From basic circuits to complex systems

Although the basic circuits of SQUIDs (Superconducting QUantum Interference Devices) are very simple, their non-linear character makes them quite complex and this in turn leads to a very rich variety of designs, functions, and applications. The aim of this contribution is to present a few instructive examples on the role of non-linearities and the methods employed to improve the performance of different components of SQUID-systems, Like the sensors themselves, the read-out electronics, and the impact of gradiometer configurations on the output signals.