• Journal of electromagnetic engineering and science
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• 제15권4호
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• pp.250-257
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• 2015

This paper presents an experimental measurement system for 3-6 GHz microwave tomography (MT) of the breast. The measurement system is constructed as a minimal test bed to verify key components such as the sensing antennas, radio frequency (RF) transceiver, sensing mechanism, and image reconstruction method for our advanced MT system detecting breast cancer at an early stage. The test bed has eight RF channels operating at 3 to 6 GHz for high spatial resolution and a two-axis scanning mechanism for three-dimensional measurement. The measurement results from the test bed are shown and discussed.

• 대한원격탐사학회지
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• 제33권1호
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• pp.47-60
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• 2017

The permafrost active layer plays an important role in permafrost dynamics. Ecological patterns, processes, and water and ice contents in the active layer are spatially and temporally complex depending on landscape heterogeneity and local-scale variations in hydrological processes. Although there has been emerging interest in the application of optical remote sensing techniques to permafrost environments, optical sensors are significantly limited in accessing information on near surface geo-cryological conditions. The primary objective of this study was to investigate capability of L-band SAR data for monitoring spatio-temporal variability of permafrost ecosystems and underlying soil conditions. This study exploits information from different polarimetric SAR observables in relation to permafrost environmental conditions. Experimental results show that each polarimetric radar observable conveys different information on permafrost environments. In the case of the dual-pol mode, the radar observables consist of two backscattering powers and one correlation coefficient between polarimetric channels. Among them, the dual-pol scattering powers are highly sensitive to freeze/thaw transition and can discriminate grasslands or ponds in thermokarst area from other permafrost ecosystems. However, it is difficult to identify the ground conditions with dual-pol observables. Additional backscattering powers and correlation coefficients obtained from quad-pol mode help understanding seasonal variations ofradar scattering and assessing geo-cryological information on soil layers. In particular, co-pol coherences atHV-basis and circular-basis were found to be very usefultools for mapping and monitoring near surface soil properties.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.359.1-359.1
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• 2016

The electromagnetic (EM) properties of media, such as propagation, focusing and scattering, strongly rely on the electric permittivity and the magnetic permeability of media. Recently, artificially-created metamaterials (MMs) composed of periodically-arranged unit cells with tailored electric permittivity and magnetic permeability have drawn wide interest due to their capability of adjusting the EM response. MM absorbers using the conventional sandwich structures usually have very high absorption at a certain frequency, and the absorption properties of MMs can be adjusted simply by changing the geometrical parameters of unit cell. In this work, we suggested an incident-angle-independent broadband perfect absorber based on resistive layers. We analyze the absorption mechanism based on the impedance matching with the free space and the distribution of surface currents at specific frequencies. From the simulation, the absorption was expected to be higher than 96% in 1.4-6.0 GHz. The corresponding experimental absorption was found to be higher than 96% in 1.4-4.0 GHz, and the absorption turned out to be slightly lower than 96% in 4.0-6.0 GHz owing to the irregularity in the thickness of resistive layers.

• 천문학회지
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• 제37권5호
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• pp.295-297
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• 2004

Observations with EUVE, ROSAT, and BeepoSAX have shown that some clusters of galaxies produce intense EUV emission. These findings have produced considerable interest; over 100 papers have been published on this topic in the refereed literature. A notable suggestion as to the source of this radiation is that it is a 'warm' (106 K) intracluster medium which, if present, would constitute the major baryonic component of the universe. A more recent variation of this theme is that this material is 'warm-hot' intergalactic material condensing onto clusters. Alternatively, inverse Compton scattering of low energy cosmic rays against cosmic microwave background photons has been proposed as the source of this emission. Various origins of these particles have been posited, including an old (${\~}$Giga year) population of cluster cosmic rays; particles associated with relativistic jets in the cluster; and cascading particles produced by shocks from sub-cluster merging. The observational situation has been quite uncertain with many reports of detections which have been subsequently contradicted by analyses carried out by other groups. Evidence supporting a thermal and a non-thermal origin has been reported. The existing EUV, FUV, and optical data will be briefly reviewed and clarified. Direct observational evidence from a number of different satellites now rules out a thermal origin for this radiation. A new examination of subtle details of the EUV data suggests a new source mechanism: inverse Compton scattered emission from secondary electrons in the cluster. This suggestion will be discussed in the context of the data.

• 한국해양환경ㆍ에너지학회지
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• 제15권3호
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• pp.208-218
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• 2012

수면에서의 마이크로웨이브 후방산란 수치 시뮬레이션 기법을 개발하였다. 수치 시뮬레이션은 수조나 실해역 실험의 대체수단으로서, 수면에서의 마이크로웨이브 후방산란 과정의 이해, 마이크로웨이브 레이더를 이용한 수면 관측시스템과 관측방법의 평가에 이용된다. 이 논문에서는 다양한 수면 조건에 대한 수치 시뮬레이션의 적용 예와 수치 시뮬레이션의 유용성에 대해서 기술하였다. 적용 예로서, 고정안테나 펄스 도플러 레이더의 1) 도플러 이미지, 2) 레이더 조사폭 영향, 3) 하천 수위 관측과, 4) 합성 개구 레이더 (SAR) 의 해면 이미지를 보여준다. 해면으로부터의 마이크로웨이브 후방산란 수치 시뮬레이션을 통하여, 1) 파랑계측에 있어서 펄스 도플러 레이더의 주파수 변조 이미지가 진폭 변조 이미지에 비해서 유용함을 보였다. 2) 연속파 레이더를 이용한 파랑계측에 있어서의 레이더 해면 조사폭의 영향에 대한 Rheem[2008]의 보고와 관련해, 레이더 조사폭이 도플러 스펙트럼에 미치는 영향을 조사하여, 파랑계측에 적합한 레이더의 조사 조건을 보였다. 3) 펄스 도플러 레이더를 이용한 해면 조위관측 알고리듬을 하천의 유속과 수위 추정에 응용함에 있에서, 알고리듬의 적용성과 계측성능을 평가했다. 4) SAR 이미지 생성 메케니즘의 이해와 SAR 이미지를 이용한 해면 관측 알고리듬의 평가를 위해, 수치 시뮬레이션을 이용하여 해면의 SAR 이미지를 생성하였다.