SQUIDSensoren

SQUIDSensoren, often referred to in English as SQUID sensors, are highly sensitive magnetometers based on superconducting quantum interference devices. They provide among the lowest detectable magnetic fields available, with sensitivity in the fT/√Hz range in optimized configurations. They are used in scientific and medical fields, often in cryogenic environments.

Operation principle: A SQUID consists of a superconducting loop interrupted by Josephson junctions. Magnetic flux threading the loop changes the superconducting phase, producing a current or voltage signal that can be read with a flux-locked loop. There are two main types: dc-SQUIDs, which use two Josephson junctions in a loop and yield a very narrow flux-to-voltage transfer function requiring feedback; and rf-SQUIDs, which use a single junction and are read out with an RF tank circuit.

Typical construction: cryogenic cooling is required, using liquid helium or closed-cycle cryocoolers; the sensors are often surrounded by magnetic shielding to reduce noise; they are integrated with cryogenic electronics and, in some cases, on-chip flux transformers to shape the effective area.

Applications: biomedical magnetoencephalography (MEG), magnetocardiography, geophysics and mineral exploration, nondestructive testing, fundamental physics experiments, and sensitive measurements in NMR and dark matter experiments; arrays of SQUID sensors enable spatial mapping of magnetic fields.

Limitations and challenges: the need for cryogenic cooling and magnetic shielding increases system complexity and cost; sensitivity to environmental magnetic noise requires careful instrumentation design; while very sensitive, dynamic range and bandwidth depend on the specific device design.