Conformity Magazine - August 2008 - (Page 48)

• Nickel-coated carbon (Ni/C) • Silver (Ag) Elastomer options include: • Silicone rubber • Fluorosilicone rubber • Ethylene propylene diene monomer (EPDM) • Fluorocarbon rubber, Viton, or Fluorel Oriented wire is a conductive elastomer in which individual conductive wires of either Monel or aluminum are impregnated into solid or sponge silicone. Newer types of RF gaskets include conductive fabric-over-foam, form-inplace conductive elastomers, and mold-in-place conductive elastomers gaskets. Selecting the Proper Materials Many factors affect the proper selection of RF gasket materials. The following list identifies some of the key issues that must be considered. The list has been developed over many years and includes essential considerations for choosing RF gasket materials to ensure that the materials achieve their advertised specifications. • Operating frequency • Materials compatibility • Corrosive considerations • EMC compliance specification (SAE, FMC, GM, etc.) • Operating environment • Load and forces • Cost • Attenuation performance • Fastening and mounting methods • Storage environment • Nuclear, biological, chemical (NBC) • Cycle life • Shielding, grounding, etc. • Electrical requirements • Materials thickness/alloy • Space and weight considerations • Product safety • Recyclability As operating frequencies continue to increase, conventional RF shielding may not perform as well as in the past. Therefore, materials such as RF absorbers are being employed to decrease high frequency emissions and increase immunity. RF absorbers are also being used in conjunction with BLS to better handle extremely high frequency issues. Longevity of the RF gasket material is affected by many factors. Compression, vibration, and number of cycles all affect longevity. In addition, whether the gasket is in shear or compression can play a role. However, galvanic compatibility is arguably the most important factor for the longevity of RF performance, especially in the automotive environment. Corrosion is a natural phenomenon that converts material from an unstable to a stable state. When corrosion is caused by an electrochemical reaction in the presence of a dissimilar metal, it is called galvanic corrosion. Several conditions can increase galvanic corrosion, including two dissimilar metals at a junction, electrical contact between two dissimilar metals, or the presence of an electrolyte. To reduce the effects of the dissimilar metals, either plate the metals or choose RF gasket materials that are galvanically compatible. Conclusion Today’s automobiles represent an impressive but complex electronic platform, and we can expect that they will only become more sophisticated and complex as time goes on. The control of electromagnetic interference is essential, not just to comply with mandatory requirements but to ensure the proper functioning of the entire system. Devices installed within automobiles and devices brought on board by passengers must not interfere with each other. This is especially true for the safe operation of the vehicle. The achievement of complete electromagnetic compatibility is essential. Proper design can only go so far to achieve EMC, especially as frequencies increase. The effective use of RF shielding, ferrite filters and RF absorbers can all play an integral role in meeting today’s regulatory requirements and in ensuring proper functionality. Gary Fenical is a technical sales representative at Laird Technologies, and can be reached at gary.fenical@lairdtech. com. Randy Andreen is general manager of the Telematics business unit at Laird, and can be reached at randy.andreen@ lairdtech.com. FAST Link www.conformity.com/2060 8 Conformity AUGUSt 2008 http://www.conformity.com/2060

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Conformity Magazine - August 2008 Contents Editor’s Note FCC Seeks Comment on Reauction of 700 MHz D Block Commission Cracks Down (Again!) on Junk Fax Marketer Canada Levies Fees for Public Safety Radio Spectrum FDA Issues Guidance on Medical Device Tracking Greenpeace Challenges Video Game Manufacturers The IEEE EMC Society: A Proud History of Accomplishments ESD Open Forum An Update on Changes to the Automotive ESD Standard, ISO 10605 Modeling of Radiated Electromagnetic Disturbances in Automotive Applications Design Issues in Automotive Radio Frequency Systems IEEE EMC Symposium IEEE 2008 Show Preview Exhibitors Buyer’s Guide Product News Most Eco-Friendly Companies Updated Standards List For the EU’s Pressure Equipment Directive Commission Issues Updated Standards List For Directive on Gas-Fired Appliances HHS Releases Fact Sheet on U.S. Imports from China Customs Agents Seize Holiday Lights IEEE PSES Symposium Set for October CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Product Reviews Advertisers

Conformity Magazine - August 2008

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