Microwave Quenching in DC-Biased Coplanar Waveguide Based on YBa2Cu3O7−δ{YBa}_{2}{Cu}_{3}{O}_{7-\delta} Thin Film

n this paper, we report on the results of features in the discovered effect of a strong change in the microwave losses (quenching) in HTS-based coplanar waveguide (CPW) at certain values of the input power Pin and direct current (dc) Idc. Two waveguides were studied: CPW-150 and CPW-75, fabricated of epitaxial 150and 75-nm YBCO films. The insertion loss of CPW IL = 10 lg (Pout/Pin) was measured versus both the operating temperature and the bias dc current Idc when a fixed level of the input X-band pulsed MW signal Pin was applied. Here Pout is the power measured at the CPW output. A pulse duration Ti was 5 μs with pulse repetition period T = 40 μs. Experiments showed a noticeable difference in specific values of I* = Idc corresponding to the Pin-dependent quenching phenomenon in CPW-150 and CPW-75. With a weak input signal, the difference in behavior of CPWs is anticipated, i.e., quenching occurs at a lower current for thinner film. For Pin > 1 W the situation is opposite, i.e., quenching for CPW-150 takes place at a lower I*. This is explained by stronger microwave heating of CPW-150

Whispering gallery mode resonators in microwave physics and technologies

We review the main results of the development of whispering gallery mode (WGM) resonators and their unique applications due to their quasi-optical functionality. Several types of advanced WGM resonators are proposed by the authors. The theoretical results are described for the resonators with an analytical solution of the electromagnetic problems. Special emphasis is given to the interaction of moving charged particles and waves of cylindrical resonators. Important aspects are described concerning the developed sapphire resonators, for which an exact solution can only be found by using specially designed computer program products. A separate section of the paper is devoted to application aspects of the WGM resonators. In particular, it describes advanced solutions for overcoming the problems of measuring the small microwave (MW) surface impedance of unconventional superconductors in the form of large-area thin films and small samples under study. In addition, a demonstration of accurate complex permittivity measurements of small volumes of lossy liquids is provided. Special emphasis is given to highly stable MW signal sources, namely Ka-band transistor-based feedback oscillator and solid-state maser WGM oscillators. Recently obtained results are presented of experimental studies of the auto-oscillatory system developed on the basis of the WGM resonator with relativistic electron beam

Millimeter-Wave WGM Resonator-Based Characterization of Continuous and Noncontinuous Ultrathin Cu Films

We analyze the experimental data on the evolution of the microwave (MW) response of the whispering gallery mode (WGM) resonator. The focus is on the thickness df variation of the conducting endplates (CEPs) from df exceeding skin layer thickness δs to dfłlδ s down to df = 0, i.e., with no CEPs. The analysis was performed by comparing the numerical simulation results obtained using COMSOL software with the authors' experimental data on the response of the Ka-band sapphire WGM resonator. The nonmonotonic change in the WGM resonator response with decreasing thickness df is explained using the metal-insulator percolation model proposed by Krupka et al. We use a different resonator (quasi-optical) technique and different mode polarization, namely, the HE14 1 δ mode. The artificially introduced discontinuity of the ultrathin film, resulting in a sharp growth of the Q-factor is analogous with the percolation material structure. The revealed effect may be useful for the development of MW devices with dynamically controlled properties of metamaterials

Microwave characterization of low-molecular-weight antioxidant specific biomarkers

Antioxidants play a crucial role in the life sciences, as the regulators of biochemical reactions. We studied the dielectric properties of the low-molecular weight antioxidant specific biomarkers sodium ascorbate and glutathione in solutions of different concentrations. The biomarkers are multifunctional metabolites relevant to the reactive oxygen species (ROS) scavenging system of cells. The newly developed high-Q microwave whispering-gallery-mode (WGM) dielectric resonator based technique was applied. The technique allows investigation of liquids of nanoliter volumes filled in microfluidic channel within several milliseconds. The revealed peculiarities in the dependence of permittivity on concentrations of the sodium ascorbate and glutathione solutions are explained by differences in relaxation times and loses introduced by molecules of different shapes. We suggest that this novel approach offers the potential for the detection and characterization of ROS-relevant biomarkers with millisecond-time resolution

Quartz Whispering-Gallery-Mode Resonator With Microfluidic Chip as Sensor for Permittivity Measurement of Liquids

Studies of biological solutions require high measurement accuracy, the ability to detect low changes in substance concentration, and small amounts of the liquid under test. A microwave complex permittivity measurement technique based on a high-quality-factor whispering-gallery-mode resonator with a microfluidic chip allows small amounts of dielectric liquids to be investigated with high accuracy. An existing technique based on a sapphire resonator does not provide for a low-concentration detection limit for substances with low molecular weight. Here, we present an advanced technique based on a quartz dielectric resonator. The detection limit obtained for glucose in water solution was found to be about one order of magnitude lower for the quartz resonator cell than for the sapphire-resonator-based measurement cell. The limit is about or lower than the concentration of glucose in human blood. This fact means that the technique can be used as the sensor for investigations of biological solutions in the microwave range. A study of glucose, lactalbumin, and bovine serum albumin was successfully performed in the Ka -band using the developed sensor