The Microwave Surface Resistance of Superconducting Lead, Trapped Magnetic Flux, and a New Magnetometer Using Superconductivity

摘要

An investigation has been made into the causes of the residual surface resistance which is always observed in superconductors at microwave frequencies. A new and extremely sensitive magnetometer has been developed which uses unique properties of superconductivity. Calculations and measurements indicate that this magnetometer can detect a field change of 3 x 10 to the minus 10th power gauss in a loop with 1 cm radius. The magnetometer uses a superconducting loop in which a field change is translated into a persistent current. Linking the loop is a cylinder of superconductor which can be switched alternately between the normal and superconducting states at a frequency of 150 KHz. Since the magnetic flux linking a superconducting cylinder is quantized, inductive impulses are given to the loop, and a large oscillation is built up which is proportional to the persistent current. The result is an output power equivalent to spinning the sensing loop at a frequency approximately 1,000,000 Hz. This accounts for the great sensitivity. (Author)