Ultrathin broadband microwave absorbers using ferromagnetic films

•The ultrathin broadband absorber using relaxation type of magnetic film is discussed.•The optimal absorption condition for magnetic film absorber is derived.•A periodic multilayer structure is used to meet the optimal absorption condition.•The absorbers are demonstrated using the Ni–Zn–Co ferrite film and iron nanofilm.

We have theoretically studied the absorption performances of microwave absorbers made of ferromagnetic films. For films with different frequency dispersive types of permeability, we have found that only the films with relaxation type of permeability can be used to realize broadband microwave absorbers with thin thickness. The condition for optimal absorption has also been derived. As the demonstrations, we have designed the magnetic film absorbers using Ni–Zn–Co ferrite film and iron nanofilm, respectively. Deploying periodic multilayer structure, the absorbers work at the optimal absorption condition. The numerical results show our absorbers have good absorption performances in broadband microwave frequency range.