Multi-Channel High Tc SQUID

Hideo ITOZAKI  Saburo TANAKA  Tatsuoki NAGAISHI  Hisashi KADO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E77-C   No.8   pp.1185-1190
Publication Date: 1994/08/25
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Section on Superconducting Devices)
Category: HTS
Keyword: 
super conductive electronics,  high Tc superconductor,  SQUID,  step edge junction,  biomagnetic signals,  magnetocardiogram,  

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Summary: 
A multi-channel high temperature superconducting interference device (high Tc SQUID) system with high magnetic field resolution has been developed. Step edge junctions were employed as weakly coupled Josephson junctions for the SQUID. These junctions worked well and their I-V curves fit the resistively shunted junction (RSJ) model. The SQUID design was investigated to improve magnetic field resolution. The size of the SQUID's center hole was investigated, and we found the optimized size of the hole to be about 25 µm. Meissner effect of superconductor was used in order to concentrate magnetic fluxes. A large washer SQUID and a flux concentrating plate was developed to concentrate magnetic flux to the SQUID center hole. The magnetic field resolution became 370 fT/Hz at 10 Hz and 220 fT/Hz at 10 kHz. This field resolution was enough to detect biomagnetic signals such as magnetocardiac signals. The SQUID was mounted on a special chip carrier and was sealed with epoxy resin for protection from humidity. We have designed and developed a 4-channel and a 16-channel high Tc SQUID system. We used them in a magnetically shielded room to measure magnetic signals of the human heart. We obtained clear multi-channel magnetocardiac signals, which showed clear so called QRS and T wave peaks. A clear isofield contour map of magnetocardiac signals was also obtained. These data indicated that high Tc SQUID is feasible for these biomagnetic applications.