RF Suppression

Often, when RF 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 are sheet and castable materials which have high RF loss, either dielectric or magnetic, 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, and are not designed to attenuate far field planar waves.

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 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 materials 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 dielectric 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.

(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.


Magnetic Materials

(310-4) C-RAM GDSS A silicone sheet material which has high loss over a broad microwave frequency range.

(310-5) C-RAM FDSS A silicone sheet material which has high loss below 1 GHz

(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.

(310-7) 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.

(330-3) C-RAM KR and (330-4) KRS Two component castable materials. KR is epoxy based and KRS is silicone based. Can be poured into place and cured, resulting in the same magnetic properties as the various grades of C-RAM RGDS.