• Journal of the Korean Magnetics Society
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• v.27 no.2
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• pp.49-53
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• 2017

Metamaterials composed of split cut wire (SCW) on grounded polyimide film substrate have been investigated for the aim of electromagnetic wave absorbers operated in THz frequency band. Reflection loss and current density distributions are numerically simulated with variations of the SCW geometries using the commercial software. The minimum reflection loss lower than -20 dB has been identified at 5.5~6.5 THz. The simulated resonance frequency and reflection loss can be explained on the basis of the circuit theory of an inductance-capacitance (L-C) resonator. Dual-band absorption can be obtained by arrangement of two SCWs of different length on the top layer of the grounded substrate, which is due to multiple magnetic resonances by scaling of SCWs. With increasing the side spacing between SCWs, a more enhanced absorption peak is observed at the first resonance frequency that is shifted to a lower frequency.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.5
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• pp.1035-1041
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• 2017

In magnetic resonance-based wireless power transfer (WPT) systems, frequency splitting phenomenon, in which power transfer efficiency (PTE) decreases seriously as resonators are close to each other, is the problem that we should address for reliable power transfer in short distance. In this paper, we present WPT systems using an equivalent circuit model and analyze PTE and marginal coupling coefficient ($k_{split}$) where the frequency splitting occurs. In addition, we perform circuit-level simulations using Advanced Design System, and show that the achievable PTE is different for the structures of resonators when k>$k_{split}$. We confirm that higher PTE can be ensured as k increases in the case of identical resonators, while PTE is degraded as k increases in the case of non-identical resonators. Therefore, in short distance, in which k>$k_{split}$, it is more efficient for achieving reliable PTE to use identical resonators rather than non-identical resonators.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.249-252
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• 2003

Acoustic behavior in combustion chamber with acoustic cavity is numerically investigated by adopting linear acoustic analysis. Helmholtz-type resonator is employed as a cavity model to suppress acoustic instability. The tuning frequency of acoustic cavity is adjusted by varying the sound speed in acoustic cavity. Acoustic pressure responses of chamber to acoustic oscillating excitation are shown md acoustic damping effect of acoustic cavity is quantified by damping factor. As the tuning frequency approaches the target frequency of the resonant mode, mode split from the original resonant mode to lower and upper modes appears and thereby damping effect is degraded. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic cavity tuned to maximum frequency of those of the possible splitted upper modes.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.352-358
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• 2018

A split-capacitor (SC) dual-active-bridge (DAB) converter is proposed in this study. The DC-link capacitors of input and output are split in the proposed converter. The primary and secondary windings of transformer are connected to the midpoints of the DC-links. Hence, the SC DAB converter can inherently prevent transformer from saturation. Although the switch current stress of the proposed converter is twice that of the conventional DAB converter, the switch voltage stress is reduced by half. Therefore, the proposed converter can reduce switching loss and achieve high efficiency in a high switching frequency. Given the SC structure, the proposed converter can readily be connected to neutral-point-clamped- or half-bridge-type converters. The topology of the proposed converter is presented and the operating principle is analyzed in detail. A 3-kW hardware prototype was built and tested to verify the performance of the proposed converter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.918-923
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• 2009

In this paper, a design method of the compact narrow band filter on the microstrip board is proposed using complementary split-ring resonators(CSRRs). The design technique of this filter is based on cascading filter stages consisting of the combination of circular CSRRs, capacitive gaps between patches, and inductive grounded stubs with the meander configuration. By these means, it was possible to get the nearly symmetric frequency responses, adjustable bandwidths, compact sizes. And also excellent characteristic of the out-of-band rejection is achieved in contrast to the conventional filter design technique. The measured insertion shows good results about -4.0dB at the center frequency($f_0=1GHz$) and passband return loss is less than -9.4dB. The 3dB fractional bandwidth(FBW) is approximately 4%. The results of the frequency response measured on the fabricated band pass filter substrate show satisfactory agreement with the simulated frequency responses by the HFSS in the region of interest.

