• Journal of The Korean Astronomical Society
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• v.50 no.4
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• pp.125-129
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• 2017

We investigate the solar cycle variation of microwave and extreme ultraviolet (EUV) intensity in latitude to compare microwave polar brightening (MPB) with the EUV polar coronal hole (CH). For this study, we used the full-sun images observed in 17 GHz of the Nobeyama Radioheliograph from 1992 July to 2016 November and in two EUV channels of the Atmospheric Imaging Assembly (AIA) $193{\AA}$ and $171{\AA}$ on the Solar Dynamics Observatory (SDO) from 2011 January to 2016 November. As a result, we found that the polar intensity in EUV is anti-correlated with the polar intensity in microwave. Since the depression of EUV intensity in the pole is mostly owing to the CH appearance and continuation there, the anti-correlation in the intensity implies the intimate association between the polar CH and the MPB. Considering the report of Gopalswamy et al. (1999) that the enhanced microwave brightness in the CH is seen above the enhanced photospheric magnetic field, we suggest that the pole area during the solar minimum has a stronger magnetic field than the quiet sun level and such a strong field in the pole results in the formation of the polar CH. The emission mechanism of the MPB and the physical link with the polar CH are not still fully understood. It is necessary to investigate the MPB using high resolution microwave imaging data, which can be obtained by the high performance large-array radio observatories such as the ALMA project.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.31.4-32
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• 2008

The microwave instruments are used many areas of the space remote sensing and space science applications. The imaging radar of synthetic aperture radar (SAR) is well known microwave radar sensor for earth surface and ocean research. Unlike radar, microwave radiometer is passive instrument and it measures the emission energy of target, i.e. brightness temperature BT, from earth surface and atmosphere. From measured BT, the geophysical data like cloud liquid water, water vapor, sea surface temperature, surface permittivity can be retrieved. In this paper, the radiometer characteristics, system configuration and principle of BT measurement are described. Also the radiometer instruments TRMM, GPM, SMOS for earth climate, and ocean salinity research are introduce. As first korean microwave payload on STSAT-2, the DREAM (Dual-channels Radiometer for Earth and Atmosphere Monitoring) is described the mission, system configuration and operation plan for life time of two years. The main issues of DREAM unlike other spaceborne radiometers, will be addressed. The calibration is the one of main issues of DREAM mission and how it contribute on the space borne radiometer. In conclusion, the radiometer instrument to space science application will be considered.

• Journal of electromagnetic engineering and science
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• v.14 no.4
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• pp.332-335
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• 2014

This paper investigates the phase singularity problem in microwave image reconstruction utilizing unwrapped phase data. The measured phases of the electric fields in most microwave measurement systems are wrapped. Thus, a certain phase unwrapping process is necessary for reconstruction of the image of a high contrast object. This unwrapping, however, is difficult in the presence of scattering nulls on/near the unwrapping path. At the null point, the phase value will be rendered, resulting in a poor image reconstruction. In this paper, we investigate the phase singularity arising from electromagnetic scattering nulls in microwave breast tomographic imaging. We then propose a transformation technique for the measured electric fields that avoids phase singularity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.348-351
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• 2013

Recently, a brain imaging system with microwave devices has been proposed. The brain imaging system requires a small antenna which has ultra wide band(UWB) operating frequency bandwidth(0.5~2 GHz) and non-varying boresight of antenna over the frequency band. This paper proposes asymmetric corrugations on a tapered slot antenna (TSA) so that the size of the TSA is reduced by 14 % while 10 dB return loss bandwidth is satisfied over the operating frequency band from 0.5 GHz to 2 GHz. A miniaturized TSA with symmetric corrugations shows tilted boresight whilst frequency is getting lower; however, the proposed TSA with asymmetric corrugations maintains direction of boresight for different frequencies. This enhancements make an asymmetric corrugated TSA meet the requirement of the brain imaing system.

• Journal of The Korean Astronomical Society
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• v.36 no.spc1
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• pp.29-36
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• 2003

Quiescent solar radiation, at microwave spectral regime, is dominated by gyroresonant and thermal Bremsstrahlung radiations from hot electrons residing in solar active region corona. These radiations are known to provide excellent diagnostics on the coronal temperature, density, and magnetic field, provided that spatially resolved spectra are available from observations. In this paper we present an imaging spectroscopy implemented for a bipolar active region, AR 7912, using the multifrequency interferometric data from the Owens Valley Solar Array (OVSA), as processed with a new imaging technique, so-called Spatio-Spectral Maximum Entropy Method (SSMEM). From the microwave maps at 26 frequencies in the range of 1.2-12.4 GHz at both right- and left-circular polarizations, we construct spatially resolved brightness spectra in every reconstructed pixel of about 2 arcsec interval. These spectra allowed us to determine 2-D distribution of electron temperature, magnetic field of coronal base, and emission measure at the coronal base above the active region. We briefly compare the present result with existing studies of the coronal active regions.

