• 한국전자파학회논문지
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• 제27권5호
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• pp.463-470
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• 2016

본 논문에서는 다중 편파(polarimetry) 데이터를 이용한 산란점(scattering center) 추출 알고리즘을 소개하고자 한다. 산란파 계산을 위해 상용 툴인 VIRAF(virtual aircraft framework)의 물리 광학법(Physical Optics: PO)/물리광학 회절이론(Physical Theory of Diffraction: PTD)을 사용하여 표적 표면과 모서리에 의한 산란을 각각 계산하였다. 또한, 단위 변환(unitary transformation)을 이용하여 선형 기저(linear basis) 기반 4-채널 데이터를 수평/수직-좌원형 기저(horizontal/vertical-circular basis) 2-채널 데이터로 변환하였고, 그 결과 데이터를 코히런트하게 압축할 수 있었다. 스펙트럼 추정 방법(spectral estimation technique)에 하나인 2차원 RELAX 알고리즘을 사용하여 산란점(scattering center) 추출을 하였고, 편파 방향과 관측각도 변화에 따른 산란현상을 각각 분석하였다.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2011년도 자성 및 자성재료 국제학술대회
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• pp.101-101
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• 2011

The control of magnetization by an electric field at room temperature remains as one of great challenges in materials science. Multiferroics, in which magnetism and ferroelectricity coexist and couple to each other, could be the most plausible candidate to realize this long-sought capability. While recent intensive research on the multiferroics has made significant progress in sensitive, magnetic control of electric polarization, the electrical control of magnetization, the converse effect, has been observed only in a limited range far below room temperature. Here we demonstrate at room temperature the control of both electric polarization by a magnetic field and magnetization by an electric field in a multiferroic hexaferrite. The electric polarization rapidly increases in a magnetic field as low as 5 mT and the magnetoelectric susceptibility reaches up to 3200 ps/m, the highest value in single phase materials. The magnetization is also modulated up to 0.34 mB per formula unit in an electric field of 1.14 MV/m. Furthermore, this compound allows nonvolatile, magnetoelectric reading- and writing-operations entirely at room temperature. Four different magnetic/electric field writing conditions generate repeatable, distinct M versus E curves without dissipation, offering an unprecedented opportunity for a multi-bit memory or a spintronic device applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.296-296
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• 2014

We investigate experimentally and theoretically the splitting of surface plasmon (SP) resonance peaks under TE- and TM-polarized illumination. The SP structure at infrared wavelength is fabricated with a 2-dimensional square periodic array of circular holes penetrating through Au (gold) film. In brief, the processing steps to fabricate the SP structure are as follows. (i) A standard optical lithography was performed to produce to a periodic array of photoresist (PR) circular cylinders. (ii) After the PR pattern, e-beam evaporation was used to deposit a 50-nm thick layer of Au. (iii) A lift-off processing with acetone to remove the PR layer, leading to final structure (pitch, $p=2.2{\mu}m$; aperture size, $d=1.1{\mu}m$) as shown in Fig. 1(a). The transmission is measured using a Nicolet Fourier-transform infrared spectroscopy (FTIR) at the incident angle from $0^{\circ}$ to $36^{\circ}$ with a step of $4^{\circ}$ both in TE and TM polarization. Measured first and second order SP resonances at interface between Au and GaAs exhibit the splitting into two branches under TM-polarized light as shown in Fig. 1(b). However, as the incidence angle under TE polarization is increased, the $1^{st}$ order SP resonance peak blue-shifts slightly while the splitting of $2^{nd}$ order SP resonance peak tends to be larger (not shown here). For the purpose of understanding our experimental results qualitatively, SP resonance peak wavelengths can be calculated from momentum matching condition (black circle depicted in Fig. 2(b)), $k_{sp}=k_{\parallel}{\pm}iG_x{\pm}jG_y$, where $k_{sp}$ is the SP wavevector, $k_{\parallel}$ is the in-plane component of incident light wavevector, i and j are SP coupling order, and G is the grating momentum wavevector. Moreover, for better understanding we performed 3D full field electromagnetic simulations of SP structure using a finite integration technique (CST Microwave Studio). Fig. 1(b) shows an excellent agreement between the experimental, calculated and CST-simulated splitting of SP resonance peaks with various incidence angles under TM-polarized illumination (TE results are not shown here). The simulated z-component electric field (Ez) distribution at incident angle, $4^{\circ}$ and $16^{\circ}$ under TM polarization and at the corresponding SP resonance wavelength is shown in Fig. 1(c). The analysis and comparison of theoretical results with experiment indicates a good agreement of the splitting behavior of the surface plasmon resonance modes at oblique incidence both in TE and TM polarization.

