The Kemvent Range

The Kemvent Range

A range of low cost plastic EMC vents for use with 40, 60, 80, 92 & 120mm fans. They provide RFI/EMI shielding where applications demand a cost effective solution, whilst still providing an adequate shielding performance for most commercial applications of over 50db up to 10 GHz.

The Hi-impact ABS UL94V-0 fire retardant moulding is fitted with one layer of 3.2mm cell x 6.35mm thick aluminium honeycomb and an electrically conductive nickel/copper fabric over foam gasket to ground the honeycomb to the metalwork.

As well as providing RFI/EMI shielding the fan vents ensure good thermal management of an electronics enclosure ensuring a good exchange of air. The vents have 4 countersunk holes to suit standard fan mountings so are easy to fit with no modification.

The measured shielding performance in accordance with Mil Std 285 is shown below (based on tested performance of an 80mm sized vent).

Frequency Field Typical (db)
200KHz H 53
100MHz E 102
500MHz P 85
2GHz P 74
10GHz P 58

Kemtron manufacture and supply a full range of RFI/EMI shielding gaskets and components including electrically conductive elastomers, knitted wire mesh gasket strip, conductive fabric over foam gaskets, beryllium copper finger stock, shielded optical windows and more.

For more information on our ventilation products, please click here.

EMC for defence and aerospace

RFI/EMI (radio frequency interference/electromagnetic interference) shielding for Aerospace and Defence applications The defence and aerospace industry have always been the main drivers for RFI/EMI shielding products, those drivers being security in particular the susceptibility of some computer and telecommunications devices to emit electromagnetic radiation (EMR) in a manner that can be used to reconstruct intelligible data. This was known as the TEMPEST program which later became the acronym “Telecommunications Electronics Material Protected from Emanating Spurious Transmissions”. Battlefield drivers are 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. Physical drivers are harsh temperature environments from -40c to + 200c, resistance to fuels, chemicals and agents such as NBC (nuclear, biological and chemical) wash down. Galvanic corrosion issues caused by salt fog in marine environments. EMC is the acronym for electromagnetic compatibility which means the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to other equipment in that environment. Electronics engineers are very familiar with this and will consider in their design good board layout, filtering, grounding, signal integrity etc. to try resolving 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 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 joint unevenness can be addressed by using more fixings to get good contact between the mating surfaces and at lower frequencies this can work. Example at 100MHz to achieve 20db shielding, gaps of 150mm are acceptable, this reduces to 15mm at 40db – the fixings are getting more and more, at 1GHz it’s impossible, as to achieve 40db the gap is now 1.5mm. These seams need to be filled with a conductive gasket, this 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 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 most preferred EMI shielding gaskets types in the Aerospace/military communications industry are. The base Elastomer is silicone for normal environments and fluorosilicone for fuel and oil resistance, both offer a wide temperature range of -40 to +160 and up to +200 for…