• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.4
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• pp.328-336
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• 2020

This paper presents an asymptotic analysis method using the PO(physical optics) approximation technique to analyze the scattering contribution of an electrically large object partially coated with a radar absorbing material(RAM). By using the feature of the PO technique that can calculate the equivalent current value for each mesh independently, instead of analyzing the entire structure, scattering analysis was performed only by calculating the current on the area where the RAM coating is applied. By the numerical examples, the accuracy and the computation time of the proposed method were verified, and the computational efficiency of inverse synthetic aperture radar(ISAR) of the electrically large objects that require enormous resources is improved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.473-476
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• 1997

Focused Ar ion laser beam can be utilized to fabricate microstructures on silicon substrate as well as other materials(e.g. such as ceramic). The laser using in this study is an argon ion laser with maximum power of 6 W, wavelength of 514 nm. This laser beam is focused by objectives with a high numerical aperture, a long working distance. We have achieved line width about 1 ${\mu}{\textrm}{m}$ with high scan speed. The resolution for Si machining is determined by the selectivity of the chemical reaction rather than the laser spot size. In this study, we have obtained the maximum etch rate of 434.7 ${\mu}{\textrm}{m}$/sec with high aspect ratio. The characteristics of etched groove was investigated by scanning electron microscope(SEM) and auger electron spectroscopy(AES). It is assumed that the technique using arson ion laser is applicab1e to fabricate microstructures.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.388-390
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• 1994

We are familiar with the holography in these days. For making holography the coherent sources like LASER are used in many fields. But coherent holography has many problems. Coherent holography needs many instrument for practical use like 3-D TV case. In solving the problem we use the non-coherent source. Nowadays many methods like conoscopic holo graphy using anisotropic crystal, shadow casting and interferometric systems are suggested. In this paper we make the hologram using the triangular interferometric systems. [1],[2],[3],[4]. We explain the afocal and double-afocal system which consists of the triangular interferometric system. The holography made in one point and two point cases is imaged on CCD camera and we handle the image data digitally for the reconstruction efficiently. In reconstructing the hologram the Fraunhofer diffraction theory is used. We adopt the rectangular aperture for the convenience of calculation. In the future we must reconstruct the perfect 3-Dimensional object by optical method. For this, we have many problems like resolution problem. We must solve these problem for perfect reconstruction.

• Transactions of the Society of Information Storage Systems
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• v.2 no.1
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• pp.13-20
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• 2006

In this paper, we propose novel optics design for media inside near-field recording(NFR) using hemispherical solid immersion lens(HMS). To obtain strong advantage of data protection and high data capacity simultaneously, HMS based near field optics using aplanatic position of super hemisphere is designed. In this design, to improve small optical tolerance of this aplanatic position, additional aspheric lens surface is added on top of the HMS and it is combined with zoom optics which composed of two single lenses having low numerical aperture(NA). Also, to compensate chromatic aberration which happens seriously in optics using blue laser diode, diffractive optical element is used. Using zoom optics, additional aspheric lens surface, and diffractive optical element together, wavefront aberration and chromatic aberration are effectively reduced in broad range of cover layer thickness and wavelength variation. In addition, in this paper, effect of gap induced aberration is investigated by analyzing different behavior of each TM and TE wave for designed media inside dual-layer NFR optics.

• Transactions of the Society of Information Storage Systems
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• v.2 no.1
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• pp.79-84
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• 2006

The next generation of optical storage systems requires higher numerical aperture(NA) objective lenses and shorter wavelength laser in order to improve the unit areal density. A blu-ray technology satisfies a miniaturization and a high capacity which are the requirements of the portable device. In this paper, we analyze the optical performance of hybrid micro lens and do active alignment. The hybrid micro lens is manufactured by using a wafer based fabrication technology. Optical components of hybrid micro lens are evaluated. The measurement of the optical power, the spot size and the wavefront error are performed to evaluate the hybrid micro lens with NA 0.85. Using the measured data, we estimate if the performance of hybrid micro lens corresponds to the designed performance. After the performance of hybrid micro lens is evaluated. the integrated optical pickup and the hybrid micro lens are assembled by active alignment using UV curing and the optical performance of SFFOP is satisfied with BD specifications.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.152-152
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• 2018

Soil moisture is a important factor in hydrologic analysis. So, if we have spatially distributed soil moisture data, it can help to study much research in a various field. Recently, there are a lot of satellite derived soil moisture data, and it can be served through web freely. Especially, NASA (National Aeronautics and Space Administration) launched the Soil Moisture Aperture Passive (SMAP) satellite for mapping global soil moisture on 31 January 2015. SMAP data have many advantages for study, for example, SMAP data has higher spatial resolution than other satellited derived data. However, becuase many satellited derived soil moisture data have a limitation to data accuracy, if we have ancillary materials for improving data accuracy, it can be used. So, in this study, after applying the alogorithm, which is data assimilation methods, applicability of satellite derived soil moisture data was analyzed. Among the various data assimilation methods, in this study, Model Output Statistics (MOS) technique was used for improving satellite derived soil moisture data. Model Output Statistics (MOS) is a type of statistical post-processing, a class of techniques used to improve numerical weather models' ability to forecast by relating model outputs to observational or additional model data.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.3
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• pp.208-218
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• 2012

