Absorptive optical bistability at microwave frequencies

Summary Intrinsic absorptive bistability and hysteresis cycles in a steady-state regime are obtained at microwave frequencies. A theory is presented which takes into account the Gaussian shape of the fundamental mode excited into the resonator and is compared with the experimental results.

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Riassunto Sono state osservate la bistabilità assorbitiva intrinseca e l’isteresi nel caso stazionario, operando alle frequenze delle microonde. Si presenta una teoria che tiene conto della forma gaussiana del modo fondamentale eccitato nel risuonatore e che è confrontata con i risultati sperimentali.

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Резюме На микроволновых пастотах наблюдаются внутренняя абсорбционная бистабильность и гистерезисные циклы в стационарном режиме. Предлагается теория, которая учитывает гауссову форму основной моды, возбужденноц в резонаторе, и которая сравнивается с экспериментальными резулстатами.

     

Nuclear magnetic resonance at microwave frequencies

Instrumental requirements for pulsed NMR studies of hyperfine splittings in rate-earth metals and compounds are considered, with particular attention to factors affecting the design of the specimen cavity. A spin-echo spectrometer for hyperfine studies in the 2 to 8 GHz frequency range is described.     

Nonlinear waves in waveguides at microwave frequencies

The process of nonlinear-wave formation in a waveguide at microwave frequencies is studied theoretically. It is shown that a nonlinear wave in the form of a pulsating soliton is formed under conditions of uniform spectrum-line broadening. The possibility of experimental observation of the phenomenon is considered.Tbilisi State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 5, pp. 475–480, May, 1992.     

Dielectric relaxation in benzotrihalides at microwave frequencies

The permittivity and dielectric loss of benzotrifluoride and benzotrichloride in benzene and decalin solution have been measured at four microwave frequencies viz., 30.25, 24.50, 18.26 and 9.83 GHz and also at 1 MHz and optical frequency at 35°C. The permittivity and dielectric loss at different frequencies have been plotted against concentration in wt. fraction. The slopes of these straight lines have been used for complex plane plots (a″ vs a′. The dispersion locus for the main dispersion region for both compounds in benzene and decalin are Debye semicircles. The values of relaxation times for overall rotation (τ ₁) and group rotation (τ₂) have been found out and reported. Whereas τ₁ is found to be viscosity dependent, τ₂ is practically independent of viscosity. The relaxation time for group rotation has been found to vary with the frame to which it is attached. Dipole moments of the compounds in both benzene and decalin have been reported.     

High-efficiency reflection phase tunable metasurface at near-infrared frequencies

The realization of active modulation of reflection phase based on metasurfaces is of great significance for flexible control of electromagnetic wavefront, which makes metasurfaces have practical application values in polarization conversion, beam steering, metalens, etc. In this paper, a reflection phase tunable gap-surface plasmon(GSP) metasurface based on phase change materials Ge_2Sb_2Te_5(GST) is designed and experimentally demonstrated. By virtue of the characteristics of large permittivities difference before and after GST phase transition and the existence of stable intermediate states, the continuous modulation of near-infrared reflection phase larger than 200°has been realized. At the same time, through the reasonable design of the structure sizes, the reflection has been maintained at about 0.4 and basically does not change with the GST phase transition, which improved the working efficiency of the metasurface significantly. In addition, the coupled-mode theory(CMT) is introduced to make a full analysis of the modulation mechanism of the reflection phase,which proves that the phase transition of GST can induce the transition of metasurface working state from overcoupling mode to critical coupling mode. The improvement of the metasurface working efficiency has practical values for wavefront modulation.     

Radio emission of extensive air showers at microwave frequencies

It is found that the power of the incoherent radiation of ionization electrons of an extensive air shower in the frequency range of 150 GHz is more than 10^–24 W/m²Hz, with the shower energy ~10¹⁸ eV at a distance of 5 km from its axis. This means that, unlike fluorescent detectors, a radio telescope with an effective area of more than 300 m² can monitor the trajectory of showers with an energy higher than 10¹⁸ eV at any time of the day regardless of the weather. The spectrum maximum near the frequency of 150 GHz is roughly three orders of magnitude higher than the value experimentally measured in the characteristic band (~5-10 GHz).     

Dielectric behaviour of ketone-amine binary mixtures at microwave frequencies

Values of dielectric constant (ε′) and loss factor (ε″) have been experimentally determined for binary liquid mixtures of ethyl methyl ketone+ethylenediamine and methyl isobutyl ketone+ethylenediamine at 9.44 GHz microwave frequencies at 30°C. The values ofε′ andε″ have been used to evaluate the molar polarization, apparent polarization and the excess permittivities. Excess refractive index, viscosity and activation energy of viscous flow have also been estimated. These parameters have been used to explain the formation of 1:1 complexes for both the systems.     

