The design and analysis of a DC SQUID for a SQUID microscope

[摘要] This thesis relates to the analysis and design of a SQUID microscope. Superconductor theory is discussedin depth to provide a thorough understanding of Josephson junctions and of dc SQUID magnetometers.The behaviour and suitability of different types of single-layer dc SQUIDs are looked at. The quality ofthe superconducting material patterned onto a substrate and the Josephson junction design used affectthe behaviour of a practical dc SQUID. Noise and cooling play an integral part in the design and operationof a dc SQUID. The source of noise is looked at in an effort to minimize its effect. Cryocooling is essentialto real world operation so different cooling strategies and their consequences are analyzed. This thesisfocuses on modeling the behaviour of the dc SQUID to creating a practical system for use inside a SQUIDmicroscope. Operating the dc SQUID with the appropriate electronics will linearize the device, reducethe effect of noise, and create a device with wide bandwidth. Each step in creating a practical systemis discussed in detail. Simulations are used to create models predicting the behaviour of the dc SQUIDand the electronics. They are then used to design and create practical electronic systems. Measurementsare performed on Josephson junctions and dc SQUID magnetometers using the designed electronics. TheJosephson junctions behave as predicted and were successfully tested. The dc SQUIDs did not behave aspredicted and were not successfully tested. The SQUIDs were damaged, either by a malfunction in thecryocooler or through age related deterioration. A full test of the flux-locked loop was not possible andthe dc SQUID was not linearized.

[发布机构] Stellenbosch University