Why is Flexible Graphite Used for EMI Shielding?
Flexible graphite is a versatile material used in many useful applications like: heat and chemical resistant gaskets, seals, and liners; thermal conductive seals; sheet lubricants; heat barriers. But flexible graphite can be used for more than just thermal and chemical resistance applications.
As society becomes more dependent on electronic devices, disruptions to our electronics becomes a growing concern. Any device with an electric circuit can be a victim or source of electromagnetic interference (EMI). Simply put, an EMI is a disruption of an electric circuit due to some electromagnetic event. And flexible graphite can be used to manage EMIs.
One way of managing EMIs (also known as RFIs, radio frequency interference, when in the radio frequency range) is through the use of EMI shielding, either to protect from or contain disruptive signals. Natural sources of EMI can be produced from lighting storms, cosmic events, and terrestrial magnetic field events, but the majority of problematic EMI originates from man-made sources generated from electronics. Material used for EMI shielding must be:
EMI shielding – Conductive
Any EMI shielding material must be electrically conductive. Conductivity of the shielding material can vary, but conductivity is necessary in order to produce a Faraday cage effect. A Faraday cage or Faraday shield is any type of enclosure formed of conductive material. This effect is actually what protects a person who is inside their car during a storm if their vehicle happens to get hit by a lightning strike. Most people think a car’s rubber tires insulate them from lightning, but a typical lightning strike averages 300 million volts at 30 thousand amps. Rubber is an insulator, but at this voltage and current electricity will still conduct through the tires. Instead, the car’s metal frame acts as a Faraday cage and passes the electricity around the car’s cabin to ground, protecting the passengers inside. Similarly, EMI shielding forms a conductive cage that will ground incoming interference or neutralize outgoing noise. Graphite is electrically conductive, and flexible graphite is made from expandable flake graphite.
EMI shielding – Versatile
EMI shielding material must also be versatile. The number of electronic devices needing protection from EMIs grows daily and each device has parameters that are unique in volume, geometry, and weight. Metals conduct electricity well but may not serve as ideal EMI shielding material if a given application requires lightweight material in an unorthodox space. Flexible graphite is easily shaped and lighter than metals with the same volume.
EMI shielding – Resilient
EMI shielding materials may be subject to harsh chemical or thermal environments. Flexible graphite is strong, yet compressible. It is chemical resistant, heat and flame resistant. Flexible graphite also has low creep relaxation, meaning it maintains its structure well under compression. Given these useful features it makes sense why flexible graphite is a popular material choice in the gasket industry. In fact, flexible graphite is used to make EMI shielding gaskets (a subset of EMI shielding not covered in this article).
EMI Shielding is Vast
The number of EMI shielding materials are uncountable. Metal foil inside coaxial cable and mesh screens on microwave ovens are two other types of electromagnetic shielding seen in everyday life. The need for countless material types is clear given all the different types of devices needing protection. Problems caused by EMIs range from minor annoyances like a disruption in your smartphone, to more serious concerns like a possible disruption of a pacemaker’s operation. Flexible graphite is only one of many choices, but it is an ideal choice given your application.