RF 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 foam 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 offers these materials in sheet form, and can custom die-cut or waterjet-cut parts to a drawing. These materials are supplied with a pressure-sensitive adhesive backing (peel-and-stick), or more durable adhesives options for extreme conditions.

Click the links below to learn more about each standard product

Foam Materials

MT Dielectric Data
Reticulated Foam Absorber Sheets – C-RAM AR (320-3)
Broadband Carbon/Foam Flexible Sheet Absorber – C-RAM LF (320-1)
For a list of additional foam materials, please see our 320 Series

Magnetic Materials

Thin, Flexible, Tuned Frequency Magnetic Sheet Absorber – C-RAM FLX (310-1)
High Loss Magnetic Sheet Absorber For Surface Waves – C-RAM GDSS (310-4)
800 MHz Tuned Magnetic Sheet Absorber – C-RAM GDSS (310-2)
Thin, High Loss Silicone Rubber Sheet Absorber – C-RAM GDX (310-11)
Flexible Iron/Silicone High Loss Stock – C-RAM RGD-S (330-2)
High Loss Magnetic Sheet Absorber For Surface Waves – C-RAM FDSS (310-5)
High Loss UHF Absorber Sheet – C-RAM FFS-125 (310-6)
Flexible Broadband Magnetic Sheet Absorber - C-RAM FF-2 (310-7)
Magnetic Materials Dielectric Data
Flexible, Broadband Magnetic Microwave Absorber C-RAM FGMM (310-10)

For a list of additional rubber materials, please see our 310 Series
For a list of additional castable materials, please see our 330 Series

Room Temperature Curing Versions of Iron Loaded Epoxies – Application Note 300-11
C-RAM Millimeter Wave - Application Note 300-13
MS Pressure Sensitive Adhesive Option for Absorber Sheet – Application Note 300-17