Optolite shielded EMC/RFI filter windows have been designed
for electronic displays, combining a high level of electromagnetic
shielding with excellent contrast enhancement.
They are used extensively to minimise radio frequency emissions
generated by enclosed electronic equipment and to protect electronic
equipment from electromagnetic interference arising from external
sources.
Features • Up to70dB attenuation
• In clear HSR (High Scratch Resistance) or selected coloured
band pass filters to suit most displays
• Available flat or curved
• Laminated glass or plastic
• Excellent impact abrasion, heat and chemical resistance for
Optolite Clear HSR
• Light weight
• Robust construction
• Optional blackened wire mesh to reduce mesh reflections
• Cast-in non glare finishes to cut down front surface reflections
• Mesh incorporated at any desired angle
• Edge termination services available
• Fabricated to customer requirements
Optolite shielded windows have a highly conductive micro-fine wire
mesh which attenuates EMI/RFI emissions. Different meshes to suit
varying applications are available.
Optolite shielded EMC/RFI filters are cast in-house as a one piece filter with the
mesh totally encapsulated. This approach offers customers a more
cost-effective and robust solution to shielding problems, totally
eliminating delamination and optical imperfections which can affect
ordinary laminated windows.
Typical Applications of Optolite Shielded
Windows • Aerospace and Defence
• Radio and telecommunication
• Industrial Manufacturing Equipment
• Medical and Scientific Apparatus
• Information Technology Equipment
• Flat Panel Displays in Electronic Equipment
Properties
Shielding
Absorption of electromagnetic energy is mainly dependant on the
mesh conductivity, wire diameter, weave density, electrical contact
between intersecting wires, mesh material and edge terminations.
The shield effectiveness, measured by using the "Hole-in-the-Wall"
technique, is typically between 60dB and 70dB from 100KHz to 1GHz
for blackened stainless steel meshes.
Optical Characteristics
It is important to colour match band pass filters to the particular
display characteristics. Optolite transmission, absorption and reflectance
are dependant on the filter band pass colour, mesh density and non
glare finish. Also, by casting the material as a one piece filter,
the transmission is improved by reducing the number of internal
reflecting surfaces from four to two compared to laminated windows.
Physical Design
Optolite shielded EMC/RFI windows are supplied fabricated to customer requirements.
Overall standard thicknesses are 2.5, 3, 4, 6mm. Other, non-standard
thicknesses, from 1mm upwards, are also available to order together
with an optional non glare finish.
Mesh
Various types of mesh are offered which can be treated to produce
a matt black non reflective finish. Alternatively, a standard metallic
finish can be incorporated in band pass filters where the colour
reduces the need for blackened mesh. Typically, the wire diameters
range from .025mm to 0.5mm and the weave densities vary from 50
O.P.I. (Opening per inch) to 200 O.P.I. mesh. The mesh can be set
at any angle up to 45° in more demanding applications to restrict
the possibility of moiré fringes where this is important.
Weight
For larger displays, weight can be an extremely important consideration
in the design of shielded filters. Optolite Clear HSR and Optolite
coloured acrylic filters weigh only half as much as glass. Additionally,
an acrylic filter is up to five times as resistant to breakage as
a comparable glass filter.
Edge Termination
In one piece filters, the conductive mesh is exposed along the edge
of the optolite filter after it is cut to size. A silver conductive
bussbar is added to the edge and then extended, if required, to
the front or rear surface.
The conductive circuit from the mesh is then completed either through
the bussbar or else via a conductive elastomer gasket attached to
the bussbar. Other edge termination methods are also available.
Gasket
The conductive gasket consists typically of aluminium or monel wires,
which are crimped for maximum pressure. The wires are oriented perpendicular
to the mating surfaces and integrally bonded into a silicone elastomer.
The elastomer acts either as an environmental seal or as a pressure
seal. Again, other types of gaskets are also available.
Instrument Plastics Ltd will be pleased to advise on the design
and construction of Optolite shielded windows for specific applications.
Instrument Plastics Limited has a policy of
continual improvement of products and so reserves the right to change
the product specification without notice.
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