• Title/Summary/Keyword: Multi-Coil

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A Study on the Difference Method of Magnetic Resonance Signal Measurement when Using Multi-channel Coil and Parallel Imaging

  • Choi, Kwan-Woo;Lee, Ho-Beom;Son, Soon-Yong;Jeong, Mi-Ae
    • Journal of Magnetics
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    • v.22 no.2
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    • pp.220-226
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    • 2017
  • SNR (signal to ratio) is a criterion for providing objective information for evaluating the performance of a magnetic resonance imaging device, and is an important measurement standard for evaluating the quality of MR (Magnetic Resonance) image. The purpose of our study is to evaluate the correct SNR measurement for multi-channel coil and parallel imaging. As a result of research, we found that both T1 and T2 weighted images show the narrowest confidence interval of the method recommended by NEMA (The National Electrical manufacturers Association) 1 having a single measurement method, whereas the ACR (American College of Radiology) measurement method using a multi-channel coil and a parallel imaging technique shows the widest confidence interval. There is a significance in that we quantitatively verified the inaccurate problems of a signal to noise ratio using a ACR measurement method when using a multi-channel coil and a parallel imaging technique of which method does not satisfy the preconditions that researchers could overlook.

Coil Gun Electromagnetic Launcher (EML) System with Multi-stage Electromagnetic Coils

  • Lee, Su-Jeong;Kim, Ji-Hun;Song, Bong Sob;Kim, Jin Ho
    • Journal of Magnetics
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    • v.18 no.4
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    • pp.481-486
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    • 2013
  • An electromagnetic launcher (EML) system accelerates and launches a projectile by converting electric energy into kinetic energy. There are two types of EML systems under development: the rail gun and the coil gun. A railgun comprises a pair of parallel conducting rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail, but the high mechanical friction between the projectile and the rail can damage the projectile. A coil gun launches the projectile by the attractive magnetic force of the electromagnetic coil. A higher projectile muzzle velocity needs multiple stages of electromagnetic coils, which makes the coil gun EML system longer. As a result, the installation cost of a coil gun EML system is very high due to the large installation site needed for the EML. We present a coil gun EML system that has a new structure and arrangement for multiple electromagnetic coils to reduce the length of the system. A mathematical model of the proposed coil gun EML system is developed in order to calculate the magnetic field and forces, and to simulate the muzzle velocity of a projectile by driving and switching the electric current into multiple stages of electromagnetic coils. Using the proposed design, the length of the coil gun EML system is shortened by 31% compared with a conventional coil gun system while satisfying a target projectile muzzle velocity of over 100 m/s.

A study on the application of Rogowski coil on the LTCC (저온소성 다층 세라믹 기판에 로고스키코일을 내장한 전류센서에 관한 연구)

  • Park, Sung-Hyun;Kim, Eun-Sup;Shin, Byoung-Chul
    • Journal of Sensor Science and Technology
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    • v.19 no.6
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    • pp.475-482
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    • 2010
  • Rogowski coil which detects magnetic flux on current changes. It is used for digital integration with watt-hour meter's current sensor, because, Rogowski coil has non-cored or non-magnetic core structure, so that, it cannot be saturated magnetically. This is a study for inventing accurate electric current sensors that have been applied on multi-layer ceramic substrate. We have confirmed its properties from each different layer's materials and pattern sizes by MWS 3D Electromagnetic field analysis program. And, after sensor manufacturing on multi-layer ceramic substrate, we confirmed its sensing quality is reliable as accurate electric current sensor for watt-hour meter.

Development of a 1.8T HTS Insert Coil for High Field Magnet (고자장 자석용 1.8T HTS insert 코일 개발)

  • Bae, Joon-Han;Seong, Ki-Chul
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.56 no.6
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    • pp.1035-1038
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    • 2007
  • We designed and manufactured a 1.8T high temperature superconducting(HTS) insert coil for a NMR magnet operated at 4.2 K. Suitable HTS superconductor and HTS coil were carefully designed and developed. We have selected multi-filamentary Bi2223 conductor fabricated by American Superconductor Corporation(AMSC). The selected conductor consists of Bi2223 filaments of 55, silver stabilizer and stainless steel reinforcement tapes. Therefore, it shows good hoop strength as well as compression tolerance. The conductor has a tape cross-section of 0.31mm x 4.8mm. the Bi2223 conductor shows large anisotropy of critical current. The critical current of conductor in magnetic field parallel to the flat surface are much higher than that in magnetic field perpendicular. The HTS coil has an inner diameter of 78 mm, an outer diameter of 127 mm and a coil length of 600 mm. In this paper, the detailed design, fabrication and test results on the HTS insert coil are presented.

Effect of a Coil Shape on an Impulse Velocity of the Electromagnetic Welding (전자기 용접의 충돌 속도에 대한 코일 형상의 영향)

  • Park, H.;Lee, K.;Lee, J.;Lee, Y.;Kim, D.
    • Transactions of Materials Processing
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    • v.28 no.3
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    • pp.135-144
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    • 2019
  • Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.

