EMI Shielding for Aerospace, Defense & Marine

EMI SHIELDING SOLUTIONS IN AEROSPACE, DEFENSE & MARINE

The Aerospace and defense industries have always been the main drivers for RFI/EMI shielding design and products. Achieving EMC (electromagnetic compatibility) in this sector is safety-critical, whereas in everyday life it can just be a frustrating nuisance.

Aircraft can get struck by lightning with regular occurrence, which will cause an electromagnetic pulse or EMP. EMP will have a devastating effect on electronic circuitry, so it is important that the aircraft has a path for the lightning to continue without causing damage. Space is another matter; satellites are in a very hostile electromagnetic environment with solar flares that can emit a coronal mass ejection. We are protected on Earth by the magnetosphere, but satellites don’t have that advantage, so shielding is paramount to ensure the safety of the satellite and its systems. Greater integration of electronics means electromagnetic compatibility between systems is of utmost importance to ensure they work in harmony and do not interfere with each other. Aircraft are more fly-by-wire than mechanical systems, with complex software operating computerised systems. Sensors measuring the aircraft environment, flight data, etc., all need to communicate with each other, operate independently, and provide backup for system failure or malfunction. Electronics engineers are very familiar with this and will consider in their design good board layout, filtering, grounding, signal integrity, etc., to try to resolve EMI at its source. However, shielding of the enclosure is just as important and solves the problem of radiated emissions and susceptibility. Mating surfaces on an enclosure can look very flat, and you think there is full metal-to-metal contact, but in a mass production process, nothing can be that flat, and gaps will exist. These gaps are slots and can become radiating antennas. This joint unevenness can be addressed by using an electrical gasket and adding more fixings to get good contact between the mating surfaces.

RFI/EMI shielding is a mechanical fix for an electrical problem, and the enclosure design engineer should be aware of the types of gaskets available and their different attributes and ensure there is enough land area on the enclosure seams, doors, etc. to fit the gasket. In Aerospace, the weight and size of equipment and systems are important, so miniaturisation, where possible, is used. This means that the shielding options available to the design engineers must also be small and offer good shielding. Electrically conductive elastomers are the best option for Aerospace as the material can be moulded, extruded or fabricated into very small components or deposited directly onto hardware. Many electrically conductive fillers are available to suit shielding requirements, and a fluorosilicone base meets the needs of resistance to fuel oils, etc.

ARMORED VEHICLE APPLICATION

Information Distribution System

SHIELDING TYPE	FEATURES	BENEFITS
Conductive elastomer O ring seals	• Conductive elastomers can provide great EMI shielding performance on casing lids • Range of different materials and profiles available to suit the application including a UL94-V0 material	• Material options to provide required EMI performance and galvanic compatibility • Provide low-contact resistance between connector and enclosure
Connector gasket	• Meet MIL-C standard sizes, and common sub D connector gaskets.	• Ensures electrical bonding between the surfaces with a very low contact resistance
EMI O-ring	• Compression molded • Compliant with MIL-FTL-38999, MILDTL-26482, MIL-DTL-81511.	• Maintain the integrity of the seal • Ideal where small cross section and/or small inside diameter is required.