Multichannel DC SQUID sensor array for biomagnetic applications

A biomagnetic multichannel system for medical diagnosis of the brain and heart has been developed. 37 axial first order gradiometers (manufactured as flexible superconducting printed circuits) are arranged in a circular flat array of 19 cm in diameter. Additionally, three orthogonal magnetometers are provided. The DC SQUIDs are fabricated in all-Nb technology, ten on a chip. The sensor system is operated in a shielded room with two layers of soft magnetic material and one layer of Al. The everyday noise level is 10 fT/Hz^1/2 at frequencies above 10 Hz. Within two years of operation in a normal urban surrounding, useful clinical applications have been demonstrated (e.g., for epilepsy and heart arrhythmias). For the first time current sources of sporadic events causing epilepsy or ventricular extrasystoles have been localized from coherent recordings of complete biomagnetic field distributions with spatial resolution of millimeters and temporal resolution of 1 ms