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다양한 기저선을 갖는 1차 및 2차 미분계의 신호크기 및 신호 대 잡음비 조사
강찬석,유권규,이용호,권혁찬,김진목,박용기,이순걸,Kang, C.S.,Yu, K.K.,Lee, Y.H.,Kwon, H.,Kim, J.M.,Park, Y.K.,Lee, S.G. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
We investigated signal-to-noise ratios (SNRs) of magnetocardiography (MCG) signals using the first-order and the second-order gradiometers of different baselines. The MCG signals were recorded using a measurement system with 61 magnetometers which measured the normal magnetic component to the chest surface. The distance between the chest surface and the bottom of the dewar was changed from 0 cm to 15 cm, and the MCGs were measured for each distance. By subtracting the other signals (distance = 1 to 15 cm) from the reference signal (distance =0 cm), we could simulate the first-order and the second-order gradiometer signals with various baselines. In addition, to evaluate the reproducibility of the simulation, we fabricated the wire wound first-order and second-order gradiometers which measured a normal magnetic component to the chest surface. The baselines of the first-order gradiometers were, respectively, 50 mm, 70 mm and 100 mm and the baseline of the second-order gradiometer was 50 mm. Using these gradiometers, we recorded the MCG signal and compared the SNR between the simulation and the measurement.
강찬석,이용호,권혁찬,김진목,유권규,박용기,이순걸,Kang, C.S.,Lee, Y.H.,Kwon, H.,Kim, J.M.,Yu, K.K.,Park, Y.K.,Lee, S.G. 한국초전도학회 2007 Progress in superconductivity Vol.8 No.2
We developed a SQUID magnetometer based on Double Relaxation Oscillation SQUID(DROS) for measuring magnetocardiography(MCG). Since DROS provides a 10 times larger flux-to-voltage transfer coefficient than the conventional DC-SQUID, simple flux-locked loop electronics could be used for SQUID operation. Especially, we adopted an external feedback to eliminate the magnetic coupling with adjacent channels. When the DROS magnetometer was operated inside a magnetically shielded room, average magnetic field noise was about 5 $fT/^{\surd}Hz$ at 100 Hz. Using the DROS magnetometer, we constructed a multichannel MCG system. The system consisted of 61 magnetometers are arranged in a hexagonal structure and measures a vertical magnetic-field component to the chest surface. The distance between adjacent channels is 26 mm and the magnetometers cover a circular area with a diameter of 208 mm. We recorded the MCG signals with this system and confirmed the magnetic field distribution and the myocardinal current distribution.
강찬석,김기웅,유권규,이성주,권혁찬,황성민,이용호,김진목,이상길,Kang, C.S.,Kim, K.,Yu, K.K.,Lee, S.J.,Kwon, H.,Hwang, S.M.,Lee, Y.H.,Kim, J.M.,Lee, S.K. 한국초전도학회 2009 Progress in superconductivity Vol.10 No.2
A current limiter was manufactured using a Josephson junction array to cut off an excessive current flowing into the SQUID sensor. The Fabricateed Josephson junction array was connected in series with a flux transformer that consists of a pick-up coil and an input coil, and the flux transformer was inductively coupled with a Double Relaxation Oscillation SQUID(DROS). The flux-voltage modulation curve was induced by applying an AC magnetic field whose magnitude was far smaller than that of the DC magnetic field. A change in the flux-voltage modulation curve of the SQUID was observed while the DC magnetic field was increased, to qualitatively examine the current limiting characteristic of the Josephson junction array. As a result, it was found that the SQUID flux-voltage modulation curve disappeared at the critical current of the Josephson junction array, which indicates that the Josephson junction array properly works as a current limiter.
김지은,김인선,강찬석,권혁찬,김진목,이용호,김기웅,Kim, J.E.,Kim, I.S.,Kang, C.S.,Kwon, H.,Kim, J.M.,Lee, Y.H.,Kim, K. 한국초전도학회 2011 Progress in superconductivity Vol.13 No.1
We developed a four-channel first order gradiometer system to measure magnetoencephalogram for mice. We used double relaxation oscillation SQUID (DROS). The diameter of the pickup coil is 4 mm and the distance between the coils is 5 mm. Coil distance was designed to have good spatial resolution for a small mouse brain. We evaluated the current dipole localization confidence region for a mouse brain, using the spherical conductor model. The white noise of the measurement system was about 30 fT/$Hz^{1/2}$/cm when measured in a magnetically shielded room. We measured magnetic signal from a phantom having the same size of a mouse brain, which was filled with 0.9% saline solution. The results suggest that the developed system has a feasibility to study the functions of brain of small animals.