U V Varada Raju

Bio: U V Varada Raju is an academic researcher. The author has contributed to research in topics: Shields & High-temperature superconductivity. The author has an hindex of 1, co-authored 1 publications receiving 2 citations.

Magnetic shielding using high-temperature superconductors

Abstract: Magnetic shields of various high-temperature superconductors, YBa2Cu3O7−x (YBCO), YBa2Cu3O7−x-Ag composites (random inclusions as well as non-random coatings) and Bi2Sr2Ca2Cu3Ox (BSCCO) were prepared by uniaxial as well as isostatic compression with various dimensions. The shielding properties were measured at 77 K for dc and ac magnetic fields in the range of frequencies from 100 Hz to 10 kHz. The critical penetration field (CPF), defined as the value of the applied magnetic field at which a detectable field was observed inside the cylinder, varied from cylinder to cylinder and also with the ageing of the cylinders in the case of YBCO shields. The highest value of CPF was 16 G at 77 K for YBCO shield prepared by isostatic compression. Even though the stability of BSCCO shields with respect to ageing is good, the CPF values are very low compared to those for YBCO. Detailed studies were performed in the case of YBCO shields. The CPF decreased as a function of time over a period of 90 days. The CPF decreased as the frequency of the applied field was increased. The wave form of the field inside the pot for a sinusoidal applied field was highly distorted and showed the presence of higher harmonics with appreciable amplitude. The wave form was Fourier-analysed to yield the field inside the shield along with the harmonics. The shields with Ag addition seem to give better performance at high fields.

Magnetic shielding and harmonic generation in high-Tc superconducting tubes

Abstract: Magnetic shielding and harmonic generation in a sintered Y1Ba2Cu3O7-x tube, subjected to an incident AC magnetic field, has been studied. This study has shown that the onset of superconductivity in the specimen introduces a magnetic shielding of about 25 dB. Odd harmonics are generated during the propagation of the AC magnetic field. Flux trapping occurs in the specimen for frequencies less than 10 kHz. This trapped flux behaves as a superimposed DC magnetic field and results in a low shielding effectiveness and generation of even harmonics in the transmitted waveform.

Superconducting materials for electronic applications

Abstract: Shielding elements were made of bulk material or thick films. The bulk route is determined by large-scale processing. After an axial or isostatic pressing of the fine-grained powder composed of BSCCO, Y-123 and Nd-123, the material was sintered/textured and annealed in special programs. Then the characterization of the materials and a measurement of magnetic fields was done with the help of a specially constructed measuring apparatus with Hall- and SQUID-sensors. The objective of the thick film route was to get large, coated superconducting work pieces of YBCO and BSCCO (plates or cylinders) with current density of >1000 kA/cm 2 (and/or a shielding effect of >1 mT). Thick films were made by plasma spraying and paste technology. Substrates used were ZrO 2 , MgO, SrTiO 3 , BaZrO 3 and others. In some cases the work pieces were treated with laser radiation. After laser and thermal treatment the surface was more dense, the cracks were cured and the current density was increased by more than two times.