For many years, design and electrical engineers, OEMs, metal suppliers and fabricators worldwide have believed that MuMETAL is the industry standard. Many professionals use the MuMETAL name as a generic term, but they do not realize that it is a registered trade name. MuMETAL®, a high nickel content alloy specified for low-frequency shielding applications, is used to resolve electromagnetic interference (EMI) problems.

“Engineers understand that proper material selection is crucial and care must be taken to ensure consistency, quality and shielding efficiency of the materials used for custom shields and production parts as other companies may misrepresent this brand,” stated Mark D. Wickler, president and CEO of Magnetic Shield Corporation.

Figure 1. MuMETAL is available in a variety of prefabricated stock forms and sizes. Custom prototyping and fabrication to spec is available for specialized applications or custom drawings. Source: Magnetic Shielding Corp.Figure 1. MuMETAL is available in a variety of prefabricated stock forms and sizes. Custom prototyping and fabrication to spec is available for specialized applications or custom drawings. Source: Magnetic Shielding Corp.The MuMETAL formulation and exacting specifications provide maximum magnetic permeability or the highest degree of shielding for use in most electrical and electronic applications implemented today. Design and electrical engineers across a wide array of industries face challenges of increased complexity when creating new product design drawings for all types of electronic device and component layouts. Designers often encounter problems with densely packed electronic assemblies that have internal components interfering with each other.

When the electromagnetic interference (EMI) includes low frequency fields (30 to 300 Hz), magnetic shielding is essential to assure proper operation of the electronic equipment without failure. Engineers must also design and manufacture products, equipment, machinery, devices, parts and instrumentation to meet applicable regulations or standards. Because MuMETAL is an industry reference material with different characteristics than proprietary alloys, it can be used when the specification or the application calls for a magnetically soft or high permeability material.

One of the most important design questions is whether the source field is internal or external, and which field is most economical and practical to shield. Internal interference is created by designed-in components located within a circuit, system, enclosure, piece of equipment or room. External interference or the H-field source is created by unwanted nearby fields radiating from power lines, circuits, electrical enclosures, transformers, electro-magnetic machinery and the earth’s magnetism. Secondly, 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. All interference sources must be shielded, or the sensitive device will still be affected. The usual approach is to shield the sensitive device, preventing interference from present and future sources. A hands-on approach to solving a shielding problem can be accomplished with the use of a lab kit, testing and prototyping.

Mr. Wickler also spoke about the importance of continued lab testing, “Over several decades, we have performed hundreds of laboratory tests and calculated thousands of shielding equations — all in an effort to continually validate the theoretical application of magnetic interference control in both AC and DC applications, and to aid engineers in shield design. A documented and effective reference tool, the B-H curve chart depicts the material capabilities to attenuate and absorb a wide range of magnetic fields.”

Shielding efficiency is a result of material composition, specific gravity, thickness, grain structure within the alloy and hardness. Material selection depends on the strength of the unwanted field (H) and the amount of field attenuation required. MuMETAL is the preferred solution because of its reliable performance in reducing low-frequency electromagnetic interference (EMI). Available as stress annealed sheet stock, MuMETAL is used for fabricated shields such as enclosures, cylinders, cans, channels or 3D boxes. Complex cylindrical shaped shields are the most efficient for redirecting and reducing magnetic fields. Typically, hydrogen atmospherically controlled perfection annealing or final annealing is required after stamping, machining, bending, rolling, severe forming or welding. This is crucial in relieving material stress and developing the alloy’s maximum shielding performance. The perfection annealed fabricated shields and parts are then tested at an in-house quality control lab to certify that the demanding specifications are met.

Figure 2. The B-H Curve of MuMETAL. Source: Magnetic Shielding Corp.Figure 2. The B-H Curve of MuMETAL. Source: Magnetic Shielding Corp.Theory behind the B-H curve is well documented and remains an effective reference tool. By use of the B-H curve, shielding alloys MuMETAL®, Co-NETIC® AA, Co-NETIC® B and NETIC® have been developed and refined to offer the most effective shielding characteristics for a variety of applications and markets. The B-H curve (Figure 2) depicts the materials' capabilities to attenuate and absorb a wide range of magnetic fields.

Located in the Chicago metro area, Magnetic Shield Corporation has been a leader in the custom shielding fabrication market, and a manufacturer and supplier for over 75 years. The company provides expertise and engineering consulting on thousands of projects, applications and shielding designs. For more information regarding proprietary shielding alloys and forms available, wiring and cable shielding, Zero Gauss Chambers, and modular MuROOMS, visit the Magnetic Shield and Mu-METAL websites.