complete path for the field lines, so that they do not exit the material in a place where they will cause unintended interference.

Should the source of interference or the sensitive device be shielded?
The answer to this question depends on several factors. Shielding the source may involve stronger fields, and therefore thicker materials. One must be sure that all interference sources are shielded, or the sensitive device will still be affected. The usual approach is to shield the sensitive device. This prevents interference from both present and future sources. Many electromagnetic shielding solutions begin with our Magnetic Shielding Lab Kit. This kit enables a "hands-on" approach to solving a shielding problem.

Does cutting the alloy destroy its properties?
This concern about the magnetic shielding alloys arises because they do have a sensitivity to mechanical shock - bending, forming, even severe flexing may give some reduction in the alloy's magnetic permeability. Modern, vacuum-refined alloys have a lower sensitivity to shock, and normally withstand regular handling without significant loss of properties. Cutting by shearing, EDM, waterjet, photo-chemical etching, or blanking die typically only affects that portion of the alloy immediately adjacent to the edge, and the shield will exhibit normal shielding performance.

Why must MUMETAL® alloy be final annealed to develop magnetic shielding performance?
To obtain optimum magnetic properties, annealing MUMETAL® alloy following fabrication is essential. This should be done in a furnace that allows for careful control of the annealing temperature and cooling rate. Optimum properties are reached in a pure hydrogen atmosphere.

What effect does heating the magnetic material have on its magnetic shielding properties?
MUMETAL® has a positive coefficient of permeability with respect to temperature. This is a quick way of saying that the permeability increases as temperature increases. This occurs until operating temperature nears the Curie temperature (850ºF.), defined as the temperature where permeability goes to 1 and the alloy becomes magnetically transparent. At operating temperatures above the Curie temperature, the shield will not provide any attenuation of the magnetic field. Roll off of permeability begins as operating temperature nears (within 25ºF) the Curie temperature listed, so a safety factor for allowable operating temperature should be used.

Note: Temporary temperature excursions above Curie temperature do not degrade the alloys. Shielding function is restored when the temperature again falls below Curie point.

Commerce Related Questions

Do you accept purchase orders?
Yes, with the following limitations. We offer Net 30 terms only with pre-approved credit, based on completion of credit verification using three customer-supplied U.S. credit references.

Initial orders that require faster service may be accommodated with either wire transfers, credit (or procurement) cards or C.O.D..

Is there a minimum order quantity?
Our minimum order is a single standard sheet (30" x 120" - can be sheared for shipment).

Do you have materials in inventory, ready for shipment?
Yes, we maintain a substantial inventory of the raw material sheets.

What size is your raw material sheet?
Our smallest standard sheet size of MUMETAL® is 30" x 120". We will sell one sheet of MUMETAL® and Shear for Shipment as a minimum order. The standard sheared sheet size is 30" x 30", which can be shipped by UPS and Federal Express.

What are your shipping terms?
Magnetic Shield Corp. ships Ex-Factory, Bensenville, Illinois, 60106 U.S.A.

Do you ship internationally?
Frequently. Magnetic Shield is known world-wide for the quality and reliability of our materials, and manufacturing processes. The primary restriction on shipment of our materials into other countries is adherence to the rules and regulations as stated by the U.S. Department of Commerce "Export Regulation & Restrictions, Bureau of Industries and Security".

Are there any special requirements for shipping magnetic shielding material?
While there are no requirements for shipping our materials other than protective coverings to prevent damage, recently certain international countries have instituted new rules regarding receipt of materials in wooden crates. If the destination country requires the use of a "Certificated" wood (specifying it is free of larvae and/or insects), an additional charge will be made for this special crating.