For electronics used in critical applications, there can be zero allowance of electromagnetic interference (EMI). These include medical, military and aerospace electronics, as well as mass transit systems and vehicular control systems. EMI can come from both manmade and natural sources, but their resulting disturbances can lead to data loss, system failure, or even loss of life.
Electromagnetic energy (EME) is crucial for engineers to understand so that interference can be avoided or minimalized. Designing gaskets without knowledge of EME can mean parts that lack adequate protection in the radio frequency (RF) spectrum, and also interfere with wireless communications with their signal transmission.
As well as a knowledge of EME, in order to best combat electromagnetic interference, the source of the interruption must be identified.
Major Sources of EMI
- Ambient EMI: This type of interference is caused by man-made and natural sources. Man-made ambient electromagnetic interference includes arc welders, brush motors, and computer circuits. Natural sources of ambient EMI include lightening, solar magnetic storms, and the Earth’s magnetic field flux.
- Power Quality EMI: This type of interference can be the result of a blackout or brownout, electrical fast transitions (EFT), electrical noise or faults on the power line, and voltage sags or spikes.
Specific challenges in the interference of electromagnetic energy of applications for railroad and mass transit systems, medical equipment, and military applications must also be considered. Individual EMI for these applications are:
Railroad and Mass Transit Systems
- Emissions from train control and propulsion systems
- High voltage contact switching
- Third rail shoes
- Train signaling and control systems
- Electrical equipment in surgical units
- Life support devices
- Patient telemetry and assistance equipment
- X-ray machines
- Electronic warfare
- High-altitude nuclear electromagnetic pulse (HNEMP)
- High-power microwave weapons E-bombs EMP cannons
EMI Shielding Gasket Materials
Electromagnetic shielding gaskets are devices that protect electronics from interference. In the past, EMI shielding was made from metal sheets that formed into shapes to fit electronic housings and enclosures.
Flexible metal screens, metal wires, and metal foams are the EMI shielding materials most commonly used today. Metallic ink coatings are also frequently applied to the interior of electronic enclosures to provide EMI shielding.
For designers who need to meet a variety of challenges, silicones filled with metal or metal-coated particles may be the solution. The versatility of silicone blocks EMI, provides conductivity, and ensures sealing from harsh environmental conditions.
Due to innovations in silicone compounding, the demanding requirements of specific projects can be met with particle-filled elastomers. Unlike previous shielding elastomers, new materials contain adequate metal filler to ensure EMI shielding and electrical conductivity. The elastomers are also cost-effective since they don’t deform or stretch during production, reducing waste and product malformation. For applications that require added strength, various high-durometer, silicones can be installed and used. This helps to prevent brittleness and tearing during EMI gasket fabrication.
Electromagnetic interference can be an obstacle for any electronics, but in critical applications, it is imperative to limit or nullify its occurrence. When designing for medical, military and aerospace electronics, as well as mass transit systems and vehicular control systems, it is crucial that EMI from both manmade and natural sources be mitigated. The varied choices of electronic shielding materials allows design to be both functional and protected from EMI.