S.G. Wang

Application of high temperature superconducting quantum interference devices in transient electromagnetic method for magnetotelluric soundings

Abstract We have explored the application of high temperature superconducting interference devices (SQUIDs) in the artificial source magnetotelluric sounding. Field experiments were performed to test the high T c SQUID in transient electromagnetic source. It showed that the SQUID sensor has some advantages over the conventional inductive sensor, and also revealed some problems. Theoretical studies have been carried out to investigate the prospects and limitations of the SQUID sensor.

HRXRD analysis for YBa2Cu3O7-x deposited on {001} LaAlO3

Abstract YBa 2 Cu 3 O 7- x (YBCO) superconducting film was fabricated on {001} LaAlO 3 (LAO) substrate by pulse laser deposition (PLD), and its microstructure was examined by high resolution X-ray diffraction technology (HRXRD), such as pole figure, rocking curve, reciprocal space mapping. The results show that the YBCO crystalline alignment is almost {001} YBCO //{001} LAO , 〈100〉 YBCO //〈100〉 LAO besides 2% {001} YBCO //{001} LAO , 〈110〉 YBCO //〈100〉 LAO . The out-plane alignment of YBCO is some spreading (the breadth is 0.75°). There are 90°±0.65°〈110〉 twin domains in the film, which is caused by the high local stress and stress difference between 〈100〉 and 〈010〉 during the tetragonal to orthorhombic phase transition.

Measurements of the magnetocardiography in unshielded environment using high-Tc rf SQUID gradiometer

Abstract We recorded the 9-point magnetocardiography (MCG) of a normal person in an unshielded environment by using a first-order gradiometer made by subtracting the outputs of two high-T c YBCO rf SQUID magnetometers. A compensation method was used to cancel the 50Hz line interference. After data processing an averaging, the fine structures of the heart signal (P-wave, Q,R,S-complex, T-wave) could be seen clearly and a SNR of 120 could be obtained.

Improving on the yield and performance of high Tc rf SQUIDs

Abstract A method to control and determined the critical currents I c of step-edge junctions has been developed. Using this method, the critical currents of step-edge junctions are easily adjusted to within a range useful for obtaining high performance rf SQUID magnetometers or gradiometers.

Optimizing the slew rate of SQUID system

Abstract We study optimization of the slew rate of SQUID (Superconducting QUantum Interference Device) systems both theoretically and experimentally. Considering the total equivalent noise flux input in the SQUID, both for SQUID electronics with one pole and for electronics with two poles and one zero, we get new formulas for slew rate and find the optimum bandwidth for the maximum slew rate. For SQUID electronics with one pole, the optimum bandwidth and corresponding maximum slew rate are both proportional to S Φ −1 . While for systems with two poles and one zero, the optimum bandwidth and corresponding maximum slew rate are proportional to S Φ −1 and S Φ −2 respectively. The SQUID sensors and a multi flux quanta electronic simulator are used in the experiment and the results are in good agreement with analysis.

Fabrication of low noise High-Tc bicrystal junction rf SQUID

Abstract We fabricate rf superconducting quantum interference devices (SQUIDs) using a YBCO bicrystal junction, which is made on a chip consisting of a 10×12mm2 YSZ bicrystal substrate with a 24° angle of in-plane misorientation. The magnetic field sensitivity is 84 fT/Hz 1 2 . The tank frequency at which the rf SQUID operated is near 800MHz. According to our result, the boundary across the superconducting loop does not show significant effects on the 1/f noise level.

The effect of excess current on high-c superconducting step-edge Josephson junctions

Abstract In this paper, we discuss the effect of excess current on SQUID performance, and point out that excess current may be the reason leading to a lower yield rate of rf SQUIDs.

Ditch-typed step-edge grain boundary junction and rf SQUID

Abstract Ditch-typed step-edge junctions and rf SQUIDs were fabricated from epitaxial YBa 2 Cu 3 O 7 films on SrTiO 3 substrates. The ditch on the substrate was milled by Ar-ion, using YBCO film and photoresist as masks. The structure of the SQUID is a planar square washer. The size of the outer washer and center hole is 9×9 mm 2 and 200×200 μm 2 respectively. The voltage-flux modulation was clearly observed at a bias frequency of 150 MHz. At 77 K, a white flux noise of 4.0×10 −4 Φ 0 /Hz 1/2 and a field resolution of 480 fT/Hz 1/2 have been obtained at 5 Hz.