• Journal of the Korean Society for Precision Engineering
• /
• v.18 no.6
• /
• pp.93-101
• /
• 2001

This paper presents modeling of an inductive micro position sensing system and its analysis. The parameters affected the system response are excitation frequency, turn ratio, input position, air-gap size, load resistance, and geometric dimensions. To analyze the system, we try to establish a modeling based on an equivalent magnetic circuit with permeances. The model is verified by the experimental results from 1 kHz to 20 kHz. The magnetic circuit model is well fitted to the experimental data except a little error due to LC resonance in the large turn-ratio system. Modeling enables us to theoretically approach the response characteristics. Based on the magnetic circuit model, system parameters can be selected in such a way to obtain the required characteristics such as high sensitivity, good linearity, or small size.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.22 no.2
• /
• pp.177-186
• /
• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects in underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05a
• /
• pp.11-20
• /
• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects on underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Journal of the Korean Magnetic Resonance Society
• /
• v.24 no.2
• /
• pp.59-65
• /
• 2020

Nitrogen-Vacancy (NV) center in diamond has been an emerging versatile tool for quantum sensing applications. Amongst various applications, nano-scale nuclear magnetic resonance (NMR) using a single or ensemble NV centers has demonstrated promising results, opening possibility of a single molecule NMR for its chemical structural studies or multi-nuclear spin spectroscopy for quantum information science. However, there is a key challenge, which limited the spectral resolution of NMR detection using NV centers; the interrogation duration for NV-NMR detection technique has been limited by the NV sensor spin lifetime (T₁ ~ 3ms), which is orders of magnitude shorter than the coherence times of nuclear spins in bulk liquid samples (T₂ ~ 1s) or intrinsic ¹³C nuclear spins in diamond. Recent studies have shown that quantum memory technique or synchronized readout detection technique can further narrow down the spectral linewidth of NMR signal. In this short review paper, we overview basic concepts of nanoscale NMR using NV centers, and introduce further developments in high spectral resolution NV NMR studies.

• Investigative Magnetic Resonance Imaging
• /
• v.23 no.1
• /
• pp.1-16
• /
• 2019

Dynamic contrast enhanced (DCE) magnetic resonance (MR) imaging plays an important role in non-invasive detection and characterization of primary and metastatic lesions in the liver. Recently, efforts have been made to improve spatial and temporal resolution of DCE liver MRI for arterial phase imaging. Review of recent publications related to arterial phase imaging of the liver indicates that there exist primarily two approaches: breath-hold and free-breathing. For breath-hold imaging, acquiring multiple arterial phase images in a breath-hold is the preferred approach over conventional single-phase imaging. For free-breathing imaging, a combination of three-dimensional (3D) stack-of-stars golden-angle sampling and compressed sensing parallel imaging reconstruction is one of emerging techniques. Self-gating can be used to decrease respiratory motion artifact. This article introduces recent MRI technologies relevant to hepatic arterial phase imaging, including differential subsampling with Cartesian ordering (DISCO), golden-angle radial sparse parallel (GRASP), and X-D GRASP. This article also describes techniques related to dynamic 3D image reconstruction of the liver from golden-angle stack-of-stars data.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2007.06a
• /
• pp.59-60
• /
• 2007

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.5
• /
• pp.429-434
• /
• 2003

The magnetic field sensor was fabricated with superconducting ceramics of BiPbSrCaCuO system. The sensor at liquid nitrogen temperature showed the increase of electrical resistance by applying magnetic field. Actually, the voltage drop across the sensor was changed from zero to a value more than 100 $\mu\textrm{V}$ by the applied magnetic field. The change of electrical resistance depended on magnetic field. The sensitivity of this sensor was 2.9 $\Omega$/T. The sensing limit was about 1.5${\times}$10$\^$-5/ T. The increase of electrical resistance by the magnetic field was ascribed to a modification of the Josephson junctions due to the penetrating magnetic flux into the superconducting material. Considering the observed properties of the superconductor with trapped magnetic flux, a magnetic sensor was fabricated to detect simultaneously both the intensity and the direction of the magnetic field.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07a
• /
• pp.115-118
• /
• 2003

The sensor at liquid nitrogen temperature showed the increase of electrical resistance by applying magnetic field. Actually, the voltage drop across the sensor was changed from zero to a value more than $100\;{\mu}V$ by the applied magnetic field. The change of electrical resistance depended on magnetic field. The sensitivity of this sensor was $2.9\;{\Omega}/T$. The sensing limit was about $1.5{\times}10^{-5}\;T$. The increase of electrical resistance by the magnetic field was ascribed to a modification of the Josephson junctions due to the penetrating magnetic flux into the superconducting material. Considering the observed properties of the superconductor with trapped magnetic flux, a magnetic sensor was fabricated to detect simultaneously both the intensity and the direction of the magnetic field.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2003.10a
• /
• pp.69-71
• /
• 2003

The magnetic field sensor was fabricated with superconducting ceramics of YBaCuO system. The sensor at liquid nitrogen temperature showed the increase of electrical resistance by applying magnetic field. Actually the voltage drop across the sensor was changed from zero to a value more than 100 $mutextrm{V}$ by the applied magnetic field. The change in electrical resistance depended on magnetic field. The sensitivity of this sensor was 2.9 $\Omega$/T. The sensing limit was about $1.5\times$10$^{-5}$. The increase of electrical resistance by the magnetic field was ascribed to a modification of the Josephson junctions due to the penetrating magnetic flux into the superconducting material. Considering the observed properties of the superconductor with trapped magnetic flux, a magnetic sensor was fabricated to detect simultaneously both the intensity and the direction of the magnetic field.

• Korean Journal of Remote Sensing
• /
• v.21 no.1
• /
• pp.91-98
• /
• 2005

On board satellite magnetometer measures all possible magnetic components, such as the core and crustal components from the inner Earth, and magnetospheric, ionospheric and' its coupled components from the outer Earth. Due to its dipole and non-dipole features, separation of the respective component from the measurements is most difficult unless the comprehensive knowledge of each field characteristics and the consequent modeling methods are solidly constructed. Especially, regional long wavelength magnetic signals of the crust are strongly masked by the main field and dynamic external field and hence difficult to isolate in the satellite measurements. In particular, the un-modeled effects of the strong auroral external fields and the complicated behavior of the core field near the geomagnetic poles conspire to greatly reduce the crustal magnetic signal-to-noise ratio in the polar region relative to the rest of the Earth. We can, however, use spectral correlation theory to filter the static lithospheric and core field components from the dynamic external field effects that are closely related to the geomagnetic storms affecting ionospheric current disturbances. To help isolate regional lithospheric anomalies from core field components, the correlations between CHAMP magnetic anomalies and the pseudo-magnetic effects inferred from satellite gravity-derived crustal thickness variations can also be exploited, Isolation of long wavelengths resulted from the respective source is the key to understand and improve the models of the external magnetic components as well as of the lower crustal structures. We expect to model the external field variations that might also be affected by a sudden upheaval like tsunami by using our algorithm after isolating any internal field components.