Control System for Readout Electronics of Multi-Channel Magnetocardiographs Using High-Temperature DC Superconducting Quantum Interference Devices

We aimed to develop a control system for multichannel magnetocardiography (MCG) based on a high-temperature DC superconducting quantum interference device (high-T_c SQUID). To create this system, we used one oscillator as an AC bias controller to operate a multichannel high-T_c SQUID. To optimize the SQUID parameters (such as the AC bias, offset voltage), two new control sequences based on a cross-correlation method and a fast Fourier transform method were developed. Using the AC bias controller and the sequences, the typical white noise level of the SQUID was about 50–60 fT Hz^-1/2 around 100 Hz. Multichannel MCG signals were detected clearly in the system with the SQUIDs. We conclude that our control system with one oscillator and new protocols can reliably operate a multichannel SQUID.