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SQUID Gradiometer Using Planar Coupling

IP.com Disclosure Number: IPCOM000062195D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Ketchen, MB: AUTHOR

Abstract

This article relates generally to gradiometers using superconducting quantum interference devices (SQUIDS) and, more particularly, to a technique of using planar coupling between the gradiometer and SQUID. Thin film gradiometers have significantly improved sensitivity due to decreased noise when constructed of a planar set of parallel or series-wound pick-up loops efficiently coupled to a planar, symmetric two-hole or figure-eight SQUID. Highly sensitive SQUID gradiometers principally employ pick-up loop designs of either series or parallel loop configurations, such as shown in Figs. 1 and 2, respectively. The net applied flux for the two pick-up loops 1 and 2 in Fig. 1 equals the difference in flux applied to the two loops and, for the parallel case of loops 3 and 4 (Fig. 2), the net applied flux is half that difference.

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SQUID Gradiometer Using Planar Coupling

This article relates generally to gradiometers using superconducting quantum interference devices (SQUIDS) and, more particularly, to a technique of using planar coupling between the gradiometer and SQUID. Thin film gradiometers have significantly improved sensitivity due to decreased noise when constructed of a planar set of parallel or series-wound pick-up loops efficiently coupled to a planar, symmetric two-hole or figure-eight SQUID. Highly sensitive SQUID gradiometers principally employ pick-up loop designs of either series or parallel loop configurations, such as shown in Figs. 1 and 2, respectively. The net applied flux for the two pick-up loops 1 and 2 in Fig. 1 equals the difference in flux applied to the two loops and, for the parallel case of loops 3 and 4 (Fig. 2), the net applied flux is half that difference. The associated DC SQUID should be either the two-hole type or the figure-eight type. By connecting a tightly coupled planar SQUID into the gradiometer, white noise can be decreased by a factor of about 200 over what it would be for a directly coupled SQUID. Two designs of planar coupled SQUIDS that provide this improved efficiency and are insensitive to uniform flux changes in the ambient field are shown in Figs. 3 and 4. In Fig. 3, the two-hole SQUID layout consists of a pair of interconnected square washers 10 and 11, each of inductance 2L and each coupled to a spiral coil with the spiral coils wound in opposite senses. The coils are connected along strips 12 and 13 on either side of split 14 to counterelectrode 15 via shunted tunnel junctions 16. Floating ground p...