• Journal of Sensor Science and Technology
• /
• v.13 no.2
• /
• pp.110-113
• /
• 2004

We have designed and fabricated the YBCO single layer directly-coupled SQUID magnetometers for the purpose of magnetocardiography in a magnetically disturbed environment. The SQUID magnetometers were designed three different types of pickup coil such as solid type, PL type I and PL type II for further stable fluxed-locked-loop operation without magnetic shielding. Magnetometer was fabricated with a single layer YBCO thin film deposited on STO(100) bicrystal substrate with misorientation angle of $30^{\circ}$. We have achieved a magnetic field noise BN of 30 fT/$Hz^{1/2}$ at 100 Hz, and less than 70 fT/$Hz^{1/2}$ at 1 Hz. The PL type II SQUIDs have exhibited the most stable fluxed-locked-loop operation in a magnetically unshielded environment.

• Journal of Powder Materials
• /
• v.21 no.6
• /
• pp.429-433
• /
• 2014

This study investigated the magnetic properties and frequency dispersion of complex permeability of Ni-Zn-Co ferrites used for magnetic shielding in near field communication (NFC) system. The sintered specimens of $(Ni_{0.7}Zn_{0.3})_{1-x}Co_xFe_2O_4$ composition were prepared by the conventional ceramic processing. The coercive force and saturation magnetization were measured by vibrating sample magnetometer. The complex permeability was measured by RF impedance analyzer in the range of 1 MHz~1.8 GHz. The coercive force increased and saturation magnetization decreased with increasing the Co substitution. The real and imaginary parts of complex permeability decreased and the resonance frequency increased with Co substitution, which was attributed to the increase in crystal anisotropy field and reduction in saturation magnetization. The effect of Co substitution could be found in reducing the magnetic loss to nearly zero at the operating frequency of NFC (13.56 MHz).

• Journal of Powder Materials
• /
• v.23 no.2
• /
• pp.132-135
• /
• 2016

This study investigates the influence of sintering temperature on the magnetic properties and frequency dispersion of the complex permeability of Ni-Zn-Cu ferrites used for magnetic shielding in near-field communication (NFC) systems. Sintered specimens of $(Ni_{0.7}Zn_{0.3})_{0.96}Cu_{0.04}Fe_2O_4$ are prepared by conventional ceramic processing. The complex permeability is measured by an RF impedance analyzer in the range of 1 MHz to 1.8 GHz. The real and imaginary parts of the complex permeability depend sensitively on the sintering temperature, which is closely related to the microstructure, including grain size and pore distribution. In particular, internal pores within grains produced by rapid grain growth decrease the permeability and increase the magnetic loss at the operating frequency of NFC (13.56 MHz). At the optimized sintering temperature ($1225-1250^{\circ}C$), the highest permeability and lowest magnetic loss can be obtained.

• Journal of Biomedical Engineering Research
• /
• v.18 no.4
• /
• pp.421-428
• /
• 1997

Magnetic field sensors made from superconducting quantum interference device (SQUID) are the most sensitive low-frequency sensors available, enabling measurements of extremely weak magnetic fields from the brain. Neuromagnetic measurements allow superior spatial resolution, compared with the present electric measurements, and superior temporal resolution, compared with the fMRl and PET, providing useful informations for the functional diagnoses of the brain. We developed a 4-channel SQUID system for neuromagnetic applications. The main features of the system are its simple readout electronics and compact pickup coil structure. A magnetically shielded room has been constructed for the reduction of environmental magnetic noises. The developed SQUID system has noise level lower than the magnetic noise from the brain. Magnetic field signals of the spontaneous r-rhythm activity and auditory evoked magnetic fields have been measured.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.49 no.5
• /
• pp.291-296
• /
• 2000

Recently large size color TV and computer monitor are very popular and a lot techniques are being developed to get a high quality picture on the screen through reducing the convergence error among the red, green and blue beams and achieving a high focusing. One of the techniques is considering the mutual effects of the components of the Brown tube. The magnetic deflection yoke, especially, stands immediately next to the electron gun and generates the leakage magnetic fields at the electron gun which affects the trajectories of the electron beams inside the gun. Hence a shield cup made of thin conducting plate is located at the end of electron gun in order to shield the leakage flux from the deflection yoke. Since the red, green and blue beams are placed unsymmetrically the shielding effects of the shield cup on the beams are not same and eddy current controller, made of thin conducting plate, is auxiliary placed inside the shield cup. In this paper a transient magnetic field analysis algorithm is developed using boundary element method, and applied to the analysis of the shielding effects of the eddy current controller of shield cup in an electron gun.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.8 no.4
• /
• pp.22-29
• /
• 1994

