Shielding materials such as gaskets often provide an environmental seal in addition to suppressing radio interference. These are commonly rubberized materials, such as silicone rubber or fluorosilicone rubber with embedded silver-plated silver or copper particles to enhance conductivity. They are formed into sheets, such as 12 x 12 in., which can then be die-cut into the shapes and forms needed to seal an enclosure. In addition, nickel and graphite are more commonly used in EM/RF shields for their dimensional stability. For example, nickel-graphite-filled silicone rubber is a compressible material that provides a high level of EM/RF shielding; it also forms a reliable environmental seal due to the compression. Shielding solutions continue to evolve over time, with newer base materials (such as graphene) attracting a great deal of attention for its light weight and capability of achieving high SE levels.

Depending upon the requirements, some applications may require EMI/RFI filters (Fig. 2) to screen interference, but these are usually more severe cases. Such filters add weight and cost; typically, lower-weight, lower-cost shielding solutions are preferable, such as simple meshes or shielding gaskets. A mesh can be effective at blocking EMI/RFI as long as the size of the mesh is smaller than the wavelength of the frequencies of interest. If it is larger than the wavelengths of the signals of interest, those signals will get through, although they may be somewhat attenuated by the partial action of the mesh.

2. In some extreme cases, EMI/RFI filters may be needed to perform frequency-selective attenuation of unwanted signal energy in an electronic design. (Photo courtesy of Tech-Etch.)

How much EMI/RFI shielding can be achieved by a gasket or other shielding material at a given frequency? The amount of shielding is a function of the material and the frequency of concern, as well as the form in which the shielding material is applied—such as in the form of a shielding window or gasket. Most suppliers of shielding products, like Chomerics, will work closely with customers to even die-cut shielding gaskets as needed for different product enclosures. As an example, Chomerics offers a 200-page-plus online catalog devoted to shielding products, with materials that include shielding vents and windows, shielding adhesives, wire mesh gaskets, and cable shielding.

The firm also offers design services and supports its analysis through computer-aided-engineering (CAE) tools, such as finite-element-analysis (FEA) software. While shielding solutions tend to vary by material and by frequency, the firm is best known for its standard CHO-SEAL 1310 conductive elastomer material. This provides better than 60 dB SE from 200 MHz to 10 GHz, with higher values of SE available as needed. Similarly, Leader Tech offers a large catalog of conductive elastomer materials for free download from their website.

Due to its expanding use of RF/microwave technologies, the modern automobile is becoming one of the more challenging electronic environments. With its many different systems—from high-frequency (HF) through millimeter-wave frequencies—newer automobiles are resident to a large number of RF/microwave signals within a tightly confined space. That space is also subject to shock, vibration, and wide temperature extremes.

Problems from EMI in a newer automobile can stem from collision-avoidance radar systems, from built-in Global Positioning System (GPS)/navigation systems, fuel control systems, adaptive cruise control systems, and electronic ignition systems, just to name a few. Shielding materials are now essential components in most automotive electronic systems, for proper compliance and operation of those systems along with their coexistence with other automotive electronic systems and other external electronic systems, such as wireless garage-door openers.

Editor’s Note: The companies mentioned in this report are only a few examples of many high-quality suppliers of shielding materials and services. Any search for such suppliers can be made easier with the aid of the Microwaves & RF Product Data Directory.