• Nuclear Engineering and Technology
• /
• 제52권10호
• /
• pp.2250-2261
• /
• 2020

Accurate localization of radioactive materials is crucial in homeland security and radiological emergencies. Coded-aperture gamma camera is an interesting solution for such applications and can be developed into portable real-time imaging devices. However, traditional reconstruction methods cannot effectively deal with signal-independent noise, thereby hindering low-noise real-time imaging. In this study, a novel reconstruction method with excellent noise-suppression capability based on a multi-layer perceptron (MLP) is proposed. A coded-aperture gamma camera based on pixel detector and coded-aperture mask was constructed, and the process of radioactive source imaging was simulated. Results showed that the MLP method performs better in noise suppression than the traditional correlation analysis method. When the Co-57 source with an activity of 1 MBq was at 289 different positions within the field of view which correspond to 289 different pixels in the reconstructed image, the average contrast-to-noise ratio (CNR) obtained by the MLP method was 21.82, whereas that obtained by the correlation analysis method was 5.85. The variance in CNR of the MLP method is larger than that of correlation analysis, which means the MLP method has some instability in certain conditions.

• 대한전자공학회논문지TC
• /
• 제43권12호
• /
• pp.75-82
• /
• 2006

본 논문에서는 개구를 갖는 접지면의 높은 특성 임피던스를 이용하여 주파수에 대한 민감도가 좋고 높은 품질 계수를 갖는 미앤더 라인 인덕터들을 설계하였다. 주파수에 대한 민감도는 자기 공진 주파수 (SRF) 대신에 해석 주파수 범위에 대한 유효 인덕턴스 변화량으로 새로 정의 되었다. 등가 집중 소자 회로는 고주파 인덕터의 특성을 설명하기 위해 전개되었다. 개구 접지면을 갖는 4 nH 미앤더 라인 인덕터는 0.45 nH/GHz의 좋은 민감도와 0.7 GHz에서 86의 Q 값을 갖는다.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
• /
• pp.332-335
• /
• 2008

Newly developing SAR (Synthetic Aperture Radar) sensors commonly include high resolution X-band those data are expected to contribute various applications. Recent few studies are presenting potential of X-band SAR data in forest related application. This study tried to investigate the relationship between forest stand parameters and multi-band SAR normalized backscattering. Multi-band SAR data was radiometric corrected to compare signal from different forest stand condition. Then correlation coefficients were estimated between attribute of forest stand map and normalized backscattering coefficients. Although overall correlation coefficients are not high, only X-band shows strong relationship with DBH class than other bands. The signal of C- and L-band is composed of a large number of discrete tree components such as leaves, stems, even background soil. In forest, strength of radar backscattering is affected by complex parameters. Further study might be considered more various forest stand parameters such as canopy density, stand height, volume, and biomass.

• 전기학회논문지
• /
• 제60권2호
• /
• pp.431-434
• /
• 2011

In this paper, bandwidth enhanced design of dielectric resonator antenna fabricated in multi-layer substrate is introduced. The proposed dielectric resonator antenna is operating with fundamental TE101 mode and higher-order TM111 mode. Each resonance frequency is dependent on resonator dimensions. As increasing the height of radiating aperture, the higher-order TM111 mode resonance frequency approach the fundamental TE101 mode resonance frequency and the antenna bandwidth increase by double resonance. Three different aperture height size antennas that operated at 7GHz are fabricated in FR4 multi-layer substrate. Measured 10 dB matching bandwidth is 8 percent for single resonace antenna and 18 percent for double resonance antenna.

• 우주기술과 응용
• /
• 제1권2호
• /
• pp.268-281
• /
• 2021

합성 개구 레이다(SAR, synthetic aperture radar)는 주야간 및 기상 조건에 구애받지 않고 원하는 지점을 관측할 수 있다는 장점으로 인해 최근 그 수요가 점점 늘어나고 있다. SAR 위성으로 관측한 원시 데이터는 위성궤도보정, 방사보정, multi-looking, geocoding과 같은 전처리 과정이 필요하며, 사용자의 목적에 따라 물체 탐지, 변화탐지, DEM(Digital Elevation Model) 등 영상 활용을 하기 위해서는 추가적인 처리 과정이 요구된다. 이러한 전처리와 연산과정은 매우 복잡하며 많은 시간과 컴퓨팅 자원을 필요로 한다. 주로 SAR 영상을 활용하는 기관에서는 영상을 편리하고 쉽게 처리하기 위해 각 기관의 활용 목적에 맞는 분석도구를 개발하여 사용 및 외부 수요자들에게 제공하고 있다. 본 논문에서는 국내외에서 이용하고 있는 대표적인 SAR 분석도구들의 기능 및 특성에 대해 소개하고자 한다.

