EMI gaskets

July 1, 1997

7 Min Read
EMI gaskets

Spotlight on IV Components


EMI gaskets

The shielding performance of a spiral gasket has been combined with the sealing of an elastomer. The Flexi-Shield gasket resists compression set, comes in a very-low-force version, and is as easy to handle and use as a rubber elastomer. It is groove mounted and flexes easily to conform to various shapes. The spiral design flexes to fill uneven joint surfaces and has no pieces that could break off and short out equipment. Standard materials are stainless steel and beryllium copper, and tin plating is available for better conductivity or corrosion resistance. Cross-sectional diameters range from 0.063 to 0.125 in. Spira, 12721 Saticoy St. S., North Hollywood, CA 91605. (818/764-8222)


Grounding cable clamps

Lightweight resin-made grounding cable clamps are copper plated to ensure simultaneous fastening and grounding for power/signal coaxial and braid shielded cables in the diameter range of 0.118 to 0.315 in. The elasticity of the resin material and the high conductivity of the copper plating provide stability of the electrical contact, even under conditions of heavy vibration. Intermark Inc., One Penn Plaza, Ste. 4526, New York, NY 10119. (212/629-3620)


Combination hook and stick shielding

Combination hook and stick EMI/RFI shielding provides good durability because the leading edge of the gasket actually hooks over the mounting flange for full protection. With one side hooked over the flange, and the opposing side attached by pressure-sensitive adhesive, beryllium copper hook-on shielding offers a self-locating, secure installation for bidirectional applications. The gaskets provide EMI/RFI shielding to 100-dB attenuation levels. Smooth to the touch, they require only a low closing force while providing 360° of snag-free operation. Tech-Etch Inc., 45 Aldrin Rd., Plymouth, MA 02360. (508/747-0300)


Shielding structure material

An RFI-shielding structure material is available in any shape and in a variety of sizes for use as wall-to-wall shielding. MSD-4 can also be used for discrete wraparound components to envelope sources of RFI emissions within a digital system. The material provides system protection in attenuating radiated electromagnetic interference between systems that originate this interference, as well as systems susceptible to such interference. MSD-4 shielding structures diminish the strength of radiated, extraneous noise, and each structure is custom configured to assure attenuation compatibility within any CB matrix. The structures may function as stand-alone shields or be designed into the matrix of the manufacturer's membrane touch switch. Topflight Corp., P.O. Box 2847, York, PA 17404. (800/233-9836)


Form-in-place gasket

A form-in-place EMI gasket is a silicone elastomer filled with a silver-plated copper conductive particle that cures to create a flexible EMI shield and environmental seal. The gasketing is applied on a one- or two-dimensional plane to metal or plastic housings by means of a computer-controlled process that precisely dispenses the material onto flanges as narrow as 0.030 in. It eliminates the expensive tooling costs associated with molded conductive-elastomer designs. Shielding effectiveness is 75 dB at 10 MHz. Tecknit, 129 Dermody St., Cranford, NJ 07016. (908/272-5500)


RFI/EMI environmental seal

A double-bulb elastomer shielding gasket ensures protection from moisture and outside contaminants for electronic enclosures. The tandem conductive portion is a highly conductive coextruded outer layer that provides over 100 dB of shielding effectiveness up to 1 GHz. Vanguard Products Corp., 87 Newton Rd., Danbury, CT 06810. (203/744-7265)

Optical filters

H-100 thermosetting polyester and H-911 allyl diglycol carbonate EMI/RFI optical filters are chemical- and scratch-resistant plastics with excellent optical qualities. The optional low-reflectance surface finish on the filters is cast into the material so that it can't be rubbed or cleaned off. Both plastics are available in a wide variety of thicknesses. The H-100 filters can be custom color-matched to reduce color change due to EMI/RFI coatings. Homalite, 11 Brookside Dr., Wilmington, DE 19804. (800/346-7802)


EMI shielding products

A company's EMI shielding products are made from highly conductive claddings, resilient urethane foam, structural laminates, and corrosion-resistant coatings. The company's full line of EMI products are designed to meet the needs of engineers and designers in the medical electronics industry. Products include gaskets, laminates, envelopes, and fabric tapes. Schlegel Corp., 1555 Jefferson Rd., Rochester, NY 14623. (800/204-0863)


