Band-pass microstripe filters using high-temperature superconducting films

Results are presented of a simulation and experimental investigation of band-pass filters consisting of coupled microstripe resonators fabricated using high-temperature superconducting films. It was shown that by using reliable models of high-temperature superconducting filter elements and careful design, it is possible to synthesize high-temperature superconducting filters as an integrated circuit without using additional tuning elements. Two filter configurations were investigated at a frequency of 1.75 GHz with a 4% pass band. A significant result is that the calculated and experimental characteristics of both filter configurations show very satisfactory agreement. Pis’ma Zh. Tekh. Fiz. 24, 50–54 (December 26, 1998)     

Nonlinear damping in mechanical resonators made from carbon nanotubes and graphene

The theory of damping is discussed in Newton's Principia and has been tested in objects as diverse as the Foucault pendulum, the mirrors in gravitational-wave detectors and submicrometre mechanical resonators. In general, the damping observed in these systems can be described by a linear damping force. Advances in nanofabrication mean that it is now possible to explore damping in systems with one or more atomic-scale dimensions. Here we study the damping of mechanical resonators based on carbon nanotubes and graphene sheets. The damping is found to strongly depend on the amplitude of motion, and can be described by a nonlinear rather than a linear damping force. We exploit the nonlinear nature of damping in these systems to improve the figures of merit for both nanotube and graphene resonators. For instance, we achieve a quality factor of 100,000 for a graphene resonator.     

Small helical antenna made of high-temperature superconducting thick film

To realize a highly efficient small antenna, high-T _c superconducting thick films with zirconia cores are adopted in order to fabricate both a self-resonating small helical radiator and a quarter-wave matching circuit. The actual gain of a superconducting antenna measured at 478 MHz using a 1/70-wavelength radiator was 4.9 dB higher than that of a copper antenna.     

Nonlinear dynamics in superconducting films

The theory of Halperin and Nelson describes the linear response of a superconducting film close to the Kosterlitz-Thouless transition to an ac field. We have extended this theory so as to describe the non-linear response in lowest order in the driving field. Two effects are predicted: the response at the driving frequency becomes non-linear, and odd harmonics are generated. We calculate explicitly the size and temperature dependence of these effects when the response is generated and detected by an identical pair of coils placed symmetrically either side of the film.     

Features of technology of high-temperature superconductor films for microwave filters

The characteristics of fourth-order bandpass microwave filters based on high-temperature super-conductor (HTS) films have been numerically simulated and experimentally measured for the devices based on YBCO films purchased from Theva GmbH (Munich) and manufactured at the Institute for Physics of Microstructures (Nizhni Novgorod). Experimental data were used to determine the parameters of the surface impedance model for the HTS films. The results show that HTS-based filters with high performance characteristics can be obtained using HTS films manufactured by different technologies.     

On the thermal mechanism of microwave breakdown of high-temperature superconducting films

Theoretical arguments supporting the thermal nature of the microwave breakdown of high-temperature superconducting films are compared with experimental data. A comparison of the theoretical and experimental values of the threshold field for breakdown of a uniform film, B _f, and the threshold field for breakdown at nonsuperconducting defects, B _d, confirms the dependence corresponding to a thermal mechanism: B _f, B _d∝ (T _c-T ₀)^1/2. It is shown that the space-time picture of the observed breakdown is apparently due to overheating of the film near defects with a size of 10⁻⁵–10⁻⁶ m. The amplitude of the breakdown field may ultimately be limited by the abrupt decrease in the energy of critical disturbances for the initiation of breakdown. Pis’ma Zh. Tekh. Fiz. 24, 12–17 (June 12, 1998)     

Modeling and experimental investigation of microstrip resonators and filters based on High-Temperature Superconductor films

Complex approach to the investigation of microstrip resonators and filters based on High-Temperature Superconductor (HTS) films is described, which includes modeling of the electrodynamic parameters of HTS films, designing of microstrip resonators and filters, their manufacturing, and testing. Test samples were prepared using YBCO films on 0.5-mm-thick lanthanum aluminate substrates. The resonators and filter structures were patterned using ion-beam photolithography. Experimental data were used to determine the parameters of the model of surface impedance of the YBCO film and the film thickness and permittivity. Adequacy of the model and reliability of the model parameters, which were used for the synthesis and design of a 4th-order filter, were confirmed by coincidence of the experimental and calculated characteristics.     

