A direct current superconducting quantum interference device gradiometer with a digital signal processor controlled flux-locked loop and comparison with a conventional analog feedback scheme

Journal Article · Mon Jan 01 04:00:00 EST 1996 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.1146575· OSTI ID:253546

Kung, P J ^[1]; Bracht, R R ^[2]; Flynn, E R ^[1]; Lewis, P S ^[2]

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1. Biophysics Group P-6, MS M715, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2. Systems and Robotics Group ESA-6, MS J580, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

A double-washer dc superconducting quantum interference device (SQUID) gradiometer with a flux-locked loop (FLL) based on a digital signal processor (DSP) has been developed for biomagnetic applications. All of the analog electronics in the conventional FLL are replaced and implemented by the DSP except for the low-noise field-effect transistor preamplifier at the front end of the signal recovery components. The DSP performs the signal demodulation by synchronously sampling the recovered signals and applying the appropriate full wave rectification. The signals are then integrated, filtered, and applied to the output. At 4.2 K, the white flux noise of the gradiometer measured in a DSP FLL mode is about 4{mu}{phi}{sub 0}/{radical}Hz and the noise at 1 Hz is 13 {mu}{phi}{sub 0}/{radical}Hz. The corresponding noise levels in the gradiometer operated by the conventional FLL are 1.8 and 3{mu}{phi}{sub 0}/{radical}Hz. The poorer system performance in the DSP FLL compared to the analog FLL is mainly caused by the ambient field noise and interference signals picked up through the connecting cables. Additional noise is also added to the overall noise floor by the instruments employed in the DSP system in the present prototype setup. Further improvement in the noise characteristics and the dynamic behavior of the DSP SQUID gradiometer is expected when a better configuration of DSP with the associated I/O devices is implemented. Additional improvements of the DSP programs are expected by incorporating higher-order integration, adaptive control, and noise reduction schemes. {copyright} {ital 1996 American Institute of Physics.}

• Research Organization: Los Alamos National Laboratory
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 253546
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 1 Vol. 67; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
DATA PROCESSING
DIAGNOSTIC TECHNIQUES
DIGITAL SYSTEMS
FIELD GRADIENTS
MAGNETIC FIELDS
MEDICINE
SIGNAL-TO-NOISE RATIO
SQUID DEVICES