Miniaturized superconducting quantum interference magnetometers for high sensitivity applications

A miniaturized niobium based dc superconducting quantum interference device SQUID magnetometer for high magnetic field sensitivity applications has been developed. The sensing coil consists of an integrated square superconducting coil with a length of 3 mm, involving a device area much smaller with respect to the standard SQUID magnetometers with a comparable magnetic field sensitivity; so it allows increasing the spatial resolution keeping the magnetic field sensitivity unaltered. Furthermore, a small pickup coil minimizes its antenna gain, reducing the radio frequency interference. At T=4.2 K, the sensors have shown smooth and resonance free V- characteristics and an intrinsic white magnetic field noise spectral density as low as 5.8 fT/Hz 1/2 , measured in flux locked loop configuration. The good agreement with the theoretical predictions guarantees the reliability and the controllability of the sensors. Due to their compactness and good characteristic parameters, such sensors are suitable for large multichannel systems used in biomagnetic imaging.