Quietshield Gaskets & Shielding
flexible, conformable and
Fabric-Over-Foam Gaskets are low cost,
soft and easy to apply. These gaskets are
lightweight Quietshield
available in a variety of materials and
profiles, including rectangular, D shaped,
products deliver effective
FL shaped and DD shaped FC68-FC69
EMI shielding across seams
Waved Metal and Fabric-Over-Foam
or gaps within an enclosure
I/O Gaskets are flat products used to
provide a ground contact between a
metal connector and the electronic
enclosure or mating connector FC70
Shielding Tapes and Fabrics are flexible,
lightweight, and easy-to-install shielding
materials offering high conductivity with
a low electrical resistance and are
available in a variety of fabric styles FC71
Wire Mesh Gaskets are available
as all mesh or elastomer core mesh
gaskets. They provide excellent heat
and corrosion resistance and are used
between two surfaces to maintain
electrical continuity while shielding
electromagnetic waves FC72
Conductive Silicone is used for its heat
resistant properties and can be produced
in many different forms such as sheets,
molded parts, die-cuts or strips. These
conductive elastomers are water resistant,
can eliminate static electricity, and act
as an absorber at high frequencies FC73
FC65Shielding Theory and Introduction
Shielding Theory
The shield will continue to function as long as there are
Electromagnetic shielding is used to prevent electromagnetic
no holes in the electromagnetic shield which would allow
signals such as radio signals from leaving or entering a box
the currents to flow from one side of the shield to the other.
or enclosure. Signals inadvertently emitted by an electronic
Holes are a necessity in an electronic enclosure. Connectors,
device can cause distortion or interruption in normal radio
wires, and cables are needed to transmit information to and
communications in a localized area. This is the basis of
from electronic devices. Doors and covers are needed to
most laws and regulations concerning electromagnetic
get access to components to maintenance, service, and
interference. In addition, normal radio signals can cause
keypads may also be required. The problem is that all of
unprotected electronic devices to malfunction. Depending
these items cause openings in the shield which reduce
on the devices function, a malfunction in the device could
the performance of the shield.
be a minor inconvenience such as static on a radio, or life
threatening such as the malfunction of a life support system
Special devices such as shielding gaskets, shielding
at a hospital.
ventilation panels, shielded filtered connectors, and shielded
switches minimize the effect of a hole in the shield.
Introduction The length of the hole and wavelength of the signal
that needs to be shielded are the major factors determining
The electromagnetic shield in most cases is the electronic
the shielding effectiveness of an electronic enclosure. The
housing itself. The housing/shield forms a metal cage around
distance between spotwelds, or screws which hold a metal
the electronic circuits in a device. Most of the electromagnetic
housing together count as long narrow holes. Higher frequencies
signal is absorbed with a small portion (3 to 10 dB) of the
(lower wavelengths) flow more easily through smaller holes,
signal reflected off the metal housing. Most of the absorbed
and so the highest frequency needed to be shielded is
signal creates alternating currents at radio frequencies
the frequency of concern when designing shielding.
which travels on the surface of metal. This allows the
electromagnetic shield to keep signals from outside the Aperture versus frequency charts can give a rough
enclosure on the outside of the shield and signals from estimate of the shielding effectiveness of a metallic
inside signals on the inside of the shield. electronic housing.
SHIELDINGEFFECTIVENESS
TYPICAL SHIELDINGEFFECTIVENESS
100. 110
40 dB 20 dB
60 dB
100
Wavelength
90
10.
to
Frequency
80
80 dB
70
1.
60
50
.1
40
30
.01
20
10
.001 0
100 KHz 1 MHz 10MHz 100MHz 1GHz 10GHz 100GHz 0 100 200 300 400 500 600 700 800 900 1000
Frequency (MHz) Frequency (MHz)
Test Methods:ASTM D-4935-89
Test Fixture: Flanged coaxial transmission line
API TECHNOLOGIES 8061 Avonia Rd. Fairview, PA 16415 Ph: 814-474-1571 Fax: 814-474-3110 eis.apitech.com
FC66
API TECHNOLOGIES SPECTRUM CONTROL GmbH Hansastrasse 6 91126 Schwabach, Germany Phone: (49)-9122-795-0 Fax: (49)-9122-795-58
Aperture Length (Wavelength - Inches)
Shielding Effectiveness (dB)