Use of magnetic field screening by high-temperature superconducting films to switch microwave signals

The efficiency with which YBCO films screen an alternating magnetic field near the superconducting transition was measured. In the decimeter range measurements were made of the characteristics of a switch whose operating principle was based on the change in the screening of an alternating magnetic field by a superconducting transition. Pis’ma Zh. Tekh. Fiz. 24, 76–81 (July 12, 1998)     

Phase noise in surface-acoustic-wave filters and resonators

Measurements of the phase noise modulation imparted on UHF carriers by surface-acoustic-wave (SAW) filters and resonators have been made using an HP 3047 spectrum analyzer. Three different types of SAW phase noise were observed. One type can be explained by temperature fluctuations. It is characterized by a spectral density of phase fluctuations which decreases as 1/f(2). The predominant noise mechanism in most SAW devices has a 1/f spectral density. The source of this noise is unknown, but it appears to be associated with both acoustic propagation and transduction. In filters fabricated on lithium niobate substrates, a third noise mechanism is evidenced. This mechanism produces nonstationary noise bursts that appear to originate in the transducer region. Experiments have been carried out on substrate materials, transducer metallizations, and over acoustic path lengths. The means by which low-frequency fluctuations are mixed to the carrier frequency have been studied.     

Influence of desorption on the composition of high-temperature superconducting thin films during magnetron sputtering

Results are presented of investigations to study how desorption caused by interaction between the surface of condensation and the plasma particles affects the composition of thin films of Y-Ba-Cu-O high-temperature superconductors during magnetron sputtering. An analysis of the current-voltage characteristics of Langmuir probes was used to determine the floating potential of the substrate at various working gas pressures. Electron Auger spectroscopy was used to determine the atomic composition of films obtained at various substrate bias voltages. It was established that during magnetron sputtering of Y-Ba-Cu-O films the formation of the condensate composition may be strongly influenced by selective desorption of components from the substrate and the surrounding structural elements as a result of bombardment by plasma ions accelerated in the floating potential field. Pis’ma Zh. Tekh. Fiz. 24, 13–18 (December 26, 1998)     

On a modified Kim-Anderson model of the current-voltage characteristics of high-temperature superconducting ceramics

In comparison with the classical Kim-Anderson model for the current-voltage characteristics of type-II superconductors, another model with a less sharp pinning potential is presented. In addition to the approximate solution, for currents close to the critical one, a complete solution of this model is derived, which better fits the experimentally obtained current-voltage characteristics.     

Study of flow fractionation characteristics of magnetic chromatography utilizing high-temperature superconducting bulk magnet

Abstract

We present numerical simulation of separating magnetic particles with different magnetic susceptibilities by magnetic chromatography using a high-temperature superconducting bulk magnet. The transient transport is numerically simulated for two kinds of particles having different magnetic susceptibilities. The time evolutions were calculated for the particle concentration in the narrow channel of the spiral arrangement placed in the magnetic field. The field is produced by the highly magnetized high-temperature superconducting bulk magnet. The numerical results show the flow velocity difference of the particle transport corresponding to the difference in the magnetic susceptibility, as well as the possible separation of paramagnetic particles of 20 nm diameter.     

