Superconducting quantum interference device (SQUID) magnetometers

Abstract

Direct Current Superconducting QUantum Interference Devices (dc SQUIDs) are sensors for the detection of magnetic flux or any physical quantity that can be transformed into magnetic flux. They consist of a superconducting loop interrupted by two resistively shunted Josephson tunnel junctions. Typically operated at 4.2 K, they exhibit magnetic flux noise levels of the order of 1 μΦ0/ Hz1/2, corresponding to a noise energy of 10−32 J/Hz1/2. They can be used for example as magnetometers, magnetic gradiometers, current sensors and voltmeters, susceptometers or (rf) amplifier. With their large bandwidth and flat frequency response ranging from dc to GHz, they are excellent suited for a wide variety of applications, such as e.g. biomagnetism and geophysical exploration to the detection of gravity waves and magnetic resonance.