• Proceedings of the KSME Conference
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• 2001.11a
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• pp.477-482
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• 2001

To realize higher track density of HDD, the servo bandwidth should be higher, however, is limited by the mechanical resonances of the arm, coil of the VCM and ball bearing pivot. The dual-stage actuator systems have been suggested as a possible solution. For the dual-stage actuator systems based on the suspension, the suspension resonance frequencies in the radial access direction are important factors to increase a servo bandwidth, however the improvement of these frequencies may affect the shock resistance performance and spring constant. The slider's flying stability can be deteriorated by the change of a vertical stiffness. In this work, we have investigated a suspension design scheme possessing a milliactuator for dual-stage actuator systems and also achieved higher mechanical characteristics. Design parameters are deduced by finite element analysis with sensitivity function. It is confirmed that the proposed suspension with the milliactuator has the capability of fine tracking motion, due to its hinge structure on the spring region, and achieves higher mechanical resonance frequencies in the radial access direction with a high-shock resistance and a low-spring constant.

• The Korean Journal of Ceramics
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• v.7 no.1
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• pp.30-35
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• 2001

The contribution of the non-$180^{\circ}C$ domains to the electric-field-induced strains (EFI-strains) of PZT ceramics was evaluated by an XRD method and by an interferometric method. The XRD intensity ratio of 200 and 002 diffraction peaks of tetragonal PZT was measured under strong electric fields. The amount of the $90^{\circ}$ domain reorientation was evaluated and the strain due to the domain reorientation was calculated. It was confirmed that the EFI-strain of PZT ceramics was equal to the sum of the strain calculated from the d$_33$ constant determined by the resonance-antiresonance method and the strain due to the $90^{\circ}$ domain reorientation. The amount of the $90^{\circ}$domain reorientation has a linear relation with the c/a ratio in the "soft" PZT ceramics. A Mech-Zehnder interferometer was constructed to measure the EFI-strains vs. electric-field curves of PZT ceramics as a function of frequency. The EFI-strain vs. electric-field curve showed a hysteresis due to the effect of the non-$180^{\circ}$ domain reorientation when the applied voltage was high and its frequency was low. The apparent piezoelectric constant increased from the d$_33$ value determined by the resonance-antiresonance method with decreasing frequency. This deviation was attributed to the non-$180^{\circ}$ domain contribution.tribution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.157-160
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• 2001

We have investigated the Dielectric and Piezoelectric properties of $xPb(R_{1/2}Ta_{1/2})O_3-(1-x)Pb(Zr_{0.52}Ti_{0.48})O_3$ (R=Al,Y) solid solutions in which R ions are substituted for Al and Y ions. The maximum value of electromechanical coupling factor kp of 55% and 51% were obtained at the composition of 5mol% PAT and 5mol% PYT. However mechanical quality factor$(Q_m)$ had a minimum value of 44 and 69 at the composition of 5mol% PAT and 5mol% PYT. Also, the maximum value of piezoelectctric constant of $d_{33}(329[pC/N])$ and $d_{33}(310[pC/N])$ were obtained at the composition of 5mol% PAT and 5mol% PYT.

• Nuclear Engineering and Technology
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• v.37 no.2
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• pp.201-206
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• 2005

Fretting, which is a special type of wear, is defined as small amplitude relative motion along the contacting interface between two materials. The structural integrity of steam generators in nuclear power plants is very much dependent upon the fretting wear characteristics of Inconel 690 U-tubes. In this study, a finite element model that can simulate fretting wear on the secondary side of the steam generator was developed and used for a quantitative investigation of the fretting wear phenomenon. Finite element modeling of elastic contact wear problems was performed to demonstrate the feasibility of applying the finite element method to fretting wear problems. The elastic beam problem, with existing solutions, is treated as a numerical example. By introducing a control parameter s, which scaled up the wear constant and scaled down the cycle numbers, the algorithm was shown to greatly reduce the time required for the analysis. The work rate model was adopted in the wear model. In the three-dimensional finite element analysis, a quarterly symmetric model was used to simulate cross tubes contacting at right angles. The wear constant of Inconel 690 in the work rate model was taken as $K=26.7{\times}10^{-15}\;Pa^{-1}$ from experimental data obtained using a fretting wear test rig with a piezoelectric actuator. The analyses revealed donut-shaped wear along the contacting boundary, which is a typical feature of fretting wear.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2093-2096
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• 2011

In this study, lead-free $(Na_{0.5}K_{0.5})NbO_3-BiTiO_3$ ceramics were fabricated by a conventional mixed oxide method. Structural and electrical properties of lead-free $(Na_{0.5}K_{0.5})NbO_3$ ceramics with the variation of $BiTiO_3$ were investigated. The results of X-ray diffraction analysis showed a typical polycrystalline perovskite structure without presence of the second phase in all specimens. Sintered density increased with an increasing of BTO and the specimen added with 0.07 mol% of $BiTiO_3$ showed the maximum value of 97.8%. Average grain size decreased and densification increased with an increasing of $BiTiO_3$ contents. The electromechanical coupling factor of the 0.01 mol% $BiTiO_3$ doped NKN specimens was 0.32. Dielectric constant, dielectric loss and Curie temperature of the 0.07 mol% $BiTiO_3$ doped NKN specimens were 1185, 0.145% and $400^{\circ}C$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.798-801
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• 2004

