In our “Joint Research Lab on Superconductivity and Bioelectronics” in conjunction with Shanghai Institute of Microsystem and Information Technology (SIMIT) and in cooperation with Dr. Michael Mück (ez SQUID, Sinn, Germany), we work on low-Tc dc SQUID design and readout. The aim of the work is to develop SQUID sensors and simple low noise electronics which are suitable for multi-channel SQUID instrumentation such as Magnetoencephalography (MEG) and Magnetocardiography (MCG) systems.
For this purpose, we study low-noise readout at different bias modes such as voltage bias, and feedback schemes such as the SQUID bootstrap circuit (SBC). We analyze the equivalent flux noise contribution of the readout electronics for different parameters of the voltage feedback circuit such as Johnson noise contribution of the SQUID and mutual inductance. The measured SQUID noise in our scheme comes close to the noise of the two-stage scheme, i.e. reading out one SQUID by another SQUID, which can be considered as the optimum readout approach.
Jia Zeng, Yi Zhang, Michael Mück, Hans-Joachim Krause, Alex I. Braginski, Xiangyan Kong, Xiaoming Xie, Andreas Offenhäusser, Mianheng Jiang, High intrinsic noise and absence of hysteresis in superconducting quantum interference devices with large Steward-McCumber parameter, Applied physics letters 103, 042601 (2013).
Jia Zeng, Yi Zhang, Michael Mück, Hans-Joachim Krause, Alex I. Braginski, Xiangyan Kong, Xiaoming Xie, Andreas Offenhäusser, Mianheng Jiang, Study of weakly damped superconducting quantum interference devices operated in different bias modes in presence of external shunt resistance, Appl. Phys. Lett. 103, 122605 (2013).