• 비파괴검사학회지
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• 제37권1호
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• pp.37-43
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• 2017

초음파탐상법을 이용하여 마이크로미터의 크기 작은 결함을 검출하기 위해서는 높은 공진주파수와 큰 분해능의 초음파 변환기가 필요하다. 초음파 변환기의 공진주파수와 분해능은 변환기에 사용된 압전소자의 두께, 후면재 및 탐상 시스템 간의 전기 임피던스 정합과 밀접한 관련이 있으며, 이 중 전기 임피던스 매칭은 초음파 변환기와 초음파탐상 시스템 사이의 서로 다른 입 출력단을 연결하는 과정에서, 두 연결단의 전기적 임피던스 차이에 의한 에너지 반사와 손실을 줄이는 중요한 역할을 한다. 임피던스 정합에서 흔히 많이 사용하는 방법은 LC-정합회로이다. 이러한 LC-정합을 통해 탐상 시스템과 초음파 변환기의 전기 임피던스를 $50{\Omega}$으로 맞추어 두 연결단 사이의 임피던스 차이를 보정해 줌으로서 초음파 변환기에서 발생되는 전기신호의 손실을 줄 수 있다. 본 연구에서는 15 MHz의 공진주파수를 가지는 광대역 수침형 초음파 탐촉자를 제작하고 광대역 특성을 갖는 초음파 변환기를 위한 LC 임피던스 정합법을 적용하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 학술대회 논문집 전문대학교육위원
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• pp.35-39
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• 2001

The purpose of this paper is improvement the piezoelectric of Polyvinylidene fluoride(PVDF) organic thin films is fabricated by vapor deposition method. The piezoelectric of PVDF organic thin films attributed to dipole orientation in crystalline region. Also, the piezoelectric characteristic reduced that dipole moments orientation in crystalline region interfered with impurity carriers. Therefore, PVDF organic thin films fabricated with high substrate temperature condition for crystallinity improvement. The crystallinity of PVDF organic thin films fabricated by this condition increase from 47 to 67.8%. The ion density of PVDF organic thin films fabricated by substrate temperature variation from $30^{\circ}C$ to $105^{\circ}C$ decreased from $1.62{\times}10^{16}cm^3$ to $6.75{\times}10^{11}cm^3$ when temperature and frequency were $100^{\circ}C$, 10Hz, respectively. The $d_{33}$ and piezo-voltage coefficient of PVDF organic thin films increased from 20pPC/N to 33pC/N and $162.9{\times}10^{-3}V{\cdot}m/N$ to $283.2{\times}10^{-3}V{\cdot}m/N$, respectively. For the sake of the applications of piezoelectric sensor, we analyzed the output voltage characteristic as a function of the distance between an oscillator of 28kHz and PVDF organic thin film transducer. From this, we found that the output voltage is inversely proportional to the distance. At this time, the period was about $35.798{\mu}s$ and equal the oscillator frequency.

• 한국전기전자재료학회논문지
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• 제28권2호
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• pp.69-74
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• 2015

Recently, energy harvesting technology is increasing due to the fossil fuel shortages. Energy harvesting is generating electrical energy from wasted energies as sunlight, wind, waves, pressure, and vibration etc. Energy harvesting is one of the alternatives of fossil fuel. One of the energy harvesting technologies, the piezoelectric energy harvesting has been actively studied. Piezoelectric generating uses a positive piezoelectric effect which produces electrical energy when mechanical vibration is applied to the piezoelectric device. Piezoelectric energy harvesting has an advantage in that it is relatively not affected by weather, area and place. Also, stable and sustainable energy generation is possible. However, the output power is relatively low, so in this paper, newly designed honeycomb shaped piezoelectric energy harvesting device for increasing a generating efficiency. The output characteristics of the piezoelectric harvesting device were analyzed according to the change of parameters by using the finite element method analysis program. One model which has high output voltage was selected and a prototype of the honeycomb shaped piezoelectric harvesting device was fabricated. Experimental results from the fabricated device were compared to the analyzed results. After the AC-DC converting, the power of one honeycomb shaped piezoelectric energy harvesting device was measured 2.3[mW] at road resistance 5.1[$K{\Omega}$]. And output power was increased the number of harvesting device when piezoelectric energy harvesting device were connected in series and parallel.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.152-152
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• 2016

Anodizing is a technology to generate thicker and high-quality films than natural oxide films by treating metals via electrochemical methods. It is a technique to develop metals for various uses, and extensive research on the commercial use has been performed for a long time. Aluminum anodic oxide (AAO) is generate oxide films, whose sizes and characteristics depending on the types of electrolytes, voltages, temperatures and time. Electrochemical manufacturing method of nano structure is an efficient technology in terms of cost reduction, high productivity and complicated shapes, which receives the spotlight in diverse areas. The sulfuric acid was used as an anodizing electrolyte, controlling its temperature to $10^{\circ}C$. The anode was 5083 Al alloy with dimension of $5(t){\times}20{\times}20mm$ while the cathode was the platinum. The distance between the anode and the cathode was maintained at 3 cm. Agitation was introduced by magnetic stirrer at 300 rpm to prevent localized temperature rise that hinders stable growth of oxide layer. In order to observe surface characteristics with applied current density, the electrolyte temperature, concentration was maintained at constant condition for $10^{\circ}C$, 10 vol.%, respectively. To prevent hindrance of stable growth of oxide layer due to local temperature increase during the experiment, stirring was maintained at constant rate. In addition, using galvanostatic method, it was maintained at current density of $10{\sim}30mA/cm^2$ for 40 minutes. The cavitation experiment was carried out with an ultrasonic vibratory apparatus using piezo-electric effect with modified ASTM-G32. The peak-to-peak amplitude was $30{\mu}m$ and the distance between the horn tip and specimen was 1 mm. The specimen after the experiment was cleaned in an ultrasonic, dried in a vacuum oven for more than 24 hours, and weighed with an electric balance. The surface damage morphology was observed with 3D analysis microscope. As a result of the investigation, differences were observed surface hardness and anti-cavitation characteristics depending on the development of oxide film with applied current density.

