Electromagnetic interference (EMI) is the phenomenon that occurs when signal noise from one electronic circuit or device disrupts the function of others around it. While generally unnoticed in everyday life, EMI can pose significant risks in aviation, with the capacity to disrupt vital avionic and communication systems. To safeguard against this, aircraft employ several physical security measures throughout to halt the propagation of these harmful signals. In this blog, we will discuss everything you need to know about EMI in the context of aviation, including the threat posed to aerospace operations and how it is prevented.
Every device that produces an electrical charge creates an electromagnetic field, that of which varies in magnitude depending on how frequently the current changes. The energy created by this field can disrupt the function of local electronic devices, particularly those sensitive to excess noise. Before adequate protection was installed on commercial aircraft, there were several shocking stories of passenger-owned devices disrupting vital flight systems. For example, in 1995, a passenger's laptop was thought to be the cause of an autopilot disconnect that occurred during cruising altitude. In addition to passenger devices, native aircraft circuits may also be at fault if not properly shielded. Furthermore, uncontrolled sources of EMI such as solar flares, lighting, and electrostatic discharge have all caused well-documented instances of avionics disruptions.
The first tool used in combating EMI is a comprehensive and regularly updated database of all frequency-generating components found on the aircraft. These may include digital circuits and telemetry, among many other vital pieces of equipment. It is also critical to document the respective operating frequencies of these different devices in order to prevent overlapping wherever possible.
The most important aspect of EMI prevention is shielding, which involves coating electromagnetic field-producing components and circuits with a conductive material. Shield efficacy is highly variable, depending on the material used, as well as the size of the target component. The most common materials used in shielding are those found in common sheet metal, such as copper, brass, nickel, silver, and steel. Another consideration in regards to aviation is corrosion since the physical deterioration of the shielding material can portend excess EMI. As such, any shielding components should be regularly inspected for their integrity and replaced when required.
When shielding takes place at the level of a circuit or PCB, it is considered board-level shielding (BLS). Here, the board or circuit is surrounded by a six-sided shield, which serves the purpose of preventing excess energy from propagating from the devices while also protecting it from neighboring emitters. When configured with high-frequency devices, it is crucial to have adequate thermal management by means of thermal pads or other mechanisms since heat and frequency track together.
Gasketing is another commonly used shielding method in aviation, which involves filling any holes or seams with a conductive material to ensure a smooth current throughout. Beryllium copper gaskets are typically used on aircraft, despite being more expensive than other options, due to their versatility in shape and superior conductivity. Wire mesh and conductive elastomers are also used in some circumstances, but these designs are more prone to corrosion, making their use in aerospace limited.
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