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Product category: Gaskets, Seals and Screens
News Release from: Laird Technologies | Subject: RF gaskets
Edited by the Electronicstalk Editorial Team on 11 October 2005

Ten considerations when specifying an RF
gasket

Compiling a list of essential requirements is an ideal way to reduce cost and improve the performance of RF gaskets in specific applications says Gary Fenical from Laird Technologies.

For decades we have been asked to provide "an RF gasket that will give me 100dB from 10kHz to 18GHz" Although there are such gaskets, except for rare applications, no one needs such a gasket

A list of essential requirements needed to properly specify just what is required is the way to reduce cost and improve the performance of RF gaskets in specific applications.

The list is not in order of importance because the entire list is of equal importance.

Not considering any one of the factors will potentially cause the gasketed joint to give problems either immediately or in the future.

The first consideration is the operating frequency.

Trying to specify and RF gasket without knowing the frequency or frequencies that need to be attenuated is like shooting in the dark.

As mentioned in the introduction, there are gaskets that can provide high shielding effectiveness over vast frequency ranges.

However, it is more economical and efficient to shield the frequencies that are exceeding the limits required or causing susceptibility problems.

Many times, gaskets made of less costly materials may be used.

Gaskets may be placed at strategic locations and at calculated distances rather than using continuous lengths, again saving money by using less material.

As operating frequencies continue to go higher, traditional RF gaskets may not provide the desired results.

RF absorbers are now being used in conjunction with RF gaskets or alone in many applications.

Remember that it is not just the fundamental frequency that may be causing problems, but the harmonics as well.

The FCC requires unintentional radiators to be tested to five times the highest used frequency within the device and for intentional radiators it is increased to 10 times the highest frequency used within the device.

If you are having susceptibility or crosstalk problems, again don't look only to the fundamental frequencies but remember to look at the harmonics as well.

The next consideration is attenuation.

Shielding effectiveness values in excess of 100dB and even in excess of 120dB across wide frequency ranges can be achieved by many gasket materials and geometries.

It must be understood, that to achieve such results, the gasket must be installed exactly to specifications and on very conductive materials.

Installing high-performance RF gaskets on less conductive surfaces reduce their shielding effectiveness.

Materials or platings such as nickel, zinc, chromate, and others reduce maximum the shielding effectiveness available from more conductive RF gasket materials and platings.

The attenuation of RF gasketed joint is also greatly effected by the mechanical characteristics of the joint and ultimately, the mechanical "fit" of the RF gasket.

In over 20 years of working with RF gasket materials, I have never seen the gasket fail or not provide its specified shielding effectiveness.

Any failures have always been poor design of the application or the RF gasket being installed on lower conductive surfaces.