• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.75-75
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• 2003

본 연구에서는 대기 중 극 미량으로 존재하는 환경 유해 가스 성분을 검출할 수 있는 미세 소자로의 응용을 위해 마이크로 칸티레버를 제작하고 가스 센서로의 활용 가능성을 검토하였다. 마이크로 칸티레버는 크게 구동층 캐패시터로서 대표적인 압전 재료인 Pb(Zr,Ti)O$_3$ (PZT)를 사용하고 SiNx 박막을 지지층으로 하는 형태로 제작되었다. 제작된 마이크로 칸티레버는 치수 및 형상에 따라 17~29 KHz 의 기본 공진 주파수 값을 나타내었다. Electron beam evaporator를 이용한 copper (Cu) 박막의 단계적인 증착을 통해 칸티 레버 표면에 질량을 증가시키고 그에 따른 마이크로 칸티레버의 공진주파수 변화를 관찰한 결과 질량 증가에 대해 34 Hz/ng의 선형적인 주파수 감소를 나타내었으며, 이로부터 694.4 $\textrm{cm}^2$/g 의 gravimetric sensitivity factor를 얼을 수 있었다. 마이크로칸티레버의 가스 감지능력 시험을 위해 가스 흡착층으로 일차 알콜류의 vapor를 흡착 하는 것으로 보고된 poly methyl metacrytate (PMMA)를 마이크로 칸티레버 표면에 코팅하였다. 마이크로칸티 레버의 기본 공진 주파수 및 PMMA 흡착층 형성과 가스의 흡착에 따른 주파수 변화는 마이크로 칸티 레버로부터 의 전기적 신호를 이용하는 복소 임피던스 분석에 의해 측정되었다. PMMA가 코팅된 마이크로 칸티레버는 ethanol 및 methanol vapor 의 농도가 증가함에 따라 선형적인 공진주파수 감소를 나타내었으며, methanol vapor 의 경우 0.06 Hz/ppm 의 가스 검출 감도를 얻을 수 있었다.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.333-334
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• 2013

본 논문은 비자성체 유도가열을 위한 Half-Bridge 공진형 컨버터의 고조파 운전방법을 분석한다. 비자성체 용기를 유도가열하기 위해서는 자성체 용기보다 높은 주파수의 공진전류를 필요로 하며, 반도체 소자의 선정 및 손실에 어려움을 야기한다. 이 문제를 극복하기 위하여 스위칭 주파수보다 높은 공진 전류를 운용하는 고조파 운전방법을 적용하고, 분석한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.11
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• pp.1121-1127
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• 2014

In this paper, a planar frequency reconfigurable antenna is proposed with variable capacitors. The proposed one is designed with a planar monopole, and varies resonant frequencies by variable capacitive loading of a varactor diode. The equivalent circuit and electromagnetic(EM) simulation are utilized for the analysis at the variable characteristic design of the antenna, and the same radiation performance. The implemented frequency variable monopole antenna has been verified by comparing prototypes with designed capacitors and ones with biased varactor diodes. The proposed antenna has presented the resonant frequency variations from 2.25 GHz to 2.42 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.5
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• pp.755-762
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• 2000

In this work, we present the resonant frequencies, Qrad, and impedance bandwidth of rectangular dielectric resonator antenna(DRA)for a broad range of aspect ratios using Dielectric Waveguide Model. These presented data are compared with simulation and measurement. The DRA having relative permittivities of 37.84 and 90 have been fed by a coaxial cable and fed using a aperture-coupled method for comparisions. The approximate resonant frequencies are shown to have the prediction error of about 8% and impedance bandwidth is found to have large prediction variation according to feeding method. The data presented in this paper can be used when the aspect ratios of DRA have to be determined for a given resonant frequency and impedance bandwidth.

• Korean Journal of Agricultural Science
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• v.30 no.2
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• pp.175-183
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• 2003

