Integrated LTS gradiometer SQUID systems for unshielded measurements in a disturbed environment

Abstract

Various types of thin-film dc gradiometer SQUIDs with integrated pickup loops were investigated. The SQUIDs were prepared on a 5 mm × 10 mm chip in the well developed Nb-NbO x -Pb/Au/In technology. It was shown that the SQUIDs work in an unshielded environment. Our best SQUIDs have a field gradient sensitivity better then 30 fT cm −1 Hz −1/2 . All gradiometers have some response to a homogeneous field, i.e., a parasitic area. The effective pickup area, the field gradient sensitivity, and the components of the parasitic area for the field perpendicular and parallel to the gradiometer plane were measured for all types of gradiometer. The calculations of flux coupling efficiency are compared with experimental results. The origins of parasitic area are discussed. A further reduction of external disturbances was achieved by using an electronic second-order gradiometer. Examples of magnetocardiographic measurement in a physical laboratory without any shielding with first and second-order gradiometers are shown.

Long baseline LTS SQUID gradiometers with sub-μm sized Josephson junctions

“…The four design variants of implementing thin film LTS SQUID based gradiometers (first-order and planar-type) are introduced e.g. in [24]. The gradiometric sensors in the present work were made as gradiometric pickup loops integrated on chip with Nb based SQUIDs.…”

“…When considering the type of gradiometer, referred to [24], for < A 3 cm Chip 2 single layer designs were implemented such as washer or galvanometer SQUIDs. For larger areas galvanometer type SQUIDs are feasible, too.…”

Integrated SQUID gradiometers for measurement in disturbed environments

“…The inductance of the rectangular SQUID was estimated with three different formulas: for coplanar lines [6], for a round washer, and for a quadratic washer [7], where the rectangular SQUID hole was approximated by a quadratic or a round one having the same area. Contributions of kinetic inductances were also included assuming a London penetration depth of 300 nm.…”

“…The calculation is described in [7]. The parasitic area A, is much larger for the HTS galvanometer SQUID and is due to the magnetometer structure of the SQUID itself.…”

Inversion of Geo-Magnetic SQUID Gradiometer Prospection Data Using Polyhedral Model Interpretation of Elongated Anomalies

“…In order to realize a very fast, efficient, and sensitive tool for geo-magnetic mapping, a measurement system on the base of superconducting quantum interference devices (SQUIDs) was jointly developed at IPHT Jena and Supracon AG [1]. The cryo-cooled sensors are produced in thin-film technology and constructed as planar-type magnetometers or gradiometers [2]. The gradiometers used in the system are very sensitive [field resolution of below 100 fT/(m √ Hz) within a frequency band from Measurement system of IPHT Jena and Supracon AG in the field at the steppe in Central Mongolia in 2010.…”