A Novel RF Resonator for Human-body MRI at 3 T

손혁우,조영기,Hyoungsuk Yoo 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.6

A square-slot-loaded (SSL) radio-frequency (RF) resonator using a microstrip transmission line(MTL) is designed for human-body magnetic resonance imaging (MRI) at 3 T MRI. The SSL RFresonator shows improved RF magnetic fields resulting in more homogenous fields near the centerof the phantom than traditional RF resonators using MTL. A multichannel body coil using theSSL RF resonators is also simulated and provides improved parallel excitation performance. Inaddition, RF shimming for homogenization can be effectively controlled by adjusting the inputs tothe eight resonators. Numerical results are obtained by using a spherical phantom and a realistichuman-body model at 3 T to calculate the B+1 fields.

Theoretical and Experimental Investigation on the Probe Design of a Ridge-loaded Slot Type for Near-Field Scanning Microwave Microscope

손혁우,조영기,김병문,홍재표 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.5

In this paper, a rectangular waveguide probe with a ridge-loaded straight slot (RLSS) is presented for a near-field scanning microwave microscope (NSMM). The RLSS is located laterally at the end wall of the cavity and is loaded on double ridges in a narrow straight slot to improve the spatial resolution compared with a straight slot. The probe consists of a rectangular cavity with an RLSS and a feed section of a WR-90 rectangular waveguide. When the proposed NSMM is located at distance of 0.1mm in front of a substrate without patches or strips, the simulated full width at half maximum (FWHM) of the probe improve by approximately 31.5 % compared with that of a straight slot without ridges. One dimensional scanning of the E-plane on a sample under test was conducted, and the reflection coefficient of the near-field scanning probe is presented.

CSLR을 갖는 인셋 급전 패치 안테나 설계 및 제작

손혁우,김병문,박진택,홍재표,Son, Hyeok-Woo,Kim, Byung-Mun,Park, Jin-Taek,Hong, Jae-Pyo 한국전자통신학회 2015 한국전자통신학회 논문지 Vol.10 No.5

본 논문에서는 인셋 급전 구조에서 마이크로스트립 패치 안테나 소형화를 위해 접지면에 CSLR 9개 적용한 안테나('CSLR 09' 안테나)와 8개 적용한 안테나('CSLR 08' 안테나)를 설계한 후, 유전율 2.5, 두께 0.787 mm인 기판으로 안테나를 제작하여 반사손실과 복사패턴에 대한 이론 결과와 실험 결과를 비교하였다. 'CSLR 09'와 'CSLR 08' 안테나의 이론 결과에서는 공진주파수 2.82 GHz에 반사손실이 각각 -25.35 dB와 -16.77 dB를 보였고, 측정결과에서는 공진주파수 2.885 GHz에 반사손실이 각각 -30.72 dB와 -14.90 dB를 나타내어 두 경우 모두에서 거의 일치하는 결과를 얻었다. 또한 E-면과 H-면 복사패턴에 대한 실험 결과에서도 이론 결과와 거의 일치하는 양호한 결과를 얻었다. In this paper, design and fabrication for inset fed microstrip patch antennas applied to the $3{\times}3$ array CSLR and eight CSLR, respectively, to the ground plane are studied. The theoretical results are compared to the experimental results for the return loss and radiation pattern. For 'CSLR 09' antenna, the theoretical result for the resonant frequency and the return loss are 2.82 GHz and - 25.35 dB, respectively. The experimental results are obtained for a 2.885 GHz, -30.72 dB. Theoretical results for the resonant frequency and the return loss of the 'CSLR 08' antenna are 2.82 GHz, -16.77 dB, respectively, and the experimental results are obtained for a 2.885 GHz, -14.90 dB. In addition, E-plane and H-plane radiation patterns in comparison with designed and fabricated antennas are in good agreement.

마이크로스트립을 이용한 인체 머리용 8 채널 RF Coil을 위한 RF 공진기

손혁우(Hyeok-Woo Son),조영기(Young-Ki Cho),유형석(Hyoungsuk Yoo) 대한전기학회 2013 대한전기학회 학술대회 논문집 Vol.2013 No.10

베체트병의 사중치료

손혁우(Hyuck Woo Son),이주화(Ju Hwa Lee),주명진(Myung Jin Joo) 대한안과학회 2000 대한안과학회지 Vol.41 No.10

3 T 자기공명영상시스템에서의 SRR을 이용한 RF 공진기

손혁우(Hyeok-Woo Son),조영기(Young-Ki Cho),유형석(Hyoungsuk Yoo) 대한전기학회 2015 전기학회논문지 Vol.64 No.2

This paper demonstrates a new radio frequency (RF) resonator at 3 T magnetic resonance imaging (MRI) system. An approach based on a split ring resonator (SRR) having effective metamaterial properties is investigated. Electromagnetic simulation results are compared for RF resonators and discussed in detail at 3 T. A new RF resonator has approximately 10% higher magnetic fields at the center of the human phantom than the previous RF resonator.

Transmission-line Analysis of an Epsilon Near Zero Tunneling Circuit Using a Double Ridge Rectangular Waveguide

김병문,손혁우,조영기,홍재표 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.5

We present a simple method for efficient modeling of the tunneling effect in an Epsilon Near Zero(ENZ) channel waveguide based on a transmission-line model. The proposed ENZ channel uses adouble-ridge rectangular waveguide (RWG) and is located in the middle of the input-output standardrectangular waveguides (IORWG). The height of the channel waveguide is much smaller thanthat of the IORWG. The detailed design of the ENZ channel is presented, and the optimum lengthfor tunneling phenomena is calculated. These theoretical studies highlight the substantial differencesbetween this unique tunneling phenomenon and higher-frequency Fabry-Perot resonances. Weperform a simulation for the designed ENZ channel by using a commercial FEM simulator. Thesimulated and the measured results for the fabricated ENZ channel structure are in good agreement.

