• International Journal of Internet, Broadcasting and Communication
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• 제4권1호
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• pp.1-2
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• 2012

A speaker is a system which produces sound through electromechanical operations. It transforms electronic signals into audible sound signals. Almost all speakers are three dimensional. These days, many mobile electronic devices such as mobile electronic devices have become smaller and thinner. A problem with this miniaturization, however, is that the volume of speakers has also decreased. In contrast to conventional three dimensional speakers, we have invented a new type of two dimensional flexible speaker by utilizing the reverse piezoelectric effect.

• 한국전기전자재료학회논문지
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• 제21권6호
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• pp.503-508
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• 2008

In order to reduce the piezoelectric field originated from the well layer which resides in InGaN/GaN light emitting diode, InGaN/GaN superlattice buffer layers were grown at the bottom and the top of the active layer. Measuring the photoluminescence spectra with different reverse bias voltages clearly revealed the condition of the flat band under which the transition energy is maximized and the linewidth is minimized. Accordingly, the piezoelectric field of $In_{0.15}Ga_{0.85}N$ in our sample was estimated as -1.08 MV/cm. It is less than half the value reported in the previous studies, and it is evidenced that the strain has reduced due to the superlattice buffer layers.

• 한국산업융합학회 논문집
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• 제26권1호
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• pp.193-199
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• 2023

In this study, an analysis was conducted to analyze the structural stability of the piezoelectric power generation module and to determine the optimal burying hole interval for concrete, the installation site of the power generation module. A piezoelectric element refers to a functional ceramic having a piezoelectric direct effect that converts mechanical energy into electrical energy and a piezoelectric reverse effect. In the analysis of the piezoelectric power generation module, the load condition was applied with about 16 tons and a total of 10 wheels in consideration of the container trailer. The purpose was to evaluate the stability of major components of the piezoelectric power generation module through finite element analysis. In order to determine the optimal burying location of the concrete ground for burying the piezoelectric power generation module, the stability of the ground structure according to the distance of the holes was determined. As a result of the analysis, the maximum stress of the piezoelectric power generation module was generated in the support spring, showing a stress of about 276.7 MPa. It was found that the spacing of holes for embedding the piezoelectric power generation module should be set to a minimum of 100 mm or more.

• 한국전기전자재료학회논문지
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• 제18권11호
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• pp.1048-1055
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• 2005

The formula to calculate a variation of optical path length of single crystal by the electric field was derived by this study. The formula was applied to $Bi_{12}SiO_{20}$ single crystal. The results are as follows. In case of the applied electric field in the body diagonal direction and the passing light along the same direction, the variation of optical path length had the largest value. The symmetry of the space distribution of optical path length satisfied $E3C_2\;8C_3$, the set of elements of the symmetry of $Bi_{12}SiO_{20}$ single crystal. The property which gave the largest influence to the variation of optical path length is the strain of length by the Inverse piezoelectric effect. The second influence, is the variation of the refractive index by the electro-optic effect. The variation of optical path length by the inverse piezoelectric effect and by the electro-optic effect have a reverse sign each other.

• Smart Structures and Systems
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• 제25권1호
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• pp.97-104
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• 2020

Due to the superior properties of nanoparticles, using them has been increased in concrete production technology. In this study, the effect of zinc oxide (ZnO) nanoparticles on the mechanical and smart properties of concrete was studied. At the first, the ZnO nanoparticles are dispersed in water using shaker, magnetic stirrer and ultrasonic devices. The nanoparticles with 3.5, 0.25, 0.75, and 1.0 volume percent are added to the concrete mixture and replaced by the appropriate amount of cement to compare with the control sample without any additives. In order to study the mechanical and smart properties of the concrete, the cubic samples for determining the compressive strength and cylindrical samples for determining tensile strength with different amounts of ZnO nanoparticles are produced and tested. The most important finding of this paper is about the smartness of the concrete due to the piezoelectric properties of the ZnO nanoparticles. In other words, the concrete in this study can produce the voltage when subjected to mechanical load and vice versa it can induce the mechanical displacement when subjected to external voltage. The experimental results show that the best volume percent for ZnO nanoparticles in 28-day samples is 0.5%. In other words, adding 0.5% ZnO nanoparticles to the concrete instead of cement leads to increases of 18.70% and 3.77% in the compressive and tensile strengths, respectively. In addition, it shows the best direct and reverse piezoelectric properties. It is also worth to mention that adding 3.5% zinc oxide nanoparticles, the setting of cement is stopped in the concrete mixture.

