• Proceedings of the IEEK Conference
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• 2003.07c
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• pp.2749-2752
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• 2003

Magnetocardiography is a very weak biomagnetic field generated from the heart. Since the magnitude of the biomagnetic field is in the order of a few pico Tesla, it is measured with a superconducting quantum interference device (SQUID). SQUID is a transducer converting magnetic flux to voltage, however, its range of linear conversion is very restricted. In order to overcome the narrow dynamic range. a flux locked loop is used to feedback the output field with opposite polarity to the input field so that the total Held becomes zero. This prevents the operating point of the SQUID from moving too far away from the null point thereby escape from the linear region. In this paper, an emulator for the SQUID sensor and feedback coil is proposed. Magnetic courting between the original field and the generated field by the feedback coil is emulated by electronic circuits. By using the emulator, FLL circuits are analyzed and optimized without SQUID sensors. The emulator may be used as a test signal for multi-channel gain calibration and system maintenance.

• Journal of Magnetics
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• v.11 no.4
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• pp.189-194
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• 2006

The recent development of bio-conjugated magnetic nanoparticles offers many opportunities for applications in the field of biomedicine. In particular, the use of magnetic nanoparticles for biosensing has generated widespread research efforts following the progress of various magnetic field sensors. Here we demonstrate substrate-free biosensing approaches based on the Brownian rotation of ferromagnetic nanoparticles suspended in liquids. The signal transduction is through the measurement of the magnetic ac susceptibility as a function of frequency, whose peak position changes due to the modification of the hydrodynamic radius of bio-conjugated magnetic nanoparticles upon binding to target bio-molecules. The advantage of this approach includes its relative simplicity and integrity compared to methods that use substrate-based stray-field detectors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.444-447
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• 2004

A heart diagnosis system adopts hundreds of Superconducting Quantum Interface Device(SQUID) sensors for precision MCG(Magnetocardiogram) or MEG(Magnetoencephalogram) signal acquisitions. This system requires correct and real-time data acquisition from the sensors in a required sampling interval, i.e., 1 mili-second. This paper presents our hardware design and test results, to acquire data from 256 channel analog signal with 1-ksample/sec speed, using 12-bit 8-channel ADC devices, SPI interfaces, parallel interfaces, and 8-bit microprocessors. We chose to implement parallel data transfer between microprocessors as an effective way of achieving such data collection. Our result concludes that the data collection can be done in 250 ${\mu}sec$ time-interval.

• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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• pp.1-6
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• 2007

As very sensitive magnetic field sensors, superconducting quantum interference devices (SQUIDs) are used to measure magnetic field signals from the human heart. By analyzing these cardiomagnetic signals, functional diagnoses of heart can be done. In order to measure weak biomagnetic signals, we need a multichannel SQUID array with sensor coverage large enough to cover the whole heart to enable the measurement in a single position setting. In this paper, we review the recent development of SQUID systems for measuring cardiomagnetic fields, with special emphasis on SQUID types.

• Progress in Superconductivity
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• v.10 no.2
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• pp.139-143
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• 2009

We have fabricated a low-noise 61-channel axial-type first-order gradiometer system for measuring fetal magnetocardiography(MCG) signals. Superconducting quantum interference device(SQUID) sensor was based on double relaxation oscillation SQUID(DROS) for detecting biomagnetic signal, such as MCG, magnetoencphalogram(MEG) and fetal-MCG. The SQUID sensor detected axial component of fetal MCG signal. The pickup coil of SQUID sensor was wound with 120 ${\mu}m$ NbTi wire on bobbin(20 mm diameter) and was a first-order gradiometer to reject the environment noise. The sensors have low white noise of 3 $fT/Hz^{1/2}$ at 100 Hz on average. The fetal MCG was measured from $24{\sim}36$ weeks fetus in a magnetically shielded room(MSR) with shielding factor of 35 dB at 0.1 Hz and 80 dB at 100 Hz(comparatively mild shielding). The MCG signal contained maternal and fetal MCG. Fetal MCG could be distinguished relatively easily from maternal MCG by using independent component analysis(ICA) filter. In addition, we could observe T peak as well as QRS wave, respectively. It will be useful in detecting fetal cardiac diseases.