Improved SQUID Sensors for Biomagnetic Imaging

Abstract

Improved niobium-based SQUID sensors in a magnetometer and a gradiometer configuration are presented. The SQUID magnetometer has an integrated square superconducting sensing coil with an area of 9 mm2, much smaller than a typical SQUID magnetometers keeping a comparable magnetic field sensitivity but a higher spatial resolution. At T = 4.2 K, an intrinsic magnetic field noise spectral density of 5.8 fT/?Hz, has been measured in the flux locked loop configuration. The SQUID planar gradiometer with a long baseline (50 mm) has a pickup antenna consisting of a series of two integrated rectangular coils inductively coupled to the SQUID in a double washer configuration. At T = 4.2 K a magnetic flux noise spectral density of 3 ??0/?Hz has been measured. The spectral density of the magnetic field noise referred to one sensing coil, is 3.0 fT/?Hz resulting in a gradient spectral noise of 0.6 fT/cm · ?Hz.