• The Journal of the Acoustical Society of Korea
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• v.22 no.6
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• pp.482-488
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• 2003

Line may receiver contains an ambiguity on conjugate bearings, because of lacking aperture in transverse direction. To solve the left/right bearing ambiguity of line-array receiver we used line-array with cardioid beam. In addition, the synthetic aperture method adopts coherent processing of sub-aperture signals at successive time intervals in the beam domain. We presented performances about division of left/right bearing ambiguity according to array synthetic number of times in this paper.

• Journal of the Korea Society of Computer and Information
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• v.8 no.1
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• pp.90-96
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• 2003

In this paper, arranged the isotropic point source of N number with the structure which is identical with the receive area. And against the array structure which has the radiation pattern which is identical with the receive area it researched. The arranged the element space flees grating lobe and in order to set the characteristic of optimum with half-wave equally space it selects. After inducing the array factor of each array structure, it calculated a radiation pattern. As a result of, the radiation pattern of the each Planar array antenna with structure of the receive area was similar and the possibility of getting an beam characteristic it was.

• Current Optics and Photonics
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• v.3 no.4
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• pp.285-291
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• 2019

We have studied the behavior of light in the intermediate regime between a single nanoslit and an infinite nanoslit array. We first calculated the optical characteristics of a small number of nanoslits using finite element numerical analysis. The phase variance of the proposed nanoslit model shows a gradual phase shift between a single nanoslit and ideal nanoslit array, which stabilizes before the total array length becomes ${\sim}0.5{\lambda}$. Next, we designed a transmission-enhanced Fresnel zone plate by applying the phase characteristics from the small-number nanoslit model. The virtual-point-source method suggests that the proposed Fresnel zone plate with phase-invariant nanoslits achieves 2.34x higher transmission efficiency than a conventional Fresnel zone plate. Our report describes the intermediate behaviors of a nanoslit array, which could also benefit subwavelength metallic structure research of metasurfaces.

• Korean Journal of Optics and Photonics
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• v.26 no.4
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• pp.226-232
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• 2015

A double-layer LED array together with an illumination optical system is proposed as a possible light source for LC projection display systems for large screens, up to $8m{\times}6m$ (400 inches diagonal). The heat dissipation problem of the LED array is solved by arranging the LEDs in double layers, and thermal analysis shows its effectiveness. The light from the LEDs in the back layer can be transmitted through the front layer without significant loss by arranging the LEDs in non-overlapping positions in the two layers and inserting suitable microlenses between the two layers and holes in the first layer. Together with the double-layer LEDs, an illumination optical system is designed to illuminate liquid crystal panels with good uniformity and appropriate matching with the projection optics.

• The Journal of the Acoustical Society of Korea
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• v.43 no.4
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• pp.466-475
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• 2024

Matched-Field Processing (MFP) is a model-based approach that requires accurate knowledge of the ocean environment and array geometry (e.g., array tilt) to localize underwater acoustic sources. Consequently, it is inherently sensitive to model mismatches. In contrast, the waveguide invariant-based approach (also known as array invariant) offers a simple and robust means for source-range estimation in shallow waters. This approach solely exploits the beam angles and travel times of multiple arrivals separated in the beam-time domain, requiring no modeling of the acoustic fields, unlike MFP. This paper extends the waveguide invariant-based approach to shallow water environments featuring a shallow pit, where the waveguide invariant is not defined due to the complex bathymetry. An in-depth performance analysis is conducted using experimental data and numerical simulations.

