The recent development of high-temperature superconducting (HTS) filters for the receiver front-end of mobile telecommunication base stations and small cryocoolers is described in this paper. The merits of the HTS filters are small size, low noise and sharp skirt. One of these filters combined with a cryogenic low-noise amplifier contributes greater noise reduction to the receiver and improves the Carrier/Noise power ratio (C/N) of the transmission. The HTS filters, having high quality factors, are also effective for reducing out-of-band interference. On the other hand, cryogenic cooling is an essential and important technology for HTS filters. A reliable, low-cost, small cryocooler is required. In the USA, HTS filter systems have been field-tested using prototype equipment with small cryocoolers.
We prepared a Bi-based superconductor using a variety of Pb-oxides and found that the samples prepared at temperatures above 830°C using Pb-oxides contained the 2223-phase; especially, the samples prepared at temperatures above 855°C using Pb2O3 showed a zero-resistance temperature above 90K. The XRD results showed that the volume fraction of the 2223-phase superconductor was increased by doping with Pb2O3. The chemical bonding nature of the samples which prepared using Pb2O3 was different from those of the samples prepared using other Pb-oxides. The results may indicate that Pb2O3 has a peculiar effect on the formation of a 2223-phase.
The mechanical properties and the axial tensile strain and transverse compressive stress dependence of the critical current (Ic) in mono-core and 19 core Bi(2212) superconducting tapes with different sheaths were evaluated at a temperature of 4.2K and a magnetic field of 14T. Replacement of the Ag sheath with an Ag-Zr alloy sheath increased the 0.2% proof stress and the tensile strain for Ic degradation onset although Ic decreased markedly. A two-layer sheath with an Ag inner layer and Ag-Zr alloy outer layer improved both the stress-strain and strain characteristics of Ic without remarkable degradation of the Ic. Increasing the number of cores from 1 to 19 degraded the tensile strain vs. Ic characteristics of the tape, although no marked change in the critical current density was observed. The alloying of the sheath also improved the transverse compressive stress vs. Ic characteristics. The effects of Zr alloying of the Ag sheath on the mechanical behavior and stress/strain dependence of the Ic of superconducting composites are briefly discussed with emphasis on texturing of oxide superconductors.