• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.193.1-193.1
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• 2016

본 연구에서 개발된 새로운 유형의 마이크로파 대기압 플라즈마 공진기는 전송선로 이론을 기반으로 하여 임피던스 값을 $50{\varphi}$으로 설계함으로써 장비 자체에 구조적인 매칭이 이루어지도록 구성하였다. 안정적인 마이크로파 대기압 플라즈마 발생을 위해 컴퓨터 시뮬레이션(HFSS, High Frequency Structural Simulator)을 이용하여 공진기의 반사계수, 공명주파수, 급전점 그리고 전기장을 계산하였다. 전송선로의 이론에서 구한 급전점과 실제 제작한 마이크로파 대기압 플라즈마 공진기의 급전점 값이 큰 차이가 없음을 확인하였다. 이를 바탕으로 제작한 공진기는 급전점 5.6 mm에서 공명주파수는 0.89 GHz, 반사계수는 -37.5 dB임을 측정하였고 신호가 입사되는 정도는 90 % 이상인 것을 확인하였다. 공진기에서 발생된 플라즈마는 6 W의 정도의 저 전력으로 발생되었으며 기체유량과 인가전력에 따른 플라즈마의 기체온도를 측정하고 광 방출 특성을 고찰하였다. 실제 제작한 마이크로파 대기압 플라즈마 발생장치는 생의학적 응용을 포함한 여러 넓은 분야에서 활용될 전망이다.

• Journal of radiological science and technology
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• v.31 no.1
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• pp.61-69
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• 2008

Diagnosis of breast ultrasound is better than mammography in the early detection of breast cancer, but, it is difficult to detect microcalcification. We studied on detection for calcification of breast tissue using acoustic resonance and power doppler with 7.5 MHz linear probe in breast ultrasound. We first constructed breast tissue phantom made of gelatin and saw breast, and then observed calcification by the change of external vibration. Calcification injected breast tissue phantom visualized the difference for brightness and region of color in ROI regions of power doppler. Acoustic resonance almost never visualized in low frequency regions, plateau constituted in about 300-400 Hz and colors vanished according to the increase of frequency.

• Korean Journal of Optics and Photonics
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• v.27 no.6
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• pp.229-232
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• 2016

Metamaterials operating in the terahertz frequency range show promising potential for use in highly sensitive microbial sensors that are capable of effectively detecting microorganisms in the ambient environment. We were able to detect extremely small numbers of microorganisms by measuring the differential transmission spectra (DTS) of the metamaterial resonances. This was possible because their sizes are on the same scale as the microgaps of the terahertz metamaterials. DTS depend critically on the number of microorganisms placed in the gap area, and their dielectric constant. In addition, these metamaterial microbial sensors are reusable, because the microorganisms can be completely removed by fungicide solution. Finite-difference time-domain simulations successfully reproduce our experimental data.

• 대한치과보철학회:학술대회논문집
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• 2002.11a
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• pp.116-116
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• 2002

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.100-109
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• 1999

A method is proposed to characterize single-fiber composite interphases from the frequency-domain characteristics of scattered ultrasonic waves, and its feasibility is investigated theoretically. It has been shown that the locations and magnitudes of the peaks and valleys in the frequency domain are affected significantly by the interphase properties, which may indicate the effectiveness of the proposed method. Although the frequency-domain behavior is basically associated with the resonance of the fiber-interphase system, it is not dominantly affected by the scatterer's resonance unlike that in the case of acoustic wave scattering. Therefore, the conventional acoustic resonant scattering theory is not directly applicable to the characterization of composite interphases. In order to solve the inverse problem of predicting the interphase properties from the frequency-domain characteristics of the ultrasonic scattered waves, an artificial neural network has been constructed. This approach has demonstrated reasonable accuracy in most cases considered in this study.

• The Journal of the Acoustical Society of Korea
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• v.30 no.4
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• pp.223-230
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• 2011

Korean bell is hung with some air gap between the bell bottom and the ground. In addition, it has a peculiar acoustic element, so called resonance cavity below the bell. A proper design of the air gap and cavity size dramatically amplifies the bell sound by resonance effect. Bell interior cavity, air gap and resonance cavity consist of an acoustic cavity system. When the acoustic cavity frequency coincides with the natural frequency of the bell body, the frequency component is significantly amplified. On the Sacred Bell of the Great King Seongdeok, this study proposes a resonance condition of the cavity system considering air gap effect for the first time. With the exact dimension of the bell, boundary element analysis is performed using SYSNOISE. Finally, this study reveals how the temperature in season influences the resonance condition and proposes a concept of variable type resonance cavity. By using the variable type resonance cavity, the cavity size is controlled on site and exact resonance is available regardless of temperature difference in season.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.523-524
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• 2008

전자빔의 산란에 의한 자기 공명현상과 지파 사이크로트론과의 상호작용에 의한 해석에서 체렌코프 발진이 일어나는 것은 확인하기 위하여 대구경 후진파 발진기를 이용한 실험을 하였다. 전자계와 전자빌의 상호작용을 위한 조절을 위하여 도파관의 반경과 진폭, 파장을 조절하였으며 이에 따른 주파수의 발진을 알수 있었다.

• Journal of the Korean Magnetics Society
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• v.5 no.3
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• pp.171-174
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• 1995

We have studied the paramagnetic $CuF_{2}$ using the techniques of pulsed nuclear magnetic resonance(NMR). The powder sample revealed two well-separated lines from the distinct $^{19}F$ sites at room temperature and at 77 K. The distinct frequency shifts of the two lines appear to arise from electron transfers. Furthermore, the two sites have very short spin-lattice relaxation times ($T_{1}$). The frequency-shifted site has the shorter $T_{1}$ than the unshifted one, reflecting the difference of the electron environments of the two sites.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.10
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• pp.1-11
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• 1998

This paper presents a new implementation method of the pulsed NMR(nuclear magnetic resonance) apparatus, which contains a single coil in a magnet console, to detect a NMR signal. Applying an RF magnetic field of 5MHz to the magnet console which is designed to have Larmor frequency of 5MHz for hydrogen atom, the hydrogen NMR signal was obtained from the glycerin which was put in the magnet console as a sample. The DC magnetic field in the magnet console was implemented with a permanent magnet of 1168 gauss and the RF magnetic field was generated appling an RF signal with the frequency of 5MHz and the current magnitude of 8A to a coil of 5.73${\mu}$H. The magnitude of the NMR signal was maximum when the RF magnetic field was generated for 2.8 ${\mu}$sec, and the period of generating the RF magnetic field was designed to 100msec for detecting the NMR signal repeatedly. The NMR signal, radiated from the sample in the magnetic console, was appeared as an amplitude-modulated signal with a frequency equal to the Larmor frequency. The signal, induced in the coil, was amplified in the tx/rx separation circuit, preamplifier and intermediate amplifier by a factor of 20.7dB, 36dB and 40dB, respectively, and the signal was detected by a synchronous detection circuits, then the NMR signal was obtained.

• Journal of the Korean Magnetics Society
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• v.16 no.5
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• pp.234-239
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• 2006

We measured the microwave permeability in the frequency range of 100 MHz$\sim$9 GHz in the exchange biased CoFe/MnIr films. The results were analyzed based on the Landau-Lifshitz-Gilbert theory. The initial permeability and ferromagnetic resonance frequency was tuned by controlling the CoFe thickness and unidirectional anisotropy. The tunable range of ferromagnetic resonance frequency was up to 20 GHz in the thin CoFe layer of 1.5 nm. The CoFe/MnIr films showed the high permeability and low loss properties in the microwave frequency range. Thus, this material could be applied to the microwave devices.