Numerical simulation technique has been developed to calculate microwave backscattering from water surface. The simulation plays a role of a substitute for experiments. Validation of the simulation was shown by comparing with experimental results. Water area observations by microwave radar have been simulated to evaluate algorithms and systems. Furthermore, the simulation can be used to understand microwave scattering mechanism on the water surface. The simulation has applied to the various methods for water area observations, and the utilizations of the simulation are introduced in this paper. In the case of fixed radar, we show following examples, 1. Radar image with a pulse Doppler radar, 2. Effect of microwave irradiation width and 3. River observation (Water level observation). In addition, another application (4.Synthetic aperture radar image) is also described. The details of the applications are as follows. 1. Radar image with a pulse Doppler radar: A new system for the sea surface observation is suggested by the simulation. A pulse Doppler radar is assumed to obtain radar images that display amplitude and frequency modulation of backscattered microwaves. The simulation results show that the radar images of the frequency modulation is useful to measure sea surface waves. 2. Effect of microwave irradiation width: It is reported (Rheem[2008]) that microwave irradiation width on the sea surface affects Doppler spectra measured by a CW (Continuous wave) Doppler radar. Therefore the relation between the microwave irradiation width and the Doppler spectra is evaluated numerically. We have shown the suitable condition for wave height estimation by a Doppler radar. 3. River observation (Water level observation): We have also evaluated algorithms to estimate water current and water level of river. The same algorithms to estimate sea surface current and sea surface level are applied to the river observation. The simulation is conducted to confirm the accuracy of the river observation by using a pulse Doppler radar. 4. Synthetic aperture radar (SAR) image: SAR images are helpful to observe the global sea surface. However, imaging mechanisms are complicated and validation of analytical algorithms by SAR images is quite difficult. In order to deal with the problems, SAR images in oceanic scenes are simulated.

• Transactions of the Society of Information Storage Systems
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• v.4 no.1
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• pp.1-5
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• 2008

Super-resolution near-field structure (super-RENS) technology and solid immersion lens (SIL) based near-field (NF) technology have been expected as promising approaches to increase data capacity or areal density of optical disc. Super-RENS technology has been studied until now using mainly numerical aperture (NA) of 0.85 far-field optical system and possibility of tangential data density increment have been presented. NF technology has been studied with NA over 1 and presented demonstration of removable performance. To achieve much higher density, approach to increase NA of super-RENS by NF technology (Near-Field Super-Resolution, NFSR) can be a candidate and we think this technology would be advantageous compared to wavelength reduction or much higher NA increment of NF technology or much smaller effective optical spot size reduction of far-field super-resolution technology. In this paper we present readout result of ROM media having monotone pits using NF optical system with wavelength of 405nm and NA of 1.84 surface type SIL. GeSbTe material was used for super resolution active layer and pit length is 37.5nm which is shorter than resolution limit 55nm. We present the feasibility of NFSR technology by confirming the CNR threshold according to readout power (Pr) and CNR 33dB over threshold Pr.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.4
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• pp.297-304
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• 1996

The purpose of this study is to observe the applicability of parabolic mild-slope equations allowing relatively large angles of wave propagation based on the use of a Pade approximant or minimax approximation and also the applicability of the models with nonlinearity of diffracted waves in the shadow zone behind coastal structures. To accomplish these objectives, numerical solutions are obtained from the above parabolic models and are compared with the results from Watanabe and Maruyama's(1984) hydraulic model test on the wave field with an impermeable detached breakwater. From this study, it is found that computed wave heights increase for the nonlinear results in comparison to the linear results due to the increased diffraction effect across the geometric shadow boundary. The model with a larger aperture with respect to the principal direction was found to spread laterally to a much greater degree where spreading angle (diffraction effect) is relatively large. which causes a distortion in the overall results due to the error accumulated by the approximation of wave length.

• The Journal of the Acoustical Society of Korea
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• v.33 no.4
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• pp.232-237
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• 2014

A passive sonar of warship is composed of several directional or omni-directional sensors. In order to model the acoustic signal received into a warship sonar, the wave propagation modeling is usually required from arbitrary noise source to all sensors equipped to the sonar. However, the full calculation for all sensors is time-consuming and the performance of sonar simulator deteriorates. In this study, we suggest an asymptotic method to estimate the sonar signal arrived to sensors adjacent to the reference sensor, where it is assumed that all information of eigenrays is known. This method is developed using Taylor series for the time delay of eigenray and similar to Fraunhofer and Fresnel approximation for sonar aperture. To validate the proposed method, some numerical experiments are performed for the passive sonar. The approximation when the second-order term is kept is vastly superior. In addition, the error criterion for each approximation is provided with a practical example.