Electromagnetic 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?
Typical materials used for electromagnetic shielding are:
- pre-tin plated steel
- carbon steel
- copper (copper alloy 770)
- nickel silver
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
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
Gasketry is frequently used for aerospace, military
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
Pre-tin plated steel is a perfect low-cost solution that works well from lower frequencies in the kHz range through frequencies into the lower GHz range. Carbon steel has a permeability value in the lower hundreds range which provides the low-frequency magnetic shielding property that is missing in alloy 770, copper, or aluminum.
The tin plating offers corrosion protection for the steel to prevent rusting as well as providing a great solderable surface to attach the shield to the traces on the surface board during assembly.
Copper is the most reliable material of choice when shielding from radio frequencies because of its ability to absorb both magnetic and radio waves. It is also highly effective in attenuating magnetic and electrical waves
Of the metals used for shielding, galvanized steel and
Some gaskets and other forms of electromagnetic shielding contain silicone filled with particles of metal, such as silver,