What You Must Know About Low Frequency Magnetic Shielding

Electronic devices like sensors, transducers, test instrumentation, and detectors need magnetic shielding materials to protect them from electromagnetic interference (EMI). If there is higher frequency interference, you can shield devices with a thin conductive metallic layer. But electrically conductive materials such as aluminum and copper are sensitive to low frequency magnetic fields causing noise in a device. As far as low frequency interference is concerned, it emanates from sources like motors, switches, transformers, and power supplies, and is a critical EMI shielding issue. Low frequency shielding is a necessity in case the accuracy of the latent circuitry is critical. Shielding can be achieved with the use of custom ferromagnetic metal alloys with high magnetic permeability. These materials help in protecting your sensitive electronic devices from the noise that magnetic fields produce. They do so by deflecting the field away from the device via the shielding material.

What You Must Know About Low Frequency Magnetic Shielding

Different Shielding Methods

Metal Constituents: Traditional metal constituents like steel castings and stampings are ideal for low-frequency EMI shielding. Most often, this method may cost you more, and the additional weight can lead to problems in a few applications. You will require thick steel material if you want the same shielding performance like those of specialty ferromagnetic alloys. In many situations, you will require steel of minimum thickness for forming operations. Some applications in which weight matters significantly, steel is often replaced with materials such as aluminum or polymers having no or little magnetic shielding ability. Such materials are frequently combined with other shielding products or solutions.

Metal Injection Molding: You can use special ferromagnetic powders that can be injection molded with a binder to design complex parts, and that serve as low frequency and effective magnetic shielding products. Once the molding process is complete, the parts are chemically or thermally treated, and are then coalesced at high temperatures to eliminate the binder. You may require secondary operations to get the final shape. Though this method can produce quality shields in intricate forms, provisions for shrinkage of parts should be considered. You must also account for mechanical considerations like frailty, porosity, and permeability. As tooling costs may be high with this process, it’s perfect for smaller parts and for high volume.

Formed Foils and Foil Lay-Up: Though sheet metal or foils are ideal for effective shielding, the lay-up approach may prove unwieldy for shielding parts with outline or contour. Opt for shielding materials that are less brittle and hence can be cut and designed according to shape. A sensitive transducer, for instance, may need a can-like material over an electronic device that is incorporated onto a circuit board or an enclosure. The shape formed must be cut and stamped from the original foil or sheet metal. It’s a cost-effective process and a comparatively easy operation. However, the forming operation minimizes the shielding effectiveness by deforming the material. It damages the main material properties that cause high permeability. The material should be annealed again in high temperature-controlled surroundings to remodel a flawless structure, and also to ensure enhanced shielding performance.

Using a High Magnetic Permeability Metal

You can employ a high magnetic permeability material coating to a part’s surface. This method is ideal for small, intricate shield shapes, and eliminates the annealing process. Coating parts together with conductive surfaces are frequently used in high frequency electromagnetic shielding in electronic devices or applications through methods like conductive paints, vapor deposition, and electrolytic or electroless plating. Thin conductive coating is the most important requirement here. And with the advancements in nanocrystalline ferromagnetic coatings, the same idea can be implemented for low frequency shielding.

A ferromagnetic alloy coating with an extremely small grain structure can attain high permeability as well as effective shielding performance compared to traditional shielding materials that achieve magnetic properties from their un-deformed, large grain structure.

Custom sheet metal stock and ferromagnetic foils are ideal for designing simple magnetic shields. However, they need to follow the annealing, forming, and assembly steps. They are not receptive to small and intricate parts. Nanocrystalline coatings offer a viable alternative and are used to achieve an effective shielding solution using a versatile magnetic shielding material. You can use it for shielding polymer, metal and composite parts.

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