Radar Absorbing Material (RAM)

Abstract

This paper briefly outlines the research and development activities in radar absorbing materials. Military defense scientists to the possibility of using coating materials to render aircraft or other military vehicles less visible to radar and, preferably, to control such visibility. The highly conducting surface of a metal vehicle is an excellent reflector of radar, but an absorbing layer would suppress the radar signal at the receiver station. Radar absorbing material currently in military and commercial use are typically composed of high concentrations of iron powders in a polymer matrix. These materials are both very heavy and very costly, two key limitations to their adoption for many applications. The performance of these coatings, particularly those using spherical particles, is dependent upon how closely the spheres are packed together. Thus the most efficient coating would be one approaching the density of solid iron with a minimum amount of resin included to electrically insulate the particles from one another. That is, the attenuation efficiency increases faster than the weight, so that a thinner coating with the same attenuation, can be used, providing an overall weight savings. Unfortunately, the particles, when produced, are of non-uniform diameter and not necessarily uniformly round. A window member composed of a transparent resin or inorganic glass with a transparent conducting film such as gold or ITO coated, is used as an electromagnetic wave shield window for stealth aircraft. However, the transparent conducting film, especially ceramic transparent conducting film such as ITO does not deform sufficiently to follow the deformation of the window material. Therefore the transparent conducting film might crack even with relatively little deformation, which can occur during an actual flight.