Applying high-T/sub C/ superconducting quantum interference devices with a room-temperature pickup coil in the measurement of impedance magnetocardiograms

A high-T/sub C/ superconducting quantum interference device (SQUID) magnetometer - in which a room-temperature pickup coil is used to detect an impedance magnetocardiogram (I-MCG) signal - has been developed. The pickup coil (30-mm diameter) is installed outside the cryostat and is connected to the input coil of the high-T/sub C/ SQUID. The magnetometer's noise level is 150 fTHz/sup -1/2/ (>10 kHz). The magnetometer was used to measure I-MCG signals (about 12 pT), which were obtained by applying an ac current (15 kHz) of constant amplitude (7 mA, peak-to-peak) to a healthy male subject.