TY - JOUR
T1 - Off-axis second-order high-TC rf SQUID gradiometer for magnetocardiography in unshielded environment
AU - Yang, Hong Chang
AU - Wang, Shu Yun
AU - Jeng, Jen Tzong
AU - Chen, Jau Han
AU - Horng, Herng Er
N1 - Funding Information:
Manuscript received August 5, 2002. This work was supported by the Ministry of Education of the R.O.C. under the program of promoting university academic excellence 91-N-FA01-2-4. H.-C. Yang, S.-Y. Wang, J.-T. Jeng, and J.-H. Chen are with the Department of Physics, National Taiwan University, Taipei 10617, Taiwan, R.O.C. (e-mail: [email protected]). H.-E. Horng is with the Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan, R.O.C. Digital Object Identifier 10.1109/TASC.2003.813853
PY - 2003/6
Y1 - 2003/6
N2 - 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.
AB - 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.
KW - Gradiometers
KW - Magnetocardiography
KW - SQUID's
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U2 - 10.1109/TASC.2003.813853
DO - 10.1109/TASC.2003.813853
M3 - Conference article
AN - SCOPUS:0041440087
SN - 1051-8223
VL - 13
SP - 360
EP - 363
JO - IEEE Transactions on Applied Superconductivity
JF - IEEE Transactions on Applied Superconductivity
IS - 2 I
T2 - 2002 Applied Superconductivity Conference
Y2 - 4 August 2002 through 9 August 2002
ER -