A. A. Barannik

Accurate microwave technique of surface resistance measurement of large-area HTS films using sapphire quasi-optical resonator

We have developed a surface resistance (R/sub s/) measurement technique for large-area high-temperature superconducting (HTS) films using quasioptical dielectric resonators (QDR) with HTS endplates (quasioptical Hakki-Coleman resonators). In this technique, the highest Q modes, namely whispering-gallery modes, in sapphire disk sandwiched between HTS films or between one HTS film and one Cu endplate are excited at K-band frequencies. The authors report on measurement results of surface resistance of 52 mm diameter high-quality YBCO thin films. The measurement results revealed that the technique is feasible for accurate R/sub s/-measurements of large-area thin films. The method is appropriate for standard measurement of R/sub s/ at millimeter wave frequencies by analogy with classic DR-based microwave technique, although QDR-based technique has some fundamental differences.

High sensitivity microwave characterization of organic molecule solutions of nanoliter volume

A microwave resonator composed of a sapphire cylinder and a quartz plate with a 400 nl cavity was developed for the determination of the complex permittivity of liquids at 10 GHz. This sensor was calibrated over a wide range of values for real and imaginary parts of permittivity. The measured resonator losses induced by the liquid were found to be proportional to the dipole relaxation time of the liquid molecules, as predicted by perturbation theory. Our analysis of weight concentration and temperature dependence of the measured inverse quality factor revealed a sensitivity of about 0.1% for aqueous solutions of glucose.

Nanoliter liquid characterization by open whispering-gallery mode dielectric resonators at millimeter wave frequencies

We present an approach for identification and concentration determination of liquids of pico to nanoliter volumes at a frequency of 35 GHz based on a whispering-gallery mode (WGM) dielectric resonator technique. A quasioptical coupling scheme based on dielectric image waveguides was employed to excite high-Q running wave WGMs with uniform azimuthal field distribution in cylindrical sapphire disks with quality factors up to 4×105 at room temperature. Measurement of the liquid induced changes in the resonator quality factor and resonance frequency has been performed for droplets down to 90 pl volume spotted at different positions on the surface of the sapphire disk. We have employed our method for concentration determination of ethanol, glucose, and albumin dissolved in water. Solutions with concentration values well below 10% could be clearly separated from pure water. Our method is promising for the characterization of biological liquids.

Whispering-Gallery-Mode Resonator Technique With Microfluidic Channel for Permittivity Measurement of Liquids

Studies of biochemical liquids require precise determination of their complex permittivity. We developed a microwave characterization technique on the basis of a high-quality whispering-gallery mode (WGM) sapphire resonator with a microfluidic channel filled with the liquid under test. A novel approach allows obtaining the complex permittivity of biochemical liquids of sub-microliter/nanoliter volumes with high accuracy. The method is based on a special procedure of analysis of the interaction of electromagnetic field with liquid in a WGM microfluidic resonator and measurements of both the WGM resonance frequency shift and the change of the inverse quality factor. The approach is successfully applied to obtain the complex permittivity in the Ka-band of glucose, albumin bovine serum, lactalbumin, and cytochrome C aqueous solutions using the developed microwave technique.

Whispering Gallery Mode Hemisphere Dielectric Resonators With Impedance Plane

The electrodynamic characteristics of a high-Q dielectric whispering gallery mode resonator in the form of a hemisphere positioned on an impedance plane were studied. The analysis of the anisotropic resonator was modeled using Maxwell equations and the impedance Leontovich boundary condition. The interaction coefficient ASj of the conductor and microwave field was determined using a frequency and field distribution of the j-type mode in the hemisphere resonator considering a perfect conducting plane. Results of the theoretical study and experimental measurements of the Teflon resonator frequency spectrum and Q factor are in good agreement. The results obtained are confirmed by calculations using Microwave Studio CST 2008. In the case of the sapphire hemispherical resonator with an impedance plane, comparison of the experimental and simulation results allows us to identify the H -type modes in the resonator and their electromagnetic field distribution. In such anisotropic hemisphere resonators, the quasi-TE modes are revealed. The modes are excited together with TE modes inherent to the isotropic resonator and they have an identical distribution of electromagnetic field.

