Reduction of ambient magnetic field noise for high-T/sub c/ SQUID applications

We discuss results of our investigations on ambient noise reduction using localized high-T/sub c/ (HTS) passive magnetic shields. We have quantified our results in terms of shielding factors for ambient noise, and signal-to-noise improvement ratio (SNIR) for source fields. Issues such as the critical fields of our HTS shields and their flux noise are also discussed. The relative merits of this and other noise reduction techniques are discussed vis-a-vis magnetocardiography (MCG) and nondestructive testing (NDT) of materials in an unshielded environment.