• 한국전산구조공학회논문집
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• 제23권1호
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• pp.9-15
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• 2010

본 논문에서는 압전복합재 작동기가 표면에 부착된 Hull 구조물의 유한요소모델을 구성하여 동적 특성을 고찰하였으며, 구조물의 진동제어 특성을 평가하였다. Hull 구조물은 양 끝이 닫혀있는 실린더형 쉘 구조물을 고려하였으며, 항공기 동체나 잠수함과 같은 수중 구조물 등의 간단한 모델로 사용될 수 있다. 구조물의 진동제어를 위해 최근 NASA Langley 연구소에서 개발된 압전복합재인 Macro-Fiber Composite(MFC)를 적용하였다. MFC는 압전세라믹 섬유를 이용하여 유연성을 향상시키고, 맞물림 전극을 적용하여 면내 방향에서 큰 압전효과를 구현할 수 있도록 하였다. 유한요소모델을 바탕으로 구조물의 지배방정식을 도출하였으며, 동적 특성을 해석하여 실제 제작된 구조물의 실험결과와 비교 검증하였다. 최적제어 알고리즘을 구성하여 구조물의 진동제어 성능을 평가하였으며, 효과적으로 구조물의 진동을 제어할 수 있음을 확인하였다.

• 비파괴검사학회지
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• 제32권5호
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• pp.585-596
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• 2012

PVDF와 P(VDF-TrFE)로 대별되는 압전고분자는 종래의 대표적인 압전재료인 PZT에 비해 전기음향변환효율이 떨어지며 내부손실이 큰 단점은 있으나, 음향임피던스가 물 또는 생체와 비슷하고 수신효율이 우수하며 광대역 특성을 나타내는 등의 장점을 가진 재료이다. 또한 다른 압전재료에 비해 얇은 막으로의 제작이 쉽고, 그 막은 유연하므로 복잡한 곡면을 갖는 고주파 초음파 트랜스듀서 재료로 유용하다. 그러한 특성은 생의학적 응용에 적합한바, 다양한 형태의 초음파 트랜스듀서가 연구 개발되어져 왔다. 본 논문에서는 먼저, 압전고분자막을 이용하여 초음파 트랜스듀서를 설계 제작하는데 있어서 고려해야할 몇 가지 주요사항을 기술하고, KLM 모델을 사용한 해석을 통하여 그 고려사항들이 트랜스듀서의 동작에 미치는 영향을 파악하였다. 다음으로, 의학적 또는 생물학적 응용을 목적으로 초음파 영상을 얻고 있는 몇몇 주요 응용분야에서 사용되는 압전고분자 트랜스듀서의 구조와 그것을 이용하여 얻은 영상의 특징에 대하여 간략히 해설하였다.

• Smart Structures and Systems
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• 제9권6호
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• pp.505-534
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• 2012

The present work deals with second order statistics of post buckling response of piezoelectric laminated composite cylindrical shell panel subjected to hygro-thermo-electro-mechanical loading with random system properties. System parameters such as the material properties, thermal expansion coefficients and lamina plate thickness are assumed to be independent of the temperature and electric field and modeled as random variables. The piezoelectric material is used in the forms of layers surface bonded on the layers of laminated composite shell panel. The mathematical formulation is based on higher order shear deformation shell theory (HSDT) with von-Karman nonlinear kinematics. A efficient $C^0$ nonlinear finite element method based on direct iterative procedure in conjunction with a first order perturbation approach (FOPT) is developed for the implementation of the proposed problems in random environment and is employed to evaluate the second order statistics (mean and variance) of the post buckling load of piezoelectric laminated cylindrical shell panel. Typical numerical results are presented to examine the effect of various environmental conditions, amplitude ratios, electrical voltages, panel side to thickness ratios, aspect ratios, boundary conditions, curvature to side ratios, lamination schemes and types of loadings with random system properties. It is observed that the piezoelectric effect has a significant influence on the stochastic post buckling response of composite shell panel under various loading conditions and some new results are presented to demonstrate the applications of present work. The results obtained using the present solution approach is validated with those results available in the literature and also with independent Monte Carlo Simulation (MCS).

