High-T_c SQUID gradiometer system for magnetocardiography in an unshielded environment

摘要

We set up an electronic gradiometer for magnetocardiography (MCG) in an unshielded environment. The electronically balanced gradiometer consists of high-temperature radio-frequency superconducting quantum interference device (rf SQUID) magnetometers. The rf SQUID magnetometers are arranged to form the electronic first-order, four-vector gradiometer, or second-order gradiometer. The output of the MCG signal was filtered by a band pass (1-30 Hz) and power line filters. We can reduce the noise to approx 1 pT Hz~(-1/2) at 1 Hz for second-order or four-vector gradiometers. Two-dimensional MCG imaging is demonstrated. The results are discussed with data measured in the moderate magnetically shielded environment.