‘Magnetic field’ is a dreaded phrase in the industrial designing space. Why do you think magnetic fields give a tough time to designers and product engineers? Well, each electrical device creates a magnetic field of its own, and each field seems to be in conflict with those around the other devices. The conflicts and interferences subsequently affect the performances of all devices that are present in an environment. Even worse is the fact that there is no way you can block or insulate these magnetic fields. What if you could make the magnetic field lines re-route around an object? Magnetic shielding is a process that makes it possible. It involves surrounding a device with the appropriate magnetic shielding material so that the magnetic flux can flow along this material, avoiding the objects inside.
What Material Types Are Fit for Dealing with Magnetic Fields?
When it comes to protecting a device from the magnetic hazards, just any material won’t do. So, the question is, which material works and which does not. The short answer is any ferromagnetic metal with a high permeability offers a great option. Permeability, according to Wikipedia, is the degree of magnetization that a material obtains in response to an applied magnetic field. To be used for magnetic shielding purposes, it is important that the material itself does not acquire the magnetic properties. Metals containing iron, nickel and cobalt meet all these criteria, and therefore make an excellent magnetic shielding material.
Steel, which is a ferromagnetic metal, is widely used for shielding purposes. It is widely available and also affordable, hence the popularity. However, if you are planning to opt for steel, remember that some types of stainless steel are not ferromagnetic.
Developed by British scientists Willoughby S. Smith and Henry J. Garnett, mu-metal is another alloy, which is widely used as an effective shielding material. It’s an alloy of 77 percent nickel, 16 percent iron, 5 percent copper, and 2 percent chromium. Thanks to its exceptionally high permeability (80,000–100,000 against only a few thousand for ordinary steel), this nickel–iron soft magnetic alloy proves to be very effective in shielding sensitive devices against static or low-frequency magnetic fields. Some other nickel–iron alloys such as permalloy have very high permeability. However, mu-metal’s advantage is that it can be easily formed into thin sheets, which is an important criterion for creating magnetic shields.
Quality comes for a price and so you cannot blame mu-metal for being on the expensive side. Designers looking to create an affordable shielding solution prefer other alloys with similar compositions over expensive mu-metal. These types of material are generally sold in rolls of foil.
Thickness of the Material
When it comes to ensuring high shielding performance, you must consider the thickness of the shielding material. If it is made too thin, the shield cannot ‘hold’ a large number of lines or flux. The shield needs to be thick enough so that it can hold as much flux as possible. Sometimes, multiple layers of material are used to increase the material’s flux-holding capacity.
So how do you decide on the thickness of your shielding material? Consider the following points:
- The size and nature of the magnetic field you’re shielding
- The shape of your device – a sphere, a closed cylinder, or some other shape
- What exactly you want to shield your device from
- What exactly you need to shield – the magnet or your magnetically sensitive device
Which magnetic shielding material is right for youdepends on your specific shielding requirements. Mu-metal is ideal for shielding low field-strength, sensitive electronics. Steel, which has a higher saturation point, is the best choice for applications involving large, powerful neodymium magnets. A company specializing in the areas of electromagnetic shielding can best guide you in this respect, and help you develop a customized shield for your specific applications. However, select a reputed name in the industry to get the right solution.