Product category:
Gaskets, Seals and Screens
News Release from: Instrument Plastics | Subject: EMI display screens
Edited by the Electronicstalk Editorial
Team on 02 September 2005
EMI display screens offer a clearer view
When shielding electronic displays against electromagnetic interference, there are a few design criteria and optical properties to take into consideration.
When shielding electronic displays against electromagnetic interference, there are a few design criteria and optical properties to take into consideration The basic design features that influence sise and thickness of the filter are the environment that the display will operate in
This article was originally published on Electronicstalk on 2 Sep 2005 at 8.00am (UK)
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Common design considerations are mesh angle, busbar contact points, surface finish, environmental seals and robustness of filter.
When shielded filter windows are placed in front of some displays, the interference that occurs is called Moire fringing.
This is the result of the mesh being located directly above the dots that make up the display.
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The effects can be very distractive and therefore further design considerations should be made.
Moire fringing is generally avoided by rotating the angle of the mesh.
Typical mesh angles are 15, 22.5, 30 and 45 degrees.
However, with some of the newer TFT displays on the market, having even finer pixel sizes and pitch, the Moire fringing would not be overcome simply by rotating the mesh.
A different mesh sise had to be employed that would give the same EMC protection and optical clarity that 100 OPI x 25um mesh provided.
Instrument Plastics can now offer as an alternative, 80 OPI x 30um mesh.
This mesh is very fine to allow high light transmission and good readability.
Equally, it gives good shielding effectiveness for a range of 1kHz to 10GHz.
This gives the same EMC protection and optical clarity provided by 100 OPI mesh, but completely eliminates the Moire fringing seen on these types of display.
One other effect that has been highlighted by new TFT displays is the specular interference on the nonglare surface of the EMC display filter.
This is caused by optical interference between the pitch of the pixels and the size of the peaks and troughs of the nonglare surface.
When this occurs a colouration and sparkle effect can be seen on a plain white screen that is then magnified when colours on the display are introduced.
This interference can cause confusion for operators working with map systems or any information displays with moving fine details.
Instrument Plastics has developed the L70 nonglare finish, which cuts down surface reflections so the display can be used in high brightness environments and eliminates specular interference giving superior optical clarity for ease of reading the display.
By combining the new L70 nonglare finish with Optolite HSR you have a material that possesses the qualities to out perform many other materials and has the approval of the MOD.
Optolite shielded filters are cast 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.
Optolite clear HSR material is recommended for displays, as it has up to 20 times the scratch resistance of acrylic, combined with optical properties similar to Crown glass.
It is also virtually immune to most common chemicals, and can operate at temperatures up to 100C.
Optolite filters increase contrast by passing the wavelengths of light from the display while partially absorbing other wavelengths of ambient light.
Selected Optolite colours are available which are matched to the transmission characteristics of the display, with a proven track record among handheld instruments and rugged displays in a variety of military environments.
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