Konstantin A. Korolev

Single and dual band 77/95/110 GHz metamaterial absorbers on flexible polyimide substrate

Ultra thin millimeter-wave absorbers on flexible polyimide substrate utilizing metamaterials are implemented for single and dual frequency bands in an emerging frequency spectrum of 77, 95, and 110 GHz. The dual band absorber is designed using a novel approach of imbedding high frequency resonator inside low frequency resonator capable of absorbing electromagnetic energy at both 77 and 110 GHz bands simultaneously. The total thickness of the absorber is just 126 μm (almost 1/20th of the wavelength). Measured peak absorptions for single frequency absorbers are 92, 94, and 99% at 77.2, 94.8, and 109.5 GHz, respectively, and for dual band absorber 92% at 77 GHz and 94% at 109.8 GHz.

Complex permittivity and permeability of strontium ferrites at millimeter waves

Magneto-optical approach for the measurements of complex dielectric permittivity and magnetic permeability of solid and powdered strontium ferrite materials has been performed in the Q-, V-, and W-band frequency ranges. Free-space quasioptical millimeter-wave spectrometer equipped with a backward-wave oscillator as a tunable source of coherent radiation provides the transmittance spectra in transverse magnetic field up to 7.5kOe. Frequency dependences of dielectric and magnetic parameters of strontium ferrites have been calculated by matching theoretical curves to the experimental transmittance spectra. Shifting of the ferromagnetic resonance to higher frequencies and broadening of the zone of strong absorption in magnetic field for solid ferrite materials have been observed.

Broadband Dielectric Characterization of Tumorous and Nontumorous Breast Tissues

The broadband dielectric properties of tumorous and nontumorous tissues were analyzed at the millimeter-wave and terahertz frequencies. Ex-vivo measurements were obtained using the backward-wave oscillator-based free-space quasi-optical spectroscopy and dispersive Fourier transform spectroscopy methods. Both techniques were modified to yield the real and imaginary parts of permittivity, absorption coefficient, refractive index, and transmission data over an extended frequency range from 30 to 900 GHz. Results reveal characteristic signatures of breast tissues and display a significant difference in the electromagnetic response of tumorous and nontumorous tissues. The techniques employed in this study provide prospects for extending ex-vivo measurements to in-vivo breast cancer detection and diagnostics.

Complex Magnetic Permeability and Dielectric Permittivity of Ferrites in Millimeter Waves

We report a first-time study of complex magnetic permeability and dielectric permittivity of 99% pure powdered barium cobalt ferrite (Ba2Co2Fe12O22) and pure solid barium hexaferrite ceramics (BaFe12O19) in a broadband millimeter-wave frequency range. We performed transmittance measurements using a free-space quasi-optical millimeter-wave spectrometer, equipped with a set of high-power backward-wave oscillators as sources of tunable coherent radiation at each Q-, V-, and W-frequency band. We calculated frequency dependences of complex permittivity for both types of ferrites using analysis of recorded high-precision transmittance spectra and obtained frequency dependences of the magnetic permeability from Schlomanns equation for partially magnetized ferrites.

Millimeter-Wave Transmittance Measurements on Ferrites Near Ferromagnetic Resonance

This paper presents complex dielectric permittivity and magnetic permeability measurements of pure and diluted barium ferrites in the millimeter-wave frequency range. A broadband quasi-optical millimeter-wave spectroscopy with backward-wave oscillators as high-power tunable sources of coherent radiation has been utilized. The real and imaginary parts of the dielectric permittivity and magnetic permeability as functions of frequency are computed from the transmittance spectra. A magneto-optical approach in millimeter waves has been successfully employed for the separation of the dielectric and magnetic effects and the simultaneous determination of the magnetic and dielectric parameters of barium ferrite materials near ferromagnetic resonance.

High Frequency Dielectric Characteristics of Tumorous and Non-tumorous Breast Tissues

The broadband dielectric properties of tumorous and non-tumorous tissues were analyzed at the microwave, millimeter wave, and terahertz ranges. In-vitro measurements were obtained using the coaxial probe and dispersive Fourier transform spectroscopy. Both techniques were modified to yield the complex real and imaginary permittivity, absorption coefficient, and refractive index. The results reveal the characteristic signatures of breast tissues and display a significant difference in the electromagnetic response of tumorous and non-tumorous tissues.

Magnetic Properties of Diluted Ferrites Near Ferromagnetic Resonance in Millimeter Waves

Transmittance measurements on diluted barium ferrite materials in broadband millimeter-wave frequency range have been performed. The measurements have been done using free-space quasi-optical spectrometer in transverse magnetic field up to 7.5 kOe. A set of backward wave oscillators have been used as sources of high power coherent radiation tunable in 34-120 GHz frequency region. A magnetooptical approach has been employed for the separation of dielectric and magnetic effects in ferrites and simultaneous determination of complex dielectric permittivity and magnetic permeability of materials. It has been shown that a variation in the chemical composition of ferrites leads to a change in the magnetic properties and absorption of materials in the millimeter waves

Ferromagnetic resonance of micro- and nano-sized hexagonal ferrite powders at millimeter waves

Complex magnetic permeability and dielectric permittivity of micro- and nano-sized powdered barium (BaFe12O19) and strontium (SrFe12O19) hexaferrites have been studied in a broadband millimeter wave frequency range (30–120 GHz). Transmittance measurements have been performed using a free-space quasi-optical millimeter wave spectrometer, equipped with a set of high-power backward wave oscillators. Real and imaginary parts of dielectric permittivity for both types of micro- and nanoferrites have been calculated using analysis of recorded high-precision transmittance spectra. Frequency dependences of the magnetic permeability have been obtained from Schlomann’s equation for partially magnetized ferrites. These materials show promise as tunable millimeter wave absorbers, based on their size-dependent absorption.

Complex Dielectric Measurements of Materials at Q- Band, V- Band and W- Band Frequencies with High Power Sources

In this paper we present a systematic study of complex dielectric permittivity of various semiconductor and dielectric materials, including highly absorbing substances, in Q-, V- and W-band frequencies. The measurements have been done using broadband quasi-optical millimeter wave spectrometer with a backward-wave oscillator (BWO) as a non-destructive high power tunable source of coherent radiation. Values of real and imaginary parts of dielectric permittivity of materials are calculated from the transmittance spectra. Refractive index data, obtained using both unbalanced waveguide bridge technique and free space measurements have been compared with previously published results. Millimeter wave and terahertz imaging and spectroscopy with high power BWO tubes as sources of coherent radiation for security applications have been briefly discussed

Magneto absorption measurements of nano-size ɛ-AlxFe2-xO3 powder materials at millimeter wavelengths

Ferromagnetic absorption spectra of ɛ-AlxFe2-xO3 powders with various x parameters and densities were obtained using free space quasi-optical spectrometer. Two absorption peaks located at around 95 and 105 GHz have been found. The 95 GHz absorption corresponds to x parameter value of 0.66; while the 105 GHz absorption corresponds to x-parameter value of 0.49. The absorption peak shifts to the lower frequency with increasing value of x parameter. The change in densities resulted in change in absorption intensity. The absorption characteristics are repeatable for these specimens prepared even at eight months interval. These absorbers are composed of ɛ-AlxFe2-xO3 nanomagnets and prepared by sol-gel techniques. Free space quasi-optical spectrometer equipped with a set of tunable backward-wave oscillators as power sources is used in this work to study the transmittance and absorption property of this series of materials at millimeter wave frequencies. The transmittance and absorbance spectra of ɛ-AlxFe2-xO3 po...