Doug Sharpe President of Elasto Proxy
Electromagnetic interference (EMI) can disrupt military electronics and endanger the lives of the war-fighters who depend on them. The causes of EMI are numerous, and include everything from electric motors and radio transmitters to computer circuits and power lines. Electronic jamming or intentional EMI (IEMI) also concerns military planners. Military radios, cameras, sensors, and telecommunications systems can experience interruptions during battlefield conditions, or suffer permanent damage.
Several global incidents underscore these concerns. In May 2012, over 500 airplanes in South Korea experienced global positioning system (GPS) failure from electromagnetic fields that were traced to the North Korean city of Kaesong. Two years earlier, North Korea reportedly purchased truck-based systems that could jam GPS signals. IEMI weapons were used in Chechnya against the Russian military, and in Moscow against a standard telephone system.
Environmental Sealing and EMI Shielding
Military environments are especially challenging, so technical buyers and electronic designers need to select materials with the right balance of properties. Particle-filled silicones are elastomeric compounds that combine the advantages of silicone with the electrical characteristics of metals. An inert, synthetic rubber, silicone offers thermal stability over a wide temperature range and resists ozone and ultraviolet (UV) light. Silicone rubber also resists water, and can be formulated to impart electrical conductivity.
When filled with metal particles, silicone compounds can be used to fabricate gaskets that provide both environmental sealing and EMI shielding. Metal fillers include particles made of pure silver, silver-plated aluminum, or silver-plated copper. Conductive silicones that are filled with silver-plated glass, nickel-plated graphite, and carbon black are also available. Before choosing a compound, however, buyers and designers need to understand application requirements and applicable military standards.
MIL-DTL-83528C is a general specification from the U.S. Department of Defense (DOD) for electrically-conductive elastomeric shielding gaskets. Released in January 2001, it supercedes the MIL-G-83528B standard that is sometimes still referenced in data sheets. MIL-DTL-83528C sets requirements for part identifying numbers (PIN) and contains a Material Type section with lettered designations for both silicone and fluorosilicone compounds.
For example, Type B materials are silver-plated, aluminum-filled silicones that are capable of 100 dB of plane wave shielding effectiveness at 10 GHz with a continuous use temperature range from -55°C to +160°C. Conductive fluorosilicone shielding materials also carry shielding effectiveness and temperature specifications, and offer resistance to solvents and jet fuels. By understanding your sealing and shielding requirements, an EMI gasket fabricator can recommend the right material.
How Can We Help You?
Does your project require a Type B silver-plated, aluminum-filled silicone with a Qualified Products List (QPL) acknowledgement from the Defense Logistics Agency (DLA)? Elasto Proxy can source cost-effective conductive compounds for you, and them custom fabricate high-quality EMI gaskets. Our solutions providers can also source EMI shielding materials that are designed to meet the requirements of other parts of the MIL-DTL-83528C specification
For over 25 years, Elasto Proxy has custom-fabricated specialty seals and custom insulation for military and defense. How can we help you with EMI gasketing? Contact us today, or join the conversation about this blog entry on LinkedIn, Facebook, Google+, and Twitter. Elasto Proxy has a YouTube channel, too. There, you’ll find our Capabilities video, as well as other informative content. Finally, please subscribe to our free e-newsletters.