S-대역용 인셋 급전 구형 마이크로스트립 패치 안테나 연구

홍재표,김병문,손혁우,조영기,Hong, Jae-Pyo,Kim, Byung-Mun,Son, Hyeok-Woo,Cho, Young-Ki 한국정보통신학회 2014 한국정보통신학회논문지 Vol.18 No.10

본 논문에서는 S-대역에서 동작하는 구형 마이크로스트립 패치 안테나의 인셋 급전 구조에 대해 연구하였다. 인셋 급전 구조에서 인셋의 길이와 폭의 변화에 따른 안테나의 반사손실 특성을 조사하였고, 결과로부터 최적 인셋 급전 안테나를 설계하고, 이득 및 복사패턴을 구하였다. 2.3 GHz에서 최적화된 안테나의 패치 크기는 $45.0mm{\times}40.9mm$, 인셋의 길이는 14 mm, 인셋의 폭은 1 mm이다. 그리고 유전율이 2.5, 두께가 0.787 mm인 기판을 사용하였으며, HFSS를 이용하여 시뮬레이션을 하였다. 인셋 급전 안테나를 제작하여 반사손실을 측정한 결과, 2.3025 GHz에서 -21.11 dB로 이론 결과와 일치함을 알 수 있었다. In this paper, the characteristics of a inset fed rectangular microstrip patch antenna for S-band applications is studied. The variations of return loss along inset length and inset width are investigated on the inset fed rectangular microstrip patch antenna. From the investigated results, the optimized inset fed antenna is designed. At the resonant frequency 2.3 GHz, the optimized dimension of the patch is $45.0mm{\times}40.9mm$. The inset length and width are 14 mm and 1 mm, respectively. The designed antenna is fabricated on the substrate which has a dielectric constant and thickness with 2.5 and 0.787 mm. Simulation results are obtained by a 3D EM(Electromagnetic) solver. The resonant frequency and return loss are measured 2.3025 GHz and -21.11 dB, respectively. The measured and simulated results of the fabricated antenna are in good agreement.

Experimental Verification of Two Kinds of Transmission Resonance Phenomena for a Narrow Slot in Thick Conducting Screen

조영기,최진영,손혁우,고지환 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.8

A microwave waveguide setup is used for the experimental verification of the presence of twokinds of transmission resonance phenomena; that are observed to occur in the case of the threedimensionalnarrow rectangular slot problem in an infinite conducting screen of finite thicknessunder an incident electromagnetic plane wave. This presence of two kinds of transmission resonancephenomena is different from the case of the two-dimensional infinitely long slit problem in a thickconducting screen in which only the Fabry-Perot(FP) resonator type occurs. The first type ofresonance phenomenon occurs near (slightly higher than) the cutoff frequency of the lowest TE10mode and mainly depends on the transverse length of the slot region inside the thick conductorirrespective of the longitudinal length of the narrow rectangular waveguide (corresponding to thethickness of the slotted thick conductor). The second is the Fabry-Perot(FP) type, which occurs atparticular longitudinal lengths of the rectangular slot region inside the thick conductor.

고자장 MRI에서의 영상 영역에 대한 B₁⁺ 균질성

김홍준(Hongjoon Kim),손혁우(HyeokWoo Son),조영기(Youngki Cho),유형석(Hyoungsuk Yoo) 한국전자파학회 2012 한국전자파학회논문지 Vol.23 No.1

정 자장(B?)의 세기가 7 T(Tesla) 또는 9.4 T 고자기장 MRI(Magnetic Resonance Imaging) 시스템은 정 자장의 세기가 1.5 T 또는 3 T MRI(Magnetic Resonance Imaging) 시스템에 비하여 인가된 RF(Radio Frequency) 필드의 높은 불균질성을 보여준다. 다채널(multi-channel) RF 코일에서는 인가된 RF 자장(B₁?)의 불균질성을 개선시키기 위해서 각각의 코일 소자(element)에 인가되는 전류의 크기와 위상을 독립적으로 조절할 수 있다. 선택된 관심 영역에서의 RF 자장이 균일하도록 RF 코일의 각 요소로 들어가는 최적화된 전류의 크기와 위상 값을 얻기 위해서 iterative 방법과 함께 convex 최적화 방법이 사용된다. 이러한 방법을 입증하기 위하여 9.4 T MRI 시스템에 RF 코일의 공진 주파수가 400 ㎒을 가지는 다채널 전송 선로 코일이 인체 두상 모형과 함께 모델링되었으며, 이 코일에 의하여 자장이 얻어진다. 9.4 T MRI 시스템을 위한 시뮬레이션 결과가 자세히 논의된다. In high static field magnetic resonance imaging(MRI) systems, B? fields of 7 T and 9.4 T, the impressed RF field shows larger inhomogeneity than in clinical MRI systems with B0 fields of 1.5 T and 3.0 T. In multi-channel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the non-uniformity of the impressed RF B₁? field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected ROI(Region of Interest). To demonstrate the technique, the multichannel transmission line coil was modeled together with a human head phantom at 400 ㎒ for the 9.4 T MRI system and B₁? fields are obtained. In this paper, all the optimized B₁? in each isolated ROIs are combined to achieve significantly improved homogeneity over the entire field of view. The simulation results for 9.4 T MRI systems are discussed in detail.