Radio Frequency Suppression
Often, when Radio Frequency sources are located inside a shielded cavity, the RF can set up resonances within the cavity, and interfere with the signal or create crosstalk with other adjacent devices. Lossy materials can be strategically placed within the cavity or housing to attenuate resonances and eliminate crosstalk.
Cuming Microwave manufactures several materials which can be used for RF suppression. These sheet materials, either dielectric carbon-based form or magnetically-loaded rubber sheets, have high RF loss and can attenuate RF fields on a surface or inside a cavity. These materials are designed to attenuate electromagnetic waves which resonate in a cavity.
There are two general types of RF suppression absorbers: dielectric (carbon based), and magnetic. Dielectric absorbers work on the electric field, and because they are resistive, they have high dielectric loss tangents and can directly attenuate currents traveling on a metallic surface. Magnetic absorbers work on the magnetic field, which has its maximum near a conducting surface. Magnetic absorbers attenuate RF through magnetic hysteresis loss which occurs when an alternating current flips the polarity of tiny magnetic crystal domains in the material. Both types are broadbanded in that they are lossy and will attenuate over a wide frequency range; they will work better at shorter wavelengths as they have more electrical thickness.
Carbon dielectric absorbers are lower in cost per unit area, and are lighter in weight. However they require a greater thickness than a corresponding magnetic absorber to work at a particular frequency. They are electrically resistive and should not come in contact with anything they might short out. Carbon absorbers can be laminated with a rubberized fabric to provide a non-conductive surface. Magnetic absorbers are heavier, more expensive, but thinner, and because they are not conductive, they can be placed anywhere.
Cuming Microwave supplies these materials in sheet form, and can custom die-cut or waterjet-cut parts to a drawing. These materials are often supplied with a pressure-sensitive adhesive backing (peel-and-stick), which works in most applications. However, in extreme conditions—elevated temperature, vibrations, etc, we recommend more durable adhesives to attach these materials.
Foam Materials
(320-2) C-RAM MT A thin carbon/urethane foam sheet available in standard thicknesses from .125 to .75 inches, and in several grades of varying resistivity
MT Dielectric Data
(320-3) C-RAM AR A reticulated (very open cell) carbon loaded foam available in a broad range of thicknesses. C-RAM AR is designed with a resistivity gradient and can double as an absorber of free-space planar waves
(320-1) C-RAM LF A series of graded multilayer urethane foam sheet materials, designed to provide -20 dB reflectivity reduction over a broad frequency range
For a list of additional products, please see our 320 Series.
Magnetic Materials
(310-1) C-RAM FLX A series of magnetic silicone rubber sheet materials, designed to provide better than -20 dB reflectivity reduction at a resonant frequency, ranging from 800 MHz to 35 GHz
(310-4) C-RAM GDSS A silicone sheet material which has high loss over a broad microwave frequency range
(310-11) C-RAM GDX A silicone sheet material which has high loss over a broad microwave frequency range
(330-2) C-RAM RGDS Available in several grades, RDGS is a silicone sheet which is heavily loaded and works well at lower microwave frequencies
(310-5) C-RAM FDSS A silicone sheet material which has high loss below 1 GHz
(310-7) C-RAM FF-2 A very high loss material in the upper UHF range
(310-6) C-RAM FFS A very broad lossy sheet material with moderate loss across UHF and microwave frequencies
Magnetic Materials Dielectric Data
For a list of additional rubber materials, please see our 310 Series.
For a list of additional castable materials, please see our 330 Series.
Application Note 300-11 - Room Temperature Curing Versions of Iron Loaded Epoxies
Application Note 300-13 - C-RAM Millimeter Wave
Application Note 300-17 - MS Pressure Sensitive Adhesive Option for Absorber Sheet
