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나노·바이오 융합응용을 위한 초상자성 Ni - Zn Ferrite의 자기적 특성연구
이승화(Seung Wha Lee),류연국(Yeon Guk Ryu),양계준(Kea Joon Yang),안중수(Jung Su An),김철성(Chul Sung Kim) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.2
Ni_(0.9)Zn_(0.1)Fe₂O₄ nanoparticles have been prepared by a sol-gel method. The structural and magnetic properties have been investigated by DTA/TGA, XRD, SEM, and Mossbauer spectroscopy, VSM. Ni_(0.9)Zn_(0.1)Fe₂O₄ powder that was annealed at 300℃ has spinel structure and behaved superparamagnetically. The estimated size of superparammagnetic Ni-Zn ferrite nanoparticle is around 10 ㎚. The hyperfine fields at 13 K for the A and B patterns were found to be 533 and 507 kOe, respectively. The blocking temperature (T_B) of superparammagnetic Ni_(0.9)Zn_(0.1)Fe₂O₄ nanoparticle is about 250 K. The magnetic anisotropy constant and relaxation time constant of Ni_(0.9)Zn_(0.1)Fe₂O₄ nanoparticle were calculated to be 1.6×10^6 ergs/㎤ and τ_0=5.0×10-¹³ s, respectively. Also, Temperature increased up to 43℃ within 10 minutes under AC magnetic field of 7㎒. It is considered that Ni_(0.9)Zn_(0.1)Fe₂O₄ powder that was annealed at 300℃ is available for biomedicine application such as hyperthermia, drug delivery system and contrast agents in MRI.
RFID 및 IEEE802.11a-b-g규격의 무선랜용 다중밴드 주파수 발생기
오남진(Nam-Jin Oh),류연국(Yeon-Guk Ryu),안중수(Jung-Soo Ahan) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.7
A new multi-carrier generation architecture is proposed that can be used for RFID reader, WLAN 802.11a-b-g. In the proposed architecture, a quadrature voltage controlled oscillator (QVCO) is implemented by coupling two differential cross-coupled LC VCOs to generate in-phase (I) and quadrature (Q) signals operating at one-thirds of the 5 ㎓ frequency range. As well, the differential second harmonic signal of the VCO core frequency is generated by mixers, and then converted to I/Q signals via a single-stage tunable polyphase filter (PPF). By single sideband (SSE) mixing of the I/Q signals of the QVCO and the PPF, cleaner carrier signal is generated in the desired frequency range from 4.9-5.8 ㎓. By including frequency dividers, the system can also be reconfigured to generate 868/915 ㎒ and 2.4 ㎓ bands.
백게이트를 통한 제 2 고조파를 직접 결합시킨 4위상 전압제어 발진기
오남진(Nam-Jin Oh),류연국(Yeon-Guk Ryu),안중수(Jung-Soo Ahan) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.7
This paper proposes a novel quadrature VCO (QVCO) based on direct back-gate second harmonic coupling. This QVCO directly couples the current sources of the conventional LC VCOs through the back-gate instead of front-gate to generate quadrature signals. Through the mechanism of second harmonic injection locking, the two LC VCOs generate quadrature signals without using on-chip transformer, or stability problem that is inherent in the direct front-gate second harmonic coupling.
Inverter-C 다위상필터를 이용한 ISM대역 다중밴드 주파수 발생기
오남진(Nam-Jin Oh),이정한(Jeonghan Lhee),류연국(Yeon-Guk Ryu),안중수(Jung-Soo Ahn) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.11
An ISM multiband carrier generation architecture is proposed that can be used for RFID reader, WLAN 802.11a-b-g using an inverter-C polyphase filter. In the proposed architecture, a quadrature voltage controlled oscillator (QVCO) is implemented by coupling two differential cross-coupled LC VCOs to generate in-phase (T) and quadrature (Q) signals operating at one-thirds of the 5 ㎓ frequency range. As well, the differential second harmonic signal of the VCO core frequency is generated by mixers, and then converted to I/Q signals via a two-stage inverter-C polyphase filter (PPF). By single sideband (SSB) mixing of the I/Q signals of the QVCO and the PPF, cleaner carrier signal is generated in the desired frequency range from 4.9-5.8 ㎓. By including frequency dividers, the system can also be reconfigured to generate 868/915 ㎒ and 2.4 ㎓ ISM bands.