In this study, in order to develop low temperature sintering ultrasonic vibrator, PCW-PMN-PZT ceramics with the amount of $Nb_2O_5$ addition were manufactured. All of the fabricated sample showed pure pervoskite structure of tetragonal phase. With increasing the amount of $Nb_2O_5$ addition, mechanical quality factor Qm were increased up to 0.2wt%$Nb_2O_5$ addition and then decreased. And also, with increasing the amount of $Nb_2O_5$ addition, grain size, kp, density and dielectric constant were linearly decreased. At the 0.2wt% $Nb_2O_5$ addition composition ceramic, kp of 0.48, Qm of 2186, ${\varepsilon}r$ of 1219 were shown, respectively. Their values were suitable for ultrasonic vibrator application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.6
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• pp.610-615
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• 2022

BaTiO₃ is one of the ferroelectric materials with excellent dielectric properties such as high dielectric constant, low dielectric loss, and is widely used for the manufacturing of capacitors, piezoelectric converters, microsensors, and ferroelectric memories. Inkjet printing is a technology which uses digital and contactless methods which significantly improves flexibility associated with material and structural design, reducing manufacturing costs. Therefore, the top and bottom electrodes, BaTiO₃ ink, and photocurable resin were all printed by an inkjet to produce a BaTiO₃ capacitor. The properties of the printed thin film were analyzed. It was confirmed that the photocurable resin ink was well-infiltrated between the BaTiO₃ powder particles printed by inkjet. The dielectric properties of the capacitor such as dielectric constant which varies in accordance with frequency, polarization and tunability that changes with voltage, were measured.

• Composites Research
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• v.29 no.4
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• pp.145-150
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• 2016

Polyvinylidene fluoride (PVDF) as a representative polymer with the piezoelectric property has been studied since the 1960s. Crystalline structure of poly(vinylidene fluoride) polymer is composed of five different crystal structure of the polymer as a semi-crystalline. Among the various crystal structures, ${\beta}-type$ crystal exhibits a piezoelectricity because the permanent dipoles are aligned in one direction. Generally ${\beta}-form$ crystal structure can be obtained through the transformation of the ${\alpha}-form$ crystal structure by the stretching and it can increase the amount through the after treatment as poling process after stretching. ${\beta}-form$ crystal structure the PVDF fibers produced by wet spinning is formed through a diffusion mechanism of a polar solvent in the coagulation bath. However, it has a disadvantage that the diffusion path of the solvent remains as pores in the fiber because the fiber solidification occurs simultaneously with the diffusion of the polar solvent. These pores play a role in reducing effect of poling process owing to effect of disturbances acting on the polarization by the electric field. In this work, the drying method using the microwave was introduced to remove more effectively the residual solvent and the pore within PVDF fibers produced through wet-spinning process and piezoelectric PVDF fibers was produced by transformation of the remaining ${\alpha}$ form crystal structure into ${\beta}-crystal$ structure through the stretching process.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.184-192
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• 2019

Compared to 31-mode rings, 33-mode rings are highly utilized as wide bandwidth underwater acoustic transducers because the electro-mechanical coupling and piezoelectric constant d are high. On the other hand, the 31-mode ring is an axial symmetry structure, so it is possible to model it as a simple two-dimensional asymmetrical model for numerical analysis, but the 33-mode ring requires a three-dimensional numerical analysis. That is, a lot of computing resources and computation time are required. In this study, the effective material properties of an equivalent 31-mode ring were derived to simulate the electro-mechano-acoustical responses of the 33-mode ring transducer. Using the effective material properties derived from this study, a numerical analysis of rings in vacuum, air backed rings in water, and FFR (Free Flooded Ring) transducers were performed to compare the responses of 33-mode rings.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.205-210
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• 2019

$Pb(Zr,Ti)O_3$ (PZT) is used for the various piezoelectric devices owing to its high piezoelectric properties. However, lead (Pb), which is contained in PZT, causes various environment contaminations. $(K,Na)NbO_3$ (NKN) is the most well-known candidate for a lead-free composition to replace PZT. A single crystal has excellent piezoelectric-properties and its properties can be changed by changing the orientation direction. It is hard to fabricate a NKN single crystal due to the sodium and potassium. Thus, $(Na,K)NbO_3-Ba(Cu,Nb)O_3$ (NKN-BCuN) is chosen to fabricate the single crystal with relative ease. NKN-BCuN pellets consist of two parts, yellow single crystals and gray poly-crystals that contain copper. The area that has a large amount of copper particles may melt at low temperature but not the other areas. The liquid phase may be responsible for the abnormal grain growth in NKN-BCuN ceramics. The dielectric constant and tan ${\delta}$ are measured to be 684 and 0.036 at 1 kHz in NKN-BCuN, respectively. The coercive field and remnant polarization are 14 kV/cm and $20{\mu}C/cm^2$.