Electro-magnetic interference (EMI) influences the design of just about any device on the market, be it a medical machine, a navigation system or a microprocessor. How do you determine the most effective form of shielding against EMI? And which materials will serve your purpose? Matmatch investigates.
What is electromagnetic interference?
Every device emits both electrical and magnetic energy by way of either conduction or radiation, but there are certain forms of energy that have a negative impact on the functionality of a nearby device. This is known as electromagnetic interference (EMI). Additionally, interference can be caused by electromagnetic radiation. The most common source of interference is radio frequencies between 1kHz and 10GHz, the so-called radio frequency interference band (RFI) in the radio astronomy field. Additional sources of interference include ambient EMI such as lightning, solar magnetic storms or arc welders, and power quality issues, including power surges, blackouts, voltage spikes and electrical noise.
Electromagnetic interference and radiation can have consequences that range from audio/video signal disturbance to loss of life, particularly when EMI influences the operation of critical devices such as life support machines or military assets designed for electronic warfare.
How is EMI regulated?
An international body known as the International Special Committee on Radio Interference (CISPR) regulates immunity of electronic devices to EMI. Additionally, regional and national standards include the European Norms (EN), the CE conformity symbol and, on a federal level in the United States, stipulations set out by the Federal Communications Commission.
What forms of electromagnetic shielding exist?
The thickness, material choice and form depends on which frequencies are to be deflected, at what intensity, whether the device is to be protected from electric or magnetic fields, or both, the shape of the device, its ability to bear weight and its exposure to the elements, among other factors. The most common forms of electromagnetic shielding are sheets of metal formed into gaskets.
Gasketry is frequently used for aerospace, military and communications applications. There are also metal foams, wires and screens. Microwaves, for example, have metal screens built into the front window to let light through while preventing EMI. Shielded copper wire mesh may be used to form a Faraday cage around an electrical cable, or shielding tape or laminate might be applied. A plastic enclosure housing an electronic device can also be spray-coated with metallic ink to protect it from EMI.
Popular Materials Used for EMI Shielding
Of the metals used for shielding, galvanized steel and aluminium are the most cost-effective and widely used. Copper, nickel, pre-tin plated carbon steel, zinc and nickel silver are also used for some purposes. Copper is the material of choice when shielding from radio frequencies because of its ability to absorb both magnetic and radio waves.
Some gaskets and other forms of electromagnetic shielding contain silicone filled with particles of metal, such as silver, silver-aluminium, silver-glass, silver-copper and nickel-graphite. These particle-filled silicones provide weather resistance and conductivity to many electronic devices, in particular, to touchscreens.
Find materials that could be used for EMI shielding on Matmatch – start with a metal foil search. Click on the image: