Yu. N. Kazantsev

The efficiency of application of magnetic polymer composites as radio-absorbing materials

The results of investigation of the complex permittivity and permeability of polymer composite materials with different magnetic fillers in the frequency range of 1 MHz to 10 GHz are presented. The possibility of controlling the frequency characteristics of permeability and permittivity and the absolute values of these parameters via the formation of hybrid composites with multicomponent magnetic filler is shown. The efficiency of application of magnetic polymer composites as absorbing materials for the RF and microwave bands is analyzed.

Radio Absorbers Based on Magnetic Polymer Composites and Frequency-Selective Surfaces

Polymer composites filled with carbonyl iron are considered. A method is proposed for extending the operating frequency band of such radio absorbers with the help of band-reflection frequency-selective surfaces (FSSs). A functional relationship between the reflection characteristics of a radio absorber and the generalized characteristics of an FSS—the resonance frequency and Q factor—is established. On the basis of the rigorous theory of integral equations, programs are developed for computation of the reflection coefficient of a radio absorber with an FSS implemented as a biperiodic lattice with ring elements. The reflection coefficients of a series of samples are measured in the frequency band 1–10 GHz.

Artificial magnetic conductors based on capacitive gratings

New realizations of artificial magnetic conductors (AMCs) based on two or more closely spaced capacitive gratings whose period is small relative to the wavelength are proposed. Simple formulas are derived for estimation of the resonance frequencies and frequency bands in which the proposed structures behave as AMCs. Angular dependencies of the resonance frequencies are found for TE and TM waves. Propagation conditions for surface waves are considered. It is shown that, at resonance frequencies, such structures support only slow TM waves with small values of the slowing factor. It is confirmed experimentally that such structures behave as AMCs in a wide interval of the angles of incidence of TE and TM waves.

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.

Extension of the operating frequency range of a dielectric radio absorber with the help of frequency-selective surfaces

A detailed study of the efficiency of frequency-selective surfaces for extension of the operating frequency range of a dielectric radio absorber is presented. The radio absorber is fabricated from the layer of a homogeneous carbon black filled material and a frequency-selective surface made of thin metal rings placed inside or on the surface of the absorber. It is shown theoretically and experimentally that insertion of a frequency-selective surface into a dielectric radio absorber makes it possible to almost double the range of operating frequencies without increasing the thickness of the absorber.

Experimental Investigation of Response of Chiral Media and “Chiral Media-Ferrite” Structures to Microwave Radiation and Governing Magnetic Field

In this paper, the results of experimental investigations of different chiral structures are reported. Individual inclusions are measured in resonant cavities and in waveguides, reflection and transmission coefficients of planar composite samples are measured in free space. The emphasis is on novel, more complex inclusions (multigone spirals, planar spirals, etc.) and on ferrite-controlled composites.

Methods for extending resonance frequency tuning ranges of frequency-selective surfaces using varactors

Methods for tuning resonance frequencies of elements of frequency-selective surfaces with the help of varactors are considered. The varactors are placed both in breaks of the conductor inside elements and in gaps between elements. Results of the approximate calculation and measurement of resonance frequencies of elements of frequency-selective surfaces of various shapes (butterfly, loop, and snake) with different-type varactors are presented. The measurement is based on the waveguide method. It is shown that, when varactors are placed in an element, the maximum relative resonance frequency change (37%) is reached with an element having a large self-capacitance (butterfly shape) and a small-capacitance varactor (MA46H120). The efficiency of the method for extending the resonance frequency tuning range of the element by means of the inductive shunting of the varactor circuit is estimated.

Identifying and separating magnetic and electric microwave responses of chiral elements

We propose a technique for identifying the type of resonance excitation by ac magnetic or electric fields in conducting chiral elements by reflection of electromagnetic waves in the standing- and travelingwave modes. The technique was tested experimentally in the microwave range and confirmed numerically. We demonstrate the possibility of broadband matching of composite radar absorbing materials with the use of a lattice of resonance elements excited by magnetic field of the wave rather instead of the traditional quarter- wavelength effects.

Compensation of reflection from an RF absorbent material with the help of a lattice of double split rings

The frequency dependences of the coefficients of reflection from a lattice of double split rings excited by an RF magnetic field and from an RF-absorbent composite based on resistive films or fibers are analyzed. It is shown that partial reflections from the surface of the composite and the closely spaced lattice can compensate each other and, thus, the reflection from the composite can be significantly reduced. It is experimentally confirmed that the reflection can be decreased by more than 15 dB as compared to the reflection from the composite in the absence of the lattice.

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.