fill the gap in defence shielding

A range of extruded and die-cut sheet elastomers are used for filling the RFI shielding gap in the defence and aerospace industries.


he defence and aerospace industries have always been major drivers for RFI/EMI shielding products. One main factor in these industries is the susceptibility of some computer and telecommunications

devices to emit electromagnetic radiation (EMR) in a manner that can be used to reconstruct intelligible data. In this case, EMC is protecting against emissions. Other factors include NEMP or nuclear

electromagnetic pulse, which is a burst of electromagnetic radiation created by nuclear explosions. The resulting rapidly changing electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges which would cause electronic equipment to fail. In this case, EMC is protecting vulnerabilities.

ELECTROMAGNETIC COMPATIBILITY EMC is the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to other equipment in that environment and without being functionally compromised by external radio frequencies. In both cases, shielding of the enclosure is an

important defence and can solve 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 reality in a mass production process, nothing can be that flat and gaps will exist. These gaps are slots and can become radiating antennas. This unevenness can be addressed by using more fixings to get good contact between the mating surfaces and at lower frequencies this can work. For example, to achieve 20db shielding at 100MHz, gaps of 150mm are acceptable. This reduces to 15mm at 40db. At higher frequencies of 1GHz, it’s impossible to close the gap as to achieve 40db, the gap is now

❱ ❱ Flat sheet EMC gaskets can be created in a number of material compositions and die-cut to suit specific sealing requirements

1.5mm. These gaps need to be filled with a conductive gasket, which will take up all the joint unevenness and, depending on the type of gasket, will also provide an environmental seal against dust and moisture.


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 the quest to reduce the size and weight of electronic equipment, there is a lot a pressure to reduce these land areas which makes this more important than ever. Electrically conductive elastomers are the

most preferred EMI shielding gasket types in the Aerospace/military communications industry. The base elastomer is silicone for normal environments and fluorosilicone for fuel and oil resistance, both offering a wide temperature range of -40°C to +160°C and up to +200°C for some grades. The conductive fillers available are silver plated aluminium, silver plated copper, pure nickel and nickel coated graphite. Kemtron’s process capability is extrusion, moulding and conductive vulcanised jointing. Many extrusion profiles are available including cords, tubes, hollow D and solid D as well as custom profiles. Extrusions are supplied in continuous lengths, cut to length or made into large or small diameter O rings which are produced by joining extruded profiles with the same conductive compound as the base material. The joint is heat vulcanised ensuring a strong conductive joint. Mouldings include sheet stock, O rings, custom shapes and gaskets. Sheets can be die cut to customer design and a conductive PSA can be applied to aid assembly.

EMC Testing Vol 2 No. 1 /// 13 Gaskets

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