Design and research of magnetic tunable frequency selective surface based on dielectric and ferrite

In this paper, a method of designing tunable bandpass frequency selective surface via ceramics and ferrite material is proposed. The ferromagnetic resonance frequency can be tuned when magnetic field is applied. According to this property, the center-frequencies of the pass and stop band can be adjusted. The proposed model is composed of the ceramic part and ferrite part, and CST simulation under C band waveguide condition is employed in the research. For the ceramic part, five high-permittivity rectangular blocks are included. The aim is to achieve negative permittivity in broad band. The band-pass and band-stop properties of the frequency selective surface are clarfied based on the effective medium theory. The stop band originates from a similar Drude resonant electric monopole in the medium. The part of ferrite is composed of ten rectangular blocks. By adjusting the applied magnetic field, the ferromagnetic resonance and negative permeability are obtained at corresponding frequencies. Based on the double negative characteristics, the two parts are combined together to realize the pass band. For instance, when the magnetic field H0 is 1700 Oe, the ferromagnetic resonance appears at a frequency of 6.778 GHz. In this case, the center frequency of the pass band is at 6.758 GHz. By interacting with the electromagnetic wave, the electric resonance can take place in the ceramic blocks, and the ferromagnetic precession will appear in the ferrite blocks. The simulation results indicate that the pass band is switchable and tunable in a range of 6-8 GHz by changing the bias magnetic field. The distributions of electric and magnetic fields, and the parameters of perimittivity, permeability and impedance are obtained and discussed. Finally, the samples are fabricated and tested. The experimental results are basically consistent with the simulation results, indicating that the double negative passband can be adjusted via the applied magnetic field. This proposal provides a route to designing all-dielectric frequency selective surface and it can be used to design multi-band or tunable frequency selective surface.