• 한국초전도학회:학술대회논문집
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• v.12
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• pp.46-46
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• 2002

• Journal of Biomedical Engineering Research
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• v.24 no.3
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• pp.159-165
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• 2003

We developed a 37-channel magnetoencephalogram (MEG) measurement system based on low-noise superconducting quantum interference device (SQUID) magnetometets, and operated the system to measure MEG signals. By using double relaxation oscillation SQUIDs with high flux-4o-voltage transfers, the SQUID outputs could be measured directly by room temperature preamplifiers and compact readout circuits were used for SQUID operation. The average field noise level of the magnetometers is about 3 fT/√Hz in the white region, low enough for MEG measurements when operated inside a magnetically shielded room. The 37 magnetometers were distributed on a hemispherical surface haying a radius of 125 mm. In addition to the 37 sensing channels. 11 reference channels were installed to pickup external noise and to form software gradiometers. A low-noise liquid helium dewar was fabricated with a liquid capacity of 30 L and boil-off rate of 4 L/d. The signal processing software consists of digital filtering, software gradiometer, isofield mapping and source localization. By using the developed system, we measured auditory-evoked fields and localized the current dipoles, demonstrating the effectiveness of the system.

• Journal of Biomedical Engineering Research
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• v.24 no.3
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• pp.167-173
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• 2003

Measuring subtle neuromagnetic signals requires eliminating background noises. Especially, a SQUID magnetometer is very sensitive to the magnetic noise even from a distant source. As typical software methods, we use the synthetic gradiometer of the adaptive filtering to reduce the noises. In this article, we present noise reduction effects in our 37-channel SQUID magnetometer system by applying each method including the frequency-domain adaptive filtering and discuss a selective application of the methods to the detection of clinical magnetoencephalogram signals.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.70-70
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• 2003

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.32-32
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• 2001

• 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
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• v.3 no.2
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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 . .

• Progress in Superconductivity
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• v.13 no.1
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• pp.18-23
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• 2011

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.