Geometrical instruments – Indicator of direction of force traversing natural media – Level or plumb – terrestrial gravitation responsive
Patent
1997-06-16
1999-05-11
Bennett, G. Bradley
Geometrical instruments
Indicator of direction of force traversing natural media
Level or plumb, terrestrial gravitation responsive
324248, 505846, G01R33/02
Patent
active
059014539
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a gradiometer with two SQUIDs each containing a SQUID loop.
For the quantitative investigation of magnetic fields or magnetic field gradients, especially in the field of nondestructive testing of workpieces or in the field of biomagnetic investigations with the aid of SQUID, a gradiometer which can suppress detrimental fields is highly desirable. The detrimental effects include fluctuations of the field of the earth as well as fields which are synthetic and electromagnetically load the environment, for example like the 50 Hz alternating current field emanating from electrical apparatus. On the basis of low T.sub.c materials, gradiometers are already known which can be produced at relatively low cost. For these purposes ductile wires are used with the aid of which closed coil pairs with partly opposing winding directions enables elimination of fields with low gradients. In the field of high T.sub.c materials, up to now no suitable wires have been provided.
From Supercond. Sci. Technol. 7 (1994), 265-268, so-called axial gradiometers are known in which two SQUIDs are arranged in planes spaced from one another up to several centimeters. Here the signals of the individual SQUIDs can be processed in separate electronic systems and subtracted from one another.
These gradiometers have the drawback of a high fabrication cost and, associated with it, the need for expensive mechanical alignments. In addition, in the case of such a gradiometer with two SQUIDS, gradient signals are suppressed only with the aid of a further, third SQUID, forming in this manner a second order gradiometer.
A gradiometer is known further from Appl. Phys. Lett. 56 (1990 1579 in which the Josephson junction lies symmetrically between two relatively widely-spaced SQUID loops and is connected with them through thin slits. Such a gradiometer has the drawback that one is limited to a relatively short base length (spacing of the middles of the respective SQUID loops from one another), since otherwise the SQUID inductivity is too large and as a result the SQUID signal is too small.
OBJECT OF THE INVENTION
It is thus the object of the invention to provide a gradiometer which is of a comparatively simple type and which is free from the drawbacks of the known gradiometers and which can achieve increased measurement precision of the magnetic field or the magnetic field gradient.
SUMMARY OF THE INVENTION
The gradiometer of the invention contains SQUIDS so arranged with respect to one another that the SQUID loops are spaced apart by a basis length L.sub.1 and lie in a plane. A flat flux concentrator is parallel to this plane and encompasses both SQUID loops, the flux concentrator being mirror symmetrical on either side of a basis line B.sub.1 connecting the centers of the two SQUID loops with each other.
A gradiometer according to the invention is provided with the SQUIDs so juxtaposed with one another that the SQUID loops are spaced by a basis length L.sub.1 from one another in a plane and a flat flux concentrator encompasses both SQUID loops parallel to this plane. Here the flux concentrator is formed laterally and mirror symmetrically with respect to the basis line connecting the centers of the two SQUID loops.
It has been found that upon the application of a homogeneous magnetic field perpendicular to the gradiometer plane, shielding currents are induced at the outer edge of the flux concentrator and which generate concentrated magnetic fields of equal size at each of the locations of the SQUIDs. By subtraction of the respective signals of the individual SQUIDS, different signals are obtained which in such a gradiometer are free from spatially homogeneous spurious signals. Inhomogeneous fields however are concentrated to different degrees in the individual SQUIDs and form in this case a difference signal differing from zero.
The gradiometer of the invention has the special advantage that a given desired basis length of the gradiometer can be selected by suitable constructive features without le
REFERENCES:
patent: 4613816 (1986-09-01), Zeamer
patent: 4761611 (1988-08-01), Hoenig
patent: 4767988 (1988-08-01), Willson
patent: 4771239 (1988-09-01), Hoenig
patent: 5053834 (1991-10-01), Simmonds
patent: 5218297 (1993-06-01), Nakane et al.
patent: 5252921 (1993-10-01), Nakane
patent: 5465049 (1995-11-01), Matsuura et al.
patent: 5625290 (1997-04-01), You
patent: 5672967 (1997-09-01), Jensen et al.
SQUID with Integral Flux Concentrator, published 2301 NTIS Tech Notes (1990) Mar.
Multi-Channel High Tc SQUID, published 2334c IEICE Transactions on Electronics, E&&-C(1994)Aug., No. 8.
A Second-Order SQUID Gradiometer Operating at 77 K, published Supercond. Sci. Technol. 7 (1994) 266-268.
High Sensitive Magnetometers and Gradiometers Based on DC SQUIDS with Flux Focuser, published IEEE Transactions on Magnetics. vol. 27, No. 2, Mar. 1991.
Design of Improved Integrated Thin-Film Planar dc SQUID Gradiometers, published J. Appl. Phys. 58 (11), Dec. 1, 1985.
Bulk BiPbSrCacuO rf SQUIDS oeprating up to 101 K, published Appl. Phys. Lett. 56 (16), Apr. 16, 1990.
Low-noise Yba.sub.2 Cu.sub.3 O.sub.7 rf SQUID magnetometer, published Appl. Phys. Lett. 60(5), Feb. 3, 1992.
Bousack Herbert
Soltner Helmut
Wolf Walter
Zhang Yi
Bennett G. Bradley
Dubno Herbert
Forschungszentrum Julich GmbH
LandOfFree
Gradiometer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gradiometer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gradiometer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-238593