A multichannel SQUID magnetometer system based on double relaxation oscillation SQUIDs
Yong-Ho Lee; Hyukchan Kwon; Jin-Mok Kim; Chan-Seok Kang; Kiwoong Kim; In-Seon Kim; Yong-Ki Park; Soon-Gul Lee
Applied Superconductivity, IEEE Transactions on
Volume 13, Issue 2, June 2003 Page(s): 755 - 758
Digital Object Identifier   10.1109/TASC.2003.814031
Summary:We constructed a multichannel superconducting quantum interference device (SQUID) magnetometer system for magnetoencephalogram measurements. The SQUID is based on the double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID and a reference junction, and shunted by a relaxation circuit of a resistor and an inductor. With the high flux-to-voltage transfers, usually larger than 1 mV/Φ₀, simple flux-locked loop circuits could be used for SQUID operation. The SQUID system consists of 37 integrated magnetometers, distributed on a hemispherical surface, and external feedback scheme was used to eliminate magnetic coupling with the adjacent channels. In addition to the 37 signal channels, 8 reference channels were installed to pickup background noise and to apply software gradiometer. The average noise level of the magnetometers is about 3 fT/√Hz at 100 Hz, operated inside a magnetically shielded room. The magnetometer system was applied to measure auditory-evoked fields.

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