• The Journal of the Acoustical Society of Korea
• /
• v.13 no.1E
• /
• pp.45-54
• /
• 1994

Characteristics of a piezoelectric material are evaluated to pick up the optimal crystal cut and propagation direction for a SAW device. For the piezoelectric single crystal $LiTaO_4$, such items are investigated as the Rayleigh wave velocity, the electromechanical coupling factor, the surface permittivity, the frequency-temperature coefficient, the air loading attenuation, the pure mode propagation, the beam steering and the misalignment sensitivity. Theoretical calculations reveal that Y-cut and Z-propagation is the optimal SAW propagation path. The results are confirmed through experiments. The method empolyed in this paper is applicable to other crystals, too, either single or poly crystals.

• Journal of KSNVE
• /
• v.6 no.1
• /
• pp.65-70
• /
• 1996

The sensor response of a piezoelectric transducer embedded in a fluid loaded structure is modeled using a hybrid numerical approach. The structure is excited by an obliquely incident acoustic wave. Finite element modeling in the structure and fluid surrounding the transducer region, is used and a plane wave representation is exploited to match the displacement field at the mathematical boundary. On this boundary, continuity of field derivatives is enforced by using a penalty factor and to further achieve transparency at the mathematical boundary, drilling degrees of freedom (d.o.f.) are introduced to ensure continuity of all derivatives. Numerical results are presented for the sensor response and it is found that the sensor at that location is not only non-intrusive but also sensitive to the characteristic of the structure.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.9
• /
• pp.985-996
• /
• 2012

An unsteadily propagating permeable crack in piezoelectric materials (PMs) under anti-plane shear mechanical loading and in-plane electric loading is studied. The equilibrium equations for a transiently propagating crack in a PM are developed, and the solutions on the stress and displacement fields for a permeable crack though an asymptotic analysis are obtained. The influences of piezoelectric constant, dielectric permittivity, time rate of change of the crack tip speed and time rate of change of stress intensity factor on the stress and displacement fields at the transiently propagating crack tip are explicitly clarified. By using the stress and displacements, the characteristics of the stress and displacement at a transiently propagating crack tip in a PM are discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.662-667
• /
• 2005

Nonlinear dynamics of active piezolaminated plates are investigated with respect to the thermopiezoelastic behaviors. For largely deformed structures with small strain, the incremental total Lagrangian formulation is presented based on the virtual work principles. A multi field layer wise finite shell element is proposed for assuring high accuracy and non-linearity of displacement, electric and thermal fields. For dynamic consideration of thermopiezoelastic snap through phenomena, the implicit Newmark's scheme with the Newton-Raphson iteration is implemented for the transient response of various piezolaminated models with symmetric or eccentric active layers. The bifurcate thermal buckling of symmetric structural models is first investigated and the characteristics of piezoelectric active responses are studied for finding snap through piezoelectric potentials and the load path tracking map. The thermoelastic stable and unstable postbuckling, thermopiezoelastic snap through phenomena with several attractors are proved using the nonlinear time responses for various initial conditions and damping loss factors. Present results show that thermopiezoelastic snap through phenomena can result in the difficulty of buckling and postbuckling control of intelligent structures.

• The Journal of the Acoustical Society of Korea
• /
• v.21 no.1
• /
• pp.56-61
• /
• 2002

In piezoelectric ultrasonic linear array transducers widely used for diagnosis, the cross talk caused by the structural cross-coupling between adjacent elements inside the transducer affects the probe performance in a significant manner. In this study, we constructed a finite element model of a piezoelectric ultrasonic transducer, and analyzed its cross talk level with respect to the shape of and materials inside the kerf, The results of this work can be utilized in optimal design of the transducers for medical diagonosis and treatment as well as W applications.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.480-483
• /
• 2008

This paper reports a piezoelectric paper made with cellulose. Since cellulose has merits in terms of biodegradability, biocompatibility, abundance in nature, lightweight and cheap, piezoelectric paper can bring a broad technological impact in many areas, for example, sensors, actuators, speakers, microphones and microelectromechanical systems. Fabrication and characterization of the piezoelectric paper are illustrated and its possibility for acoustic applications is addressed with some preliminary device demonstrations.

