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Measurement Testing
A Resource Dedicated to Environmental Testing, EMC Testing, Vibration Testing and related areas
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Mjr
Site Admin
Joined: 13 Jul 2005
Posts: 294
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 Posted: Tue Nov 15, 2005 9:01 pm Post subject: QUIETSHIELD™ from Spectrum Control |
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QUIETSHIELD™ from Spectrum Control :
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QUIETSHIELD™ EMI/RFI Gaskets maintain shielding effectiveness (SE) across a seam or gap in the electronic equipment's shielding material. They consist of metallized fabric wrapped around a neoprene elastomer core. This provides a low cost solution, which allows you to utilize many material combinations and product designs never before practical. QUIETSHIELD™ gaskets provide unique solutions to your most stringent shielding, grounding, ESD and packaging requirements. It's the cost-effective avenue for creativity in design. Profile gaskets are currently available in four shapes: 'D', 'R', 'L', and 'P'. Spectrum's proprietary manufacturing method for making profile shielding gaskets is also ideally suited to custom profiles. New shapes and sizes can be manufactured with minimal lead times and low tooling costs. Changes can be easily made to the rubber core material, type of fabric or foil covering, and adhesive systems. Shielding specialists are at your disposal to help you with your custom designs. These specialists use design for manufacturability concepts to produce designs which meet your specific requirements at a reasonable cost.
Product Facts
* Maintain Shielding Effectiveness across seams or gaps
* SE of 70 - 100dB between 1 MHz to 18 GHz
* Exclusive Quiet Contact provides instantaneous shielding effectiveness upon initial contact of gasket
* Flexible and conformable
* No creasing or tearing. Fabric tensile strength up to 80 lb./in.
* Lightweight material of 2.3-2.8 ounces/sq. yd.
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Shielding Theory
Electromagnetic shielding is used to prevent electromagnetic signals such as radio signals from leaving or entering a box or enclosure. Signals inadvertently emitted by an electronic device can cause distortion or interruption in normal radio communications in a localized area. This is the basis of most laws and regulations concerning electromagnetic interference. In addition, normal radio signals can cause unprotected electronic devices to malfunction. Depending on the devices function, a malfunction in the device could be a minor inconvenience such as static on a radio, or life threatening such as the malfunction of a life support system at a hospital. The electromagnetic shield in most cases is the electronic housing itself. The housing/shield forms a metal cage around the electronic circuits in a device. Most of the electromagnetic signal is absorbed with a small portion (3 to 10dB) of the signal reflected off the metal housing. Most of the absorbed signal creates alternating currents at radio frequencies travels on the surface of metal. This allows the electromagnetic shield to keep signals from outside the enclosure on the outside of the shield and signals from inside signals on the inside of the shield. The shield will continue to function as long as there are no holes in the electromagnetic shield which would allow the currents to flow from one side of the shield to the other. Holes are a necessity in an electronic enclosure. Connectors, wires, and cables are needed to transmit information to and from electronic devices, Doors and covers are needed to get access to components to maintenance, service, and keypads may also be required. The problem is that all of these items cause openings in the shield which reduce the performance of the shield. Special devices such as shielding gaskets, shielding ventilation panels, shielded filtered connectors, and shielded switches minimize the effect of a hole in the shield. The length of the hole and wavelength of the signal that needs to be shielded are the major factors determining the shielding effectiveness of an electronic enclosure. The distance between spotwelds, or screws which hold a metal housing together count as long narrow holes. Higher frequencies (lower wavelengths) flow more easily through smaller holes, and so the highest frequency needed to be shielded is the frequency of concern when designing shielding. Aperture versus frequency charts can give a rough estimate of the shielding effectiveness of a metallic electronic housing.
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