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Chomerics,

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Holland Shielding,
Intermark,
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MAJR,
Millerdial,
Shielding Express,
Slater Plastics (UK),
Visiontek (UK),

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Electromagnetically shielded (electrically conductive) glass and other Electromagnetically shielded transparent materials come in three basic types.

The oldest type uses a fine wire mesh, usually black. This mesh can be mounted by itself in a frame or sandwiched between two layers of glass or of transparent plastic. This type provides a level of shielding effectiveness that is adequate for some applications. It is rugged, inexpensive, and easy to handle but it has the drawback that the mesh sometimes interferes with the optical quality of the shielded window, distorting the image or producing Moire' patterns.

Conductive coatings, when applied to glass, can provide a better level of shielding effectiveness and better optical quality, the drawbacks being less ruggedness and higher cost. Like wire mesh, this is a mature technology.

Plastics that are both conductive and transparent promise to provide both ruggedness and good optical quality. This is the newest of the technologies, so check the suitability of a product before incorporating it into your Electromagnetic Compatibility or radio frequency shielding design.

Designing a shielded window is not as simple as it seems. This is because all types of shielded glass, and other materials that are both conductive and transparent, will distort the image to some extent.

The key question becomes: How much distortion is acceptable? If this is not clearly defined, the electromagnetic compatibility design engineer can find himself or herself heading down a slippery, expensive, and time consuming slope.

This is because the perceived image quality is a subjective and psychological effect that varies from individual to individual. In other words, a picture that seems to be "good enough" to you may annoying or otherwise unacceptable to your customer or to your boss. What seems to be a perfectly good image or picture to you may cause one of your customers to say "It gives me a headache."

For this reason, you and your customer should agree on two issues at the outset: a) How much optical distortion is acceptable? and b) How will we measure that optical distortion?

There are several standards for measuring image distortion. Some of them are: MIL-STD-150A, ISO 12233, the Electronic Industries Association's 1956 test pattern, and the Video Monitor Test Pattern published by the Society of Motion Picture and Television Engineers.

For more information about shielding, see: "THE SHIELDED ENCLOSURE HANDBOOK" and these COURSES. entitled:

SHIELDED ENCLOSURES

SHIELDING EFFECTIVENESS TESTING

CONSTRUCTION OF ELECTROMAGNETICALLY SHIELDED ENCLOSURES

To learn more about Electromagnetic Compatibility, see this one-day course: Introduction to Electromagnetic Compatibility"

Copyright 2006, 2007, 2008 by THE HERNDON COMPANY. All rights reserved.