Development of a heart monitoring system with high-Tc DC-SQUID gradiometers

We investigated different types of high-T_c DC-SQUID gradiometers with the aim to develop an one-channel heart monitoring system for non-invasive measurements in unshielded environment. This system could be used to obtain information about the patients condition in serial examinations and in emergency cases fast and stable. Step-edge and bicrystal Josephson junctions were used to prepare planar galvanically coupled thin film gradiometers and magnetometers. These sensors were used to carry out measurements in well-shielded and non-shielded environment and we compared the different noise properties and field gradient resolutions. With different types and sizes of high-T_c DC-SQUID sensors magnetocardiograms were measured in a magnetically shielded room. The influence of antenna configurations, SQUID parameters, and cooling conditions on the measurement of magnetocardiograms will be discussed. We investigated possibilities to suppress the earth magnetic field (with pairs of Helmholtz coils) and for noise field compensation in unshielded environment.