• 전기화학회지
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• 제26권1호
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• pp.11-18
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• 2023

전기자동차 시장의 급속한 성장으로 이차전지의 사용이 급증함에 따라 사용 후 전지의 폐기 및 재활용이 심각한 문제로 제기되고 있다. 사용 후 리튬이온 전지를 처리하기 위해서는 저장된 에너지를 제거하기 위하여 효과적으로 방전하는 과정이 필수적이다. 본 연구에서는 흑연과 LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)을 사용하여 코인셀 형태로 반쪽전지 및 완전지를 제조하였고, 이를 과방전할 때 발생하는 전기화학적 거동에 대하여 분석하였다. 반쪽전지를 사용하여 양극과 음극을 각각 과방전시키면, 양극에서는 먼저 전이금속 산화물이 금속으로 환원되는 전환반응을 겪게 되며, 음극에서는 SEI 피막의 분해에 이어 집전체인 Cu가 용출되는 부반응이 발생하였다. 또한, 이러한 과방전의 발생 시에는 큰 분극을 필요로 하였다. 완전지의 과방전 시에는 각각의 부반응이 진행되는 시점에 존재하는 큰 분극들로 인하여 부반응의 본격적인 발생 전에 0 V에 도달하여 방전이 종료되었다. 그러나, 사이클을 통하여 용량이 퇴화된 완전지의 경우에는 과방전거동이 변화하여 음극에서 Cu 집전체의 부식이 발생됨을 확인하였다. 따라서, 사용 후 전지는 사용 전의 전지와는 과방전 시에 다른 거동을 지니고 있으므로 이러한 점들이 고려되어야 한다.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.1-7
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• 2016

본 논문에서는 Ku 밴드 전체 대역에 걸쳐 광대역 주파수 특성을 얻을 수 있는 원뿔형 주름 혼안테나의 설계방법을 제안하였다. 혼안테나의 이득, 정재파비, 주편파와 교차편파의 비와 광대역 특성을 개선시키기 위하여 두 종류의 모드정합 컨버터를 원뿔형 주름 혼안테나 내부에 구성하였다. 하나의 형태는 원형도파관 종단 내부에 또 다른 형태는 혼플레어 전단에 설치하였다. 제안된 모드정합 컨버터들의 위치에 따라 두 가지 형태의 안테나 구조는 시뮬레이션을 통해 비교하고 분석되었다. 그리고 Ku 밴드 전체 주파수 대역인 12-18 GHz에서 정재파비가 2보다 작고 교차편파와 주편파의 비가 30dB, 안테나 이득이 20dB 이상인 값에서 안테나의 성능을 비교한 결과, 원형도파관 내에 모드정합 컨버터를 설계한 원뿔형 주름 혼안테나의 구조가 혼플레어 내에 모드정합 컨버터를 설계한 안테나의 구조보다 제반 성능이 더욱 안정적이고, 동시에 송수신할 수 있는 신호 주파수 대역이 광대역 특성을 갖는다. 따라서 이득과 VSWR, 복사패턴, 대역폭 등을 감안했을 때, 원형도파관 내부에 모드정합 컨버터를 설계한 구조가 좀 더 뛰어난 성능을 보였다.

