• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.97-102
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• 2005

Acoustic experiments were performed with Zostera marina to study the characteristics of backscattering of seagrass living in the bottom interface. Field experiments were conducted in the Dongdae man, Namhae for day and night to consider the effects of air-bubble from photosynthesis of seagrass. The multi-frequency (30$\~$120 kHz) responses were measured and the distributions of back scattering strength due to the movement of seagrass were Presented by PDF (probability density function) at 120 120 kHz. The results were shown both the frequency dependence and diurnal variation of the backscattering strength between day and night. This diurnal variation may be caused by the amount of oxygen in dissolved bubbles formed by Photosynthesis of seagrass.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.54-60
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• 2017

In order to identify the characteristics of the flame transfer function gain, cold-flow transfer function was introduced, which is the part of the combustion instability research. Nitrogen and carbon dioxide was used to obtain the cold-flow transfer function and input/output variables was measured by hot wire anemometry. Density and fluid flow rate affect the cold-flow transfer function gain and peak frequency. In addition, acoustic resonance frequency affects the peak frequency of gain in the fuel feeding line.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.295-295
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• 2010

생체 식립형 임플란트의 경우 성공도는 매식체의 골유착 정도에 크게 영향을 받는다. 골유착 시 임플란트의 표면 형상과 하중, 골질의 양 등 많은 요인에 영향을 받게 되므로, 임플란트의 안정성을 주기적으로 점검해야할 필요가 있다. 따라서 임플란트 안정성을 공진 주파수 분석법을 이용하여 측정하기 위해 압전소자 제작과 트랜스듀서의 구조를 설계하였다. 유한요소 해석을 통하여 압전소자와 트랜스듀서의 두께와 크기 변화를 통해 측정 주파수 범위를 10kHz대역으로 맞추었으며, 해석 결과를 토대로 샘플제작과 평가를 실시하였다. 평가 결과 시뮬레이션 해석결과와 유사한 10kHz의 주파수 대역을 가지는 것을 볼 수 있었고, 식립된 나사의 고정도가 증가할수록 주파수가 점차 증가하는 결과를 얻을 수 있었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.4
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• pp.270-277
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• 1997

Plastic anisotropy is one of important factors which determine the drawability of a steel sheet. It has been mainly measured by mechanical tensile test. From the ultrasonic velocities propagating along the relative directions to the rolling direction, CODF(crystallite orientation distribution function) can be measured and ODC's(orientation distribution coefficients) has some correlations with the plastic anisotropy. In this study the correlations between the plastic anisotropy and ODC's of the cold rolled steel sheet were measured. From the results of ultrasonic velocity measurements the average normal anisotropy, $\bar{\gamma}$ and the average planar anisotropy, ${\Delta}r$ could be predicted within the accuracy of ${\pm}0.082$ and ${\pm}0.096$, respectively. Acoustic resonance method was applied to measure the ultrasonic velocities and EMAT's were used for generating and detecting the ultrasonic waves.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.4
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• pp.652-658
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• 2006

This paper deals with an electronic ballast for hish intensity short-arc discharge lamps, which consists of a boost converter, a step down converter operated as a current source with power regulation and a low frequency inverter with external ignition circuit The ignition circuit generates high voltage pulses of 130[Hz] up to 5 [kV]. A reignition circuit is equipped in the ballast, and it operates the lamp at a regular interval for protection when an ignition fails. Acoustic resonance phenomenon was eliminated by operating a low frequency square wave voltage and current. The measured lamp voltage, current and consumption power were 123.8 [V], 8.1 [A] and 1,002 [W], respectively. From the experiment, we confirmed that the prototype ballast operates the lamp with a constant power.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.630-632
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• 2003

In this paper, we present the fabrication and performance of FBAR filters with ladder and stacked crystal filter (SCF) types. The structure of the unit resonator in our work is the solidly mounted resonator (SMR) with W/SiO$_2$ multi-layer reflectors, the return loss of of which show -24dB at resonant frequency of -2.0GHz. The $K^2$eff, Q$_{s}$, and Q$_{p}$, indicating the performance of resonator were 3.24%, 6,363 and 6,749 and were calculated for the resonator with the resonance area of 21200${\mu}{\textrm}{m}$$^2$. Based on this unit resonator, FBAR filters with ladder and SCF types were fabricated and compared. The sizes of filters were 800$\times$2000(${\mu}{\textrm}{m}$$^2$) for the ladder type and 600$\times$500(${\mu}{\textrm}{m}$$^2$) for the SCF type.e..

