High-Tc SQUID Gradiometers for Magnetocardiography in an Unshielded Environment

We have designed a magnetocardiography (MCG) system that is capable of measuring magnetocardiograms in an unshielded environment. In order to carry out such a measurement, one has to contend with various ambient noise sources. These include power line and RF interference, microphonics pickup, fluctuations in the earth’s magnetic field, and electrostatic pickup. Earlier solutions devised to overcome these problems have entailed the use of a second-order gradiometer inside a deep mine or inside a magnetically shielded enclosure [1]. Apart from the above problems which are common to both low-Tc and high-Tc SQUIDs, high-Tc SQUIDs exhibit additional 1/f noise [2]. This noise is the result of hopping of flux vortices that are trapped in the body of the field cooled high-Tc SQUID, and can only be eliminated by zero-field cooling the SQUID.