Radar absorbent material

The most common mode of aircraft detection is radar. Essentially, radar is the detection of radio waves that have been thrown out and which bounce off objects returning to the site of origin. Today s radar, if properly used, can help identify the location, speed, and identity of the aircraft. The radar cross-section (RCS) of an aircraft is how much echo the plane sends from radar. Birds have an RCS of about 0.01 m. The Stealth Bomber has an RCS of 0.75 m. The Stealth Bomber and many stealth aircraft gain their stealth character from both the shape of the aircraft and the presence of radar absorbing material (RAM), which is made to absorb and eliminate radio waves rather than reflect them. Most of the RAM materials are polymeric. 

Radar absorbing materials 2.2,1 Phenomenology of interaction 370 4.5 Influence of structural parameters of conducting polymers on their ... 

Nevertheless, several general papers have been published on stealth technology applied to aircraft such as LOCKHEED F 117 [5,6] or others [7,8,9]. The description of radar absorbing materials is restricted to iron or ferrite loaded paints or elastomers except the case of retinyl Schiff base salts [10,11]. This molecule attracted interest of many scientists in 1987. In fact this material which is a charge transfer salt derived from the A vitamin, never exhibited high-frequency dielectric constant due to its intrinsic conductivity, despite its beautiful orange colour Moreover, reference books as the one of Knott el al. [12] do not mention the use of conductive polymers for this purpose. 

The metallic aircraft surface is a reflector from the electromagnetic waves point of view (like a mirror for visible light). That is why for twenty years much work has been devoted in France and all over the world, particularly in the USA and in ex USSR, to the conception of radar absorbing materials (RAM) associated with the former optimised shape [12]. 

As evidenced by these examples, conducting polymers stand out as radar absorbing materials in that they offer engineers unlimited design possibilities. 

We have intended to show in this chapter, how conductive polymers could provide a significant improvement in designing Radar Absorbing Materials. In fact, it is mainly the wide diversity of synthesis paths which is responsible for the variety of potential applications. 

Smart skins are to be considered in the context of radar absorbing materials where solutions have been given in [113,114]. Smart microwave windows have been proposed in the context of using poly(aniline)-silver-polymer electrolyte composite materials which have shown a change in microwave reflectivity when a small electrical dc potential is applied among them [115]. An adaptive radar absorbing structure based on the topology of a Salisbury screen combined with an active frequency selective surface controlled by PIN diodes has been described in [116] which allows for superior reflectivity-bandwidth. 

R D research development R M reliability and maintainability R R repeatability and reproducibility rad That quantity of ionizing radiation that results in the absorption of 100 ergs of energy per gram of irradiated material, radome radar dome RAM radar absorbent material RAM random access memory Rapra Rubber Plastics Research Assoc. 

Sic fibres, which may be useful in designing radar absorbing materials. The different values are obtained by varying the heat treatment temperature of the fibre. 

The range of conductance attainable with polypyrrole-or polyaniline-coated fabrics make these textiles ideal for use as radar-absorbing materials. These materials... 

Graphite has been used in military applications as radar absorbing material and in antielectromagnetic interference coatings for civil purposes since it is a good microwave radiation absorber. In this field, Fan et al. (2009) observed that microwave absorption maxima of milled flake graphite and carbon nanotubes was found in the 10-15 GHz frequency range. 

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