Sol-gel 법에 의한 Co - Zn Ferrite 박막의 제조와 자기 특성에 관한 연구
이승화(Seung Wha Lee),양계준(Kea Joon Yang),류연국(Yeon Guk Ryu),안성용(Sung Yong An),김철성(Chul Sung Kim) 한국자기학회 2001 韓國磁氣學會誌 Vol.11 No.4
Co-Zn ferrite thin films grown on thermally oxidized silicon wafers were fabricated by a sol-gel method. Magnetic and structural properties of Co-Zn thin films were investigated by using x-ray diffractometer (XRD), atomic force microscopy (AFM), auger electron spectroscopy (AES) and a vibrating sample magnetometer (VSM). Co-Zn ferrite thin films annealed at 400 ℃ presented have only a single phase spinel structure without any preferred crystallite orientation. Their surface roughness of Co-Zn ferrite thin films was shown as less than 3 ㎚ and the grain size was about 40 ㎚ for annealing temperatures over 600 ℃. A moderate saturation magnetization of Co-Zn ferrite thin films for recording media was obtained in this study and there is no significant difference of their magnetic property with those external fields of parallel and perpendicular to planes of the films. The maximum value of the coercivity was obtained as 1,900 Oe for Co-Zn ferrite thin film annealed at 600 ℃.
저지대역 특성이 우수한 소형 마이크로스트립 저주파 필터
류연국 한국교통대학교 2019 한국교통대학교 논문집 Vol.54 No.-
The design of a compact microstrip lowpass filter and EM simulation are described in this paper. In recent years, wireless communication systems demand higher frequencies, higher packing densities and higher complexity of filters. In this paper a microstrip lowpass filter with 3dB cut-off frequency of 1.9GHz consisting of resonators with square type patches has been designed. The improvements of computer platform and simulation algorithm make it possible to realize practical EM simulations of real filter problems. In this paper, a microstrip resonator lowpass filter has been simulated and presented the simulation results for the designed filter.
류연국 한국교통대학교 2017 한국교통대학교 논문집 Vol.52 No.-
The design of a compact microstrip bandpass filter and EM simulation are described. In recent years, wireless communication systems demand higher frequencies, higher packing densities and higher complexity of filters. The improvements of computer platform and simulation algorithm make it possible to realize practical EM simulations of real filter problems. In this paper, a microstrip resonator bandpass filter has been designed and simulated and presented the simulation results for the designed filter.
류연국,양계준,한운동,박용만 충주대 산업과학기술연구소 1993 産業科學論文集 Vol.1 No.-
Usefulness of recent versions of PSPICE, personal computer implementation of the SPICE, circuit simulation computer software rogram is demonsterated in simulation of the hysteresis loops magnetic materials. In order to model the hysteresis loop of a particular magnetic core's B-H characteristics, the values of five parameters, which affect the shape of the hysteresis loops, must be established. There is no efficient procedure for selecting the values of five parameters. Neither the PSPICE instruction munual nor any current books or papers address this problem. This paper presents a method for illustrating the effect that each parameter has on the shape of the hysteresis loop.
柳然國,崔承烈,朴英基 충주대학교 산업대학원 2001 大學院論文輯 Vol.2 No.-
In this paper, bandstop filters have been designed by microstrip line which relative permittivity(ε_r) 2.5, thickness(h) is 0.7874[㎜]. In procedure, filter have been designed with parallel stub which has been physically simply implemented, butterworth and chebyshev type have been used with commensurate line which length of all stubs at center frequency is λ/8. On designing, Richard transformation and Kuroda identities have been used. And characteristic impedance of each section calculated, in result width and length of each section calculated. The center frequency of the filter is 3[㎓] and bandwidth is 50%, and simulated with the values of width and length of each section. Also, measured values of filter compared with simulation results. In the case of butterworth, center frequency was shifted about 0.22[㎓], bandwidth was 1.82[㎓], in the case of chebyshev, center frequency was shifted 0.2[㎓], bandwidth was 1.58[㎓]. Frequency response the chebyshev type is more sharper than butterworth type, and theoretical values of the filters are agreed with the measured values.
류연국 忠州大學校 2004 한국교통대학교 논문집 Vol.39 No.1
Recent microwave communication systems require high performance narrow band bandpass filters which have the characteristics of low insertion loss and good selectivity together in the passband. These criteria are fulfilled using dielectric resonator loaded cavity filters with low loss. To reduce size and weight is more important parameters to be considered in design of planar circuit structures. A microstrip resonator bandpass filter using a modified meander loop with perturbation has been designed and simulated. A basic resonator and filter structure is discussed and simulation data for the filter modified are presented.