Coating on EMI Shielding
Wed, 08/05/2009 - 10:45am
As hospital rooms become more high tech, an important concern for today's medical device designer is electromagnetic interference (EMI). Much attention has already been given to the infamous cell phone case which highlights interference from radio frequency signals. This article will focus on shielding devices from lower frequency electromagnetic interference.
Unlike cell phones and walkie-talkies that operate at high frequencies, sources of EMI are typically low frequency magnetic signals. Common sources in a hospital would include electrical lines (60 Hz), MRI machines, and electrical motors. Electrical devices that may be affected by EMI can include pacemakers, ECG equipment, defibrillators, imaging devices, analog sensors, and hearing devices.
The EMI problem has typically been dealt with by shielding either the source or the device, or by keeping certain equipment away from others. Materials used to shield EMI signals are ferromagnetic metals with high permeability that can range from low cost steels to highly tailored mumetal (a special alloy with extremely high permeability). For example, MRI rooms are typically shielded using silicon steel sheets that are welded together in the floors, walls, and ceiling. In devices, mumetal foils are often used, which must be cut and applied manually or formed into shape. After deformation, the foils must be annealed to recover their magnetic properties, requiring an additional process step.
Direct Coating of PartsA new way to shield medical device components is to apply a high permeability coating directly onto the device housing. Ferromagnetic coatings with nanocrystalline grain size offer permeability close to that of mumetals but do not need to be annealed. Due to their fine grain size, these coatings also have very high hardness and strength and can even add structural rigidity to polymer components. Other substrates such as aluminum castings, machined parts, or
OnlineFor additional information on the technologies and products discussed in this article, see MDT online at www.mdtmag.com or Integran Technologies Inc. at www.integran.com.