• 비파괴검사학회지
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• 제26권1호
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• pp.25-29
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• 2006

In this paper, the eddy current signals come from a pair oi transmit-receive (T/R) pancake coil on ECT array Probe are analyzed with the variations of the lift-of and of the distance between transmit and receive coils. To obtain the electromagnetic characteristics of the probes, the governing equation describing the eddy current problems is derived from Maxwell's equation and is solved using three-dimensional finite element method. Eddy current signals from T/R coils on ECT array probe have quite different characteristics compared with ones from impedance coil on rotating pancake coil probe. The results in this paper ran be helpful when the field eddy current signals from ECT array probe are evaluated.

• 전기학회논문지
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• 제63권4호
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• pp.546-550
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• 2014

In this research, we report all the elements are placed in the space above the patient table as a transmit coil to give optimized B1+ field for the body object. Through the simulations, we compared upper-and-lower parts combined 8 channel Tx array to upper only 8 channel Tx array and showed the utilities of B1+ shimming in multi-channel Tx body imaging at 3T. Half-cylinder shaped upper array shows weak B1+ field area around back of patient without B1+ shimming. After B1+ shimming, highly induced SAR places occurred in the arm region due to the close distance to the both end elements which were driven by very high RF current to enhance B1+ in back area. The proposed upper and lower combined array provides an enhanced homogeneous B1+ field in large ROI imaging as a result of shimming over the body size phantom. Through this research we proved the usefulness of the proposed insertional upper and lower parts combined transmit array for 3T body imaging.

• 대한의용생체공학회:의공학회지
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• 제29권2호
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• pp.99-106
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• 2008

To improve $B_1$ homogeneity in high field MRI, the RF power is applied to the transmit array coil elements sequentially in the time-multiplexed way. Since only a single coil element is activated in a time-multiplexing slot, the global standing wave formation in the human body is greatly suppressed. The time-multiplexing slot width is on the order of micro seconds, hence, high-order-harmonic slices can be placed far from the transmit coil and simultaneous multiple slice selection can be avoided. The $B_1$ homogeneities of a birdcage coil and an eight-channel transmit array coil have been compared through finite difference time domain simulations. The simulation results indicate that the proposed technique can reduce the peak-to-peak $B_1$ inhomogeneity down to one fourth of the transmission with a birdcage coil on the central plane of the human head model at 3 T. The mimicking experiments at 3 T, eight separate experiments with a single coil element activated and image reconstruction by combining the eight images, also show promising results. It is expected that the proposed technique has some advantages over other $B_1$ improving methods in real practice since simple RF switching circuitries are only necessary and electromagnetic coupling between the coil elements is out of concern in its realization.

• Journal of Magnetics
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• 제22권2호
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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.

• 비파괴검사학회지
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• 제37권1호
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• pp.21-28
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• 2017

배열 와전류 기술은 2차원적으로 나란히 정열된 다수의 와전류 코일로 구성된 탐촉자 면적에 대하여 기계적인 이동없이 전기적으로 주사할 수 있다. 단일 코일을 사용하는 와전류 기술과 비교하여 탐촉자가 한 번의 이동으로 넓은 영역을 검사할 뿐만 아니라 데이터 해석이 용이하여 검사 속도와 신뢰성을 향상시키는 장점이 있다. 이번 연구에서는 $2{\times}16$ 코일 배열의 배열 와전류 탐촉자와 순차적으로 송수신 코일을 선택하고 송수신 모드로 동작시키는 다중화기기를 개발하였다. 이 탐촉자를 이용하여 다양한 종류의 시편을 제작하여 표면검사를 수행하고, 와전류 신호 및 C-scan을 이미지 분석을 통해 송수신 모드 배열 와전류 기술의 특성에 대해 연구하였다.

• 조명전기설비학회논문지
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• 제22권4호
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• pp.159-165
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• 2008

