• Journal of the Korean Ceramic Society
• /
• v.22 no.2
• /
• pp.17-24
• /
• 1985

In the composition of $Pb(Mg_{0.15} W_{0.15})Ti_{0.35}-Zr_{0.35}O_3$ the effect of particle size on PbO vaporization were measured, . The initial step of discontinuous vaporization of unreated PbO during the calcining process was depended on the particle size. All additives $La_2O_3Nb_2O_5$ and $Al_2O_3$ inhibited the grain growth of the composition $Pb(Mg_{0.15} W_{0.15})Ti_{0.35}-Zr_{0.35}O_3$ +2wt% excess PbO. The dielectric and piezoelectric properties of the composition $Pb(Mg_{0.15} W_{0.15})Ti_{0.35}-Zr_{0.35}O_3$ were improved by the addition of 2wt% excess PbO and proper additive. The electromechanical planar coupling factor of 0.65 and mechnical quality factor of 390 could be obtained by adding 5wt% $Nb_2O_5$ to the composition 2wt% excess PbO+$Pb(Mg_{0.15} W_{0.15})Ti_{0.35}-Zr_{0.35}O_3$.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.4 s.175
• /
• pp.972-981
• /
• 2000

The phased array transducer has two distinct advantages. One is rapid scanning comparing with the conventional mechanical or manual scanning system. Therefore, output image is represented in real-time. The other is the dynamic focusing and the dynamic steering of ultrasonic beam. Only the delay times that are controlled electrically are used to focus and to steer beam without any lenses or wedges. In this study, the profile of the ultrasonic beam for the phased array transducer has been simulated in the Huygens principle with varying the inter-element spacing of the linear phased array transducer. From the result of this study, it was found that the ultrasonic beam spread wider as the inter-element spacing was decreased. However, the focusing effect was improved, even when the number of the element was not big. In addition, there was grating lobes that are constructed when the inter-element spacing is more than half wavelength. However, this grating lobe has lower amplitude than the main lobe.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.12
• /
• pp.126-132
• /
• 1999

The paper presents the modeling and optimal control for the reduction of transverse vibration of simply supported beam under a moving mass. The equations of motion are derived by using assumed mode method. The coriolis and centripetal accelerations are accommodated in the equations of motion to account for the dynamic effect of the traveling mass. In order to reduce the transverse vibration of the beam, an optimal controller with full state feedback is designed based on the linearized equations of motion. The optimal actuator locations are determined with the evaluation of an optimal cost functional defined by the worst initial condition with the trade-off of controlled mode performance. Numerical simulations are performed with respect to various velocities and different traveling masses. Even if the velocity of the traveling mass reaches to the critical speed which can cause the resonance of the beam, the controller with two piezoelectric actuators shows the excellent performance under severe time-varying disturbances of the system.

• Journal of the Korean Society for Precision Engineering
• /
• v.24 no.11
• /
• pp.52-58
• /
• 2007

A cutting device capable of generating various shapes of the cyclic elliptical trajectory of a cutting tool was proposed and micro v-grooving experiments were performed to investigate the characteristics of elliptical vibration cutting (EVC). The proposed cutting device is comprised of a pair of parallel piezoelectric actuators with which harmonic voltages of varying phase difference and magnitude are supplied, creating various shapes of the elliptical tool path. The attributes of the elliptical locus involving the direction of the axis of an ellipse, the rotational direction and amplitudes of a trajectory were fine-tuned for stable operation of the EVC. The EVC characteristics performed with brass and copper revealed reduction in the cutting resistance and suppression of burr formation, resulting in the enhancement of form accuracy of machined micro-features. While the effect of the EVC increases with the increase of excitation frequency and the amplitude, it is found that a change in the cutting force decreases as the amplitude of an elliptical locus increases.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.6
• /
• pp.509-516
• /
• 2007

Mathematical modeling and vibration control of a tiltrotor aircraft composite wing-rotor system are investigated in this study. A wing-mounted rotor can be tilted from the vertical position to a horizontal one, and vice versa. Effect of vibration control of the wing-rotor system via piezoelectricity is studied as a function of tilt angle, ply angle of composite wing and rotor's spin speed. Composite wing is modeled as a thin-walled box beam having a circumferentially uniform stiffness configuration that produces elastic coupling between flap-lag and between extension-twist behavior. Numerical simulations are provided and pertinent conclusions are outlined.

