The invention relates to an electromagnetic radiation absorber for a preselected frequency range, comprising: an absorbent sheet (10) located such that said electromagnetic radiation falls on it, and a conductive base (20) located under said absorbent sheet, wherein said absorbent sheet: has a total thickness e exceeding .lamda./(.epsilon.).sup.1/24, where .lamda. is the wavelength of the incident electromagnetic radiation, and is made up of a dielectric material containing amorphous magnetic microwires, the magnetic permeability of which in the preselected frequency range has an imaginary part .mu.'' which is at least 100 times greater than the corresponding real part .mu.', said microwires being distributed in a volume having a thickness e.sub.2 of at least .lamda./(.epsilon.).sup.1/216, where .epsilon. is the dielectric constant of the absorbent sheet and said volume is located a distance e.sub.3 from the conductive base that is not less than .lamda./(.epsilon.).sup.1/28.