• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.99-103
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• 2000

본 논문에서는 FM Reflectometry를 이용하여 마이크로파 대역에서 다양한 전송선로의 분산특성을 측정하였다. 실험에 사용된 전송선로는 도파관에 금속봉이 주기적으로 위치한 구조로서 Gyro-TWT의 iinteractio circuit으로 사용되기 위해서 설계되었다. 도파관에 금속봉이 주기적으로 위치한 구조의 group velocity를 측정하기 위해서 FM Reflectometry와 기존의 Network Analyzer Time Domain 기능이 사용되어졌으며, phase velocity를 측정하기위해 서 short metal plate를 이용한 방법과 High Frequency Structure Simulator (HFSS)가 이용되었다 측정된 결과는 이론치, 시뮬레이션과 비교했으며 각각의 비교는 잘 일치함을 보여 FM Reflectometry기법이 분산특성 측정에 사용되어질 수 있음을 보였다.

• Geophysics and Geophysical Exploration
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• v.22 no.1
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• pp.21-28
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• 2019

We perform a 3D tomographic inversion using surface wave dispersion curves to obtain S-velocity model and radial anisotropy beneath Saudi Arabia. The Arabian Peninsula is geologically and topographically divided into a shield and a platform. We used event data with magnitudes larger than 5.5 and epicentral distances shorter than $40^{\circ}$ during 2008 ~ 2014 from the Saudi Geological Survey. We obtained dispersion curves by using the multiple filtering technique after preprocessing the event data. We constructed SH- and SV-velocity models and consequently radial anisotropy model at 10 ~ 60 km depths by inverting Love and Rayleigh group velocity dispersion curves with period ranges of 5 ~ 140 s, respectively. We observe high-velocity anomalies beneath the Arabian shield at 10 ~ 30 km depths and low-velocity anomalies beneath the Arabian platform at 10 km depth in the SV-velocity model. This discrepancy may be caused by the difference between the Arabian shield and the Arabian platform, that is, the Arabian shield was formed in Proterozoic thereby old and cold, while the Arabian platform is covered by predominant Paleozoic, Mesozoic, and Cenozoic sedimentary layers. Also we obtained radial anisotropy by estimating the differences between SH- and SV-velocity models. Positive anisotropy is observed, which may be generated by lateral tension due to the slab pull of subducting slabs along the Zagros belt.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.324-329
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• 2001

The destructive method is reliable and widely used for the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials by nondestructive evaluation is strongly desired. In this paper, the use of guided wave was suggested for the evaluation of thermally damaged 2.25 Cr-lMo steel as an alternative way to compensate for limitations of fracture tests. The observation of microstructure variations of the material including carbide precipitation increase and spheroidization near grain boundary was conducted and the correlation with the guided wave features such as energy loss ratio and group velocity changes was investigated. Through this study, the feasibility of ultrasonic guided wave evaluation for thermally damaged materials was explored.

• Structural Engineering and Mechanics
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• v.85 no.4
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• pp.501-510
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• 2023

Horizontally polarized shear waves (SH) have numerous applications in various scientific, engineering, and medical fields. The study deals with an investigation of SH-waves in a thin microstructural plate. The plate has been mathematically modelled by employing size dependent consistent couple stress theory, which involves a length parameter, known as characteristic length. Characteristic length is assumed to be of the order of internal microstructures of the material. Dispersion relations have been calculated for the propagation of SH-waves using different set of boundary conditions. Group velocity of the SH-waves has been calculated by using an analytical approach. The mathematical results obtained in the problem are discussed in detail and the impacts of characteristic length parameter and thickness of plate are presented on phase velocity of SH-waves through graphical illustrations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.749-751
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• 2009

Optical link design technique for compensating of distorted 40 Gbps ${\times}$ 24 channels WDM signals is researched. The considered optical link consists of optical phase conjugator (OPC) placed at 100 km and 900 km, which are non-midway of total transmission distance, and dispersion management (DM). It is confirmed that optimal net residual dispersions (NRD) are 800 ps/nm and 900 ps/nm when OPC placed at 100 km and 900 km, respectively.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.353-359
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• 2000

A harmonically mode-locked fiber ring laser cavlty was theoretically analyzed. The measured charactenstlcs of a 10 GHz erbium-doped fiber ring laser were used as a basis of the theoretical analysis. From the nonlinear Schroedinger equation of an actively mode-locked erblUm-doped fiber laser. the effects of the components inside the laser cavity have been analyzed includmg nonlinear effects from group-velocity dispersion (GVD) and self-phase modulation (SPM). Usmg the analysls. we have designed a laser cavity with minimum pulsewidth and chirp by changing the intracavity optical intensity and the bandwidth of the filter. In the new design, the chirp i, reduced by 2 times and the pulsewidth by 2A times. compared to the laser used in the experiment. iment.

