V. S. Butylkin

Nonreciprocal microwave transmission in metastructures with transversely magnetized ferrite plate and a grating of resonant elements

Nonreciprocal transmission of a linearly polarized electromagnetic wave at a ferromagnetic resonance (FMR) frequency has been observed in a metastructure comprising a transversely magnetized ferrite plate and a grating of resonant elements. The nonreciprocity of wave transmission is observed for the metastructure arranged along the axis of a rectangular waveguide and even in the free space between transmitting and receiving waveguides, where the effect does not take place when there is no grating. The observed phenomenon is explained by the formation of a surface wave with elliptic or circular polarization on the grating. The nonreciprocity reaches maximum (>35 dB) under the conditions of mutual influence between the FMR and the resonance of grating elements for certain values of the certain frequency and magnetic field, which depend on the distance between the ferrite plate and the grating. The nonreciprocal effects have been observed for grating elements in the form of double split rings, polyhedral loops, and dipoles. The results may be of interest for the development of new nonreciprocal devices and multifunctional metastructures such as decoupling elements for quasi-optical systems and two-frequency decoupling filters for counterpropagating waves in the gigahertz and terahertz range.

Electrically controlled frequency bands of nonreciprocal passage of microwaves in metastructures

Measurements of the transmission coefficients of linearly polarized waves in a rectangular waveguide along a metastructure formed by a transversely magnetized ferrite plate and double-split rings with varactors indicated the presence—in addition to the ferromagnetic resonance—of a resonance region of nonreciprocal passage, which is controlled, in contrast to the ferromagnetic resonance, by the electric field. This effect manifests itself in magnetic fields substantially lower than the field exciting the ferromagnetic resonance at these frequencies. Electrically controlled nonreciprocal passage of microwaves cannot be achieved by means of known natural materials or traditional ferromagnets.

Surface waves guided by a plate made from a bianisotropic resonance metamaterial

The dispersion characteristics, the distribution of energy fluxes, and the polarization of the magnetic field of surface waves formed in free space by a bianisotropic-material layer with resonance and anisotropic chirality, permittivity, and permeability are studied theoretically. The transmission and reflection spectra for lattices of resonance planar elements exhibiting magnetoelectric interaction are investigated experimentally. The nonreciprocity of microwave transmission in structures consisting of a lattice and a transversely magnetized ferrite plate is also investigated experimentally. The qualitative agreement of experimental results and theoretical predictions is established.

Giant nonreciprocal effect under conditions of mutual influence of ferromagnetic and chiral resonances

A more than hundredfold increase in the nonreciprocity of electromagnetic wave transmission in a waveguide containing a transversely magnetized ferrite plate has been observed upon the introduction of a grating of bianisotropic elements. This effect takes place at a certain magnitude of a constant magnetic field, under the conditions of mutual influence of ferromagnetic and chiral resonances. In an evanescent regime, the non-reciprocity exhibits a severalfold increase. The effect depends on the mode of excitation of the chiral resonance, being observed in the case of excitation by a magnetic component of the microwave field.

Electrically controlled nonreciprocity inversion of microwave transmission in a metastructure based on ferrite and a varactor-loaded dipole

A possibility of electrical control of nonreciprocity inversion of microwave propagation when using a metastructure with a ferrite plate and varactor-loaded dipole is demonstrated. In contrast to conven-tional methods, the inversion occurs without ferrite remagnetization. It is reached by varying the constant bias voltage on varactor that enables the tuning of the resonance frequency of dipole to the frequency of ferromagnetic resonance. This effect occurs due to the fact that a magnetic field with elliptical polarization is formed near a dipole as a result of superposition of incident and scattered waves, rotating in one direction below the resonance frequency of dipole and in the opposite direction above the frequency of this resonance.

Nonreciprocal transmission spectrum of a ferrite plate-resonant element grating metasandwich with split resonance

It is established that, when microwaves propagate in a structure comprising a ferrite plate and a grating of conducting resonant elements (situated on or close to the plate), the nonreciprocal wave transmission is accompanied by a nonreciprocal splitting of the microwave resonance at the grating frequency and by an expansion of the resonance bandwidth upon application of a constant magnetic field with a magnitude about one order smaller than that of the field exciting the ferromagnetic resonance (FMR). The sign of the nonreciprocity changes when the ferrite is arranged on the opposite side of the grating and/or when the applied constant magnetic field reaches a level at which the difference between the FMR and the grating resonance frequencies changes sign.

A composite medium with simultaneously negative permittivity and permeability

A new composite medium that possesses simultaneously negative permittivity and permeability in the microwave wavelength range is proposed. The medium is composed of evanescent waveguide structures responsible for the negative permittivity, with embedded cylindrical elements of a one-dimensional chiral medium accounting for the negative permeability. The evanescent waveguide structures exhibit blooming and antiresonances in the reflection coefficient.

Voltage tunable microwave multiband filters through meta-interferometer.

First it has been observed that microwave interferometer with embedded metastructure, meta-surface or meta-atom as voltage-controlled original beam-splitter can show new functionalities, such as specific selective control of line width and intensity, as well line shape and position in multiband spectral filtering. We realize and investigate modified meta-interferometer on basis of rectangular waveguide tee with varactor-loaded conductive resonance elements as a beam splitter at 3 – 6 GHz. It is achieved tunable considerable narrowing and 0.15 – 0.2 GHz shifting of band; switching between stop-band (-25 dB) and pass-band (-2;-5 dB), as well widening and intensification of each filtering band by turns in dependence on resonance element properties and bias voltage 0 – 10 V. The results open up a new approach to implement switchable and tunable multiband microwave filters.

Electrically and Optically Controlled Wideband Matching of Radio-Absorbing Composites to the Ambient Space

Microwave radio-absorbing metastructures are proposed that possess controlled broadband matching to the ambient space by virtue of an array of varactor-loaded chiral and annular elements in which magnetic resonance are excited. Experimentally in a rectangular waveguide and numerically in free space, it is shown that the tuning of the magnetic resonance frequency leads to a shift in the matching frequency region. The electric control of the magnetic resonance and, accordingly, the matching (25% relative tuning) is achieved by the variation in the reverse bias voltage at the varactor, and the optical control is achieved by directing a red laser pointer to a photodiode connected to the varactor in the photodiode mode.

Specificities of the Microwave Reflection Coefficients of Magnetically Excited Chiral and Ring Conductive Elements for Separation of Magnetic and Electric Responses and Broadband Matching of Radio Absorbing Composites

Distinctive features of the resonance responses of the reflection of microwaves from conducting double and single split-ring resonators, making it possible to distinguish between the magnetic and electric responses and identify the magnetic response of elements of different shapes, are studied experimentally in a rectangular waveguide and numerically in free space. It is shown that the specificities of the frequency dependence of the magnetic response can be used for broadband matching of radio absorbing composites.