Shielded window construction

Cast window

Cast windows are produced by casting a sheet of mesh directly in a thermoset polyester (CR39) or acrylic resin. The resin may be tinted a wide range of colours to suit the display it is intended for or have filters such as polarizers cast in. In particular polyester or CR39 cast windows have exceptional high temperature stability and very good scratch resistance.

Edge bonded window

A basic method of construction where two or more layers are made up into a window by applying a bead of adhesive or strip of adhesive tape around the window perimeter. The window may be as simple as a layer of mesh bonded to a glass or acrylic blank for example, but would more usually be a layer of mesh held between two window panels. This method allows special purpose filters such as a circular polarizer to be easily incorporated. This method of window construction is low cost but not recommended for uses where it may be subject to vibration or shock.

Fully laminated window

As the name suggests fully laminated windows are bonded over their full (screen) area. This is achieved by laying up the screen assembly in the required configuration but interleaving with an adhesive interlayer material. The assembly is then subject to heat and pressure under carefully controlled conditions that results in a fully bonded and sealed window. This window construction has excellent physical properties and in particular is very resistant to impact, shock and vibration. Fully laminated polycarbonate windows are exceptionally tough and suitable for some of the most demanding applications. Glass, acrylic or polycarbonate may be laminated using this technique and in each case enhancing the properties of the original material. It is possible to laminate in special purpose filters or contrast windows with tinted/coloured materials.

ITO coated / metal film windows

We are also able to supply shielded windows based on a variety of substrates including glass, polycarbonate or acrylic or polyester coated with vacuum deposited thin films of ITO or selected metals. The films applied in this way are very thin and can have light transmissions of around 80 – 90% mid-spectrum. These transparent conductive film coated substrates may then be laminated with other materials to improve ruggedness and/or optical properties as required. The main advantage of these window types is that they allow the display to be viewed clearly without the minor distortion or ‘fringing’ that can occur sometimes with mesh windows. However mesh windows offer higher levels shielding performance and therefore ITO and metal film windows are not suitable for some applications.

Window termination

As with all EMI shielding components correct low impedance termination to an enclosure or panel is critical to the performance of a window. Once again, there are a number of options depending on the end specification for the equipment. An overview of the main methods follows below.

Pre-mounted in frame

The window can be supplied already set into a frame complete with gasket/s, drilled holes or fasteners ready to install. Such assemblies can be designed for internal or external mounting

Bonding

An electrically conductive adhesive may be used to directly attach a shielded window. Normally connection to the window is made via a silver paint busbar around the perimeter of the window that in turn picks up on the conductive mesh or conductive film. For higher levels of mechanical and shielding performance it is possible to bond the screen itself using a structural adhesive and then terminate the mesh directly to the enclosure either with a conductive adhesive or mechanical means.

Pre-fitted gasket

The window may be built up incorporating conductive and/or environmental seals as required. This eliminates the often awkward or time consuming process of assembly for the customer and ensures that the window will be fully functional as received. A wide range of gasket types may be utilised ranging from the straightforward but effective window mesh over elastomer core to high performance electrically conductive elastomers. 

...to types of shielded windows.

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