Study of flow fractionation characteristics of magnetic chromatography utilizing high-temperature superconducting bulk magnet

We present numerical simulation of separating magnetic particles with different magnetic susceptibilities by magnetic chromatography using a high-temperature superconducting bulk magnet. The transient transport is numerically simulated for two kinds of particles having different magnetic susceptibilities. The time evolutions were calculated for the particle concentration in the narrow channel of the spiral arrangement placed in the magnetic field. The field is produced by the highly magnetized high-temperature superconducting bulk magnet. The numerical results show the flow velocity difference of the particle transport corresponding to the difference in the magnetic susceptibility, as well as the possible separation of paramagnetic particles of 20 nm diameter.     

Hysteresis in theIc(H) characteristics of high-temperature superconducting ceramics and thin films

The experimental hysteretic behavior of the transport critical current observed in ceramic Y-Ba-Cu-O and (Bi-Pb)-Sr-Ca-Cu-O, as well as thin film Y-Ba-Cu-O, are presented. The data are analyzed semiqualitatively. The results show certain similarities among the ceramic samples and the films.     

Dynamic response characteristics of the high-temperature superconducting maglev system under lateral eccentric distance

Off-centre operation of high-temperature superconducting (HTS) maglev systems caused by inevitable conditions such as the misregistration of vehicle, crosswind and curve negotiation, may change the distribution of the trapped flux in the HTS bulks and the magnetic interaction between HTS bulks and the PMG. It impacts on the performance of HTS maglev, and more seriously makes the maglev vehicle overturned. Therefore, understanding the performance of the HTS maglev in off-center operation is very important. In this paper, the dynamic response characteristics of a cryostat with twenty-four onboard YBaCuO superconductor bulks were experimentally investigated at different eccentric distances under loads before the initial FC process. Parameters such as vibration accelerations, displacement, natural frequency and dynamic stiffness were acquired and analyzed via the B&K vibration analyzer and laser displacement sensors. Results suggest that the natural frequency and dynamic stiffness of the maglev vehicle would be obviously reduced with the eccentric distance, posing negative effects on the stability of HTS maglev.     

High Q printed helical resonators for oscillators and filters

High Q compact printed helical resonators which operate from around 1.8 to 2 GHz are described. These consist of a multilayer printed circuit board (PCB) incorporating a printed helical transmission line. Loss in the via hole is reduced by ensuring that the standing wave current at this point is near zero. This ensures a significant increase in Q. Further increased energy storage per unit volume is achieved due to the 3-D helical nature of the resonator. Unloaded Qs of 235 and 195 have been obtained on low loss PCBs with dielectric constants of 2.2 and 10.5, respectively. Two applications for these resonators are described in this paper. The first is the design of a compact low noise oscillator where the ratio of QL/Q0, and hence insertion loss, is adjusted for low noise. The 2-GHz oscillator demonstrates a phase noise of -120 dBc/Hz at 10 kHz which is predicted exactly by the theory. The second is a three-section filter designed to offer the response required by the front end filter of a modern GSM mobile telephone. In the filter design three helical resonators are coupled together to produce a completely printed triplate bandpass filter.     

Local characteristics of heat-radiation superconductor detectors based on high-temperature superconductor films

Relations are proposed for evaluating the local values of the thermal sensitivity, speed of response, and resolution of a heat radiation detector based on high-temperature superconductor films.Moscow Institute of Engineering Physics. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 6, pp. 873–877.     

On conduction-cooling of a high-temperature superconducting cable

Current generation high-temperature superconducting (HTS) power transmission cables use liquid nitrogen as a coolant that circulates along the cable. In this work, the use of axial conduction-cooling in attaining HTS temperatures in transmission lines is proposed. Liquid coolant use is envisioned only at periodic length intervals along the transmission lines, in combination with insulation and copper. The proposed concept is feasible due to the high thermal conductivity of pure copper at cryogenic temperatures. A basic design for the insulated cable is proposed and a detailed numerical simulation of heat transfer in such a cable is carried out for various case studies considering the superconducting materials MgB₂ and BSCCO-2223.