MICROWAVE SCREEN WITH MAGNETICALLY CONTROLLED ATTENUATION

Abstract

The efiect of magnetic bias on dielectric spectra of composite sheets fllled with Fe or Co-based microwires is studied experimentally and via simulation. The permittivity is measured using a free-space technique within the frequency band from 6 to 12GHz. The bias is applied either parallel or perpendicular to the microwave electric fleld; the bias strength varies from 0 to 2.5kOe. The composites with Fe-based wires reveal a single region of bias dependent permittivity under bias about 800{1000Oe. The composites with Co- based wires reveal two such regions: the high-fleld region is close to that of composites with Fe wires, and the low-fleld region corresponds to the coercive fleld of Co wires (2{3Oe). The high-fleld efiect is related to the dependence of ferromagnetic resonance (FMR) parameters on bias; the low-fleld efiect is related to the rearrangement of the domain structure of Co-based wires. The interference of magnetoimpedance and dipole resonance is analyzed, revealing the efiects ofi wire length, diameter, parameters of magnetic resonance and composite structure. The results are considered in view of application to the problem of controlled microwave attenuation. Simulation shows that the narrower is the FMR spectrum and the higher is the admissible loss of a sheet in a transparent state, the wider is the dynamic range of attenuation control. The attenuation range of a lattice of continuous wires is smaller than that of a screen with identical wire sections, where the magnetoimpedance efiect is amplifled resonantly. At 15GHz frequency the strength of the bias switching opaque sheet with Fe-based wires to the transparent state is about 2000Oe. For 3dB admissible loss, the range of attenuation control about 10dB is feasible in a composite with aligned wire sections. If the aligned sections are distributed regularly, the loss in a transparent state is about 1dB lower.