ABSTRACT
The superconducting quantum interference device (SQUID) is a highly sensitive detector for magnetic flux or any quantity that can be efficiently converted into flux. This chapter provides a short introduction into the basic function of a SQUID, its operation, and its design for magnetic field and current sensing. It shows by several examples that the device is very versatile and important for a variety of applications such as biomagnetism, astronomy, low-temperature physics, and metrology. The chapter measures with the commercial variant of the electronics and include the noise contribution from the preamplifier and shows the noise spectra as examples. The dc SQUID is dominant in the field of Nbbased sensors, and the rf SQUID is practically obsolete. The dc SQUID is based on two effects: flux quantization and superconducting tunneling. The chapter presents equations for calculating the inductance and the effective field-sensitive area of two representative superconducting structures.
