In numerous technical fields dependent on ultra-high frequencies, such as for example detection equipment, it is necessary to have materials absorbing ultra-high frequency waves to prevent, for example, stray couplings between the transmitting and receiving antenna when the latter are separated. These materials also play a decisive part in the research and development of radar antennas and more generally in telecommunications in special chambers called "anechoic rooms". The walls thereof are completely covered with a material which absorbs ultrahigh frequency waves in order that only the direct incident wave is received by the antenna in question.
The prior art absorbent materials can be subdivided into two main categories:
absorbent materials with a low reflection coefficient and moderate attenuation, generally in the form of an alveolar material with communicating cavities or foam; PA1 absorbent materials with high attenuation and whose reflection coefficient, with a by no means negligible reflection coefficient and in the form of rigid blocks.
The first type of absorbent material is generally obtained from a porous material or a foam, whose cavities are interconnected. By successively immersing the material in a suspension of carbon in very fine powder form and drying, an absorbant material is obtained having the properties indicated in the first category. However, this absorbant material has the disadvantage of a thermal behaviour not exceeding 100.degree. C., high moisture absorption due to the interlinked cavities, so that the material becomes unsuitable due to a considerable increase in the dielectric constant and difficulties linked with the precision machining, which is particularly necessary for members located in the vicinity of antennas.
The absorbant materials in the second category generally have a high density, so that their use in even more difficult, especially in airborne equipment.