Off-axis second-order high-TC rf SQUID gradiometer for magnetocardiography in unshielded environment

Hong-Chang Yang, Shu Yun Wang, Jen Tzong Jeng, Jau Han Chen, Herng-Er Horng

    Research output: Contribution to journalConference articlepeer-review

    12 Citations (Scopus)


    We study an electronic gradiometer system for magnetocardiography (MCG) in unshielded environments. The electronically balanced gradiometer consists of three high temperature radio-frequency (rf) superconducting quantum interference device (SQUID) magnetometers, arranged in off-axis arrangement with the baseline of 6 cm to form the second order (2nd-order) gradiometer system. A set of coefficients were found to optimize the noise spectrum of the 2nd-order gradiometer via the fast Fourier transform technique by considering both the phase and the amplitude in the subtraction circuit. Besides, the signal of the 2nd-order gradiometer was filtered by notch and low frequency band pass filters. Hence, the field noise spectrum of the 2nd-order gradiometer was reduced to 1.5 pT/Hz1/2 at 60 Hz, to 1 pT/Hz1/2 at 10 Hz, and to 1.5 pT/Hz1/2 at 1 Hz. We perform MCG measurements in unshielded environments. To enhance the signal to noise ratio, the measured MCG signals were averaged according to the simultaneously recorded electrocardiogram signals recorded simultaneously. The MCG measurement was performed over several locations above the thorax of a human being. Our results demonstrate that the off-axis arrangement can offer the flexibility in the design of the SQUID-based multichannel magnetocardiogram.

    Original languageEnglish
    Pages (from-to)360-363
    Number of pages4
    JournalIEEE Transactions on Applied Superconductivity
    Issue number2 I
    Publication statusPublished - 2003 Jun
    Event2002 Applied Superconductivity Conference - Houston, TX, United States
    Duration: 2002 Aug 42002 Aug 9


    • Gradiometers
    • Magnetocardiography
    • SQUID's

    ASJC Scopus subject areas

    • Electronic, Optical and Magnetic Materials
    • Condensed Matter Physics
    • Electrical and Electronic Engineering


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