C-RAM MT
LOSSY, CARBON FILLED, FLEXIBLE FOAM SHEET STOCK
C-RAM MT is a series of flexible, lightweight lossy plastic foam sheet materials. A very broad frequency range of dielectric loss is achieved through carbon loading of the foam. C-RAM MT can be used to lower the Q of cavities, attenuate surface currents, absorb stray RF energy, isolate components and plug areas of RF leakage. It is a lossy load material; applications requiring a free space reduction of reflectivity should be addressed with C-RAM LF (see Technical Bulletin 320-1).
C-RAM MT is available in several grades with varying levels of carbon loading, and thus varying tangents. Each grade is available in a range of thicknesses. The material is a soft foam and is easily cut with a sharp knife. Cuming Corporation can also supply C-RAM MT with a peel-and-stick backing, and can die-cut or machine parts to specifications.
C-RAM MT-FR is a fire retardant grade. C-RAM MT is treated with fire retardant additives during its manufacturing cycle. C-RAM MT-FR meets UL-94-HF-2 requirements.
TYPICAL PROPERTIES
Color: Black
Density (dependent upon grade):
.06 to .13 g/cm3 (4 to 8 lb/ft3)
Service temperature: -50 to +120ºC
(-85 to +250ºF)
Tensile strength: 12 psi
Elongation, min.: 150%
Tear Strength: 1.5lb/inch
Compression set, 80%: 5%
Compression set, 90%: 10%
Resiliency: 45%
Insertion loss: see table on next page
METHOD OF APPLICATION
C-RAM MT can be readily cut with a sharp knife or a steel rule die to intricate shapes.
The normal method of applying C-RAM MT to a substrate is with a neoprene contact adhesive. For best results, the adhesive is brushed or rolled onto the substrate and allowed to dry tack-free (at least one hour). Adhesive is then applied to the back of the C-RAM MT, and when the adhesive is still tacky but no longer wet (usually about 2-3 minutes), the part is pressed against the coated substrate for an immediate and permanent bond.
Cuming Microwave offers Cambond 808, a solvent-based, non-flammable, neoprene contact adhesive for applying C-RAM MT (see Technical Bulletin 230-5).
As an alternative, C-RAM MT can be supplied with pressure sensitive adhesive (PSA), which is not a contact adhesive, but will provide an adequate bond in most applications, since the material is quite lightweight. Simply peel off the backing, and press the part firmly to a clean surface. The PSA will adhere with high tack to metals, wood, and many plastic surfaces.
TABLE OF INSERTION LOSS AND ATTENUATION
GRADE INSERTION LOSS. dB/cm (dB/inch) ATTENUATION, dB/cm (dB/inch)
1 GHz 3 GHz 10 GHz 3GHz
MT-14 0.2 (0.5) 0.4 (1.0) 0.9 (2.2 0.4 (1.0)
MT-16 0.7 (1.8) 1.5 (3.8) 2.0 (5~0) 1.4 (3.5)
MT-18 0.9 (2.3) 1.8 (4.0) 2.8 (7.0) 1.5 (3.7)
MT-20 1.8 (4.5) 3.2 (8.0) 5.1 (13.0) 3.0 (7.5)
MT-22 2.2 (5.5) 3.9 (10.0) 6.3 (16) 3.7 (9.5)
MT-24 3.5 (14) 11 (32) 24 (60) 11 (27)
MT-26 4.9 (19) 16 (46) 34 (89) 16 (39)
MT-30 16 (40) 24 (60) 43 (110) 19 (49)
NOTE: Insertion loss measurements include the effects of surface reflections; the above values are close to, but not exactly, linear with thickness. For example, a ¼ inch thick piece has somewhat more than 1/4th as much insertion loss as a one inch thick piece.
Attenuation is a measure of loss within a homogeneous material, and does not take into account any reflections at interfaces. It is independent of thickness. This is a calculated, not measured, value.