• The Journal of Korean Institute of Information Technology
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• v.17 no.3
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• pp.43-50
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• 2019

In this paper, we propose a S-band oscillator with a reduced electrical size by applying a vertical split ring resonator(VSRR). The VSRR is a type of split ring resonator that operates as a resonator by the capacitance and inductance generated between the microstrip lines arranged on the top and bottom of the dielectric substrate and it has an advantage that the electrical size of the resonance circuit can be reduced as compared with the conventional ring resonator. In this paper, we design a VSRR operating over S-band and an oscillator using the VSRR as the resonant circuit. The proposed oscillator showed the output of 5.9dBm at 2.4HGz and showed the phase noise characteristics of -112.58dBc at 100KHz offset frequency and -117.85dBc at 1MHz offset.

• Journal of The Korean Society of Grassland and Forage Science
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• v.25 no.2
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• pp.119-124
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• 2005

This study was conducted from March 21 to July 8 in 2004 at JeJu Island to investigate the influences of split nitrogen application times on creeping bentgrass vegetation. Nitrogen rate was 20 kg/10a and it was applied from once to 5 times. The result obtained were summarized as follows; plant height was getting longer as nitrogen was split applied from once to 5 times. So it was longest at 5 times split nitrogen application, but it was no significance from 4 to 5 times. Root length, Minolta SPAD-502 chlorophyll meter reading value, leave and root weight n[e directly proportional plant height response. Degree of land cover Iud density of creeping bentgrass increased as nitrogen was split applied from once to 5 times. But degree of land cover md density of reed decreased. The number of reed species on decreased as nitrogen was split applied from once to 5 times. Then ranking of the dominant weeds were Portulaca oleracea Polygonum hydropiper and Stellaria media (at once split time nitrogen application), Portulaca oleracea, Polygonum hydropiper and Digitaria adscendens (at 2 split times nitrogen application), Digitaria adscendens and Portulaca oleracea Polygonum hydropiper, (at 3 split times nitrogen application), Portulaca oleracea, Poa annua and Polygonum hydropiper (at 4 md 5 split times nitrogen application). These results indicate that the optimum frequency of split N applications is four times for growth of creeping bentgrass in volcanic ash soils of Jeju island.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.546-555
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• 2013

In this paper, we propose a novel method to enhance the harmonic components from the frequency lines of the passive sonar signals. For this, we first separate the stable frequency lines from unstable ones using mean and difference of spectral bins in the vernier analysis. Then we emphasize the harmonic components using autocorrelation-based postprocessing, and enhance them by reducing the background noise with the split-window two pass mean algorithm. Experimental results for real underwater acoustic data are presented with our discussions.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.4
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• pp.176-184
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• 2007

The missile for this study has shown different natural frequency characteristics depending on the test conditions; natural frequencies obtained from its flight test are higher than those in its ground test. It was found that the hinged joints connecting front airframe to rear one had the nonlinear stiffness and caused the missile to show very complex dynamic characteristics. The angular stiffness at hinged joints was calculated using 3D finite element analysis, and it was verified that there was a highly nonlinear relationship between angular stiffness and external load. Natural frequencies calculated considering the nonlinearity of angular stiffness were nearly the same as test results. Through this study, the dynamic characteristics of a missile having split airframes with hinged joints could be clearly identified and a way of maintaining its natural frequencies consistent was generated.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.120-127
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• 2000

This study is concerned with evaluating the effects of acoustic excitation on the development of two stream mixing layer generated by split plate. The ratios of two velocities U1 and U2 either side of the splitter plate were such that $U_1/U_2$=1.0 (uniform flow) or $U_1/U_2$<1.0(shear flow). The mixing layers were disturbed acoustically through the edge of split plate. Quantitative data were obtained with hot-wire anemometry. Flow visualization with smoke-wire was also employed for qualitative study. the results show that the large scale structures of mixing layers are strongly affected by excitation frequency and amplitude in both uniform and shear flows. The maximum streamwise and vertical turbulent intensities of the excited flow fields are apt to be decreased as compared with those of without excitation. The flow characteristics of uniform flow are more influenced by acoustic excitation than those of shear flow.