• 한국음향학회지
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• 제21권2호
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• pp.150-159
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• 2002

광대역 소음저감을 위한 압전지능패널에 대한 실험적 연구를 수행하였다. 압전지능패널은 기본적으로 압전재료를 부착한 평판구조물에 션트회로를 연결하고 흡음재들을 부가한 구조물이다. 압전감쇠와 수동적 특성을 혼용하여 중 주파수영역에서 흡음재의 수동적 특성을 이용하고 저주파수 영역의 공진주파수에서는 압전감쇠를 적용하여 소음저감시키는 개념이다. 저주파수 공진에서의 소음저감을 위하여 측정한 전기적 임피던스 모델을 이용하는 압전감쇠를 적용하였다. 압전감쇠를 위한 공진 션트회로는 직렬로 연결된 저항과 인덕터로 구성되었으며, 저항과 인덕터는 회로에서 소산되는 에너지가 최대가 될 수 있는 값으로 최적설계하였다. 압전지능패널의 전달소음저감 성능은 음향터널을 사용하여 실험을 수행하였다. 음향터널은 사각단면 형태이며 소음원으로 터널의 한 쪽 끝에 스피커가 설치되었다. 패널들을 터널의 중앙에 설치하여 투과 음압을 측정하였다. 흡음재와 공기층을 갖는 압전이중지능패널은 수동적 특성에 의해 저주파수 영역의 공진주파수를 제외한 중주파수 영역에서 뚜렷한 소음저감 효과를 나타내었다. 압전감쇠를 통하여, 공진주파수에서의 좋은 소음저감을 얻었다. 압전감쇠와 수동적 방법을 혼용하는 압전지능 패널은 넓은 주파수 영역에서의 소음저감을 위한 유망한 기술이다.

• 한국전자통신학회논문지
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• 제8권12호
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• pp.1875-1882
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• 2013

마이크로 어레이 기술은 유전자 네트워크의 순서 와 게놈의 통합과 같은 많은 업적을 기여하고 있으며, 이러한 기술은 유전자 발현의 패턴을 조사하기 위한 수단 등으로 잘 확립 되어있다. DNA 마이크로배열은 Affymetric 칩을 이용하여 대량의 DNA 서열을 합성 할 수 있는데 기존의 DNA 어레이 스포팅에는 일반적으로 접촉방식과 압전전자 방법등 두가지 유형이 있다. 접촉방법은 유리 슬라이드 표면과 접촉하도록 스포팅핀을 사용하는데 이 방법은 표면 매트릭스의 손상이나 상처가 발생할 수 있어 단백질이 오염 되거나 특정 결합을 방해할 위험이 있다. 반면에 압전전자 방법은 대량 생산이 가능함에도 불구하고 결과를 인쇄할 분석기가 필요하므로 현재 실험실 내에서만 수행 가능한 실정이다. 본 논문에서 유리 슬라이드 표면에 닿지 않고 지속적으로 일관성 있게 스포팅이 가능하도록 하는 진보된 방법을 제시한다.

• Macromolecular Research
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• 제17권3호
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• pp.197-202
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• 2009

Solution-based, direct-write patterning by an automated, computer-controlled, inkjet technique is of particular interest in a wide variety of industrial fields. We report the construction of three-dimensional (3D), micro-patterned structures by polymer inkjet printing. A piezoelectric, drop-on-demand (DOD) inkjet printing system and a common polymer, PVA (poly(vinyl alcohol)), were explored for 3D construction. After a systematic preliminary study with different solvent systems, a mixture of water and DMSO was chosen as an appropriate solvent for PVA inks. The use of water as a single solvent resulted in frequent PVA clogging when the nozzles were undisturbed. Among the tested polymer ink compositions, the PVA inks in a water/DMSO mixture (4/1 v/v) with concentrations of 3 to 5 g/dL proved to be appropriate for piezoelectric DOD inkjet printing because they were well within the proper viscosity and surface tension range. When a dot was printed, the so-called 'coffee-ring effect' was significant, but its appearance was not prominent in line printing. The optimal polymer inkjet printing process was repeated slice after slice up to 200 times, which produced a well-defined, 3 D micro-patterned surface. The overall results implied that piezoelectric DOD polymer inkjet printing could be a powerful, solid-freeform, fabrication technology to create a controlled 3D architecture.