• 한국세라믹학회지
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• 제50권6호
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• pp.498-503
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• 2013

Over the past decade, the feasibility of using ink-jet printing for the decoration of porcelain tiles has been explored, and significant advances have been made regarding the technologies underlying printing system and materials. An ink-jet printing system for porcelain tiles has many advantages compared with a conventional printing system, including the following: (1) it is a digital process; (2) it uses non-contact printing; (3) it allows random image generation; (4) it is a highly efficient process (reduced production cost); (5) it offers massive and continuous production; and (6) it uses inorganic pigment colorants. For these reasons, ink-jet printing systems for porcelain tiles have been commercialized and are at present rapidly spreading toceramics-leading countries such as Spain, Italy, China and Japan. We also developed a proprietary system involving a piezo-electric drop-on-demand method and an ink-circulation step. The resolution of this system is greater than 360 dpi after a heat treatment and the maximum printable width is 600 mm, even when setting the printing head unit with four digital colors (cyan, magenta, yellow, and black). In addition, we systematically developed ceramic colorant-containing inks and tile-printing technology applicable to our ink-jet printing system.

• 한국전기전자재료학회논문지
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• 제26권8호
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• pp.635-639
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• 2013

Generating output characteristics of a EYE-type piezoelectric generator depending on ceramic size and materials of the elastic body were studied. EYE-type piezoelectric-generating device consist of the ceramic was attached between the both elastic body. piezoelectric-generating is that if the tension occurred at both ends of an elastic body, the piezoelectric effect occurs at ceramics through the form change of the elastic body. The structure of this EYE-type generator use various area. than a existing type generator, because the ceramic position of the directly force at does not apply. Resonance and output characteristics of the generator were analyzed by using FEM program. Generators were fabricated on the basis of analyzed results and attached on a frequency controllable vibrator to measure output characteristics. Also, the experimental results were compared with the simulated results. As a result, output characteristics of the generator increased depending on the increase in ceramic thickness. In case of increase in ceramic width, resonance frequency of the generator also decreased.

• Smart Structures and Systems
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• 제26권3호
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• pp.331-343
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• 2020

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe₂O₄ and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

• 대한기계학회논문집B
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• 제35권10호
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• pp.1041-1046
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• 2011

본 연구에서는 레이저 쇼크 피닝으로부터 생성되는 마이크로 충격파를 정량적으로 측정하고 그 특성을 분석하였다. 레이저 쇼크 피닝은 금속 재료에서 압축 응력을 생성시키며 그 크기가 표면에서 극대화되는 특징을 가지고 있다. 펄스 Nd:YAG 레이저를 이용하여 스틸표면에 피닝 공정을 수행하였고 이에 따른 마이크로 충격파의 정량화 및 재료의 기계적 성질 변화에 대해 평가하였다. 실험적 접근으로 피에조소자를 사용하였으며 이를 통한 실제 충격파의 정량화를 제시하였다. 또한 재료 구조 특성, 재료 강도, 인장 시험 등의 기계적 특성을 분석하였다.

• 대한심미치과학회지
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• 제28권2호
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• pp.64-73
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• 2019

심한 치조골의 위축과 흡수로 인한 형태학적 변화는 임플란트의 성공적인 식립과 임플란트의 골유착에 영향을 미친다. 이를 극복하기 위한 다양한 골증대술 중 치조제분할술은 좁은 치조골 폭을 성공적으로 증대시키는 수술방법으로 보고되었다. 또한 다양하게 개발되는 임플란트 디자인과 치조제 팽창 기구 등은 심하게 흡수된 위축된 하악부위에서도 협측골 파절을 최소화할 수 있다. 가철성 부분의치의 사용으로 심하게 흡수된 하악 구치부에 치조제 분할술과 최소 크기의 블록형 골이식술을 이용해 한개의 스크류로 수용부의 고정을 획득한 후 동시적 접근법을 이용한 골이식 증례를 보고 하고자 한다. 보철과와 치주과의 협업으로 환자의 기능과 심미를 회복해준 증례로 사료된다.

• 한국결정학회지
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• 제8권1호
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• pp.26-32
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• 1997

수열법을 이용하여 압전수정을 성장하고 각종 성장결함을 분석하였다. 4 중량퍼센트 NaOH, 성장온도 $340-360^{\circ}C$, 온도구배 $20-40^{\circ}C$의 성장조건에서 (0001)방향의 ZY 종자결정, 합성수정을 원료로 하였을 경우 성장속도는 0.25-0.65 mm/day 였다. 원료로써 합성수정을 사용하고 저전위 종자결정 위에서 수평 종자결정 배치법으로 성장된 압전수정의 전위밀도는 20.0개/$cm^2$, 에치채널 밀도는 5.0개/$cm^2,\;10\mu$ 이상의 함유물 농도는 2.4개/$cm^3$, 알파값은 0.019였으며, IEC 758규격에 의한 등급분류는 에치채널 밀도 1등급, 함유물 농도 Ia등급, 알파값 A등급이었다.