• Progress in Superconductivity
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• 제13권1호
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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.

• Progress in Superconductivity
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• 제8권2호
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• pp.164-168
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• 2007

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.

• 대한의용생체공학회:의공학회지
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• 제24권3호
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• pp.159-165
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• 2003

뇌자도 측정을 위해 고감도 superconducting quantum interference device (SQUID) 자력계 및 37채널 뇌자도 측정장치를 제작하고 동작특성을 조사하였다. 자속-전압 변환계수 및 변조전압 진폭이 큰 double relaxation oscillation SQUID (DROS)를 사용함으로서 구동회로를 간단히 하였고 안정한 SQUID 동작을 실현할 수 있었다. DROS 자력계를 설계 및 제작한 결과 자력계의 평균 백색잡음은 약 3 fT/√Hz으로서 우수한 자장감도를 가짐을 확인하였다 머리의 평균곡률을 기반으로 37개의 자력계를 반구형으로 배치시켰으며, 외부잡음을 줄이기 위해 신호채널 외에 11개의 기준채널을 설치하여 소프트웨어 방법으로 합성미분계 및 적응필터링을 형성할 수 있도록 하였다 저잡음 듀아를 제작하여 동작특성을 측정한 결과 듀아 열자기 잡음이 자력계 잡음에 비해 무시할 수 있는 수준이었으며, 듀아의 용량은 30 L, 액체헬륨 증발율은 4 L/d이다. 제작된 시스템을 이용하여 청각유발 신호를 측정하고, 디지털 신호처리 및 전류원 국지화 프로그램을 구성하여 전류원의 위치를 추정함으로서 개발된 시스템을 뇌자도 측정에 활용하였다.

• Progress in Superconductivity
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• 제5권1호
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• pp.50-54
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• 2003

We have fabricated $∂^2$$B_{z}$ /$∂x^2$ type planar gradiometers and studied their properties in operation under various field conditions. $YBa_2$$Cu_3$$O_{7}$ film was deposited on $SrTiO_3$ (100) substrate by a pulsed laser deposition (PLD) system and patterned into a device by the photolithography with ion milling technique. The device consists of 3 pickup loops designed symmetrically Inner dimension and the width of the square side loops are 3.6 mm and 1.2 mm, respectively, and the corresponding dimensions of the center loop are 2.0 mm and 1.13 mm. The length of baseline gradiometer is 5.8 mm. Step-edge junction width is 3.0 $\mu\textrm{m}$ and the hole size of the SQUID loop is 3 $\mu\textrm{m}$ ${\times}$ 52 $\mu\textrm{m}$. The SQUID inductance is estimated to be 35 pH. The device was formed on a 20 mm ${\times}$ 10 mm substrate. We have tested the behavior of the device in various field conditions. The unshielded gradiometer was stable under extremely hostile conditions on a laboratory bench. Noise level 0.45 pT/$\textrm{cm}^2$/(equation omitted)Hz and 0.84 pT/$\textrm{cm}^2$/(equation omitted)Hz at 1 Hz for the shielded and the unshielded cases, which correspond to equivalent field noises of 150 fT/(equation omitted)Hz and 280 fT/(equation omitted)Hz, respectively. In spite of the short baseline of 5.8 mm, the high common-mode-rejection-ratio of the gradiometer, $10^3$, allowed us to successfully record magnetocardiogram of a human subject, which demonstrates the feasibility of the design in biomagnetic studies.