High-performance high-T/sub c/ SQUID sensors for multichannel systems in magnetically disturbed environment

We have fabricated and characterized high-T/sub c/ SQUID sensors that are suited for operation in multichannel systems in magnetically disturbed environment. Utilizing the superior properties of our 30/spl deg/ SrTiO/sub 3/ bicrystal junctions, we are able to fabricate high-performance single-layer direct-coupled SQUID magnetometers. System noise levels down to 24 fT Hz/sup -1/2/ and typical 1/f corners of 4 Hz/sup -1/2/ were obtained for devices having a 9 mm/spl times/9 mm pickup loop and a nominal SQUID inductance of 100 pH. To protect the SQUIDs from moisture, they are hermetically encapsulated in a ceramic housing. A thick film resistor integrated on the chip carrier allows one to heat the SQUID device above T/sub c/ in order to release trapped magnetic flux. For the operation of our low-noise SQUIDs, a compact direct-coupled read out electronics with a preamplifier voltage noise of 0.4 nV Hz/sup -1/2/ and 100 kHz bias reversal was developed. Sensor dynamics and linearity were investigated with regard to the operation in magnetically disturbed environment. The maximum system bandwidth and slew rate of our bias reversal electronics were 1 MHz and about 5/spl times/10/sup 5/ /spl Phi//sub 0//s, respectively. For signal frequencies /spl les/50 Hz/sup -1/2/, a minimum total harmonic distortion of -118 dB was measured, dominated by nonlinearities in the read-out electronics. A new magnetometer design with improved noise performance in magnetically disturbed environment is presented.

[1]  John Clarke,et al.  Reduction of 1/f noise in high‐Tc dc superconducting quantum interference devices cooled in an ambient magnetic field , 1996 .

[2]  Jörn Beyer,et al.  Low-noise YBa2Cu3O7−x single layer dc superconducting quantum interference device (SQUID) magnetometer based on bicrystal junctions with 30° misorientation angle , 1998 .

[3]  Dietmar Drung,et al.  Advanced Squid Read-Out Electronics , 1996 .

[4]  A. A. Fife,et al.  Noise cancellation by a whole-cortex SQUID MEG system , 1995, IEEE Transactions on Applied Superconductivity.

[5]  Kiejin Lee,et al.  Josephson effects in YBa2Cu3Oy grain boundary junctions on (100)MgO bicrystal substrates , 1995 .

[6]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[7]  Harold Weinstock,et al.  SQUID sensors : fundamentals, fabrication, and applications , 1996 .

[8]  Vittorio Foglietti,et al.  Flux dam, a method to reduce extra low frequency noise when a superconducting magnetometer is exposed to a magnetic field , 1995 .

[9]  F. Ludwig,et al.  YBA2CU3O7-X DC SQUID MAGNETOMETERS WITH BICRYSTAL JUNCTIONS FOR BIOMAGNETIC MULTICHANNEL APPLICATIONS , 1997 .

[10]  D. Drung.  Improved dc SQUID read-out electronics with low 1/f noise preamplifier , 1997 .

[11]  J. Schubert,et al.  Electronic high-temperature radio frequency superconducting quantum interference device gradiometers for unshielded environment , 1997 .

[12]  Andrew G. Glen,et al.  APPL , 2001 .

[13]  D. G. Nichols,et al.  Linearity of high‐Tc dc superconducting quantum interference device operated in a flux‐locked loop , 1996 .