• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.2
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• pp.280-283
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• 2015

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.

• Journal of electromagnetic engineering and science
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• v.9 no.3
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• pp.164-173
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• 2009

In this paper, two new circuit structures for European and U.S. ultra-wide band(UWB) bandpass filters(BPFs) with sharp roll-off characteristics are introduced. We show first that the ultra-wide bandpass property is obtained from a $\lambda$/4 open T resonator with a capacitively coupled $\lambda$/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Then, two identical capacitively coupled input/output lines, which can be $\lambda$/4-length open ends or $\lambda$/2-length short ends, with the T-resonator, are adopted to suppress lower and higher frequency components outside of the pass band. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T-resonator with the $\lambda$/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the $\lambda$/4 short-circuited line and the input/output lines are inserted between the two stacked T-resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic(LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.431-434
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• 2002

In this paper, The resonant frequencies of any modes in the dielectric resonator filter is determined by numberical analysis. The theoretical analysis for the dielectric resonator filter used Ansoft HFSS. We designed the dielectric resonator filter with resonant frequency 4.5 GHz. We describe the characteristics of delivering Power to resonator in different shaped coupling loops. Tile resonant mode of T $E_{01{\delta}}$ and T $E_{01{\delta}}$ could be selected by the horizontal and the vertical coupling loop.p.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.222-222
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• 2007

RF circuit을 구현하는데 있어서 기판의 전기적 특성을 정확하게 아는 것은 원하는 결과를 추출하기 위해 매우 중요하다. 본 연구에서는 현재 사용되고 있는 PI 기판의 전기적인 특성인 유효 유전율과 loss tangent 값을 T-resonator률 이용해 정확하게 측정하고자 했다. T-resonator는 microstrip 구조로 구현 되었으며 conductor material은 Cu를 사용하였다. PI 기판의 두께는 25um, Cu의 두께는 PI 기판의 종류에 따라 12um 와 18um, T-resonator line width는 50um로 구현하였다. 또한 공진 주파수에 따라 stub 길이가 다른 10개의 T-resonator를 제작하였다. PI 기판의 유효 유전율을 구하기 위해 stub 길이의 open-end effect와 T-junction effect를 고려하였으며 수식을 통해 정확한 유효 유전률을 추출하였다. 또한 PI 기판의 loss tangent 추출에 필요한 dielectric loss를 추출하기 위해 unload quality factor를 분석하였다. Unload quality factor는 dielectric loss, conductor loss, radiation loss를 구성되며 conductor loss와 radiation loss를 수식에 의해 구하고 dielectric loss를 추출 하였다. 추출 된 dielectric loss를 통해 각각의 T-resonator의 loss tangent 값을 구하였다. T-resonator를 이용한 PI 기판의 측정은 비교적 복잡한 수식에 의해 이루어지지만 정확한 data를 얻을 수 있고 다른 재료의 전기적 특성을 추출하는데 응용이 가능하다.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.157-160
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• 2001

본 논문에서 5.8GHz의 주파수 대역에서 사용할 수 있는 향상된 커플링 구조와 크기를 줄인 dual-mode microstrip bandpass filter를 설계하였다. 여기서 meander loop resonator를 쓰는 이유는 크기가 작고 방사 손실이 적으며 패턴이 간단하기 때문이다. 또한 이와 비슷한 특성을 갖는 ring, square patch, disk등은 불연속 성분을 가짐으로써 이중모드의 구현이 가능하다. 향상된 형태의 dual-mode microstrip bandpass filter의 변형된 T-shaped meander loop resonator를 소형으로 발전되고. 높은 선택도를 가지는 구조이다. 이 형태의 filter에서 150MHz의 bandwidth을 가지고 5.8GHz주파수를 가지는 구조로 설계하였다.

• Progress in Medical Physics
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• v.15 no.1
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• pp.54-58
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• 2004

The aim of this study was to develop special birdcage resonators for small objects including the human wrist, hand and small animals, using 3T MRI/MRS. Before substantial development, different types of parameters were arranged, based on theoretical analysis, through lumped element transmission line theory. The primary analysis was peformed with a network analyzer (HP 4195A) and the final experimental analysis was carried out with 3T MRI (Medinus, Korea). The manufactured birdcage resonator is typically composed of 12-element structures to which a low-pass filter is fundamentally applied. The diameter and length of each element of the birdcage resonator were as follows: (1) diameter 12 cm, length of element 22 cm, (2) diameter 15 cm, length of element 22 cm, and (2) diameter 17 cm, length of element 25 cm. Copper tape with a width of 1 cm was used for the coils. MRI acquisition parameters were TR=500 ms, TE=17 ms, and Ave=2 for T1-WT images, and TR=4,000 ms, TE=96 ms, and Ave=2 for T2-WT images. The ratio of the samples diameter to the birdcage resonators diameter was approximately 55%, 63% and 70%, respectively, for the three elements. This study determined that the best image quality and S/N ratio were obtained when the ratio of the object's diameter was approximately 50∼80%. A general theoretical analysis of the birdcage coil differs in many respects from the experimental results which were influenced by many factors that were not considering when the general theoretical analysis of the birdcage coil was peformed. The induced resistance may be considered as part of the resistive loss if the quantitative value can be determined using a radiation resistance approach.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.365-366
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• 2002

A novel TEM resonator coil was developed for the imaging of small animals. The functional elements of the TEM resonator were 8 inner conductors, distributed in a cylindrical pattern and connected at the ends with capacitors to the cylindrical outer shield. The TEM resonator coil with cavity elements was robust to the surrounding influences due to the self-shielding structure. The TEM resonator coil with high Q factor could provide high quality MR images at 3.0T MRI system. Also, the TEM resonator coil has an advantage for a fine tune with length adjustment of each cavity elements. Thus, The TEM resonator coil at 3.0T, even higher field could be used in the research studies.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.136-140
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• 2002

In this paper, newly constructed 5.6 ㎓ ring resonator by using a T-Junction and a parallel transmission line. The resonator's size reduced twice more than a current ring and a hair-pin resonator at this paper's center frequency The loaded Q value is 240∼250 at center frequency. also, It was explained by RLC equivalent equation for the resonator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.720-725
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• 2001

In this study, Pb(La,Ce)Ti $O_3$ ceramics were manufactured for 20 MHz resonator application. Electromechanical coupling factor( $k_{t}$, $k_{t3}$, mechanical quality factor( $Q_{mt}$ , $Q_{mt3}$ and dydnamic range (D.R) of thickness vibration mode were measured as the variations of $\ell$/t(length/thickness) ratio of ceramic substrates. Mechanical quality factor( $Q_{mt3}$) and dynamic range of third overtone thickness vibration mode showed the highest value of 2,773 and 52.22dB at specimen S4($\ell$/t=12), respectively. The excellent temperature stability of resonant frequency suitable for resonator application was shown, regardless of thermal shock.k.ock.k.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.151-151
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• 2001

Purpose： 3.0 Tesla whole-body resonator provides a potential to have significant increase in imag quality and resolution in high resolution application such as cardiac, spine and extremit imaging. The aim of this study is to design an optimized 3.0T whole-body coil to produce high sensitivity and quality using slotted tube resonator.