• Tunnel and Underground Space
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• v.29 no.4
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• pp.243-261
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• 2019

Microseismic monitoring technologies have been recognized for its superiority over traditional methods and are used in domestic and overseas underground mines. However, the complex gangway layout of underground mines in Korea and the mixed structure of excavated space and rock masses make it difficult to estimate the microseismic propagation and to determine the arrival time of microseismic wave. In this paper, experimental studies were carried out to determine the source location according to various arrival picking methods and dimensional conditions. The arrival picking methods used were FTC (First Threshold Cross), Picking window, AIC (Akaike Information Criterion), and 2-D and 3-D source generation experiments were performed, respectively, under the 2-D sensor array. In each experiment, source location algorithm used iterative method and genetic algorithm. The iterative method was effective when the sensor array and source generation were the same dimension, but it was not suitable to apply when the source generation was higher dimension. On the other hand, in case of source location using RCGA, the higher dimensional source location could be determined, but it took longer time to calculate. The accuracy of the arrival picking methods differed according to the source location algorithms, but picking window method showed high accuracy in overall.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.4
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• pp.152-160
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• 1999

A high speed motor has been generating a lot of attention due to its performance-more light, thin, short, compact than ordinary motors. But they have low efficiency with high frequency power source because of the iron losses which may produce too much heat as well as the copper losses occurred in the rotor windings. The Halbach array can generate the strong magnetic field systems without additional magnetic materials, therefore the iron losses can be removed. In this paper, the Halbach array is applied to the field system for the high speed motor, and three dimensional FEM is used to analyze the field of the Halbach array considering with the leakage flux. The measured values of flux density are also compared with the FEM analysis. And the magnetic characteristics of the Halbach array field system are compared with those of the conventional field systems such as slot-iron type, PM-iron type. Consequently, it is confirmed that the Halbach array field system is more suitable to the high speed motor because it has high flux density, sinusoidal flux distribution than others.

• Journal of Advanced Navigation Technology
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• v.24 no.5
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• pp.393-407
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• 2020

In order to reduce the threat by illegal unmanned aerial vehicles, a tracking system based on sound was implemented. There are three main points to the drone acoustic tracking method. First, it scans the space through variable beam formation to find a sound source and records the sound using a microphone array. Second, it classifies it into a hidden Markov model (HMM) to find out whether the sound source exists or not, and finally, the sound source is In the case of a drone, a sound source recorded and stored as a tracking reference signal based on an adaptive beam pattern is used. The simulation was performed in both the ideal condition without background noise and interference sound and the non-ideal condition with background noise and interference sound, and evaluated the tracking performance of illegal drones. The drone tracking system designed the criteria for determining the presence or absence of a drone according to the improvement of the search distance performance according to the microphone array performance and the degree of sound pattern matching, and reflected in the design of the speech reading circuit.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.23-29
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• 2017

A concept of a VSA (Virtual Source Array) is the method for an acoustic spatio-temporal focus at a selected location in the outbound direction with respect to the VSA without the need of a probe source as combines a TRP (Time-Reversal Processing) and time-delay and beam-steering. However, in TRP using the VSA concept, it is limited to the critical angle and the short distances relevant to the VSA. In this paper, the waveguide invariant theory is applied to the VSA concept to refocus the received field at ranges greater other than the critical angle and the short ranges by shifting the focused field. The suggested method is verified via numerical simulation, and the results show that the robust acoustic focusing is achieved on the selected location regardless of the limitation on the conventional VSA concept.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.103-108
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• 1999

The aim of the work described in this paper is to develop a complex underground acoustic system which detects and localizes the origin of an underground hammering sound using an array of hydrophones located about loom underground. Three different methods for the sound localization will be presented, a time-delay method, a power-attenuation method and a hybrid method. In the time-delay method, the cross correlation of the signals received from the array of sensors is used to calculate the time delays between those signals. In the power-attenuation method, the powers of the received signals provide a measure of the distances of the source from the sensors. In the hybrid method, both informations of time-delays and power-ratios are coupled together to produce better performance of position estimation. A new acoustic imaging technique has been developed for improving the hybrid method. This new acoustic imaging method shows the multi-dimensional distribution of the normalized cost function, so as to indicate the trend of the minimizing direction toward the source location. For each method the sound localization is carried out in three dimensions underground. The distance between the true and estimated origins of the source is 28m for a search area of radius 250m.