본 논문에서는 시변자계측정을 위한 센서와 형광등의 점등에 의하여 발생되는 자계의 특성에 대하여 기술하였다. 자계측정계는 동축케이블을 사용한 자기적분형 자계센서와 증폭기, 적분기로 구성하였으며 교정실험 결과, 주파수대역은 약 40Hz∼100kHz이었다. 수동점등식, 고주파점등식과 글로우점등식 등 여러 가지 점등방식의 형광등에 의하여 발생되는 자계의 파형을 측정하고, 측정된 자계의 주파수성분을 고속푸리에변환(fast Fourier transformation: FFT)기법으로 해석하였다. 형광등의 점등중에 발생되는 자계성분은 주로 기수고주파 성분이 많이 포함되어 있으며, 인덕션칵에 의하여 점등순간에는 급변성의 과도성분이 나타났다. 전자회로나 제어기기의 보호를 위한 자계차폐장치를 설계할 때에는 반드시 자계의 기수고조파성분을 고려하여야 됨이 확인되었다.

• Proceedings of the Korean Fiber Society Conference
• /
• 2002.04a
• /
• pp.355-358
• /
• 2002

고분자가 절연재료로서 사용되는 이유는 전기를 통하지 않는 절연특성을 지니고 있기 때문이며 이러한 성질은 고분자가 금속재료와 구별되는 가장 큰 특징이다. 그러나 1964년 W. A. Little 이 발표한 공액 이중결합구조를 가진 화합물은 전도성 고분자가 될 수 있다는 가설을 바탕으로 전도성 고분자에 관한 많은 연구가 진행 중에 있다. 전도성 고분자는 절연체로서의 응용에만 한정되어왔던 기존 고분자물질들과 달리 가볍고 저렴하며 단일결합과 이중결합을 교대로 하고 있는 공액 고분자 구조를 가지고 있어 다양한 화학적 합성방법에 의해 전기전도도, 유전상수, 결정 등의 물리적 성질을 조절할 수 있으며, 금속의 전기적, 자기적, 광학적 특성과 고분자의 기계적 성질을 동시에 가지므로 배터리, 축전기, 트랜지스터, 광전소자, 전자파 차폐제 등 플라스틱 전자소재의 실용적으로 인해 산업체에서도 높은 관심의 대상이다. (중략)

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 1999.02a
• /
• pp.97-100
• /
• 1999

Nowadays the high-Tc Superconducting Fault current Limiter (SFCL) is one of the superconducting devices which are very closed to commercialization. The most popular model of High-Tc SFCL is a magnetic shielding type. A superconductor of magnetic shielding type SFCL can be stable in the superconducting state, because there is no contact between the superconductor and the normal conductor. But this model needs large place to set up and in a fault condition, mechanical vibrations may happen to damage the superconductor or total device. In this paper, to solve these problems, the simplified model of magnetic shielding type SFCL was introduced.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.511-514
• /
• 2002

In this paper, we compared the characteristic of fault current liminting in the magnetic shielding type High-Tc superconducting fault current limiter(FCL) using both Piecewise linear magnetization curve and real magnetization one of iron core. From this paper, the characteristics of fault current limiting in both cases showed many differences. The latter has higher fault current than the former, because the saturation of iron core was reflected and more accumulated during fault. It is expected that the more exact characteristic of magnetic shielding type High-Tc superconducting FCL was obtained in the case of design and modeling.

• 한국초전도학회:학술대회논문집
• /
• v.10
• /
• pp.311-314
• /
• 2000

자기차폐형 고온초전도한류기에서 철심의 포화 문제와 더불어 가장 문제가 되는 것은 공극의 크기이다. 고온초전도 tube 와 철심 또는 일차 권선과 초전도 tube 사이에서의 공극은 정상상태에서 불필요한 전압강하의 원인이 된다. 이러한 전압강하는 시스템에서의 불안정성을 초래할 수 있기 때문에, 공극의 결정은 고온초전도한류기의 설계에 있어 가장 중요한 요소가 된다. 또한, 사고 발생시 나타나는 고온초전도한류기의 임피던스는 사고 전류를 제한하는 주요한 요소이다. 다양한 parameter의 변화를 통하여 고온초전도한류기의 임피던스변화를 관찰하였고, 임피던스 변화에 따른 전류제한 효과를 시뮬레이션을 통해 확인하였다. 시뮬레이션의 결과를 이용하여 440v급 Rod type 고은초전도한류기를 설계하였으며, 동작 특성을 해석하였다.