Quietshield Gaskets & Shielding - Spectrum Control

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Shielding Theory and IntroductionShielding TheoryElectromagnetic shielding is used to prevent electromagneticsignals such as radio signals from leaving or entering a boxor enclosure. Signals inadvertently emitted by an electronicdevice can cause distortion or interruption in normal radiocommunications in a localized area. This is the basis ofmost laws and regulations concerning electromagneticinterference. In addition, normal radio signals can causeunprotected electronic devices to malfunction. Dependingon the device’s function, a malfunction in the device couldbe a minor inconvenience such as static on a radio, or lifethreatening such as the malfunction of a life support systemat a hospital.IntroductionThe electromagnetic shield in most cases is the electronichousing itself. The housing/shield forms a metal cage aroundthe electronic circuits in a device. Most of the electromagneticsignal is absorbed with a small portion (3 to 10 dB) of thesignal reflected off the metal housing. Most of the absorbedsignal creates alternating currents at radio frequencies whichtravels on the surface of metal. This allows theelectromagnetic shield to keep signals from outside theenclosure on the outside of the shield and signals frominside signals on the inside of the shield.The shield will continue to function as long as there areno holes in the electromagnetic shield which would allowthe 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 andfrom electronic devices. Doors and covers are needed toget access to components to maintenance, service, andkeypads may also be required. The problem is that all ofthese items cause openings in the shield which reducethe performance of the shield.Special devices such as shielding gaskets, shieldingventilation panels, shielded filtered connectors, and shieldedswitches minimize the effect of a hole in the shield.The length of the hole and wavelength of the signalthat needs to be shielded are the major factors determiningthe shielding effectiveness of an electronic enclosure. Thedistance between spotwelds, or screws which hold a metalhousing 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 thefrequency of concern when designing shielding.Aperture versus frequency charts can give a roughestimate of the shielding effectiveness of a metallicelectronic housing.Aperture Length (Wavelength - Inches)100.10.1..1.0160 dB80 dBSHIELDING EFFECTIVENESS40 dB 20 dBWavelengthtoFrequency.001100 KHz 1 MHz 10MHz 100MHz 1GHz 10GHz 100GHzShielding Effectiveness (dB)110100908070605040302010TYPICAL SHIELDING EFFECTIVENESS00 100 200 300 400 500 600 700 800 900 1000Frequency (MHz)Frequency (MHz)Test Methods: ASTM D-4935-89Test Fixture: Flanged coaxial transmission line4SPECTRUM CONTROL INC. • 8031 Avonia Rd. • Fairview, PA 16415 • Phone: 814-474-2207 • Fax: 814-474-2208 • Web site: www.specemc.comSPECTRUM CONTROL GmbH • Hansastrasse 6 • 91126 Schwabach, Germany • Phone: (49)-9122-795-0 • Fax: (49)-9122-795-58
Quietshield Fabric-over-Foam GasketsFeatures■■■■■Maintain shielding effectiveness across seams or gapsShielding Effectiveness (SE) of 70 - 100 dB between1 MHz to 18 GHzFlexible and conformableNo creasing or tearingLightweight materialProfile GasketsQuietshield EMI/RFI Gaskets maintain shielding effectiveness(SE) across a seam or gap in the electronic equipment’sshielding material.Quietshield gaskets provide unique solutions to yourmost stringent shielding, grounding, ESD and packagingrequirements. It’s the cost-effective avenue for creativity indesign. These gaskets consist of polyurethane foamcombined with highly conductive fabrics. Specially designedpolyurethane foam is soft, resilient and provides the perfectfit. Our gaskets are made with seven different types offabric plating and two types of thermal adhesive, standardor flame retardant. Our flame retardant adhesive complieswith UL94VTM-1 and VTM-0. If necessary, the polyurethanefoam core can also be plated with Cu and Ni to provideadditional conductivity.Fabric-over-Foam Gaskets, unlike elastomer or fingerstrip gaskets, provide softness for easy application witha variety of materials and designs at low cost. The bestquality with high conductivity, low electrical resistance andminimum oxidation can be achieved by using gold gasketswith additional gold plating to provide superior shielding.Profile gaskets are currently available in a variety of shapesand lengths. Spectrum Control’s gaskets provide a variety ofapplications with lightweight and flexible solutions. Variousthicknesses and shapes are available. These range fromcommonly used ones such as rectangular and “D” shape,to uncommon ones such as FL-shape (folding leaf) andDD-shape (Double DD-shape). We are able to producegaskets with different shapes and sizes, based upon thecustomer’s requests.The mounting style available for most profile gaskets ispressure sensitive adhesive.These adhesives allow simpleplace and press mounting on smooth and clean metalsurfaces.The parts can be cut to the desired length withcommon scissors or ordered to the exact length required.The adhesive provides high strength with aggressive initialtack, which increases in strength over time or after exposureto elevated temperatures.I/O GasketsSpectrum Control offers a complete line of standard andcustom I/O connector Electromagnetic Shielding Gaskets.I/O gaskets are flat gaskets used to provide a groundcontact between a metal connector and the electronicenclosure or mating connector. They insure that the shieldremains continuous from the input/output cable to theelectronic enclosure.I/O Gaskets are available in the same materials as thefabric-over-foam profile gaskets, or as all-metal waved gaskets.Spectrum Control’s line of metal waved gaskets isdesigned to minimize the gaps between a D-Sub connectorand the panel it is mounted to. These gaskets ensure themaximum “gap length” will not exceed the wave pitch, 0.200"(5.08 MM), even on surfaces with poor flatness. This ensuresmaximum filter performance to 1GHz and beyond.TestASTMTestPerformanceShielding Effectiveness, dB 70-100Compression Set % D3574 7.9Compression Load Deflection, D3574 15PSICompression at Max Load 60%Water Absorption D1667 5.8(Foam Only) %Abrasion Resistance, D3885 Excellent3,000 CyclesUltra Violet Exposure D750 No Visible ChangeFungus Exposure G21 Small GrowthOperating Temperature C D746 -40˚ to +90˚Flammability Rating UL94 VTM1, VTM0Conductivity, OHMS/SQUnexposed 0.2Weathered (100 HRS) 0.3Fungus 0.2Salt 0.2DC Conductivity.2 Ohms/SQTensile Strength80 lb/inSPECTRUM CONTROL INC. • 8031 Avonia Rd. • Fairview, PA 16415 • Phone: 814-474-2207 • Fax: 814-474-2208 • Web site: www.specemc.comSPECTRUM CONTROL GmbH • Hansastrasse 6 • 91126 Schwabach, Germany • Phone: (49)-9122-795-0 • Fax: (49)-9122-795-585
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Page 9 and 10: Wire Mesh GasketsSpectrum Control
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Quietshield Gaskets & Shielding - Spectrum Control

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