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1327-1336
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• 2001

The structural modes driven by the low wave-number components of smooth elastic wall pressure provide a relatively weak coupling between the flow and the wall motion. If the elastic thin plate has any resonant mode whose wave-number of resonance coincides with $\omega$/U$\sub$c/, the power will be transmitted to those modes of vibration by the flows. We examine the problem in which the elastic thin plate is subject to pressure fluctuations under turbulent boundary layer. Measurements are presented of the frequency spectra of the near- and far-field pressures and radiated sound contributed by the various wave modes of the thin elastic plate. Dispersion equation for wave motions of elastic plate is used to investigate the effect of bending waves of relatively low wave number on radiated sound. The low wave-number motion of elastic plate is observed to have much less influence on the low-frequency energy of wall pressure fluctuations than that of the rediated sound. High amplitude events of the wall pressure are observed to weakly couple with high-frequency energy of radiated sound for case of low tension applied to the plate. The sound source localization is applied to the measurement of radiated sound by using acoustic mirror system.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.54.2-54.2
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• 2010

최근까지는 주로 비정질 실리콘이 디스플레이의 채널층으로 상용화 되어왔다. 비정질 실리콘 기반의 박막 트랜지스터는 제작의 경제성 및 균일성을 가지고 있어서 널리 상용화되고 있다. 하지만 비정질 실리콘의 구조적인 문제인 낮은 전자 이동도(< $1\;cm^2/Vs$)로 인하여 디스플레이의 대면적화에 부적합하며, 광학적으로 불투명한 특성을 갖기 때문에 차세대 디스플레이의 응용에 불리한 점이 있다. 이런 문제점의 대안으로 현재 국내외 여러 연구 그룹에서 산화물 기반의 반도체를 박막 트랜지스터의 채널층으로 사용하려는 연구가 진행중이다. 산화물 기반의 반도체는 밴드갭이 넓어서 광학적으로 투명하고, 상온에서 증착이 가능하며, 비정질 실리콘에 비해 월등히 우수한 이동도를 가짐으로 디스플레이의 대면적화에 유리하다. 특히 Zinc Oxide의 경우, band gap이 3.4eV로써, transparent conductors, varistors, surface acoustic waves, gas sensors, piezoelectric transducers 그리고 UV detectors 등의 많은 응용에 쓰이고 있다. 또한, a-Si TFTs에 비해 ZnO-based TFTs의 경우 우수한 소자 성능과 신뢰성을 나타내며, 대면적 제조시 우수한 균일성 및 낮은 생산비용이 장점이다. 그러나 ZnO-baesd TFTs의 경우 일정한 bias 아래에서 threshold voltage가 이동하는 문제점이 displays의 소자로 적용하는데 매우 중요하고 문제점으로 여겨진다. 특히 gate insulator와 channel layer사이의 interface에서의 defect에 의한 charge trapping이 이러한 문제점들을 야기한다고 보고되어진다. 본 연구에서는 Zinc Oxide 기반의 박막 트랜지스터를 DC magnetron sputtering을 이용하여 상온에서 제작을 하였다. 또한, $Si_3N_4$ 기판 위에 electron cyclotron resonance (ECR) $O_2$ plasma 처리와 plasma-enhanced chemical vapor deposition (PECVD)를 통하여 $SiO_2$ 를 10nm 증착을 하여 interface의 개선을 시도하였다. 그리고 TFTs 소자의 출력 특성 및 전이 특성을 평가를 하였고, 소자의 field effect mobility의 값이 향상을 하였다. 또한 Temperature, Bias Temperature stability의 조건에서 안정성을 평가를 하였다. 이러한 interface treatment는 안정성의 향상을 시킴으로써 대면적 디스플레의 적용에 비정질 실리콘을 대체할 유력한 물질이라고 생각된다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.3
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• pp.228-238
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• 2002

This paper presents a digital controller of the electronic ballast using high frequency modulation method for the metal halide lamp. The proposed controller includes the control algorithm for soft starting, no load protection, over current protection and power control. The proposed digital controller, moreover, has the high frequency modulation scheme and the tracking algorithm to avoid acoustic resonance phenomena. For the math production with the low cost using the ASICs (Application Specific Integrated Circuit), the proposed digital controller has been designed with the FPGAs(Field Programmable Gate array) only, without any microprocessor. In this paper, the detail digital control algorithms are described and the experimental results of prototype 150w metal halide electronic ballast are presented.

• The Journal of the Acoustical Society of Korea
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• v.30 no.8
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• pp.436-445
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• 2011

In this paper, equivalent properties of 2-2 mode piezocomposites were studied. Variation of the properties of 2-2 mode piezocomposites was analyzed by the finite element method, and the result was compared with experimental measurement data to confirm the validity of the analysis. The equivalent properties of a single phase material to represent the piezocomposite composed of PZT-5H and polymer were derived by the asymptotic averaging method. Accuracy of the derived equivalent properties was enhanced by minimizing the discrepancy between the impedance spectra of full 2-2 piezocomposite and equivalent single phase material resonators of various vibration modes by the least square method. The equivalent properties of 2-2 piezocomposites derived in this study can be utilized to the design of diverse acoustic sensors.