• Journal of Advanced Navigation Technology
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• v.22 no.3
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• pp.240-245
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• 2018

A flexible dispersion-managed link configuration is proposed by using single-mode fibers (SMFs) and dispersion-compensating fibers (DCFs) with irregular dispersion coefficients and lengths over all fiber spans for compensating of WDM channels distortion due to the group velocity dispersion and nonlinear effects of optical fibers. The flexibility of link is enabled by artificially distributing of these fibers based on the dispersion coefficients of DCFs in each half transmission section. The simultaneous ascending and descending (AD) distribution of the DCF's coefficients before and after the optical phase conjugator, respectively, best compensates the distorted wavelength division multiplexed signals in the optical link. Therefore, to improve the compensation effect of the distorted WDM channels, AD distribution is needed to choice regardless of fiber lengths and the residual dispersion per span and fiber's dispersion coefficients.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.61-70
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• 2006

3-D S-wave velocity model in the southern Korean Peninsula is investigated by using the joint inversion of receiver functions and surface-wave dispersion. A peninsula average Rayleigh-wave phase velocity in the 10-150 seconds range and tomographic estimates of the Rayleigh and Love wave group velocities in the 0.5-20 seconds period range determined using a $12.5{\times}12.5\;km$ grid for the southern part of the peninsula are used for the inversion. Receiver functions were determined from broadband (STS-2), short-period (SS-1) and acceleration (Episensor) channels of 95 stations. The dense distribution of the stations in the Peninsula permits us to examine the 3-D crustal structure in detail. The inversion result shows the variation and characteristics of S-wave velocity in the crust and upper mantle of the southern Korean Peninsula very well.

• Korean Journal of Radiology
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• v.23 no.2
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• pp.237-245
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• 2022

Objective: Viscoelasticity is an essential feature of nerves, although little is known about their viscous properties. The discovery of shear wave dispersion (SWD) imaging has presented a new approach for the non-invasive evaluation of tissue viscosity. The present study investigated the feasibility of using SWD imaging to evaluate diabetic neuropathy using the sciatic nerve in a diabetic rat model. Materials and Methods: This study included 11 diabetic rats in the diabetic group and 12 healthy rats in the control group. Bilateral sciatic nerves were evaluated 3 months after treatment with streptozotocin. We measured the nerve cross-sectional area (CSA), nerve stiffness using shear wave elastography (SWE), and nerve viscosity using SWD imaging. The motor nerve conduction velocity (MNCV) was also measured. These four indicators and the histology of the sciatic nerves were then compared between the two groups. The performance of CSA, SWE, and SWD imaging in distinguishing the two groups was assessed using receiver operating characteristic (ROC) analysis. Results: Nerve CSA, stiffness, and viscosity in the diabetic group was significantly higher than those in the control group (all p < 0.05). The results also revealed a significantly lower MNCV in the diabetic group (p = 0.005). Additionally, the density of myelinated fibers was significantly lower in the diabetic group (p = 0.004). The average thickness of the myelin sheath was also lower in the diabetic group (p = 0.012). The area under the ROC curve for distinguishing the diabetic neuropathy group from the control group was 0.876 for SWD imaging, which was significantly greater than 0.677 for CSA (p = 0.030) and 0.705 for SWE (p = 0.035). Conclusion: Sciatic nerve viscosity measured using SWD imaging was significantly higher in diabetic rats. The viscosity measured using SWD imaging performed well in distinguishing the diabetic neuropathy group from the control group. Therefore, SWD imaging may be a promising method for the evaluation of diabetic neuropathy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.7-15
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• 2008

In this paper, it is investigated that the limitation due to the asymmetry of optical power with respect to optical phase conjugator(OPC) in mid-span spectral inversion(MSSI) for compensating optical signal distortion due to group velocity dispersion(GVD) and nonlinearities generated in fiber by combining with lumped dispersion management(DM) technique into MSSI. Two kinds of lumped DM configuration(configuration A and configuration B) are considered and compared each other in this research. Configuration A consists of two dispersion compensating fiber(DCF) span positioned after transmitter and before receiver, respectively. Configuration B consists of two dispersion compensating fiber(DCF) span positioned before and after OPC placed at middle of total transmission link, respectively. It is confirmed that the transmission performances are more improved by the configuration A combined with MSSI than configuration B. Also, it is confirmed that the best performance of overall channels are obtained by making net residual dispersion(NRD) to have positive value in self phase modulation(SPM)-limited WDM transmission systems, irrelevant to the configuration of DM.