• Korean Journal of Radiology
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• v.23 no.1
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• pp.42-51
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• 2022

Objective: This study aimed to investigate the direction of tissue contraction after microwave ablation in ex vivo bovine liver models. Materials and Methods: Ablation procedures were conducted in a total of 90 sites in ex vivo bovine liver models, including the surface (n = 60) and parenchyma (n = 30), to examine the direction of contraction of the tissue in the peripheral and central regions from the microwave antenna. Three commercially available 2.45-GHz microwave systems (Emprint, Neuwave, and Surblate) were used. For surface ablation, the lengths of two overlapped square markers were measured after 2.5- and 5-minutes ablations (n = 10 ablations for each system for each ablation time). For parenchyma ablation, seven predetermined distances between the markers were measured on the cutting plane after 5- and 10-minutes ablations (n = 5 ablations for each system for each ablation time). The contraction in the radial and longitudinal directions and the sphericity index (SI) of the ablation zones were compared between the three systems using analysis of variance. Results: In the surface ablation experiment, the mean longitudinal contraction ratio and SI from a 5-minutes ablation using the Emprint, Neuwave, and Surblate systems were 28.92% and 1.04, 20.10% and 0.53, and 24.90% and 0.45, respectively (p < 0.001). A positive correlation between longitudinal contraction and SI was noted, and a similar radial contraction was observed. In the parenchyma ablation experiment, the mean longitudinal contraction ratio and SI from a 10-minutes ablation using the three pieces of equipment were 38.60% and 1.06, 32.45% and 0.61, and 28.50% and 0.50, respectively (p < 0.001). There was a significant difference in the longitudinal contraction properties, whereas there was no significant difference in the radial contraction properties. Conclusion: The degree of longitudinal contraction showed significant differences depending on the microwave ablation equipment, which may affect the SI of the ablation zone.

• Electronics and Telecommunications Trends
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• v.34 no.5
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• pp.26-35
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• 2019

Modern imaging technologies utilizing electromagnetic waves are indispensable in our daily lives. Applications, such as television and smartphone screens, radar imaging for weather forecast, and medical imaging, can be attributed to technology developments in various electromagnetic regions. Terahertz (THz) waves, electromagnetic (EM) waves located between far infrared and microwave regions, had left unexplored EM waves. Recent advances in technology have led to various two-dimensional and three-dimensional THz imaging techniques. In this article, we explain THz imaging techniques as well as the experimental results from our laboratory. Additionally, we introduce commercial THz cameras developed worldwide. Finally, we present the applications of THz imaging techniques.

• Journal of electromagnetic engineering and science
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• v.16 no.1
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• pp.1-6
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• 2016

Computer simulations were conducted to demonstrate the generation of microwave-induced thermoacoustic signal. The simulations began with modelling an object with a biological tissue characteristic and irradiating it with a microwave pulse. The time-varying heating function data at every particular point on the illuminated object were obtained from absorbed electric field data from the simulation result. The thermoacoustic signal received at a point transducer at a particular distance from the object was generated by applying heating function data to the thermoacoustic equation. These simulations can be used as a foundation for understanding how thermoacoustic signal is generated and can be applied as a basis for thermoacoustic imaging simulations and experiments in future research.

• Journal of electromagnetic engineering and science
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• v.10 no.4
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• pp.199-205
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• 2010

This paper presents a tumor detection system for breast cancer that utilizes two-dimensional (2D) image reconstruction with microwave tomographic imaging. The breast cancer detection system under development consists of 16 transmit/receive antennas, and the microwave tomography system operates at 900 MHz. To solve a 2D inverse scattering problem, the method of moments (MoM) is employed for forward problem solving, and the simplex method employed as an optimization algorithm. The results of the reconstructed image show that the method accurately shows the position of a breast tumor.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.2
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• pp.47-55
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• 1996

A microwave incoherent imaging method for a conducting cyliner by using multi-frequency tiem-harmonic field is presented in this study. In this paper, an incoherent intensity pattern of th econducting cylinder is obtained by averagin gout the multi-frequency intensities of the coherent field such as the time-harmonic field scattered from this cylinder. This phenomenon is hsown numerically in scattering by a conducting circular cylinder illuminated by the time-harmonic plane wave, and is interpreted analytically by the mutual coherence functon defined as a frequency-averaged intensity of the time-harmonic fields in th frequency domain.