• 전기전자학회논문지
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• 제22권1호
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• pp.205-208
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• 2018

본 연구에서는 상시불통형 p-AlGaN-게이트 질화갈륨(GaN) 이종접합 트랜지스터의 신뢰성 평가를 위한 가속열화 시험 조건을 수립하기 위해 게이트 전압 열화 시험을 진행하였다. 상시불통형 트랜지스터의 동작 조건을 고려하여 기존 상시도통형 쇼트키-게이트 소자평가에 사용되는 게이트 역전압 시험과 더불어 순전압 시험을 수행하여 열화특성을 분석하였다. 기존 상시도통형 소자와 달리 상시불통형 소자에서는 게이트 역전압 시험에 의한 열화는 관찰되지 않은 반면, 게이트 순전압 시험에서 심한 열화가 관찰되었다. 상시불통형 질화갈륨 전력 반도체 소자의 신뢰성 평가에 게이트 순전압 열화 시험이 포함되어야 함을 제안한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.124-124
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• 2010

Much interest has been focused on InGaN-based materials and their quantum structures due to their optoelectronics applications such as light emitting diode (LED) and photovoltaic devices, because of its high thermal conductivity, high optical efficiency, and direct wide band gap, in spite of their high density of threading dislocations. Build-in internal field-induced quantum-confined Stark effect in InGaN/GaN quantum well LED structures results in a spatial separation of electrons and holes, which leads to a reduction of radiative recombination rate. Therefore, many growth techniques have been developed by utilizing lateral over-growth mode or by inserting additional layers such as patterned layer and superlattices for reducing threading dislocations and internal fields. In this work, we investigated various characteristics of InGaN multiple quantum wells (MQWs) LED structures grown on selectively wet-etched porous (SWEP) GaN template layer and compared with those grown on non-porous GaN template layer over c-plane sapphire substrates. From the surface morphology measured by atomic force microscope, high resolution X-ray diffraction analysis, low temperature photoluminescence (PL) and PL excitation measurements, good structural and optical properties were observed on both LED structures. However, InGaN MQWs LED structures grown on SWEP GaN template layer show relatively low In composition, thin well width, and blue shift of PL spectra on MQW emission. These results were explained by rough surface of template layer, reduction of residual compressive stress, and less piezoelectric field on MQWs by utilizing SWEP GaN template layer. Better electrical properties were also observed for InGaN MQWs on SWEP GaN template layer, specially at reverse operating condition for I-V measurements.

• 한국산학기술학회논문지
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• 제20권3호
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• pp.513-519
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• 2019

배수 시스템에서 오염퇴적물이 장기간 발생하게 되면 배수관 폐색현상을 일으켜 유지관리가 어렵고 배수관의 잔류수압이 커져 파손의 위험이 있다. 이에 본 연구에서는 PVDF 필름에 의해 발생하는 진동에너지를 활용하여 물리/화학적 폐색에 의한 터널배수 시스템 폐색을 감소시키는 시스템을 구축하였다. 또한, PVDF 필름을 기존 배수재와 융합한 하이브리드 배수재와 역압전 효과를 일으킬 수 있는 구동장치로 배수재 유지관리 시스템을 개발하였다. 터널 배수관 유지관리 성능을 고찰하기 위하여 실내조건에서 오염퇴적물을 모사하고 진동조건에서 폐색저감 효율을 관찰하였다. 그 결과 개발된 PVDF 필름 구동 장비로 20분 내외의 진동에너지를 발생하여 씻겨나간 오염퇴적물의 잔류면적을 측정한 결과 74.62%의 오염퇴적물 제거효과를 볼 수 있었다. 현장 적용성 평가를 위하여 PVDF 필름을 배수관에 부착하고 장기적으로 음압측정을 하여 실내실험으로부터의 측정 음압과 비교하여 현장실험의 대응율을 제시하였다. 현장실험은 터널 배수관으로부터 내부에 폐색이 주로 발생하는 구간인 종배수관과 횡배수관에 PVDF 필름을 부착하였고 터널현장 음압측정 실험으로부터 오염물퇴적 제거효율은 실내실험대비 현장 대응율은 90% 이상으로 확인됐다.