Superconducting magnetometers

Abstract

2014 Under the proper circumstances a current carrying superconductor can generate voltage. This voltage is produced by supercurrent oscillations at frequency 03C9 = 2e/0127 V 2014 a phenomena similar to the Josephson effect in superconducting tunnel junctions. Various structures have been fabricated in which this quantum relation dominates the electrical behavior. These thin film structures have been developed into reliable sensor elements which have been incorporated into various electronic instruments 2014 particularly magnetometers. These instruments include a differential magnetometer with a one second response time and sensitivity greater than 10-10 gauss and a digital magnetometer counting in increments of 1/4h/2e at a rate up to 104 per second. The fundamental principles of these instruments will be discussed as well as their present operational limitations.

Weakly superconducting circuits

“…This response is indicative primarily of AM and again is what was anticipated in (8a) when the principal effect of the superconducting ring is as a parametric resistance. The R F drive levels required for maximum response in these two situations also differed by approximately the ratio of 10: 1, (wL/R(wide) : l), as expected from (8). By driving the tank circuit from a constant current source this variation in impedance shows up as a signal voltage which is often used as the basis for magnetometer circuits.…”

“…This limit has been analyzed previously [8] and it was found that this situation produces a signal with large harmonic content whose amplitude at the drive frequency (w) is Fig. 2.…”

“…2 shows a microphotograph of a phase slip junction in a hard superconducting thin-film ring. This same junction was tested at two different widths to examine the effects of resistance relative to inductive impedance as expressed in (8). In the photograph on the left of Fig.…”

Impedance Matching a Josephson Galvanometer by Means of a Superconducting Transformer

“…as the working temperature T is lowered and becomes ( 5) We may summarize these results as follows. Suppose that we start with a low value of R, so that L >> LG' and that the voltmeter is ideal.…”

Advances in SQUID magnetometers

“…During the past two years, the energy sensitivity of dc SQUIDs (Superconducting QUantum Interference Devices) [1] has improved by mor~ than 3 orders of magnitude, whi le that of rf SQUIDs [2,3] has improved by perhaps an order of magnitude. The purpose of this article is to review briefly these ~ advances, and to make some assessment of possible future trends.…”