Design of high resolution HTS-SQUID magnetometers for biomagnetic imaging

To image the magnetic fields produced by action, injury and development currents in isolated living tissue or small animal preparations one requires a field sensitivity of a few hundred fT/root Hz together with a sub-millimeter spatial resolution. The design constraints of HTS bicrystal SQUID magnetometers with sub-millimeter resolution are analyzed in order to maximize field sensitivity. The desired combination of sensitivity and spatial resolution can be achieved by a multiloop magnetometer of 600 mu m in diameter. Our calculations predict a magnetic field sensitivity of 120 fTHz(-1/2) for sensors with more than five loops. Decreasing the sensor size to 300 pm results in a field sensitivity of 320 fTHz(-1/2) requiring four loops.