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Miniaturized T-DMB Antenna With a Low–Loss Ni–Mn–Co Ferrite for Mobile Handset Applications
Jeong Keun Ji,Won Ki Ahn,Jun Sig Kum,Sang Hoon Park,Gi Ho Kim,Won Mo Seong IEEE 2010 IEEE magnetics letters Vol.1 No.-
<P>In this paper, a low-loss Ni-Mn-Co ferrite (Ni<SUB>0.76</SUB>Mn<SUB>0.24-x</SUB>Co<SUB>x</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> with x = 0-0.04) has been developed for miniaturization and performance improvement of mobile handset antennas. The developed ferrite material has almost equal permittivity and permeability of 7-9, as well as sufficiently low dielectric and magnetic loss tangent less than 0.001 and 0.01 below 200 MHz, respectively. Miniaturization factor of about 8 and normalized impedance of about 1 were obtained at 200 MHz. A helical antenna operating at terrestrial digital multimedia broadcasting (T-DMB, 174-216 MHz) band was fabricated on the ferrite substrate, which has compact size, low loss, wide bandwidth, and good radiation performance.</P>
van der Waals gap-inserted light-emitting p–n heterojunction of ZnO nanorods/graphene/p-GaN film
Sung Ho Moon,Junseok Jeong,Gwan Woo Kim,Dae Kwon Jin,Yong-Jin Kim,Jong Kyu Kim,Keun Soo Kim,Gunn Kim,Young Joon Hong 한국물리학회 2020 Current Applied Physics Vol.20 No.2
We report on the electroluminescent (EL) and electrical characteristics of graphene-inserted ZnO nanorods (NRs)/p-GaN heterojunction diode. In a comparative study, ZnO NRs/p-GaN and ZnO NRs/graphene/p-GaN heterojunctions exhibit white and yellow EL emissions, respectively, at reverse bias (rb) voltages. The different EL colors are results of different dichromatic EL peak intensity ratios between 2.25 and 2.8 eV light emissions which are originated from ZnO and p-GaN sides, respectively. The 2.25 eV EL is predominant in both the heterojunctions, because of recombination by numerous electrons tunneled from p-GaN to ZnO across the thin barriers of the staggered broken gap with a large band offset in ZnO/p-GaN and the van der Waals (vdW) gap formed by graphene insertion at ZnO NRs/p-GaN. However, as for the 2.8 eV EL intensity, ZnO NRs/graphene/p- GaN hardly shows the EL emission, whereas ZnO NRs/p-GaN exhibits the substantially strong EL peak. We discuss that the significantly reduced 2.8 eV EL emission of ZnO NRs/graphene/p-GaN is a result of decreased depletion layer thickness at p-GaN side where the recombination events occur for 2.8 eV EL before the reverse bias-driven tunneling because the insertion of graphene (or vdW gap barrier) inhibits the carrier diffusion whose amount determines the depletion thickness when forming the heterojunctions. This study opens a way of suppressing (or enhancing) the specific EL wavelength for the dichromatic EL-emitting heterojunctions simply by inserting atom-thick vdW layer.
A Study on the Enhanced Congestion Control Mechanism for Multimedia Traffic in Sensor Networks
Jeong-Hyeon Park,Jun-Hyoung Kim,Sung-Keun Lee 보안공학연구지원센터 2015 International Journal of Multimedia and Ubiquitous Vol.10 No.8
Modern network sensors can gather multimedia data as well as scalar data. And these sensors compose WMSN. Wireless multimedia sensor network is sensitive to latency. Also, it transfers mass multimedia data of various forms. This thesis proposes a routing technique based on traffic priority in order to improve the multimedia data transfer by minimizing latency. In addition, it proposes a congestion control mechanism that uses packet service time, packet inter-arrival time, buffer usage, etc. In this thesis, we verified the reduction of packet latency by the priority of a packet as a consequence of performance analysis through simulation method. Also, we confirmed that the proposed mechanism maintained a reliable network state by preventing packet loss due to network overload.