Experimental Study on Compact type CO2 Gas Cooler(1) - Heat Flowrate and Pressure Drop in a Multi-Tube-In-Tube Helical Coil Type Gas Cooler - (CO2 가스쿨러용 콤팩트열교환기 개발에 관한 연구(1) -다중관식 헬리컬 코일형 가스냉각기내 CO2의 열유량과 압력강하-)

  • Oh, Hoo-Kyu;Son, Chang-Hyo
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.1
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    • pp.30-36
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    • 2010
  • The heat flowrate and pressure drop of $CO_2$ in a multi-tube-in-tube helical coil type gas cooler were investigated experimentally. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], respectively and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The heat flowrate of $CO_2$ in the test section is increased with the increase in mass flowrate of coolant, the cooling pressure and mass flowrate of $CO_2$. The pressure drop of $CO_2$ is decreased with the decrease in mass flowrate of coolant and $CO_2$, but decreased with increase in cooling pressure of $CO_2$. The heat flowrate of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler is greatly higher than that of $CO_2$ in the double pipe type gas cooler, while the pressure drop of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler is greatly lower than that of $CO_2$ in the double pipe type gas cooler. Therefore, in case of the application of $CO_2$ at the multi-tube-in-tube helical coil type gas cooler, it is expected to carry out the high-efficiency, high-performance and compactness of gas cooler.

Analysis of the Bird-cage Receiver Coil of a MRI System Employing a Equivalent Circuit Model Based on a Transmission Matrix (전송행렬 기반 등가 회로 모델을 이용한 자기공명영상 장치용 새장형 수신 코일 해석)

  • Kim, Hyun Deok
    • Journal of Korea Multimedia Society
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    • v.20 no.7
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    • pp.1024-1029
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    • 2017
  • A novel analytic solution has been derived for the bird-cage receiver coil of a magnetic resonance imaging (MRI) system, which is widely used in 3-dimensional medical imaging, by transforming the coil into an equivalent circuit model by using a transmission matrix-based circuit analysis. The bird-cage coil composed of N legs is divided into a cell for which input impedance is to be analyzed and the remaining N-1 cells, and then a transmission matrix corresponding to the N-1 cells is converted into a circuit to transform the 3-dimensional bird-cage coil into the 2-dimensional equivalent circuit model, which is suitable to derive the analytic solution for the input impedance. The proposed method derives directly the analytic solution for the input impedance at an arbitrary point of the coil unlike the conventional analytic solution of a bird-cage coil, so that it can be used not only for resonance frequency calculations but also for various coil characteristics analyses. Since the analytic solution agreed well with the results of computational simulations, it can be useful for the impedance matching of a coil and the analysis and the design of a multi-tune bird-cage coil.

A Process for the Control of Cell Size of 6061 Al foams by Multi-step Induction Heating Method (다출력 유도가열 공정을 이용한 다공질 6061 알루미늄 합금의 기공 제어 공정)

  • 윤성원;강충길
    • Transactions of Materials Processing
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    • v.12 no.5
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    • pp.449-456
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    • 2003
  • Multi-step induction heating process was applied to the powder compact melting technique as a new heating process to achieve pinpoint accuracy, faster cycle time, repeatability, non-contact and energy-efficient heat in a minimal amount of time. The objective of this study is the establishment of the input data diagram of multi step induction heating process for automation of the fabrication process of 6061 Al foams with desired density. At first, proper induction coil was designed to obtain a uniform temperature distribution over the entire cross sectional area of specimen. By using this coil, foaming experiments were performed to investigate the multi-step induction heating conditions such as capacity, temperature and time conditions of each heating and holding step. On the basis of the obtained multi-step induction heating conditions, relationship between final heating temperature and fraction of porosity was investigated.

Preliminary Results of 7-Channel Insertional pTx Array Coil for 3T MRI

  • Ryu, Yeun Chul
    • Journal of Magnetics
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    • v.22 no.2
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    • pp.238-243
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    • 2017
  • In this research, we report the preliminary results of an insertional type parallel transmission (pTx) array that has 7-elements that are placed in the space above a patient table as a transmit (Tx) coil to give an RF transmission ($B_1{^+}$) field for the body object of a 3 Tesla (T) MRI system. In previous research, we have tried to compare the performances of different coil elements and array geometries for a pTx body image. Based on these results, we attempt to obtain a human image with the proposed pTx array. Through the simulation and experimental results, we introduce a possible structure of multi-channel Tx array and verify the utility of a multi-channel Tx body image using $B_1{^+}$ shimming. The insertional pTx array, combined with a receiver (Rx) array coil, provides an enhanced $B_1{^+}$ field homogeneity in a large ROI image as a result of $B_1{^+}$ shimming applied over the full body size object. Through this research, we hope to determine the usefulness of the proposed insertional type RF coil combination for 3 T body imaging.

Signal Intensity Changes according to Coil Position Changes in MRI using 6 Channel SENSE Cardiac Array Coils (6채널 SENSE Cardiac Array 코일을 이용한 검사 시 코일의 위치 변화에 따른 신호강도)

  • Choi, Kwan-Woo;Son, Soon-Yong;Yoo, Beong-Gyu
    • Journal of the Korean Society of Radiology
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    • v.12 no.5
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    • pp.699-706
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    • 2018
  • In this study, we measured signal intensities according to array coil position changes to provide reference data of coil directions and the distances as it deters image quality unless the coils are aligned properly. The multi-purpose MRI phantom was placed in body array coils, and it was moved to the top, bottom, left, and right directions by 2 cm from the center to 10 cm. After obtaining images, signal intensities were measured and compared. The results of this study were as follows: Except for the upward direction, the signal intensities of the reference signal was not significantly different from that of the reference signal intensity within 2cm in both T1 and T2-weighted images. In conclusion, in clinical circumstances which various challenges exist to align the coils exactly on the same lines, array coils should be positioned at least within 2 cm from the center except for the upward direction, on the same line to prevent the image qualities are lowered.