Laminated film and sheet EMC filters

Emi/rfi shielding of a display filter can be achieved by using a lamination of various emi shielding film and sheet materials. Either a conductive coating, or a metal mesh layer can be incorporated into the window. Both options must be grounded to the frame of the device to give an effective shield.

The diagram below illustrates the basic design which could be used with emi shielded plastic or other emi shielded materials:

Laminated film and sheet EMC filters Image 1

Surface finish 

It is important to select the most suitable surface finish for each application.

Elements of Emi/rfi shieldings 

There are a variety of mesh types and conductive coatings that are specified for emc shielded windows and emc shielding upgrades. 

Meshes are traditionally specified in terms of material, wire treatment, count (opi) and thickness. These meshes are usually made from stainless steel or copper wires that can then be coated and blackened to prevent surface reflections. 

Optical Filters has developed EmiClare a new generation of emi shielding using a mesh that has been specifically designed for shielding displays. This mesh provides high levels of emi/rfi shielding while preserving the brightness and clarity of the display. These emi shielding products do away with complicated and unnecessary specification of wire count (opi), thickness and treatment. You simply need to specify EmiClare mesh and the angle of the mesh that you require. 

Termination Methods for emi shielded windows 

There are several forms of termination in use for shielded windows. Detailed here are those methods that are cost effective and have proven, with over eleven years of emi shielding applications experience, to provide an efficient termination. 

Mesh extensions can be specified for glass and plastic emi shielding windows. If properly installed into the aperture they yield a higher rf attenuation than a busbar / gasket combination. This edge form is recommended for large format windows and low frequency applications.

Square edge with a mesh extension
Step edge with a mesh extension

Machined Edges, Busbar and Gasket

The laminate build and the step profile must be co-ordinated to ensure that the step finishes in a substrate The busbar must include the face that sections the mesh. Depending on the termination required it could be extended over one or both surfaces of the window.
If a gasket is used, the step depth should be designed to allow for the correct compression of the gasket On compression, the conductive surface of the gasket should maximize contact area with the busbar.

Termination methods for mesh extension windows

The most effective termination is to clamp the mesh extension to the enclosure. This can be done for windows with either a step or a square edge. This termination is not possible with the new generation of ultra-fine meshes.
An effective compression gasket can be formed by taking the mesh over a compression gasket material such as neoprene.
A mesh extension can be combined with a silver busbar and a conductive compression gasket. Unless there is a special gasket requirement, this termination is not recommended on the basis of cost. It is effective if a combination gasket is required to give both an environmental and rfi seal.
For large windows such as rack enclosure doors, a cost effective option is to cut the mesh extension close to the edge of the window and finish it with a conductive tape carried over to both faces of the window. This is preferable to a simple mesh extension, which from our experience, is often torn when handling large windows.

Termination options

EmiClare Ultra windows are made to order and can be supplied with the following termination options.

Extended mesh 
Allowing direct clamping of the mesh
Extended mesh & gasket 
For a more control and rugged integration
Silver busbar 
Highly conductive painted finish

Window dimensions

EmiClare Ultra can be made from a very small single LED size up to the very large sizes often used on public information displays or shielded rooms. Common dimensions are linked to the typically display sizes like 6.4", 10.4", 12.1", 15", 15", 17", 24" etc.

Substrates Options

  • Glass
    • Glass is more cost effective per sq meter than plastic and is a superior optical material.
    • With optional surface finishes of Non-Glare dispersive etch or Multi-layer Anti-reflective coating.
    • Glass is strengthened due to the lamination process but can also be further improved with Chemical toughening.
  • Polycarbonate
    • Polycarbonate is stronger and lighter than glass and is supplied with either a clear hard coating for its chemical resistance and surface hardness or a matte, non-glare finish to control surface reflections.
    • An Anti-reflective polycarbonate with anti-finger print coating is also available.

Extra functions and filters

  • Louver light control film for privacy or contrast enhancement.
  • Linear and circular polarizer from Optical Filters range of XP technical polarizers
  • NVIS night vision goggle compatibility filters.
  • NIR blocking film for the control of solar radiation.
  • ThermoClare transparent heater for de-frosting and anti-misting.
  • Touch enabled front surface with the addition of resistive, capacitive or infrared touch screen solutions