Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1994-08-17
1997-09-09
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetometers
505846, G01R 33035, H01L 3922, H01F 502
Patent
active
056660529
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a magnetic sensor having a superconducting quantum interference device (SQUID) which is in the superconducting state on a level of cryogenic temperature, and relates to a magnetic detecting device in which the magnetic sensor is combined with a cryogenic refrigerator. In particular, this invention pertains to thermal conduction structure of a superconducting pick-up coil in a magnetic-flux input circuit which is connected to the SQUID.
BACKGROUND ART
Conventionally, there is known, as one of superconducting devices, a SQUID using Josephson effect. By connecting the SQUID to a magnetic-flux input circuit having a superconducting pick-up coil, there can be obtained a SQUID magnetometer as a kind of magnetic sensor for measuring an extremely faint magnetic field, i.e., a magnetic field generated from faint current in a living body such as a magnetocardiogram, a magnetic field generated from a microscopic magnetic substance in a living body.
When the SQUID magnetometer is cooled to a level of cryogenic temperature, that is, to a temperature level on which the SQUID and the superconducting coil turn to the superconducting state, there may be applied a method of cooling the SQUID magnetometer in such a manner that liquid helium on the level of cryogenic temperature is stored in a cryogenic container (cryostat) and the SQUID magnetometer is steeped in the liquid helium so as to be cooled. In this case, generally, a cooling head of a refrigerator for generating cool condition is entered in the cryogenic container and helium gas evaporated in the container is recondensed into liquid by the refrigerator.
In the above method, since the SQUID magnetometer is steeped in liquid helium, the SQUID magnetometer can be cooled at a short time.
On the other hand, since the cooling of the SQUID magnetometer is carried out by the medium of the liquid helium in the cryogenic container, its cooling system becomes large-sized and its operational performance is deteriorated. In addition, it requires much skill to treat the liquid helium and, depending on circumstances, a careless treatment of the liquid helium may cause a trouble.
Further, since the container in which the liquid helium is stored is not filled to the uppermost end thereof with the liquid helium, the temperature at the inside of the container increases toward the upper part of the container. As a result, a thermal gradient occurs at the inside of the container. This thermal gradient disadvantageously limits an angle capable of inclination of the container. Due to this disadvantage, when a biomagnetic field is measured, it becomes difficult to optionally set the SQUID, the pick-up coil and such in accordance with the condition (posture) of a subject. This is a problem which cannot be disregard.
Therefore, attention has been paid to a conventional method of contacting the SQUID magnetometer with the cooling head of the refrigerator in order that heat can be directly transmitted thereby cooling the SQUID magnetometer (for example, refer to the Japanese Patent Application Laid Open Gazette No. 2-302680).
In this case, the SQUID magnetometer, the pick-up coil and such are attached and thermally connected to a final cooling stage to be cooled below a transition temperature of superconductivity by the cryogenic refrigerator. Accordingly, if only the operation of the cryogenic refrigerator is controlled, selection makes possible between the superconducting state and the normal conducting state. This does not require to move the SQUID, the pick-up coil and such for the above selection.
On the other hand, when the SQUID magnetometer is cooled by the refrigerator in the above way, there is generated the following two problems. The pick-up coil of the magnetic-flux input circuit is generally wound into loops around a tubular bobbin made of resin. However, since the thermal conductivity of the resin forming the bobbin is low, it is very difficult to cool the pick-up coil around the bobbin to its transition temperature of superconducti
REFERENCES:
patent: 4693000 (1987-09-01), Hoenig
patent: 5349291 (1994-09-01), Kotani et al.
Mulder, G. B. J. et al., "The application of heat drains in superconducting solenoids for AC purposes", Abstract, Proceedings of the Eleventh International Cryogenic Engineering Conference, ICEC 11, Berlin, West Gernamy, 22-25 Apr. 1986, ISBN 0-408-01258-7, 1986, Guildford, UK, Butterworths, UK.
Pennell, G. F. and Varmha, R., "Plastic Bobbin with Metal Heat Sink", IBM Technical Disclosure Bulletin, vol. 24, No. 7A, Dec. 1981, New York, US, p. 3347.
Blanche Bradley D.
Daikin Industries Ltd.
Ferguson Jr. Gerald J.
Snow Walter E.
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