• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.976-983
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• 2000

In this paper, Bridcage type RF coils used widely as RF coils for MRI and its applicable type, spiral type RF coil are analyzed and designed using FDTD method. In low tesla (IT, 1.5T) MRI system, several tools have been used for the analysis and design of the RF coils for MRI. This includes, so-called, LC equivalent circuit method for predicting the resonance frequency of the coil and the Biot-Savart law to determine the field distribution within the coil. Both of the circuit analysis and Biot-Savart law are low frequency techniques. Therefore, at high frequency applications, the circuit model approximation breaks down because the coil geometry is a significant fraction of the wavelength. In this paper, we analyzed and designed RF coils for 3T MRI using FDTD method. This method is a full wave analysis and very accurate at low and high frequencies. Also, this RF coils are actually fabricated and FDTD models of RF coils for MRI are proven.

• Journal of IKEEE
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• v.23 no.3
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• pp.762-767
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• 2019

The plane-wave shielding effectiveness is typically measured for horizontal and vertical polarizations using a linearly polarized antenna. However, this typical measurement method results in big evaluation fees due to very long measurement time as well as huge idle space for maintenance, these problems is more severe especially in large shielded enclosures such as EMP protection facilities to be built in indoor buildings and underground. This paper describes the design and fabrication process and results of a planar log-spiral antenna applicable to the evaluation of the electromagnetic shielding effectiveness of a large EMP protection facility. Since the proposed antenna has a circular polarization, there is no need to separately measure the horizontal and vertical polarizations. Therefore, the measurement time can be shortened by more than 1/2, and further, its small volume with a planar structure can reduce greatly idle space required for the maintenance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.595-598
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• 2006

In this letter, a compact rectangular spiral antenna is proposed. Instead of a center excitation of conventional spiral antennas, the proposed antenna is adopted a modified feed network, feeding at the end of the spiral. The matching circuit of $'{\sqsupset}'$ shape is added at the feeding point. With this matching circuit, we can easily match the input impedance well, without the limit of the space. The parameter which determines the circular wave characteristic is explained, and the design guideline of the proposed antenna is presented. We design a proposed antenna operating at 9.5 GHz. Its size is only $0.6\lambda_g\times0.6\lambda_g$. The simulated bandwidth of the input impedance $(S11\leq-10)$ is 8.12% and that of $(AR\leq-3)$ is 4.62%, which is excellent characteristics as compared to its simple structure.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.5
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• pp.16-22
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• 2001

A novel microstrip circular slot antenna fed by a spiral line is presented in this paper. This antenna is a planar equivalent structure of an eccentric spiral antenna generates a circularly-polarized wave. We have investigated the input impedance and radiation characteristics of this antenna by using an EM (electromagnetic) simulator, and obtained a design method [or optimum structure. The main characteristic of the antenna is that the main beam direction is off-normal to the antenna plane and moves linearly into ${\theta }$ and ${\phi }$ direction as the frequency increases. This feature allows one to predict the main beam direction easily for a given operating frequency. This antenna has axial ratio lower than 3 dB in the direction of main beam over one octave bandwidth.

• The Journal of Korean Society for Radiation Therapy
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• v.2 no.1
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• pp.23-29
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• 1987

The general features and measured results of the 143cm, variable-energy, three sector-focused MC-50 cyclotron installed at Korea Cancer Center Hospital are described. The MC-50 cyclotron is designed to produce beams of protons, deuterons, He-3 and alpha particles of maximum energies 50MeV, 25MeV, 66MeV and 50MeV respectively to be used for neutron therapy and radioisotope production. The azimuthal field variation is produced by three sets of spiral ridges having a maximum spiral angle of $55^{\circ}$. The RF system, a two-dee quarter-wave system is designed to provide a continuously variable frequency from 15.5 to 26.8 MHz. The first external beam was obtained in January 1986. Subsequent internal ana external beam studies with protons and alphas show a well-behaved beam through the whole beam transport system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.4
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• pp.323-330
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• 2010

An efficient wave energy converter with new overtopping flow device on which spiral reefs are attached is proposed by Maritime and Ocean Engineering Research Institute in Korea and its candidate substructures such as monopile, tripod and jacket are designed. This study investigates modal characteristics of the substructures by analyzing natural frequencies and mode shapes. Based on the modal analysis results, relative strength, governing modes and some complementary design strategies of each candidate substructure are compared and discussed considering water depth conditions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.562-571
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• 2008

In this paper, we propose a novel structure of a spiral antenna with a CP characteristic for RFID reader in UHF band. Since the proposed antenna can be built by printing on a FR-4 substrate, it is appropriate for low-cost mass-production. The antenna is designed to operate in UHF band of $860{\sim}960$ MHz. The CP bandwidth is Increased enough to cover an overall UHF RFID band by using a spiral structure for the antenna arm. The matching bandwidth is broadened by using a quarter-wave transformer between the fred and the antenna body. The proposed antenna has advantages of its easy gain and pattern control with a small antenna size. The measured antenna performance shows the matching bandwidth of 13%, the CP bandwidth of 23%, and the gain of 6.5 dBi. This verifies that the proposed antenna is appropriate for RFID antennas in UHF band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.12
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• pp.1370-1382
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• 2007

In this paper, the spiral planar monopole antenna mounted on a Cellular/WCDMA handset is designed. Frequency characteristics is optimized with various design parameters. The two spiral lines are adopted in order to implement Cellular frequency bandwidth and WCDMA frequency bandwidth. The bandwidth of the realized antenna is $0.805{\sim}0.892$ GHz(10 %) and $1.867{\sim}2.302$ GHz(21 %) for VSWR${\leq}2$ which contain the proposed frequency bandwidth. In human head, the simulated value on 1 g and 10 g averaged SAR caused by electromagnetic wave radiated in the designed antenna is compared with the measured value. As a result, the measured values of 1 g and 10 g averaged SAR were similar to the simulated values, which were lower than the SAR guidelines.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.1
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• pp.42-46
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• 2003

In this paper, an MMIC broadband amplifier for wireless communication systems has been developed by using an active feedback method. This active feedback operates at much higher frequencies than a method by a spiral inductor feedback and its size is independent of the inductance value. The MMIC broadband amplifier was designed using a $0.5{\;}{\mutextrm{m}}$ MESFET library. The fabricated chip area was $1.4{\;}mm{\;}{\times}{\;}1.4{\;}mm. Measurement showed a gain of 18 dB with a gain flatness of ${\pm}3$ dB in a 1.5 GHz~3.5 GHz band. The maximum output power and the minimum noise figure were 14 dBm and 2.5 dB in the same band, respectively.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.895-900
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• 2001

It is very important for impact analysis to reflect the dynamic characteristics of materials as well as the static characteristics. As the dynamic behavior of a material is different from the static(or quasi-static) one due to the inertia effect and the stress wave propagation, an adequate experimental technique has to be developed to obtain the dynamic responses for the corresponding level of the strain rate. To determine the dynamic characteristics of materials, the Hopkinson bar (compression type) experiment is carried out. For using dynamic material properties, Johnson-Cook model is applied in impact analysis with explicit finite element method