Microwave Screen With Magnetically Controlled Attenuation

Abstract

Abstract-The effect of magnetic bias on dielectric spectra of composite sheets filled 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 12 GHz. The bias is applied either parallel or perpendicular to the microwave electric field; the bias strength varies from 0 to 2.5 kOe. The composites with Fe-based wires reveal a single region of bias dependent permittivity under bias about 800-1000 Oe. The composites with Cobased wires reveal two such regions: the high-field region is close to that of composites with Fe wires, and the low-field region corresponds to the coercive field of Co wires (2-3 Oe). The high-field effect is related to the dependence of ferromagnetic resonance (FMR) parameters on bias; the low-field effect is related to the rearrangement of the domain structure of Co-based wires. The interference of magnetoimpedance and dipole resonance is analyzed, revealing the effects off 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 effect is amplified resonantly. At 15 GHz frequency the strength of the bias switching opaque sheet with Fe-based wires to the transparent state is about 2000 Oe. For 3 dB admissible loss, the range of attenuation control about 10 dB is feasible in a composite with aligned wire sections. If the aligned sections are distributed regularly, the loss in a transparent state is about 1 dB lower.

Spoof plasmons in corrugated semiconductors

“…For instance, in the case of a = 0.4d and h = 2.5d, the attenuation coefficient of the spoof SPPs is 23 m −1 for f = 0.6 THz, and it increases up to 59 m −1 for f = 0.8 THz and 134 for f = 1 THz, respectively. Compared to a metal THz waveguide described in [44], the corrugated semiconductor surface exhibits relatively high loss for guiding THz wave. The mentioned outcome appears due to the fact that the permittivity of metal is smaller than that of silicon.…”

Theory of ferromagnetic wires resonating in the proximity of a ground plane: Application to artificial impedance surfaces

“…Among them, ferromagnetic wires have been proposed for the design of electromagnetic absorbers, [5][6][7] transmission control screens, 8,9 electromagnetic shields, 10 artificial surfaces, 11 and noninvasive testing devices. 12 In addition, ferromagnetic wires are used as the elementary inclusion of artificial electromagnetic materials, such as artificial dielectrics with magnetically controllable permittivity, [13][14][15][16] and magnetic materials with adjustable permeability.…”

Magnetic field-dependent effective microwave properties of microwire-epoxy composites

“…Most recently, microwave absorption, electromagnetic compatibility, and non-destructive testing applications were also developed in the microwave and millimetre-wave applications. [2][3][4][5][6] They are desirable elements for configurating microwave tuneable devices through indirect field tuning; and a few recent studies have demonstrated such feature in microwirebased composite materials. 5,7 At gigahertz frequency range, microwires behave collectively like dipoles when they interact with an incident microwave field.…”

“…6,8 Several studies have been performed on the influence of a magnetic field on the effective scattering parameters and the permittivity of wire composites containing periodic arrays of ferromagnetic wires. 6,[9][10][11] However, the above mentioned studies have not been extended to composite materials obtained by randomly dispersing microwires in a polymer matrix. The short wire inclusion can be considered as elementary scatterers when the electromagnetic wave propagates in the composite and induces an electric dipole moment in each inclusion.…”

“…The second resonance phenomenon is associated with the ferromagnetic resonance ($2.3 GHz) which is in close proximity to the dipole one. 6,17 It is worth noting that when FMR occurs at sufficient high magnetic field, the skin depth is minimum leading to maximum dielectric losses. 14 As is now well established, the Co-based amorphous wires possess remark-able GMI properties.…”