Superconducting quantum interference magnetometer for large multichannel systems with low crosstalk level

Magnetometers based on Superconducting Quantum Interference Device (SQUID) are widely employed in high sensitivity magnetometry. In particular, new multichannel sys- tems for biomagnetic applications require many sensors which are very close to each other giving the crosstalk disturbance between the neighboring channel. Here, we present ex- perimental results about a fully integrated dc-SQUID magnetometer, based on niobium technology, having a suitable design which allows to reduce crosstalk due to both the feedback coil and wires. The crosstalk level measurements relative to a particular arrangement of sensors are reported. In such configuration, four magnetometers are placed over a square board 30 mm in side with a distance between their sensor centers of 14 mm. The measurements have been performed in a 4 He cryostat at T = 4.2 K in a flux-locked loop configuration using a readout electronics with a direct coupled scheme. The experimental data have shown a substantial reduction of crosstalk among neighboring sensors with respect to a traditional feedback coil. Furthermore, the field noise measurements have ensured that the new pickup and feedback coils design does not introduce any noise level degradation.