본 논문에서는 전자기 유한요소 해석을 통하여 배열와전류프로브의 T/R 코일의 와전류탐상 특성을 해석하였다. 신호해석을 위해 사용된 결함은 Notch 결함이며, 결함의 깊이는 관두께를 기준으로 40[%]로 하였으며, 결함의 위치는 관의 내부 및 외부에 있는 것으로 하였다. Transmit 코일을 중심으로 Receive 코일의 위치를 원주방향으로 $0[^{\circ}]$, $30[^{\circ}]$, $60[^{\circ}]$, $90[^{\circ}]$에 위치시키면서 신호해석을 수행하였다. 프로브의 전자기적 특성을 해석하기 위하여 맥스웰 방정식을 이용하여 지배방정식을 유도하였고, 이를 3차원 유한요소법을 이용하여 수치 해석을 수행하였다. 두 종류 결함의 수치해석 비교 결과 내부결함의 신호가 외부결함보다 크게 발생하였고, Transmit 코일에 대한 Receive 코일의 각도 및 위치 변화시 결함신호의 차이를 확인할 수 있었다. ASME 표준 시험편을 이용한 배열와전류 프로브의 와전류탐상 실험신호와 비교결과 유사한 신호를 확인할 수 있었다. 본 논문의 결과는 배열와전류 프로브의 와전류 탐상 신호 평가시 도움이 될 것이다.

• 대한의용생체공학회:의공학회지
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• 제29권4호
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• pp.267-271
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• 2008

The RF shimming technique has been used to improve the transmit RF field homogeneity in highfield MRI. In the RF shimming technique, the amplitude and phase of the driving currents in each coil element are optimized to get homogenous flip angle or uniform image intensity. The inductive and capacitive coupling between the coil elements may degrade the RF field homogeneity if not taken into account in the optimization procedure. In this paper, we have analyzed the coupling effects on the RF shimming using a sixteen-element TEM RF coil model operating at 300 MHz. We have found that the coupling effects on the RF shimming can be reduced by putting high dielectric material between the active rung and the shield.

• Investigative Magnetic Resonance Imaging
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• 제16권2호
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• pp.103-114
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• 2012

목적: 7T 악관절 자기공명상의 개선을 위해 제안된 4 채널 스파이럴 코일과 그를 구동시키기 위한 회로는 자기장의 분포, 송신 전용필드, 신호 대 잡음 비, 그리고 악관절 영상에 대하여 일반적인 단일 루프 형태의 코일과 비교되었다. 대상과 방법: 단일 채널 그리고 4 채널 스파이럴 코일은 단일 루프 형태의 코일에 대해 전자기장 시뮬레이션으로 자기장의 분포 및 송신 전용 필드에 대해서 비교 되었고, 7T에서 이를 평가하고자 송신전용 필드와 더불어 자기장의 분포 역시 비교 평가되었다. 결과: 전자기장 시뮬레이션의 결과와 7T 자기공명영상에서 4 채널 스파이럴 코일은 기존에 사용되는 일반적인 구조인 단일 루프 코일에 비해 상대적으로 우수한 자기장의 분포 및 송신 전용 필드를 보였다. 결론: 7T에서는 코일의 구조에 비해 상대적으로 영상화되는 물질의 특성에 더욱더 의존적이나, 각각의 코일은 다른 필드 분포를 나타냄으로써 최적화된 코일은 악관절 영상과 같은 특정 용도로 사용될 수 있음을 확인하였다.

• 전기학회논문지
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• 제63권3호
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• pp.404-408
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• 2014

In this research we evaluate the excitation homogeneity and SAR of three different Tx arrays after B1+ Shimming in the human body at 3T. Through the simulations, we compared the field properties that are standard deviation and mean value of transverse magnetization for 1) strip line TEM array, 2) rectangular loop array, 3) combined array of strip line element and rectangular loop and shown the utilities of B1+ shimming in human body model. After B1+ shimming, it is evaluated four different types of SAR for body mesh through whole body simulation; those are average, maximum 1-cell, maximum 1-gram, and maximum 10-gram SAR. It appears that in this particular comparison an array based on strip line elements can produce better homogeneity and lower SAR than an array of rectangular loops or an array of combined elements (strip line and loop). While many factors are considered in designing coils for production, it is hoped that methods and results like these will be used in the future to guide decisions and maximize benefit.

• 한국생산제조학회지
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• 제25권1호
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• pp.48-53
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• 2016

An EMAT can be used to reliably detect defects as it serves as a non-contact transducer with the ability to transmit ultrasonic waves into specimens without couplant. Moreover, an EMAT can easily generate desired waves by altering the design of the coil and magnet. This study proposes an SH-EMAT to evaluate the integrity of the TIG welding part. A stainless steel was welded using the TIG welding method. The welding current was varied to create artificial defects. Both the PA-UT and the RT were applied to verify the defect size. The experimental results generated by using the EMAT were compared with those methods. The amplitude was observed to decrease with an increase in the defect size. These results confirmed that the presence of defects can be reliably detected by attenuation of signal amplitude. The results demonstrated that the proposed method is suitable for evaluating the integrity of TIG welding.