Introduction to SQUID Sensors for Electronics Engineers

TL;DR

This paper introduces the principles and components of SQUID sensors, explaining their operation and similarities to conventional circuits, aimed at electronics engineers unfamiliar with superconductor physics.

Contribution

It provides a comprehensive introduction to SQUID sensors, covering superconductor elements, hybrid systems, and their circuit analogies, bridging the gap for electronics engineers.

Findings

SQUIDs operate as RLC networks driven by Josephson currents.

SQUIDs function as magnetic-field-effect transistors (MFETs).

They serve as linear current amplifiers for magnetic-field sensing.

Abstract

Flux transformers and superconducting quantum interference devices (SQUIDs) are two key superconducting devices used in the cutting-edge magnetic-field sensor systems, such as magnetocardiography (MCG) and magnetoencephalography (MEG). They are superconductor integrated circuits enabled by two superconductor elements, superconductor wire and Josephson junction, based on Meissner effect and Josephson effect. The principles of SQUID sensors are unfamiliar for electronics engineers who are trained with semiconductor electronics, due to the superconductor physics. We present an introduction to SQUID sensors, ranged from superconductor elements to the superconductor-semiconductor hybrid system. It is demonstrated that, SQUIDs inside are the resistor-inductor-capacitor (RLC) network driven by Josephson currents, and share the common network equation with normal RLC circuits; SQUID outside are magnetic-field-effect transistors (MFETs), and are dual to the semiconductor FETs in signal conversions; SQUID magnetic-field sensors are linear current amplifiers, as semiconductor FET electric-field sensors are linear voltage amplifiers.