radarabsorbent

Radar-absorbent, often called radar-absorbing material or RAM, refers to materials and structures designed to reduce the radar cross-section of an object by absorbing incident electromagnetic energy rather than reflecting it. RAM is used primarily to improve stealth performance by lowering detectability in radar systems. Absorption converts energy into heat through dielectric and magnetic losses, and sometimes through engineered resonance.

RAM can be applied as coatings, laminates, or structured surfaces. Common families include dielectric polymer films loaded with conductive fillers (carbon, carbon nanotubes, graphite), ferrite and magnetic ceramic composites, and metamaterial-based absorbers with resonant unit cells. Traditional constructions include Salisbury-screen and Jaumann absorbers, which achieve absorption through a layer of lossy material backed by a conductor, or multiple layers with progressively tuned impedance.

Design considerations include impedance matching to the surrounding air, thickness versus bandwidth, weight, temperature stability, and environmental durability. Broad-band RAM often combines multiple mechanisms and layers to achieve acceptable performance over a range of frequencies and incidence angles. Surface shaping and edge treatment also play a critical role in minimizing scattered reflections.

Applications are most common in defense, where RAM coatings and structures are used on aircraft, ships, and missiles to reduce radar visibility. RAM can also be employed in antenna covers and RF shielding where reduced backscatter is desirable. Limitations include added weight, manufacturing complexity, cost, and performance sensitivity to temperature, aging, and mechanical damage. RAM performance is assessed by measuring radar cross-section in controlled facilities and by evaluating bandwidth, angle dependence, and thermal stability over service conditions.