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Naju, South Korea

Lee S.,Chungbuk National University | Kim N.,Chungbuk National University | Keum H.-S.,Electromagnetic Technology Institution | Kim B.-H.,Electromagnetic Technology Institution | And 2 more authors.
IEEE International Symposium on Electromagnetic Compatibility | Year: 2014

Recently, the PDP TV, WPT systems, etc. which radiates the electromagnetic fields of the frequency range below 30 MHz are widely provided. The measurement methods for electromagnetic interference or susceptibility generated by these devices are required, and the site validation methods are also required by the standardization. The reference site method (RSM) is an alter native method for the validation of compliance test site instead of the NSA method as known in the document, CSIPR 16-1-4. However, there is only standardization for the frequency range above 30 M Hz. To investigate and analyze the validity of the reference site method, we have verified the validation of the RSM by the experiment in the standard site The calculated standard deviation of the average antenna pair reference does not exceed 0.6 dB at the measurement distance of 10 m and 3 m Inaddition, the calculated site attenuations are satisfied at 3 m distance but exceeded at 10 m distance Therefore, results of 3 m test distance are more reasonable and suitable than results of 10 m test distance Also, maximum power signals might be a 25 dB higher than the ambient signals because of the ambient noise. © 2014 The Institute of Electronics, Information and Communication Engineer. Source

Kim K.J.,Yonsei University | Choi W.C.,Yonsei University | Yoon Y.J.,Yonsei University | Bae S.-H.,National Radio Research Agency
2015 International Workshop on Antenna Technology, iWAT 2015 | Year: 2015

The 8×8 array applicator for 915 MHz hyperthermia proposed. Proposed array applicator is 8×8 lattice array with and without phased feeding. 8×8 lattice array with same phase is for superficial hyperthermia. 8×8 lattice array with phased feeding is for ultra-superficial hyperthermia, which has deeper treatment area. 8×8 lattice array without phased feeding has 61 % effective treatment area of array size in 2 cm depth from skin surface. 8×8 lattice array with phased feeding has penetration enhancement from 34 mm to 49 mm. © 2015 IEEE. Source

Khuyen B.X.,Hanyang University | Tung B.S.,Hanyang University | Yoo Y.J.,Hanyang University | Kim Y.J.,Hanyang University | And 3 more authors.
Current Applied Physics | Year: 2016

An ultrathin and angularly stable metamaterial perfect absorber (MPA) is demonstrated for VHF-band using four connected split-square resonators structure and low-cost fabrication process. The total incoming energy of electromagnetic wave (at 250 MHz) is consumed inside the efficient thickness, which is 240 times smaller than the absorption wavelength of MPA. Our MPA works well for a very wide range of incident angle up to 45° of electromagnetic wave and exhibits the polarization-independent behavior. Furthermore, by scaling the initial design and integrating a ferroelectric material (strontium titanate), a thermo-tunable ultrathin MPA is realized in the THz region. At room temperature (300 K), the thickness of THz MPA reaches roundly 1/300 of the working wavelength. In addition, a fractional frequency shift of 49% at the absorption over 90% can be controlled in the varied temperature range from 150 to 400 K. Our results presents good candidates for potential devices operating from the radio to the THz range. © 2016 Elsevier B.V. All rights reserved. Source

Park J.,Korea Astronomy and Space Science Institute | Kwak Y.-S.,Korea Astronomy and Space Science Institute | Mun J.-C.,National Radio Research Agency | Min K.W.,Korea Advanced Institute of Science and Technology
Journal of Astronomy and Space Science | Year: 2015

In this study, we estimated the topside scale height of plasma density (Hm) using the Swarm constellation and ionosondes in Korea. The Hm above Korean Peninsula is generally around 50 km. Statistical distributions of the topside scale height exhibited a complex dependence upon local time and season. The results were in general agreement with those of Tulasi Ram et al. (2009), who used the same method to calculate the topside scale height in a mid-latitude region. On the contrary, our results did not fully coincide with those obtained by Liu et al. (2007), who used electron density profiles from Arecibo Incoherent Scatter Radar (ISR) between 1966 and 2002. The disagreement may result from the limitations in our approximation method and data coverage used for estimations, as well as the inherent dependence of Hm on Geographic LONgitude (GLON). © 2015. The Korean Space Science Society. Source

Khuyen B.X.,Hanyang University | Tung B.S.,Hanyang University | Dung N.V.,Hanyang University | Yoo Y.J.,Hanyang University | And 5 more authors.
Journal of Applied Physics | Year: 2015

We numerically and experimentally demonstrated a metamaterial perfect absorber (MPA) in MHz region based on a planar sandwiched metal-dielectric-metal structure. First, the single-peak perfect absorption was obtained at 400MHz. The ratios of the periodicity of unit cells and the thickness to the absorption wavelength are 1/12 and 1/94, respectively. The advantage of structural design and the mechanism for the low-frequency MPA are described in detail by the comparison between calculation, simulation, and experiment. Influence of the incident angle of electromagnetic (EM) wave for both transverse-electric (TE) and transverse-magnetic (TM) polarization on absorption was also investigated, and the absorption was maintained to be above 95% at incident angles up to 30°. Finally, we propose a self-asymmetric structure, which induces the dual-band perfect absorption in the same range of frequency. The EM behavior of the excitation modes and the mechanism of the dual-band MPA are clearly explained. Especially, when two resonance modes are finely controlled to be close enough, the bandwidth (full width at half maximum) of MPA is enhanced to be nearly wider twice than that in case of single-peak perfect absorption. The enhanced bandwidth is still well preserved by varying the incident angle up to 30°for both TE and TM polarization. The results were also confirmed by both simulation and experiment. Our work is promising for potential practical applications in the radio range, such as radio-frequency shielding devices, single/dual-frequency filters, and switching devices. © 2015 AIP Publishing LLC. Source

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