Giant magnetoimpedance in glass-covered amorphous microwires at microwave frequencies

In this work, results on the giant magnetoimpedance (GMI) of a glass-covered amorphous microwires with nominal compositions Co_70.4Fe_4.6Si₁₅B₁₀ and Fe_77.5Si_7.5B₁₅ are presented. The impedance Z=R+iX has been investigated as function of frequency (up to 1.8 GHz) and magnetic field (up to ±400 Oe), using a HP4396B impedance analyzer and an appropriate coaxial microwave cavity. The effects of the thermal treatments (Joule heating, from 20 mA up to 100 mA for 10 min) for anisotropy induction and, as a consequence, for GMI effect have been investigated.     

Studies on 1-D metallic complexes at microwave frequencies

The conductivity and dielectric constant at 35 GHz are reported for eight partially oxidised tetracyanoplatinate and bis (oxalato) platinate salts. Whenever possible the results are compared with those obtained from dc measurements.     

Identifying magnetic response of split-ring resonators at microwave frequencies

In this study we provide experimental methods to identify the magnetic resonance of split ring resonantors (SRR) at the microwave frequency regime. Transmission measurements were performed on both single SRR unit cell and periodic arrays of SRRs. The magnetic response of the SRR structure was demonstrated by comparing the transmission spectra of SRRs with closed ring resonators (CRR). Effects of the changes in the effective dielectric constant of the SRR medium on the band-gaps of SRR are investigated experimentally. SRRs not only exhibit a magnetic resonance band gap but also a band gap due to the electric resonance. Finally, we present the effect of electric coupling to the magnetic resonance of bianisotropic SRRs by utilizing SRRs with different orientations, and incident electromagnetic wave polarizations.     

Investigation of materials at microwave frequencies using microstrip sensors

Microstrip sensors are developed for measurements of dielectric and magnetic characteristics of materials in a wide range of frequencies 20–10,000 MHz. Their operation is based on both conventional resonance measurements techniques and an original method for measuring position and depth of the attenuation pole that is a point of mutual compensation of the inductive and capacitive interaction of microstrip conductors. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 46–53, September, 2006.     

A dual-mode microwave resonator for double electron-electron spin resonance spectroscopy at W-band microwave frequencies

We present a dual-mode resonator operating at/near 94 GHz (W-band) microwave frequencies and supporting two microwave modes with the same field polarization at the sample position. Numerical analysis shows that the frequencies of both modes as well as their frequency separation can be tuned in a broad range up to GHz. The resonator was constructed to perform pulsed ELDOR experiments with a variable separation of "pump" and "detection" frequencies up to Δν=350 MHz. To examine its performance, test ESE/PELDOR experiments were performed on a representative biradical system.     

Electromagnetic absorption properties of flowerlike cobalt composites at microwave frequencies

In this work,we report the electromagnetic absorption(EMA) properties of composites consisting of micrometersized cobalt with flowerlike architecture synthesized by a facile hydrothermal reduction method.Compared with the conventional spherical Co-paraffin composites,the flowerlike Co-paraffin composites are favorable with respect to EMA performance in the low frequency region,ascribing interfacial polarization loss and Ohmic loss to the improvement in the impedance match.     

Observation of anomalous transmission modes in nickel at microwave frequencies

A study has been made of the transmission of energy through nickel crystals in magnetic fields up to 13 kG using incident microwave power at 9.37 GHz. The transmission spectrum has been studied as a function of temperature and magnetic field orientation relative to the sample surface. A new set of anomalous transmission modes has been observed with the field perpendicular to the sample plane; these modes cannot be explained within the framework of existing theoretical models describing the resonance excitation of sound in ferromagnetic metals by electromagnetic waves.     

左手材料的反射特性与负折射率行为

利用平板波导法研究了不同入射角度下周期排列开口谐振环负磁导率材料、周期排列金属杆负介电常数材料以及左手材料微波反射特性，并利用劈尖法研究了左手材料的负折射特性.实验结果表明：负磁导率材料反射率曲线形成反射峰，其对应的反射峰频率与材料的谐振频率一致；负介电常数材料反射率接近0dB；左手材料出现单个反射较小的反射峰，其峰值反射率随入射角度的增大而变大，即反射能力增强，且反射峰与透射峰有相对频移.劈尖法测量还表明，左手材料在9800MHz频率附近出现负折射现象，其折射率n为-0.796. 关键词： 左手材料 反射 负折射率     

Broadband amplification of spoof surface plasmon polaritons at microwave frequencies

Efficient amplification of spoof surface plasmon polaritons (SPPs) is proposed at microwave frequencies by using a subwavelength‐scale amplifier. For this purpose, a special plasmonic waveguide composed of two ultrathin corrugated metallic strips on top and bottom surfaces of a dielectric substrate with mirror symmetry is presented, which is easy to integrate with the amplifier. It is shown that spoof SPPs are able to propagate on the plasmonic waveguide in broadband with low loss and strong subwavelength effect. By loading a low‐noise amplifier chip produced by the semiconductor technology, the first experiment is demonstrated to amplify spoof SPPs at microwave frequencies (from 6 to 20GHz) with high gain (around 20dB), which can be directly used as a SPP amplifier device. The features of strong field confinement, high efficiency, broadband operation, and significant amplification of the spoof SPPs may advance a big step towards other active SPP components and integrated circuits.