SU1758529A1 - Method and transducer for nondestructive measurement of superconductor microwave parameters - Google Patents

Abstract

This invention relates to microwave measurement technology. The purpose of the invention is to increase the sensitivity and provide measurements of the density of the critical current of a superconductor in a wide frequency range. The method of non-destructive microwave parameters of a superconductor includes exposing the sample under test with a microwave signal of frequency fi with power PI and receiving an inverted signal, additional exposure of the sample under test with a microwave signal of frequency fa with power P2 "Pi, while the signal of frequency fi modulating in amplitude with frequency fa The signal power of the frequency f increases smoothly until the moment when the component appears at the reflected signal at the modulation frequency fa, the power Pi & the frequencies fi corresponding to this moment and determine the critical current density of the superconductor from the measured power using a mathematical expression relating the desired and measured values. 2 sec. and 1 z.p. f-ly, 2 ill. (L

Description

The invention relates to a measuring microwave technique and can be used to measure electric microwave parameters, including critical current density, superconducting materials in the form of films, on local surface areas with dimensions much smaller than the wavelength of the microwave radiation used for measurement.

The purpose of the invention is to increase the sensitivity and provide measurements of the critical density of the current of a superconductor in a wide frequency range.

FIG. 1 shows the design of a sensor that implements a method for non-destructive use of microwave parameters of a superconductor; in fig. 2 - a sensor with a superconductor installed, a slit.

The proposed method is based on measuring changes in the reflection coefficient of a device as a function of the power level of the frequency f 1 incident on the sample under study by modulating the amplitude of the signal at the frequency f and the subsequent selection in the reflected signal at the frequency of the modulation frequency fa, which allows to significantly increase the sensitivity of measurements. In the proposed measurement method, the modulator of a signal at frequency fi is the medium itself, therefore, the modulated signal at frequency f2 contains information about the parameters of the medium being studied.

Sensor for measuring microwave parameters contains 1 measuring lines with

cl

ate yu

sizes much smaller than the microwave radiation wavelength located in the metallization window 2 of the dielectric plate 3, while one end of the measuring line section 1 is connected to the metallization 2 of the plate 3 and the other to the microwave-mode transformer A of the stripline 5, located on the other side of the dielectric the plate 3 is co-aligned with the length 1 of the measuring line; the transformer 4, made in the form of an expanding strip of metal foil, forms a galvanic contact 6 with a strip line 5, and an angle of 7 tivolezhaschim this side is connected to the segment 1 measurement mis- line; On the surface of the segment 1 of the measuring line and the metallization 2, a dielectric film 8 is applied. When superimposed on the surface of the device (on the film 8 of the dielectric) of the investigated superconducting sample 9 (Fig. 2) cut 1 measuring line the film 8 of the dielectric and the surface of the superconducting sample 9 form a piece of asymmetrical strip line 10. for which the ground conductor superconducting surface of sample 9. At that, sections 11 and 12 of metallization 2, located near both ends of segment 1 of the measuring line, together with dielectric film 8 and the surface of sample 9, which lies above sections 11 and 12 of metal two capacitors with high capacitance.

Section 1 of the measuring line with longitudinal and transverse dimensions much smaller than the wavelength of the microwave radiation, located in the metallization window 2, can be made either in the form of a metal strip or in the form of a circular conductor. In this case, the transverse dimensions of the window are chosen much larger than the transverse dimensions of segment 1 to prevent the microwave mode of the slot line between the edges of the window and section 1 from being excited, and the longitudinal dimensions of the window are chosen in the order of the length of the segment 1.

A microwave mode transformer 4 made in the form of a strip of metal foil with a smoothly varying width along the entire length is located in the groove of the dielectric plate 3, made from the side of the strip line 5 along its axis in a plane, perpendicular to the plate 3.

A method for non-destructive measurement of the microwave parameters of a superconductor is carried out as follows.

