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Electromagnetic interference (or EMI, also called radio frequency interference or RFI) affects an electrical circuit because of external electromagnetic conduction or electromagnetic radiation. It can interrupt, obstruct, or otherwise affect the circuit’s performance. The source may be any object, artificial or natural, that carries rapidly changing electrical current. It often affects the reception of AM radio in built-up areas, as well as mobile phone, FM radio and TV reception.
There are basically two main times of EMI or RFI – narrowband and broadband, and anywhere where electrical power is turned on and off rapidly is potentially a source.
Narrowband interference is generally caused by intentional transmissions including radio and television stations, pager transmitters, mobile phones and so on. Broadband interference usually comes from incidental radio frequency EMItters, including electric power transmission lines, electric motors and thermostats, among others.
Of course, one of the best ways to deal with EMI is with some EMI shielding, or RFI shielding. EMI shielding is an electromagnetic compliant shield which protects electronic components and prevents stops them escaping beyond the EMC shield.
EMI shielding reduces unwanted reflections from front surfaces, with RFI shielding filters in thicknesses of 0.5, 1.0, 1.5, 2.0, 3.0mm. There are also various EMI shielding thicknesses and light tolerances.
The most reliable, inexpensive, and trouble-free EMI shielding or RFI shielding method available at the moment is spray coating using paints containing conductive metal particles. The best metals in RFI shielding are those which do not lose conductivity due to oxidation. These consist of gold, platinum, palladium, iridium, silver and osmium. The least expensive to use in RFI shielding is silver. A coating containing fine silver particles is an excellent as a conductor and for EMI shielding. Paints containing fine silver particles have been available a long time and their performance in EMI shielding is excellent.
RFI Shielding for busbars.
A busbar should also have its own protection or RFI shielding. In electric power distribution, a busbar means the thick strips of copper or aluminium which conduct electricity within an electrical apparatus.
The size of the busbar is important in deciding the maximum amount of current which can be safely carried. A busbar can have a cross-sectional area as small as 10 mm² but an electrical substation may use a much larger size of busbar.
A busbar is usually either a flat strip or hollow tube. A busbar more than about 8 mm thick is inefficient, so hollow or flat shapes prevail in higher current applications.
A busbar may either be supported on insulators, or else insulation may completely surround it. A busbar may be protected from accidental contact either by a metal enclosure or by elevation out of normal reach.
A neutral busbar may also be insulated, while an earth busbar is generally bolted directly on to any metal chassis of their enclosure. A busbar may be enclosed in a metal housing, or one busbar may be connected to another and to electrical apparatus by bolted or clamp connections.
Optical Filters
Optical filters usually belong to one of two categories. The simplest, physically, are absorptive optical filters, while the second category, interference or dichroic optical filters, can be quite complex. Optical filters selectively transmit light with certain properties (often, a particular range of wavelengths or range of colours of light), while blocking the rest.
Optical filters are commonly used in photography, optical instruments, and to colour stage lighting. In astronomy, optical filters can be used to eliminate light from the sun or other star which is brighter than the object being viewed. Even seeing Mercury can require the use of optical filters in far northern countries.
Optical Filters and RFI Shielding from Instrument Plastics
At Instrument Plastics, we specialise in designing and making RFI, infrared and optical filters for electronic displays.
Over the last 22 years, we’ve developed a wide range of products, and become a leader in the British and UK markets for optical filters as well as RFI shielding.
One example of our EMI shielding is an Optolite IR, an infrared acrylic filter with a broad band which transmits infrared radiation. This form of EMI shielding can be used in photometric systems which operate in environments with high radiation levels.
Optolite IR EMI shielding or RFI shielding eliminates the visible spectrum and so in effect makes the system better by boosting the signal-to-noise ratio. Typical applications for this type of RFI shielding include security systems, presence sensing devices, proximity sensors and scanners. This type of EMI shielding has excellent transmittance and a non-glare finish.
We are an EMI shielding authorised distributor for polarising filters and custom-made RFI shielding polarising and non-polarising filters which increase the readability of electronic displays. That’s because our optical filters enhance contrast and reduce reflections while at the same time providing protection and improving the overall appearance of the display.
Our EMI shielding is produced to the specifications our customers require, and there is only a short delivery time for our RFI shielding. Among the many customers who use our shield material are organisations working in the aerospace, defence, science, medicine, electronics, stress analysis and photographic industries.
You can read more about our optical filters and other products on our user-friendly web site. We’re also delighted to announce our new online store is now open, so many of our products can now be ordered online through our secure online shopping system.
Other exciting new developments include the launch of a range of optical filter windows, and an extended range of light diffusion filters. Again, full details of these products can be found on our web site.
We’re based in Maidenhead, in the south of England, and will be happy to hear from you by phone or fax to discuss your needs in details. Alternatively, feel free to fill in the contact form on our web site, and we’ll be happy to receive any questions you may have. As specialists of long standing, we’re bound to have the answers – and the products you’re after.
 
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