Photochemically etched shielding

A line of photochemically etched EMI/RFI shielding and filter screens protect components and provide electrical grounding. The shields are hand formed and can be custom designed to meet the most stringent customer requirements. Also available are custom bend lines, logos, soldered or welded corners, and RF cans with removable top covers. The manufacturer provides a broad variety of standard shielding materials and metals, including stainless steel, brass, and copper. In stock are over 2000 material part numbers in thicknesses from 0.0003 to 0.90 in. Photofabrication Engineering Inc., 500 Fortune Dr., Milford, MA 01757. (508/478-2025)


Plated nylon gaskets

Self-terminating plated nylon-yarn-over-foam EMI gaskets provide minimum shielding effectiveness of 90 dB at 500 MHz to 10 GHz. Soft Knit gaskets feature closely stitched covers knit of metallized nylon yarn over UL 90 V-0­compliant neoprene sponge elastomer. With 95% minimum coverage, the low-closure-force gaskets provide optimum contact for an effective radiation barrier, which results in shielding effectiveness. Instrument Specialties Company, Inc., P.O. Box A, Delaware Water Gap, PA 18327. (717/424-8510)


Custom composite gaskets

Custom composite EMI/RFI, EMP, and environmental assembled gaskets are produced with a die-cutting method that allows the manufacturer to produce various gasket sizes with minimal tooling and material waste. The gaskets are produced by die-cutting four rubber strips and assembling and bonding them with a rubber adhesive, thereby eliminating the material waste that is to be expected from die-cutting a rectangular shape with a large center cutout. These gaskets work well under low closure force and with uneven flange surfaces. A Monel wire provides the EMI/RFI and EMP seal, and a sponge rubber provides the environmental seal. PressCut Industries, 2828 Nagle St., Dallas, TX 75220. (800/442-4924)


Ferrite RFI/EMI suppressors

A general-purpose ferrite formulation is available in a wide range of sizes for suppression of interference frequencies up to 1 GHz. Cable widths up to 64 conductors can be accommodated with adhesive or mechanical mounting options for any surface. Extrawide styles permit double looping through the same openings for intensifying the impedance in a frequency range around 100 MHz. Data signals are allowed to pass unimpeded as the higher-frequency energy is dissipated. FerriShield Inc., 350 Fifth Ave., Ste. 7505, New York, NY 10118. (212/268-4020)


EMI gaskets

EMI gaskets, featuring a conductive jacket-over-urethane-foam design, meet the stringent shielding and mechanical performance requirements of today's electronic enclosures. Soft-Shield 5000 self-terminating gaskets provide greater than 90 dB EMI shielding from 30 MHz to 1 GHz and greater than 75 dB at 10 GHz. Closure force and compression/deflection characteristics are less than 1 lb/in. The gaskets are available with a pressure-sensitive adhesive tape for easy attachment. Chomerics, 77 Dragon Ct., Woburn, MA 01888. (617/935-4850)


Special-purpose filters

Special-purpose contrast enhancement filters can be designed to incorporate EMI/RFI and ESD protection to help equipment manufacturers meet regulatory requirements. Duralan II filters can incorporate various conductive materials that can either absorb and ground or reflect radiated electronic noise. EMI/RFI protection can be achieved at various frequencies from 10 MHz to 15 GHz, depending on design options. The filters are suitable for use with most active and passive displays. They can also include polarizers, security louvers, and other specialty materials. Silver Cloud Manufacturing, 525 Orange St., Millville, NJ 08332. (609/825-8900)


Custom converting

A company offers various shielding options to reduce or eliminate EMI/RFI and electrostatic discharge from electronic components. As custom converters, the company works from customers' blueprints or with their engineers to develop shielding methods that best fit their requirements and manufacturing constraints. The company will also supply sample materials or prepare prototypes for testing in customer components and/or component assembly equipment. GM Nameplate, 2040 15th Ave. W., Seattle, WA 98119. (800/366-7668)

Return to the MPMN home page

Sign up for the QMED & MD+DI Daily newsletter.

You May Also Like