• Proceedings of the KIPE Conference
• /
• 2003.07b
• /
• pp.616-620
• /
• 2003

액정 디스플레이의 백라이트에 사용되는 냉음극 방전램프(CCFL: Cold Cathode Fluorescent Lamp) 구동 인버터의 설계함에 있어 압전 변압기(Piezoelectric Transformer)를 사용하였으며, 파라미터 선정 및 최적화를 하여 실험을 통해 검증하였다. 적용한 압전 인버터로는 푸시-풀(Push-pull)과 하프-브리지(Half-bridge) 회로이며, 휘도 제어기법으로는 아날로그(Analog)와 버스트(Burst) 방법을 사용하였다. 푸시-풀 인버터의 경우 아날로그 제어방식으로 제어전압 2.5-4.5V에서 출력전류 1-6mA(최소)로 휘도 0-100$\%$ 특성을 보였다. 입출력 효율로 18.6(최소)-90.3(최대)$\%$를 얻었으며, 버스트 제어방식에서는 듀티비 50-5$\%$에서 1-6mA의 제어 성능을 보였다. 인버터의 입출력 효율은 13.6(최소)-82.1(최대)$\%$를 얻었다.

• Proceedings of the KIPE Conference
• /
• 2003.11a
• /
• pp.197-201
• /
• 2003

액정 디스플레이의 백라이트에 사용되는 냉음극 방전램프(CCFL: Cold Cathode Fluorescent Lamp) 구동 인버터의 설계함에 있어 압전 변압기(Piezoelectric Transformer)를 사용하였으며, 파라미터 선정 및 최적화를 하여 실험을 통해 검증하였다. 적용한 압전 인버터로는 푸시-풀(Push-pull)과 하프-브리지(Half-bridge) 회로이며, 휘도 제어기법으로는 아날로그(Analog)와 버스트(Burst) 방법을 사용하였다. 푸시-풀 인버터의 경우 아날로그 제어방식으로 제어전압 2.5-4.5V에서 출력전류 1-6mA(최소)로 휘도 $0-100\%$ 특성을 보였다. 입출력 효율로 18.6(최소)-90.3(최대)$\%$를 얻었으며, 버스트 제어방식에서는 듀티비 $5-50\%$에서 1-6mA의 제어성능을 보였다. 인버터의 입출력 효율은 13.6(최소)-82.1(최대)$\%$를 얻었다.

• Composites Research
• /
• v.17 no.5
• /
• pp.7-14
• /
• 2004

This paper deals with adaptive fuzzy logic controller design to achieve proper dynamic response of a composite thin-walled beam with a tip mass. In order to check the effectiveness of this controller, three different types of control logic are selected and applied. The adaptive control capabilities provided by a system of piezoactuators bonded or embedded into the structure are also implemented in the system. Results show that the fuzzy logic controller is more effective than the proportional or velocity feedback controller for the vibration control of composite thin-walled beam with a tip mass.

• Journal of the Korean Ceramic Society
• /
• v.37 no.10
• /
• pp.1021-1024
• /
• 2000

PMN-PT계 완화형 강유전체에서 MnO$_2$첨가가 압전물성에 미치는 영향을 -40~10$0^{\circ}C$의 온도범위에 걸쳐 조사하였다. 각각의 시편들은 -4$0^{\circ}C$에서 1.0kV/mm의 전계를 10분간 가하여 분극처리를 한 후 승온하면서 공진 반공진법에 의해 압전물성을 측정하였다. 0.9MN-0.1PT계의 경우 MnO$_2$를 첨가하였을 때 $K_{p}$ 는 거의 유지되면서도 Q$_{m}$ 값이 큰 폭으로 상승하였는데, 0.5wt% MnO$_2$첨가의 경우 -4$0^{\circ}C$에서 95로부터 480으로 증가하였다. 일반 강유전체인 PZT계에 대한 MnO$_2$의 첨가효과와 비교할 때 PMN계 완화형 강유전체에서도 동일한 경향성을 보임을 확인하였다.