View A Video on Magnetic Shields - A Quick Introduction
Magnetic Shields
There are numerous applications that require magnetic shields: for instance, the medical industry often utilizes magnetic shields for their magnetic resonance imaging (MRI) equipment; the entertainment industry uses them for cathode ray tube (CRT) television picture; and the aerospace industry uses them for aircraft parts intended for space travel for protection against cosmic radiation. Magnetic shields are so crucial to these applications and more because without them, electronic devices would have to be designed differently, much larger, and would be much less efficient, or even completely unable to function as a result of not only the interference produced from other electronic devices, but from the normal earth's magnetic field as well.
Magnetic shield materials work by redirecting or absorbing EMI, rather than stopping or destroying it. The material is able to accomplish this redirection as a result of its magnetic permeability. In its most basic sense, the material provides a path of low reluctance that guides the magnetic field away from the electronic device, either by going around the electronic device or by being absorbed into the material. There are several different types of magnetic shields: filters, coatings, gaskets and enclosures. Magnetic filters are manufactured from perforated or mesh magnetic shielding materials and serve to block EMI passed through isolated power lines and power signals. By blocking the EMI, the filters reduce electromagnetic "cross-talk" between various electrical devices that run off the same power source. Magnetic coatings are often referred to as "metal inks" and typically contain copper, nickel or chromium alloys. Magnetic coatings must be sprayed on to a housing or material in order to become an effective magnetic shield. Magnetic gaskets are commonly constructed from electrically conductive rubber, metal or ceramic materials that are then combined with magnetic shielding metals such as Permalloy or Mu Metal. As a magnetic shield, a magnetic gasket functions to seals cracks, gaps and seams in machines against EMI penetration. Lastly, magnetic enclosures are typically made from aluminum, stainless steel, copper or nickel alloys. One of the most common types of magnetic shields, magnetic enclosures serve to surround the device needing to be shielded, absorbing or blocking harmful EMI.
