Development of Digital FLL System for SQUID Using Double Counter Method

• Published in: IEEE transactions on magnetics Vol. 42; no. 10; pp. 3539 - 3541
• Main Authors: Oyama, D., Kobayashi, K., Yoshizawa, M., Uchikawa, Y.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.10.2006; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Control systems; Costs; Counting circuits; Cross-disciplinary physics: materials science; rheology; Digital; Digital control; Double-counter method; Dynamic range; Dynamical systems; Dynamics; Exact sciences and technology; Flux; flux-locked loop (FLL); Frequency locked loops; Magnetic flux; Magnetic measurements; Magnetic shielding; magnetically unshielded; Magnetism; magnetocardiogram; Materials science; Noise levels; Other topics in materials science; Physics; SQUID; SQUIDs; White noise; magnetically unshielded; Proceedings; Ontogenesis; Double-counter method; flux-locked loop (FLL); SQUID; magnetocardiogram; Magnetic properties
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2006.879162

We have developed a digitally controlled flux-locked loop (FLL) system using a double-counter method to achieve both high performance and low cost. This system is composed of generally used electric devices. The system slew rate is about 1.3 k Phi 0 /s, where Phi 0 is the flux quantum. The measurable flux amplitude and dynamic range are 218 Phi 0 and 141 dB at 1 Hz and 22 Phi 0 and 121 dB at 10 Hz, respectively. A white noise level measured in the magnetically shielded room (MSR) is 36.1 fT/Hz 1/2 . Magnetic measurements with a first-order gradiometer were done outside the MSR, and the developed system can detect a magnetocardiogram in an unshielded condition