It is vital that EMI shielding enclosures function to specific requirements, whether you are protecting
sensitive data from espionage, assuring evidence for data on seized mobile devices, or testing for EMI
before product launches.
How can buyers of enclosures be sure they will perform?
Product literature supplied by vendors often provides test data, but
that must be carefully examined to see that the specific tests used
will predict the functionality of the enclosure in actual operation.
Different tests offer different insight as to effectiveness. Tests of
the enclosure’s material may give an indication of shielding effectiveness,
but this is insufficient to predict usability. The fully
assembled enclosure needs standardized testing to ascertain shielding
effectiveness. Leakage may come from seams, vents, filters, I/O
plates, or doors, shielding effectiveness should be measured through the
wall at multiple locations and at various frequencies.
The
minimum shielding effectiveness that is
recorded anywhere throughout the enclosure is the critical measure for
security applications. An IEEE-299 test of a high
attenuation tent plotted on the chart below shows shielding
effectiveness of at least 85.7 dB from 400 MHz to 18 GHz throughout this
portable chamber. Peak shielding performance of 98.7 dB was recorded at
1 GHz on the side with the door.
Specific applications may have unique shielding effectiveness
requirements. dB measurements are logarithmic, a 60 dB rating is ten
times higher then a 50 dB rating. Shielding effectiveness needs vary
greatly with the signal intensity encountered, which drops exponentially
with the distance to the source. Critical security applications to
prevent electronic eavesdropping in hotels and office buildings may need
to shield computer and cellular equipment’s RF emissions from reaching
the next room or floors above and below.
Proactively managing your RF shielding enclosure’s
procurement process is critical to assure the buyer gets the results
they need for their specific application. Specifying
shielding requirements in the request for quotation is important. For
highly critical applications, you may need to assure that the specific
enclosure you purchase, as manufactured and delivered, will actually
work for you on the site where and how it will be ultimately used. In
these sensitive situations, the request for quotation may possibly
include a receiving verification process to assure that the specific
enclosure as configured and delivered performs in the field as used.
This may require third party testing of the enclosure on the site where
it will be used, perhaps requiring the supplier to make field
modifications to adjust for any shielding issues. We at Saelig work with customers with highly sensitive requirements to
facilitate this verification process.
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