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.