A new type of EM wave absorbing coating

Research on radar anti-reflection coatings has been actively pursued both theoretically and experimentally since World War II. Interference, (1,2) dielectric (3), and magnetic-dielectric (4,5) absorptive coatings have been tried. Recently a new type of radar absorbing chaff (RAC) has been suggested (6). Calculations done at BRL indicate that by compacting the RAC filaments a new type of radar absorbing coating (called RACO) may be possible. The filaments would be fixed in a solid binder having near unity dielectric constant. The primary mechanism for attenuation of the incident radiation by a RAC cloud or RACO layer is by resistive dissipation in the relatively long, thin chaff filaments. The tiny RAC-RACO filaments have length to diameter ratios on the order of one thousand with diameters of about 500A. Filament separations in a RACO are about one-half to one-third of a filament length thus requiring the inclusion of dipole and perhaps higher order interactions. Each filament can be modeled simply as a series resistive-capacitive circuit, single filament theory will be discussed in Section 2.