Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-09-03
2001-11-27
Flynn, Nathan (Department: 2826)
Electricity: measuring and testing
Magnetic
Magnetometers
C505S161000, C257S031000
Reexamination Certificate
active
06323645
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to superconducting quantum interference devices used for measurement of a fine magnetic field, electric current, voltage, electromagnetic wave and so on and, more particularly, to a superconducting quantum interference device enabling high sensitivity measurement and spatial resolution but low in noise.
There is shown in
FIG. 7
a structural view of a superconducting quantum interference device (hereinafter abbreviated as SQUID) according to the prior art. On a substrate
5
are integrated Josephson junctions
1
, washer coils
2
, a detection coil
3
, and a feedback-modulation coil
4
. The SQUID shown in
FIG. 7
is a DC-SQUID including two Josephson junctions in a superconducting loop. The feedback-modulation coil
4
is magnetically coupled to the washer coils
2
. A superconducting loop is constituted by the detection coil
3
for external magnetic field detection, the washer coils
2
, and a pair of the Josephson junctions
1
is connected at the respective ends of the washer coils.
The SQUID is connected to an external control system
6
and supplied with a bias current Ib. The external control system
6
feeds back to the superconducting loop a control signal Im corresponding to a SQUID output Vs. The control signal Im is delivered as a magnetic signal to the superconducting loop through the feedback-modulation coil
4
magnetically coupled to the washer coil
2
. An output voltage signal Vout corresponding to an external magnetic field, which has been detected by the detection coil
3
is obtained on the external control system.
In order to obtain high spatial resolution, the detection coil has to be made small in size. Due to this, as shown in
FIG. 7
a fine detection coil
3
is integrated, together with the Josephson junctions
1
and washer coils
2
, on the substrate.
Conventionally, the SQUID used for measurement on high spatial resolution has integrated Josephson junctions and washer coils and the like, together with a fine detection coil, on a common substrate. A signal generated by a signal source is detected by the detection coil. Meanwhile, a magnetic field due to the signal source links similarly to the washer coil. In such a case, measurement is made on the basic of a magnetic field linked to both the detection coil and the washer coil. As a consequence, it is difficult to measure with accuracy a magnetic field linked only to the detection coil that is to be measured.
In the case where using a detection coil having a small detection area, there is a considerable affection of a magnetic field linked to portions other than the detection coil, and particularly the washer coil.
SUMMARY OF THE INVENTION
In order to solve the above problem, the present invention utilizes a superconductor for enclosing a loop formed by a washer coil that is formed at an upper portion or lower portion of the washer coil, or a washer coil formed on a ground plane of a superconducting thin film, thereby preventing a magnetic field caused by a signal source from being linked to portions other than a detection coil.
REFERENCES:
patent: 4489274 (1984-12-01), Berlincourt
patent: 5166614 (1992-11-01), Yokosawa et al.
patent: 5173660 (1992-12-01), Marsden
patent: 5293119 (1994-03-01), Podney
patent: 5548130 (1996-08-01), Shimizu et al.
IBM Technical Disclosure Bulletin, Mar. 1985 vol. 27, Issue 10A, pp. 5847-5848.
Morooka Toshimitsu
Odawara Akikazu
Adams & Wilks
Flynn Nathan
Seiko Instruments Inc.
Wilson Scott R.
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