Through the strip line 5, two microwave signals with frequencies fi and fz and power Pi and P2, respectively, are fed to the device with the test sample 9 installed on it,

moreover, PI P2. The frequency signal fi is amplitude modulated with the modulation frequency fa. With the help of a transformer 4 wba signal, the measuring line segment 1, which together with the surface of the superconducting sample 9, located above the segment 1, and the dielectric film 8 between them, form a segment of the asymmetrical strip line 10, for which the ground conductor is a superconducting surface sample 9 (see fig. 2), since each of the metallization sections 11, 12 2 located at the ends of segment 1 form the surface of a superconducting sample located above it, a flat capacitor is a large capacitor So, the resistance of these capacitors at the frequencies of microwave radiation, including at frequencies fi and G2, is much less than the characteristic impedance f0 of the asymmetric metric strip line 10. At the same time, a capacitor formed by the metallization section 11 short-circuits the strip line 10 , and through the capacitance formed by section 12, a segment of the strip line 10 is connected with a transformer 4. Thus, the local surface area of the sample 9, located above segment 1 of the measuring l NII, It appears included in the path of the strip line 10. This method of incorporation of 9 in the sample path line 10 precludes penetration mode microwave field in the dielectric substrate sample in the case studies of the superconductor film, and therefore the parameters line 10 does not depend on the substrate a superconductor material. Since the length of segment 1 of the measuring line is chosen to be much smaller than the wavelengths of microwave radiation, including radiation with frequencies fi and T2, the currents in capacitors formed by metallization sites 11 and 12 can be considered equal and oppositely directed at each time instant. Therefore, the field is not excited by these currents in the region of the dielectric film 8 between the metallization 2 and the superconducting surface of the sample 9, which makes it possible to neglect the radiation losses in the measurements.

The measurement of the critical density jc of the microwave current of the superconductor 9 in the local region bounded by the dimensions of segment 1 of the measuring line is carried out by gradually increasing the signal power Pi at frequency fi until it appears in the applied reflection signal at frequency f2 . A value corresponding to this moment in the power PI of the frequency частоты is recorded and the critical current density of the superconducting sample 9 is determined from it from the relation:

Jc

r-3Јf

W h

where W is the transverse size of the segment 1;

h is the depth of penetration of microwave currents into the superconductor.

Claims (3)

1. A method for non-destructive measurement of the microwave parameters of a superconductor, including exposing the sample under test to a microwave signal of frequency fi with a power Pi and receiving a reflected microwave signal and measuring the reflectance, characterized in that, in order to increase the sensitivity and provide measurements of the critical current density of the superconductor in In addition, the sample under study is exposed to a microwave signal of frequency h with power Pa, P2 "Pi, and the signal fi is modulated in amplitude with modulation frequency Tz, while the reflected signal is received at the frequency f2, the signal power of the frequency fi is gradually increased until the moment fj appears in the reflected signal component at the modulation frequency fa, the corresponding power of the frequency Pi ° of the signal fi is recorded, which determines the critical current of the superconductor dependencies, associating the desired parameter with the measured. 2. A sensor for non-destructive measurement of microwave parameters of a superconductor, comprising an input node, a measuring line section and an output node, characterized in that the measuring line segment and the input node are made on opposite sides of the dielectric plate, while the measuring line segment is made in the form of a strip of metal or round conductor with transverse and longitudinal dimensions much smaller than the microwave radiation wavelength, and placed in a window made in the metallization of the dielectric plate, transverse The dimensions of which are much larger than the transverse dimensions of the measuring line segment, and the longitudinal dimensions are about the length of the measuring line segment, with one end of the measuring line segment connected to the metallization of the dielectric plate, and the other end connected to the input node in the form of a stripline through a microwave transformer lines on the opposite side of the dielectric plate, the surface of which on the placement side of the measuring line segment is covered with a dielectric film. 3. The sensor according to claim 2, characterized in that the microwave mode transformer is made in the form of a strip of metal foil with smoothly varying width along its entire length, which is located in the groove of the dielectric plate, made from the side of the strip line along its axis in a plane perpendicular to the dielectric plate, while the strip of metal foil is connected to the strip line by one of its lateral sides and opposite to it angle - to the measuring line segment. V 1 S / 5 4 7 / FIG. 2