• Structural Engineering and Mechanics
• /
• v.63 no.1
• /
• pp.65-76
• /
• 2017

This research investigated the vibration frequency of sandwich plate made of piezoelectric fiber reinforced composite core (PFRC) and face sheets of piezomagnetic materials. The effective electroelastic constants for PFRC materials are obtained by the micromechanical approach. The resting medium of sandwich plate is modeled by Pasternak foundation including normal and shear modulus. Besides, sandwich plate is subjected to linearly varying normal stresses that change by load factor. The coupled equations of motion are derived using first order shear deformation theory (FSDT) and energy method. These equations are solved by differential quadrature method (DQM) for simply supported boundary condition. A detailed numerical study is carried out based on piezoelectricity theory to indicate the significant effect of load factor, volume fraction of fibers, modulus of elastic foundation, core-to-face sheet thickness ratio and composite materials on dimensionless frequency of sandwich plate. These findings can be used to aerospace, building and automotive industries.

• Wind and Structures
• /
• v.24 no.5
• /
• pp.431-446
• /
• 2017

As concrete is most usable material in construction industry it's been required to improve its quality. Nowadays, nanotechnology offers the possibility of great advances in construction. In this study, buckling of horizontal concrete columns reinforced with Zinc Oxide (ZnO) nanoparticles is analyzed. Due to the presence of ZnO nanoparticles which have piezoelectric properties, the structure is subjected to electric field for intelligent control. The Column is located in foundation with vertical springs and shear modulus constants. Sinusoidal shear deformation beam theory (SSDBT) is applied to model the structure mathematically. Micro-electro-mechanic model is utilized for obtaining the equivalent properties of system. Using the nonlinear stress-strain relation, energy method and Hamilton's principal, the motion equations are derived. The buckling load of the column is calculated by Difference quadrature method (DQM). The aim of this study is presenting a mathematical model to obtain the buckling load of structure as well as investigating the effect of nanotechnology and electric filed on the buckling behavior of structure. The results indicate that the negative external voltage applied to the structure, increases the stiffness and the buckling load of column. In addition, reinforcing the structure by ZnO nanoparticles, the buckling load of column is increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.11a
• /
• pp.109-112
• /
• 1998

SAW filters of transversal type were fabricated on some piezoelectric substrate of the LN 128 $^{\circ}$ Y-X waters through the simulation in which the number of IDT and window function were changed for the required frequency, and the mask making. Their IDT spacing and width were 1.63$\mu\textrm{m}$, 1.239$\mu\textrm{m}$, respectively. Titanium thin films having different thicknesses were introduced between the Al electrode and the substrate for improving the power resistance strength due to its high temperature durability and good adhesion characteristics. All of specimens showed similar insertion loss results, which means the possibility of introducing the Ti layer though it is known to have a higher resistivity leading to a worse insertion loss result. Ti inserted specimens had a better power durability than that of pure Al electrode though their thickness had no effect on the performance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.972-975
• /
• 2001

The effect of Cr$_2$O$_3$(0 to 0.5 wt%) doping on the microstructure and electrical properties of ternary Pb(Zr,Ti)O$_3$-Pb(Ni,Nb)O$_3$piezoelectric ceramic has been investigated. Abnormal grain growth (grain size 3.3 to 11.2 $\mu$m) and densification are found. Minor additives of $\leq$0.1 wt% improve the mechanical coupling factor, but with more additives of $\geq$0.2 wt% electrical properties deteriorate. Thus, these phenomna can be ascribed mainly to anomalous developed microstructure. The large grains were composed of a core region that is free of Cr and a surrounding shell region rich in Cr. The interfaces between the core and the shell were composed of misfit dislocations. The mechanical properties of the specimens were strongly influenced by this microstructural change. The microstrutural and compositonal evolution of the specimens containing different amounts of Cr$_2$O$_3$were monitored. Electrical properties were measured and related to the variations in the microstructure.

• Journal of the Korean Society for Precision Engineering
• /
• v.34 no.1
• /
• pp.53-58
• /
• 2017

A fine stage is developed for the 3-DOF error compensation of a linear axis in order to improve the positioning accuracy. This stage is designed as a planar parallel mechanism, and the joints are based on a flexure hinge to achieve ultra-precise positioning. Also, the effect of Abbe's offsets between the measuring and driving coordinate systems is minimized to ensure an exact error compensation. The mode shapes of the designed stage are analyzed to verify the desired 3-DOF motions, and the workspace and displacement of a piezoelectric actuator (PZT) for compensation are analyzed using forward and inverse kinematics. The 3-DOF error of a linear axis is measured and compensated by using the developed fine stage. A marked improvement is observed compared to the results obtained without error compensation. The peak-to-valley (PV) values of the positional and rotational errors are reduced by 92.6% and 91.3%, respectively.