• 천문학회지
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• 제38권2호
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• pp.97-100
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• 2005

The first Space-VLBI project, VSOP, started successfully with the launch of the dedicated space-VLBI satellite HALCA in 1997. The project has been in scientific operation in the 1.6 GHz and 5 GHz bands, and studies have been done mainly of the jet phenomena related to active galactic nuclei. A second generation space- VLBI project, VSOP-2, has been planned by the working group formed at ISAS/JAXA with many collaborators. The spacecraft is planned to observe in the 8, 22 and 43 GHz bands with cooled receivers for the two higher bands, and with a maximum angular resolution at 43 GHz (7 mm) of about 40 micro-arcseconds. The VSOP-2 satellite will also have the capability of the phase-reference and full polarization observations, which will produce more powerful results than those of the VSOP project. Far-future space-VLBI projects following VSOP and VSOP-2, have a large potential to achieve enough resolution and sensitivity to satisfy astronomers in future.

• Journal of Magnetics
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• 제15권2호
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• pp.51-55
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• 2010

The electronic and magnetic properties of Cu-doped GaN with a Cu concentration of 6.25% and 12.5% are examined theoretically using the full-potential linear muffin-tin orbital method. The magnetic moment of Cu atoms decreases with increasing Cu concentration. The spin-polarization of Cu atoms is reduced due to the Cu d-d interaction depending on the distance between the nearest neighbouring Cu atoms. Cu atoms exhibits a clustering tendency in GaN. For Cu-adsorbed GaN thin films with a surface coverage of 0.25, the ferromagnetic state is found to be the energetically favourable state with an induced magnetic moment of $0.54\;{\mu}_B$ per supercell.

• 천문학회보
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• 제39권2호
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• pp.62.2-62.2
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• 2014

A relativistic jet associated with active galactic nuclei (AGNs) is almost ubiquitous while its formation mechanism is still not well understood. To get a deeper understanding of how an AGN jet forms and evolves, we have obtained Very Large Baseline Array (VLBA) data of a compact and optically violent variable quasar, OVV 1633+382 which is a small line-of-sight angle version of Fanaroff-Reily type 2 galaxy. Before our data were taken, a pronounced flare had been reported at mm wavelengths, making this object an excellent laboratory to study detailed properties of a radio jet powered by an AGN. The target have been observed in 12 epochs between 2002 and 2005 at 22, 43 and 86 GHz in full polarization mode. Among these observations, in this work, we present 43 GHz total intensity maps of our target for three epochs to discuss kinematics and geometry of the jet.

• 천문학회보
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• 제37권2호
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• pp.234.2-234.2
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• 2012

As the accuracy in the measurement of cosmological parameters is ever-increasing in this era of precision cosmology, astrophysical constraints on high-redshift universe is also getting tighter. Three dimensional (3D) tomography of the high-redshift (z>~7) universe is expected to be made through the next-generation radio telescopes including various SKA pathfinders and SKA itself, which calls for extensive theoretical predictions. We present our new simulations of cosmic reionization covering the full dynamic range of radiation sources, and also the mock data for the (1) large-scale CMB polarization anisotropy for Planck mission, (2) small-scale, kinetic Sunyaev-Zel'dovich effect for South Pole Telescope project, and (3) 21-cm observations. We show that the new constraints on CMB from Planck will constrain the models of reionization significantly, which then should be tested by 3D tomography of high-redshift universe through the 21-cm observations by future radio telescopes.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.435-440
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• 2002

The objective of this study is to analyze the relationship between polarimetric radar backscatters and stand characteristics over the mountainous forest area. L- and P-band full polarimetric airborne SAR data obtained in September 2000 were processed to compare with forest stand maps and ground collected stand variables. After the geometric registration of SAR image, mean radar backscatters were extracted for those ground plots where the stand parameters, such as tree height, DBH, and basal area, were measured during and after the SAR data acquisition. Preliminary analysis was focused on the topographic influence of radar backscattering under the homogeneous forest stand condition. Topographic effects, assessed by the local incidence angles, were different obvious in L-band data while it was not clear with P-band data.