Shielding Alloys

By redirecting a magnetic field, magnetic shielding metals and alloys minimize that field’s impact on the item that’s being shielded. Used in a variety of different settings, these metals create a straightforward way for the magnetic field to serve its purpose without interfering with it. Acting as magnetic field conductors, they allow both the field itself and the equipment that’s operating in it go about their business without interfering with one another. In healthcare settings, for example, magnetic shielding isolates or blocks the magnetic field of the MRI magnet in order to eliminate unwanted interference from the MRI magnet on nearby electronic devices. Radiofrequency shielding, on the other hand, prevents the unwanted interference of noise or radiofrequencies, often in order to avoid image distortion.

How Magnetic Shielding Works

Magnetic shielding is critical when nearby devices could potentially be susceptible to magnetic interference, such as cardiac pacemakers, or other sensitive pieces of electronic or medical equipment. It’s also used when low-frequency external magnetic fields are in close proximity and have to be shielded from the magnetic or fringe field from the MRI magnet.

These alloys are also used in research labs that rely on ion microscopes and hospitals where EKG machines and other equipment must be shielded and protected from outside interference. The tests that these machines produce must be accurate, and any interference could produce anomalies in the results.

Magnetic shielding usually involves using steel or copper placed in the walls of the magnet room to capture the magnetic field. That shield them redirects the magnetic field so that it protects the item in question.

Materials for Magnetic Shielding

When selecting metals for applications where magnetic shielding is required, consider options like HyMu 80, Mu Metal2 & 47/50 and 48 & 49 alloys, all of which have high magnetic permeability and can effectively screen low-frequency or static magnetic fields.

• Hipernom Alloy is a soft magnetic allow that develops extremely high permeabilities with minimum hysterersis loss. It’s used primarily in shielding applications.

• HyMu 80 Mark II is another high-permeability alloy that provides the highest permeability in exchange for minimum hysteresis loss.

• HyMu 800 is highly-permeable and often used for tape-wound toroids and laminations made from strips that are 0.006” thick (or less).

Wear-resistant HyMu 800A is a patented nickel-iron-molybdenum soft magnetic allow that’s been using for recording head laminations. The alloy exhibits suitable magnetic characteristics for this application plus increased resistance to abrasion wear (which results in longer head life).

Other magnetic metals and alloys include Hiperco 27, Hiperco 50, Hiperco 50A and Hiperco 50B. This group of alloys is used across various different applications, including aircraft motor and generator laminations; transformer laminations; tape toroids; and as fine wire in telecommunications dry reed switches.

Making the Right Choice

Procurement professionals or engineers that are matching up their needs with the right magnetic shielding metal or alloy should work from their specifications and industry requirements, understanding that there are slight nuances among the various options. Hyperco 50, for example, has three different specifications, but not all of them will meet the requirements of the aerospace industry (which may require a test, a certain level of carbon or some other requirement).

Key points to consider when selecting magnetic shielding metals include:

1) Exactly what you want to shield
2) How much outside interference is present or expected
3) The grade of the magnetic shielding alloy that will be used

If you don’t have a specification for the metal, consider whether the material has been used before and if any previous test reports are available for that material. Also understand that because each manufacturer has its own trademark, trade name or part number for the metals that they make, knowing the material specifications, testing and/or past history of usage can help ensure that you choose the right product for the right application.