• Journal of Periodontal and Implant Science
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• 제42권3호
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• pp.88-94
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• 2012

Purpose: The use of appropriate instruments to clean surfaces with minimal change, is critical for the successful maintenance of a dental implant. However, there is no consensus about the type and methodology for such instruments. The aim of this study was to characterize changes in the roughness of titanium surfaces treated by various scaling instruments. Methods: Thirty-seven identical disks (5 mm in diameter) were investigated in this study. The specimens were divided into eight groups according to the types of instrumentation and the angle of application. Ultrasonic scaling systems were applied on a titanium disk to simulate standard clinical conditions. The equipment included a piezoelectric ultrasonic scaler with a newly developed metallic tip (NS group), a piezoelectric ultrasonic scaler with a conventional tip (CS group), a piezoelectric root planer ultrasonic scaler with a conventional tip (PR group), and a plastic hand curette (PH group). In addition, the sites treated using piezoelectric ultrasonic scaler systems were divided two sub-groups: 15 and 45 degrees. The treated titanium surfaces were observed by scanning electron microscopy (SEM), and the average surface roughness (Ra) and mean roughness profile depth (Rz) were measured with a profilometer. Results: SEM no significant changes in the titanium surfaces in the NS group, regardless of the angle of application. The PH group also showed no marked changes to the titanium surface, although some smoothening was observed. All CS and PR sites lost their original texture and showed irregular surfaces in SEM analysis. The profilometer analysis demonstrated that the roughness values (Ra and Rz) of the titanium surfaces increased in all, except the PH and NS groups, which showed roughness decreases relative to the untreated control group. The Ra value differed significantly between the NS and PR groups (P<0.05). Conclusions: The results of this study indicated that changes in or damage to titanium surfaces might be more affected by the hardness of the scaler tip than by the application method. Within the limitations of this study, the newly developed metallic scaler tip might be especially suitable for peri-implant surface decontamination, due to its limited effects on the titanium surface.

• 대한기계학회논문집A
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• 제30권4호
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• pp.364-372
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• 2006

In this paper, we present a finger tip tactile sensor which can detect contact normal force as well as slip. The sensor is made up of two different materials, such as polyvinylidene fluoride (PVDF) known as piezoelectric polymer, and pressure variable resistor ink. In order to detect slip on the surface of the object, two PVDF strips are arranged along the normal direction in the robot finger tip and the thumb tip. The surface electrode of the PVDF strip is fabricated using silk-screening technique with silver paste. Also a thin flexible force sensor is fabricated in the form of a matrix using pressure variable resistor ink in order to sense the static force. The developed tactile sensor is physically flexible and it can be deformed three-dimensionally to any shape so that it can be placed on anywhere on the curved surface. In addition, a tactile sensing system is developed, which includes miniaturized charge amplifier to amplify the small signal from the sensor, and the fast signal processing unit. The sensor system is evaluated experimentally and its effectiveness is validated.

• 센서학회지
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• 제17권2호
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• pp.127-132
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• 2008

The effect of $CeO_2$ as a sintering additive on the microstructure and the piezoelectric property of yPb$(Sb_{0.5}Nb_{0.5})O_3$-(1-y)Pb$(Zr_{0.52}Ti_{0.48})O_3$ ($0{\leq}y{\leq}0.1$, PSN-PZT) for a hypersonic sound speaker (HSS) application was investigated. The samples were sintered at $1250^{\circ}C$ for 2 h. The crystal structure and surface morphology of the samples were examined using XRD and FE-SEM, respectively. Study on the influence of $CeO_2$ additives on the dielectric and piezoelectric properties indicated that the $CeO_2$-added PSN-PZT system had a high piezoelectric properties. The optimized results of ${\varepsilon}_r=1209$, $K_p$=52% $d_{33}$=351(pC/N) and $Q_m$=1230.16 were obtained at 0.4 wt.% $CeO_2$-added PSN-PZT.

• Smart Structures and Systems
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• 제18권3호
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• pp.501-523
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• 2016

Electromechanical impedance (EMI) based structural health monitoring is performed by measuring the variation in the impedance due to the structural local damage. The impedance signals are acquired from the piezoelectric patches that are bonded on the structural surface. The impedance variation, which is directly related to the mechanical properties of the structure, indicates the presence of local structural damage. Two traditional EMI-based damage detection methods are based on calculating the difference between the measured impedance signals in the frequency domain from the baseline and the current structures. In this paper, a new structural damage detection approach by analyzing the time domain impedance responses is proposed. The measured time domain responses from the piezoelectric transducers will be used for analysis. With the use of the Time Frequency Autoregressive Moving Average (TFARMA) model, a damage index based on Singular Value Decomposition (SVD) is defined to identify the existence of the structural local damage. Experimental studies on a space steel truss bridge model in the laboratory are conducted to verify the proposed approach. Four piezoelectric transducers are attached at different locations and excited by a sweep-frequency signal. The impedance responses at different locations are analyzed with TFARMA model to investigate the effectiveness and performance of the proposed approach. The results demonstrate that the proposed approach is very sensitive and robust in detecting the bolt damage in the gusset plates of steel truss bridges.