Radiation-absorbent materials, such as pyramid sponges or radar-absorbing materials (RAM), are designed to minimize radar reflections by absorbing or dissipating the electromagnetic energy of radar waves. While these materials can significantly reduce the radar signature of an object, they do not make it completely invisible to radar.
Radar detection depends on various factors, including the shape, size, and composition of an object, as well as the frequency of the radar system being used. Even with radiation-absorbent materials applied to an aircraft's fuselage, the overall radar cross-section (RCS) reduction is limited, and the radar signature will still be influenced by the aircraft's shape, angle, and other radar-reflective surfaces such as the engines, wings, or antennas.
Radar-absorbing materials can help reduce the radar signature of an aircraft, making it more difficult to detect or track, particularly at certain radar frequencies. However, achieving true invisibility to radar requires careful design considerations, including the use of advanced shaping techniques, radar-absorbing materials, and other stealth technologies such as radar-absorbing coatings, edge alignment, and internal structure design.
It's important to note that the effectiveness of radar-absorbing materials can vary depending on the specific materials used, their thickness, the radar frequency, and other factors. Therefore, while the use of radiation-absorbent materials can contribute to reducing radar detectability, complete invisibility to radar is unlikely to be achieved solely by using these materials.