A. I. Gubin

Microwave-band reflection coefficient of high-temperature superconductor specimens in E-plane waveguide structures

The microwave-band reflectivity of high-temperature superconductor (HTSC) specimens was measured for the first time in the E-plane waveguide structures of two types: tapered waveguide termination and E-plane corner section. The measured reflection coefficient of a textured YBa2Cu3O7−δ specimen used as a tapered waveguide termination corresponds well to the theoretical curve calculated using an improved two-fluid HTSC model.

Accurate permittivity characterization of liquids by means of WGM resonator with microfluidic

Dielectric resonators are used widely for determination of materials complex permittivity. Whispering gallery mode (WGM) dielectric resonators have high quality factor values and this make it possible to achieve a high measurement precision [1]. In order to research the biological liquids in small it is reasonable to use dielectric resonators with small nonhomogeneities where the liquids under test are placed, for example the resonator with an additional thin layer [2] or with a capillary [3]. The shortcoming of these resonators is a difficult making.

WGM resonators with microfluidic channel for sub-mm wave characterization of biological liquids

We present the measurement technique for studying the electromagnetic properties of small-volume water solutions of bioliquids in sub-THz band. The measurement cell is based on the quartz resonator covered by the plastic layer with the microfluidic channel filled with the liquid under test. The experimental and numerical studies of the resonator with the microfluidic channel filled with liquids with known properties were carried out to show the suitability of the resonator structure for the permittivity measurements. The resonator structure with the microfluidic channel filled with glucose and albumine water solutions was studied experimentally. The solution permittivity values can be obtained by solving of the inverse electromagnetic problem.

Nonlinear attenuation in YBCO coplanar transmission line in applied magnetic field

It is well known that high temperature superconductors (HTS) generally reveal a nonlinear dependence of the surface impedance on the input microwave power Zs(Pin) unlike the normal metals behavior. This leads to undesirable nonlinear effects (such as: intermodulation distortions, generation of higher harmonics) in HTS passive microwave devices and strongly limits possibilities of their application even for weak microwave signals. On the other hand, strong nonlinear effects in HTS materials can be used for design of active devices, such as microwave power limiters. Similar devices have been elaborated already for application as dc and low-frequency ac current limiters in electric circuits.

Temperature dependence of the microwave conductivity of a YBCuO film in the normal state

The results of an experimental study of the fluctuation conductivity of an optimally doped YBa2Cu3O7−δ epitaxial film are presented. The results were obtained from measurements of the complex reflection coefficient of the sample at grazing incidence according to a method developed and implemented by the authors in the millimeter wavelength range. The results demonstrate good agreement with a theoretical model constructed in the framework of Gaussian theory for a frequency-limited fluctuational 2D microwave conductivity in the temperature interval 93–120K.

Microwave - to - submm wave reflection and transmission coefficients for investigation of biochemical water solutions

The investigation of the complex conductivity (or permittivity) of superconducting samples by grazing incidence microwave reflectivity measurements is a promising method to study of the samples with different thicknesses in wide temperature range (i.e. conductivity range) [1,2]. The main feature of the method is use of grazing incidence p-polarized wave in order to increase the sensitivity of the measurement, which makes possible such a kind of investigation. The sensitivity of the reflection coefficient to permittivity changes increases up to Brewster angle, which is almost 90 degrees for metals and superconductors. The method could be also useful for the investigation of complex permittivity of different liquids and biochemical solutions by measuring of reflection orand transmission coefficient of the samples under test.

Nonlinear coplanar waveguide on the basis of high-Tc superconducting thin film

Coplanar waveguides based on HTS thin films with two thicknesses were fabricated and their nonlinear properties were studied. Very weak nonlinear effect was observed at liquid nitrogen temperature. The effect increases under dc-bias applied to CW at T=77K and with increasing temperature up to critical value. The behaviour of phase coefficient for propagation constant is revealed to be strongly dependent on input power. The experimental results are in good agreement with theory, although the thermal effects are noticeable. The results show that planar transmission lines based on HTS thin films are promising structures for development of microwave signal limiters.