The smallest details are often the ones that will determine whether an EMI hardened enclosure will be compliant or will not meet EMC requirements. That’s especially true when it comes to the many bolts, screws, rods or shafts that need EMI/RFI shielding or grounding. When you have to attenuate a signal or ground components of an enclosure, don’t forget the EMI/RFI wire mesh grounding or conductive washer. Here’s what you need to know:
EMI/RFI Wire Mesh Grounding Washers
EMI/RFI wire mesh grounding washers are made from wire mesh socks that look somewhat like thin knitted metal hoses before being compressed in a die to form the washer. By altering the weight of the metal sock, various densities of washers can be made to increase or decrease the resilience. For example, a sock with a metal density of 15 to 20 percent will create a washer that can fill a gap or seam under pressure. A starting density of 30 to 40 percent can create a washer which will snuggly fit a shaft or rod, which when compressed will act as a slip-ring to ground a rotating shaft to a metal enclosure. This gives the shaft needed EMC properties, eliminating unwanted EMI/RFI noise.
Besides needing to vary the thickness and density of EMI/RFI wire mesh washers, specific applications and environments often call for specific metals used in the mesh socks. MAJR Products, for example, offers wire mesh grounding washers made of Monel, aluminum, silver plated brass, tin plated copper clad steel or beryllium copper. By varying the materials, density, thickness and inside/outside diameters, there are countless configurations and options available for any need or application within a hardened enclosure for both military and commercial uses. This gives the engineer an impressive lineup of options. Popular applications include:
- Signal and power connector panels
- Door handle shafts
- Hinge hardware
- Grounding metal structures (i.e. equipment racks) to an electronic or electrical enclosure
EMI/RFI Conductive Elastomer Washers
Conductive elastomer washers for EMI shielding and grounding are molded elastomer filled with conductive particles to provide the electrical conductivity and broadband shielding. They are made of a variety of materials including silicone, fluorosilicone, or EPDM which stands up to fuel or chemical contamination. Their conductive particles can be aluminum, copper, nickel or silver, used singularly or in various compound combinations. The various conductive materials used changes the performance characteristics of the washers and, along with varying the thicknesses, allows the washers to achieve a desired hardness and operating temperature range while accommodating differing MIL SPEC M83528/012X requirements.
- To provide moisture sealing,
- As a shock absorber,
- To enable electrical grounding.
Like their wire mesh cousins, conductive elastomer washers can be made in almost any ID or OD size.
As stated earlier, the smallest details are often the most important when achieving attenuation and grounding in hardened enclosures. With so many choices of materials, applications, where they are used and differing FCC, military and UL requirements, it’s important to use the right washer made of the right materials in the right size for any specific application. There will be times when a conductive washer should be used over a wire mesh washer, or where silver is the preferred conductor over Monel or aluminum. But that’s the beauty of EMI/RFI grounding washers – they’re as adaptable as need be.
For help in determining what and how to use when, please contact the engineers at MAJR Products by calling 877-625-6033, or feel free to ask questions using the form on either of our web pages for EMI/RFI Wire Mesh Washers or Conductive Silicone Washers.