• 대한의용생체공학회:의공학회지
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• 제18권4호
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• pp.421-428
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• 1997

초전도양자간섭소자(SQUID)를 이용한 자장센서는 현재 개발된 자장센서중에서 감도가 가장 우수한 소자로서 인체의 두뇌에서 발생하는 매우 미약한 자장에 측정이 가능하다. 뇌자도측정은 현재 많이 사용되고 있는 전기적인 측정(뇌파, 뇌유발전위) 에 비해 공간분해능이 우수하고, fMRI나 PET에 비해서는 시간분해능이 우수하므로 뇌기능연구에 유용하게 사용될 수 있다. 본 연구에서는 뇌자도 측정을 위하여 4-채널 SQUID시스템을 개발하였다. 개발된 시스템의 주요 특징은 새로운 방식의 SQUID센서를 채택함으로서 간단한 회로로써 SQUID구동이 가능하도록 하였으며, 검출코일의 신뢰성을 향상시키기 위하여 집적화된 평면형 코일을 사용하였다. 외부 환경잡음을 소거하기 위하여 자기차폐실을 설치하였고, 개발된 SQUID 시스템을 이용하여 뇌의 청각령으로부터 발생하는 자기신호를 측정하였다.

• Progress in Superconductivity
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• 제1권1호
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• pp.20-25
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• 1999

We constructed a high-$T_c$ scanning SQUID microscope (SSM) operating in the liquid nitrogen. We used a washer-type YBCO SQUID with inner and outer dimensions of $12{\mu}m$ and $36{\mu}m$, respectively, which was grown on the $SrTiO^3$ bicrystal substrate. The sample, rather than SQUID, was scanned using two stepping motors. We also developed readout electronics, stepping motor controller, and the software for system control and data display. We took images of various samples using our SSM and found that the spatial resolution is about $40{\mu}m$ and noise level is lower than $10^{-7}T/{\surd}Hz$ at 100 Hz and higher at lower frequencies. The noise level was much higher than that of a typical SQUID due to the other coupling from the electric parts. We present a simple argument on the inductive coupling between the sample and the SQUID which should be under-stood for the proper interpretation of the obtained images. By comparing the measured data with the simulation results the gap between the SQUID and the sample is estimated to be $40{\mu}m$.

• Progress in Superconductivity
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• 제3권2호
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• pp.151-158
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• 2002

We developed a useful SQUID magnetometer for biomagnetic applications, magnetoencepha-logram(MEG) and magnetocardiogram(MCG), etc. The SQUIDs are based on Double Relaxation Oscillation SQUID(DROS). DROS consists of two SQUIDs(signal SQUID and reference SQUID) in series, and a relaxation circuit of an inductor and a resistor. Specially we used single reference junction instead of the reference SQUID. The SQUIDs are based on hysteretic $Nb/AlO_{x}$Nb junctions, fabricated by using a simple four level process. Because DROS magnetometer has large flux-to-voltage transfer coefficient, we can use simple flux-locked loop electronics fur SQUID operation. When the DROS magnetometer was operated inside a magnetically shielded room, its average magnetic field noise was about 3 (equation omitted) at 100 Hz. This noise level is low enough to measure biomagnetic fields. In this paper, we describe noise characteristics of DROS magnetometer, depending on the operation condition . .

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 V
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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.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2003년도 High Temperature Superconductivity Vol.XIII
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• pp.49-49
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• 2003

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.27-32
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• 1999

We developed a 40-channel superconducting quantum interference device (SQUID) system for neuromagnetic measurements. The main features of the system are use of double relaxation oscillation SQUID (DROS), and planar gradiometer for measuring tangential field components. The DROSS with high flux-to-voltage transfers enabled direct readout of the SQUID output by room-temperature electronics and simple flux-locked loop circuits could be used for SQUID operation. The pickup coil is an integrated first-order planar gradiometer with a baseline of 40 mm. The average noise of the 40 channels is around 1.2 fT/cm/${\sqrt{Hz}}$ at 100 Hz, corresponding to the field noise of 5 fT/${\sqrt{Hz}}$ at 100 Hz, operated inside a magnetically shielded room. The 40-Channel system was applied to measure auditory-evoked neuromagnetic fields.

• 전자공학회지
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• 제25권9호
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• pp.29-38
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• 1998

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.151-154
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• 2000

We have developed a YBCO SQUID gradiometer system for the measurement of a very weak magnetic field in an unshielded environment. The system consists of a SQUID gradiometer sensor, low noise pre-amp, and FLL(fluxlocked loop) control electronics. The gradiometer sensors have been fabricated on STO bicrystal substrates, and exhibit a magnetic noise of 300 fT/${\surd}$ Hz/cm at 100 Hz. The overall magnetic field noise of the SQUID gradiometer system was about 10 pT/${\surd}$ Hz/cm at 10 Hz without any magnetic shield. The system demonstrated a high stability for a long time, and real-time measurement resolution ${\le}$ 100 pT/cm in the unshielded environments.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1998년도 추계학술대회
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• pp.191-192
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• 1998

We report on the design of a low-noise 40 channel SQUID system for biomagnetism. We used low-noise SQUID sensor with the pickup coil integrated on the same wafer as the SQUID. The SQUID electronics were simplified by increasing the voltage output of the SQUID. The SQUID insert was designed to have low thermal load, minimizing the liquid helium loss. The digital signal processing provides versatile analysis tools and the software is based on the object-oriented programming. For the effective localization of the source location, solutions of the inverse problems based on the lead-field and the simulated anneal ins were studied.

• Progress in Superconductivity
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• 제5권1호
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• pp.55-60
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• 2003

We designed and constructed integrated 3-channel flux-locked-loop (FLL) electronic system for the control and readout of high-T$_{c}$ SQUIDs. This system consists of low noise preamplifiers, integrators, interface circuits, and software. FLL operation was carried out with biased signals of 19 KHz modulated current and 150 KHz modulated flux, which are reconstructed as detected signals by preamplifier and demodulator. Computer controlled interface circuits regulate FLL circuit and adjust SQUID parameters to the optimum operating condition. The software regulates interface circuits to make an auto-tuning for the control of SQUIDs, and displays readout data from FLL circuit. 3-channel SQUID electronic system was assembled with 3 FLL-interface circuit boards and a power supply board in the aluminum case of 56 mm ${\times}$ 53 mm${\times}$ 150 mm. Overall noise of the system was around 150 fT/(equation omitted)Hz when measured in the shielded room, 200 fT/(equation omitted)Hz in a weakly shielded room, respectively.y.