Fruit and vegetables are subjected to complex dynamic stresses in the transportation environment. During a long journey from the production area to markets, there is always some degree of vibration present. Vibration inputs are transmitted from the vehicle through the packaging to the fruit. Inside, these cause sustained bouncing of fruits against each other and container wall. These steady state vibration input may cause serious fruit injury, and this damage is particularly severe whenever the fruit inside the package is free to bounce, and is vibrated at its resonance frequency. The determination of the resonance frequencies of the fruit and vegetables may help the packaging designer to determine the proper packaging system providing adequate protection for the fruit, and to understand the complex interaction between the components of fruit when they relate to expected transportation vibration inputs. Instrumentation and technologies are described for determining the vibration response characteristics of the fruits with frequency range 3 to 150 Hz. The computer program for controlling the vibration exciter and the function generator and for measuring the vibration response characteristics of the fruits was developed. The resonance frequency of the pear ranged from 64.5 to 72.2 Hz and the amplitude at resonance was between 1.78 and 2.21 G-rms. The resonance frequency and amplitude at resonance decreased with the increase of the sample mass, and they were slightly affected by mechanical properties such as bioyield deformation and rupture deformation. Regression analysis was performed among the relatively high correlated parameters from the results of correlation coefficient analysis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.368-373
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• 2006

In this paper, a CPW fed rectangular slot antenna loaded with two slots for dual band operation is presented. This antenna operates at about 2.1GHz and 3.3GHz with the broad bandwidth at these frequencies. a CPW inset structure is used to match the antenna at the two seperated frequencies. Some prototypes of the proposed dual frequency antenna have been implemented. Experimental results are presented and discussed.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.495-498
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• 2014

현재 무선충전은 자기유도와 자기공진 두 가지 방식이 주류를 이루고 있다. 자기유도 방식은 전력 송신부 코일에서 자기장을 발생시키면 그 자기장의 영향으로 수신부 코일에서 전기가 유도되는 전자기유도 원리를 이용한다. 자기공진 방식은 송신부 코일에서 공진 주파수로 진동하는 자기장을 생성, 동일한 공진 주파수로 설계된 수신부 코일에만 에너지가 집중적으로 전달되도록 한 기술이다. 최근에 스마트폰의 무선충전에 대해 관심이 높아지고 있으며, 많은 기업들이 무선충전을 개발하고 있다. 사용자에게 있어 편리함을 주는 무선충전이지만 보안위협이 존재하고, 이것에 대한 표준화와 보안대책요구사항은 체계적이지 않다. 이에 본 논문은 모바일기기에서 자기공진방식의 무선충전의 보안 위협과 보안요구사항을 정의해 분석하고 보안요구사항을 제안한다.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.216-219
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• 2005

In this study, we will explain the design, test results and analysis of system for measuring the small mass in the microgravity environment. It is so difficult to measure the mass by sensing the gravity as the ground in the microgravity environment. The suggested method is to measure the resonance frequency of a sample. The resonance frequency may be measured as a function of mass. If we know the resonance frequency of the mass, we can guess the mass by detecting the resonance frequency. Piezoelectric ceramics have the characteristics that resonance frequency is changed by total mass which are its mass and the attached mass. This system have some problems but we verified that we can measure the unknown mass using the resonance frequency as the mass.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.980-986
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• 2001

Bragg reflector type FBAR was fabricated on the Si(100) substrate. We measured a frequency response of the resonator at 5.2 GHz and analyzed it by numerical calculation considering actual acoustic losses of each layer in the structure. We fabricated nine layer Bragg reflector of W-SiO$_2$pairs using r.f. sputtering method and fabricated AlN piezoelectric and Al electrodes using pulsed dc sputtering. The return loss(S$_{11}$) of the fabricated Bragg reflector type FBAR was 12 dB at 5.38 GHz and the series resonance frequency(f$_{s}$) was 5.376 GHz and the parallel resonance frequency(f$_{p}$) was 5.3865 GHz. Effective electro-mechanical coupling constant (K$_{eff{^2}}$) and Quality factors(Q$_{s}$), the Figures of Merit of the resonator, were about 0.48% and 411, respectively. We extracted acoustic parameters of AlN piezoelectric and reflection coefficient of the Bragg reflector by numerical calculation. We could know that material acoustic impedance and wave velocity of AlN piezoelectric decreased for intrinsic value and the electromechanical coupling constant(K$_2$) value was very low owing to the poor quality of the AlN piezoelectric. Reflection coefficient of Bragg reflector was 0.99966 and reflection band was very wide from 2.5 to 9.5 GHz.

• Proceedings of the KIPE Conference
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• 2017.11a
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• pp.129-130
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• 2017

본 논문에서는 자기유도방식 무선충전 시스템의 송 수신 패드 위치 변화에 따른 공진주파수 변동을 보상하기 위한 bridgeless 정류기 동작에 대해 분석한다. Bridgeless 정류기의 스위칭 시점 및 duty 변화에 따른 공진네트워크 입력임피던스의 위상 변화를 수식적으로 분석하고, 시뮬레이션을 통하여 분석 결과를 검증한다.