Q-factor measurement of quasi-optical dielectric resonators under conditions of the whispering gallery mode degeneration removal

An approach that allows one to determine the unloaded quality factor of a quasi-optical dielectric resonator (QDR) under conditions of the resonance line splitting corresponding to twofold degenerative whispering gallery (WG) mode has been proposed. The resonator is represented by an equivalent network as two oscillatory circuits with a certain coupling between them. The approach allows one to determine the Q-factor of a single oscillatory circuit using three measured parameters, namely: 1) ratio between specific amplitudes of the resonator amplitude-frequency response (or its second derivative); 2) resonant frequency; and 3) frequency splitting of the response (or its respective second derivative). The proposed technique is illustrated by the measurements in the millimeter-wave range for sapphire quasi-optical resonators with conducting and high-T/sub c/ superconducting (HTS) film endplates.

On the low-temperature microwave response of a YBa2Cu3O7−σ epitaxial film determined by a new measurement technique

The temperature dependence of the surface resistance RS(T) of a high-quality 600‐nm thick YBa2Cu2O7−σ epitaxial film, deposited on a MgO single-crystal substrate, has been investigated. The measurements were performed in the temperature range from Tc to 2K using a new technique—the application of a sapphire hemispherical resonator with whispering gallery mode in the 8‐mm wavelength range (Ka band). The new measurement technique makes it possible to reach high measurement sensitivity for RS(T) (to 10μΩ) at low temperatures. A linear dependence of RS(T) was obtained in the range 2–15K, in agreement with d-wave symmetry of the order parameter. The value found in the present work for the residual resistance Rres=RS(T→0) shows that the microwave properties of the film are close to those of single-crystals and, apparently, the internal properties of the superconductor determine Rres. Analysis of the published data shows that Rres(ω)∼ω3∕2 for YBa2Cu3O7−σ single crystals and films, and the nature of the residual ...

A New Technique of Dielectric Characterization of Liquids

Quasi-optical dielectric resonators (QDR) with conducting endplates (CEP) are proposed and justified for measurement of complex permittivity of liquids. The structure of electromagnetic fields in the form of whispering gallery (WG) modes is calculated accurately in terms of Maxwell equations which allow one to characterize liquids from the first principles. A radially two-layered QDR has been shown to be rather convenient for microwave characterization of liquids including ones with large microwave loss. For experimental studies of a number of liquids in Ka-band the QDR in the form of a Teflon disk sandwiched between the duralumin CEP was used. Here, water has shown an unusual property. The sign of the frequency shift indicates that properties of the resonator with water layer adjacent to the solid state dielectric become nearly the same as with metal layer. The proposed measurement technique can be used also for studies of nonlinear properties of liquids.

Millimeter-Wave Surface Impedance Characterization of HTS Films and Single Crystals Using Quasi-Optical Sapphire Resonators

High-Q sapphire quasi-optical dielectric resonators (QDRs) excited on whispering-gallery modes are key techniques for accurate characterization in millimeter (mm) wavelength range of surface impedance of HTS large-area films and can be useful for impedance characterization of small HTS single crystals, including various unconventional superconductors. Hemispherical QDR-based technique for mm impedance characterization of HTS films is analysed theoretically and confirmed experimentally. Such an approach can be applied to QDR of modified forms. The temperature dependences of the YBaCuO films resistance properties using hemispherical resonator and the iron-pnictide single-crystal impedance properties using radially-slotted one are measured in Ka-band.

Q Factor of a Millimeter-Wave Sapphire Disk Resonator with Conductive End Plates

AbstractThe quality factor of a sapphire disk resonator with conductive end plates is studied theoreticallyand experimentally. The feasibity of measuring the sheet resistance of copper, titanium, and