• 한국정밀공학회지
• /
• 제28권3호
• /
• pp.383-388
• /
• 2011

The cold hollow cathode gas ion source is under development for multi aperture focused ion beam (FIB) system. In this paper, we describe the cold hollow cathode ion source design and the general ion source performance using Ar gas. The glow discharge characteristics and the ion beam current density at various operation conditions are investigated. This ion source can generate maximum ion beam current density of approximately 120 mA/$cm^2$ at ion beam potential of 10 kV. In order to effectively transport the energetic ions generated from the ion source to the multi-aperture focused ion beam(FIB) system, the einzel lens system for ion beam focusing is designed and evaluated. The ions ejected from the ion source can be forced to move near parallel to the beam axis by adjusting the potentials of the einzel lenses.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• 제27권1호
• /
• pp.56-74
• /
• 2023

In order to obtain practical and high-quality satellite images containing high-frequency components, a large aperture optical system is required, which has a limitation in that it greatly increases the payload weight. As an attempt to overcome the problem, many multi-aperture optical systems have been proposed, but in many cases, these optical systems do not include high-frequency components in all directions, and making such an high-quality image is an ill-posed problem. In this paper, we use deep learning to overcome the limitation. A deep learning model receives low-quality images as input, estimates the Point Spread Function, PSF, and combines them to output a single high-quality image. We model images obtained from three rectangular apertures arranged in a regular polygon shape. We also propose the Modulation Transfer Function Loss, MTF Loss, which can capture the high-frequency components of the images. We present qualitative and quantitative results obtained through experiments.

• Current Optics and Photonics
• /
• 제1권6호
• /
• pp.598-603
• /
• 2017

Traditional three-dimensional (3-D) laser imaging systems are based on real aperture imaging technology, whose resolution decreases as the range increases. In this paper, we develop a novel 3-D imaging technique based on the synthetic aperture technology in which the imaging resolution is significantly improved and does not degrade with the increase of the range. We consider an imaging laser radar (ladar) system using the floodlight transmitting mode and multi-beam receiving mode. High 3-D imaging resolutions are achieved by matched filtering the linear frequency modulated (LFM) signals respectively in range, synthetic aperture along-track, and the real aperture across-track. In this paper, a novel 3-D imaging signal model is given first. Because of the motion during the transmission of a sweep, the Doppler shift induced by the continuous motion is taken into account. And then, a proper algorithm for the 3-D imaging geometry is given. Finally, simulation results validate the effectiveness of the proposed technique.

• 대한음성학회지:말소리
• /
• 제41호
• /
• pp.31-47
• /
• 2001

The purpose of this study is to explain the cause of obsturents neutralization in syllable final position. Most of the previous phonological studies did not reflect phonetic reality sufficiently because of the limited use of the binary feature system. Using binary distinctive features, we can't explain the cause of neutralization. In order to explain the cause of neutralization, I use the multi-valued phonetic feature -[vocal tract aperture]. By [vocal tract aperture] I mean the distance between articulators in the hold stage. In this study, I claim that the cause of neutralization is assimilation to [vocal tract aperture] 0 degree. The neutralized sounds become aplosives, as a consequence of assimilation to [vocal tract aperture].

• 전기전자학회논문지
• /
• 제28권3호
• /
• pp.465-468
• /
• 2024

본 논문은 FMCW(frequency modulation continuous wave)기반의 비선형 레이다 플랫폼을 활용한 합성개구레이다를 제안하였다. 송·수신 주파수가 다른 비선형 레이다 시스템 플랫폼을 구성하고 FMCW신호를 활용하였으며, 플랫폼은 1.5 m 길이의 경로를 이동하면서 2차 고조파를 취득하여 비선형 합성개구레이다를 구현하였다. 선형 물체가 다수 존재하는 실내 다중 경로 환경에서 다수의 비선형 표적을 배치하여 미약한 2차 고조파를 탐지하여 합성개구레이다 영상화 과정을 거친 후, 2차원 해밍 윈도우를 통해서 이미징 성능을 향상시켰다.