High-Tc SQUID magnetometers for use in moderate magnetically-shielded room

We have fabricated and characterized high-T-c planar SQUID magnetometers an d first derivative gradiometers with directly-coupled pickup loops. The dev ices were made from single layer of YBa2Cu3O7-8 thin film on LSAT bicrystal substrate with 30 degrees or 24 degrees misorientation angle, Magnetic properties were investigated by applying a magnetic field Bo for t he SQUID magnetometer patterned with holes to reduce the maximum structural width. We found an increasing Low frequency noise with cooling fields B-0 larger than 1.5 muT This value consists with the threshold field estimated from the maximum structural width. A magnetic field noise level of 500 fT/H z(1/2) at 10 Hz was observed by using PLL electronics with a bias current r eversal in a moderate magnetically-shielded room consisting of only two 1mm thick layers of permalloy, Measurements of magnetocardiograms demonstrate the suitability of this magnetometer for biomagnetic applications. On the other hand, the gradiometer with two symmetric pickup loops was oper ated without any shielding. The performance obtained was a field gradient r esolution of about 1 pT/cmHz(1/2) at 1 kHz and 10 pT/cmHz(1/2) at 1 Hz, wit h a baseline of 4 mm, The imbalance of this gradiometer was around 0.7%, li mited by the sensitivity to homogeneous field of the SQUID itself.