• Journal of the Korean Ceramic Society
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• v.30 no.9
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• pp.761-767
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• 1993

Electrical and mechanical properties of Pb(Mg, Te, Mn, Nb)O3-PZT ceramics are investigated as a function of CeO2 addition (0 to 0.3wt%), and the output characteristics of piezoelectric transformer are also presented. The grain size decreased and the shapes of particles were more uniform with the addition of CeO2. The coercive electric field(9500V/cm), mechanical quality factor (2500) and bend strength (1065kg/$\textrm{cm}^2$) were improved by addition of CeO2 0.2wt%. After repetition of a number of stress cycles, the degradation of k33 was not found in this sample. The voltage step-up ratio (Vdc/Vrms) of piezoelectric ceramic transformer (half wavevoltage doubler, load resistor 100M.ohm) was about 950 in a linear region, its value was relatively higher than other materials.

• Journal of the Korean Magnetics Society
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• v.10 no.6
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• pp.302-309
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• 2000

An MFL (Magnetic Flux Leakage) testing system has been developed in order to inspect the non-metallic inclusions in the thin steel sheets. We have made a differential type flux-gate magnetometer using the measurement of apparent coercive field strength of soft magnetic core. The specifications of the electromagnet was determined using FEM software, and MFL testing system with 3 axis degree of freedom was constructed. The feasibility testing for non-metallic inclusion was shown using the system. By digitizing MFL signal and using 2-D graphic display, we could identify various surface defects other than the inclusions.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1593-1595
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• 2000

We present a new procedure to evaluate the degradation in a lCr-lMo-0.25V steel. The method is based on the existence of the peak of reversible permeability in the differential magnetization around the coercive field strength. The apparatus is based on the detection of the voltage induced in a surface type coil using a lock-in amplifier tuned to a frequency to the exciting one. Results obtained the reversible permeability and Vickers hardness on the annealed samples show the peak interval of reversible permeability and Vickers hardness decreased as ageing time increased. The correlation between Vickers hardness and the peak interval of reversible permeability could well be evaluated non destructively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.7
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• pp.667-672
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• 2006

Ferroelectric $Pb(Zr_{0.52}Ti_{0.48})O_3$ (PZT(52/48)) thick films were fabricated by the screen-Printing method on the alumina substrates, and $PbTiO_3$ (PT) Precursor solution, which prepared by sol-gel method, was spin-coated on the PZT(52/48) thick films to obtain a densification. Its structural and electrical properties of the PZT(52/48) thick films with the treatment of PT precursor solution coating were investigated. The particle size of the thick films was increased with increasing the number of coatings and the thickness of the PZT-6 (6: number of coatings) films was about $60{\mu}m$. The relative dielectric constant increased and the dielectric loss decreased with increasing the number of PT sol coatings. The relative dielectric constant and dielectric loss of the PZT-6 thick film were 475 and 2 %, respectively. The remanent polarization, coercive field and breakdown strength of the PZT-6 film were $32.6{\mu}C/cm^2$, 15 kV/cm and 60 kV/cm, respectively.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.9
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• pp.429-433
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• 2006

PZT(80/0) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The coating and drying procedure was repeated 4 times. And then the PZT(20/80) precusor solution was spin-coated on the PZT thick films. A concentration of a coating solution was 0.5mol/L and the number of coating was varied from 0 to 6. The porosity decreased and the grain size increased with increasing the number of coatings. The thickness of the PZT-6(6: number of coatings) films was about $60{\mu}m$. The relative dielectric constant increased and the dielectric loss decreased with increasing the number of PZT(20/80) sol coatings. The relative dielectric constant and dielectric loss of the PZT-6 thick film were 275 and 3.5%, respectively. The remanent polarization, coercive field and breakdown strength of the PZT-6 film were $19.8{\mu}C/cm^2$, 13.7kV/cm and 130kV/cm, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.10
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• pp.856-865
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• 2008

Damage mechanisms in bending piezoelectric actuators under electric fatigue loading are addressed in this work with the aid of an acoustic emission (AE) technique. Electric cyclic fatigue tests have been performed up to $10^7$ cycles on the fabricated bending piezoelectric actuators. An applied electric loading range is from -6 kV/cm to +6 kV/cm, which is below the coercive field strength of the PZT ceramic. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate and amplitude are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZ inner layer, thereby degrading the displacement performance. However, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to $10^7$ cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.9
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• pp.611-615
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• 1999

Piezoelectric properties of PMN-PZT ceramics with $CeO_2$ impurity were investigated. Mechanical quality factor, $Q_m$ of 1792, 1285 and the electromechanical coupling coefficient, $k_p$ of 0.52, 0.54 were obtained from the specimen with 0.25 and 0.5 mole % $CeO_2$ respectively. Curie temperature was decreased with the addition of $CeO_2$ while the electric coercive field was proportional to the amount of impurity. Based on the system ceramics with 0.5 mole % cerium oxide, a Rosen type piezoelectric transformer was fabricated and tested. Voltage step-up ratios of 230 and 13 were obtained from the transformer at no load and $100 k\Omega$ resistance, respectively. Experimental results showed a potential of the transformer for the practical use coupled with the expected strength increase by the grain size refinement.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.445-450
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• 2000

The integrity of the turbine rotors can be assessed by measuring reversible permeability and Vickers hardness of the aged rotors at service temperature. The measurement system of reversible permeability, which measured by applied alternating perturbing magnetic field, was constructed in order to evaluate material degradation, nondestructively. The test specimen was 1Cr-1Mo-0.25V steel used widely for turbine rotor material, and the specimens were prepared by the isothermal heat treatment at $630\;^{\circ}C$. The reversible permeability of the test materials were measured at room temperature. The peak interval of reversible permeability and Vickers hardness decreased with the increase of degradation. The degradation of test material may be determined nondestructively by the lineality of Vickers hardness and the peak interval of reversible permeability.

• Journal of the Korean Magnetics Society
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• v.27 no.1
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• pp.23-29
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• 2017

In this study, the influences of magnetization reversal and magnetic interaction on the coercivity of Sr-ferrite particles with different sizes were investigated through various magnetic measurements. The shape of the initial magnetization curve and the magnetic field dependence of the coercive force indicate that the magnetization reversal changes from domain nucleation to wall pinning as the particle size decreases. On the other hand, the Henkel plot, interaction field factor and ${\Delta}M(H)$ obtained from the DCD and IRM curves show that the strength of the dipolar interaction is increased with increasing the particle size. Therefore, it can be concluded that coercivity is closely related to magnetic interaction as well as magnetization reversal mechanism.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1717-1723
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• 2007

In this study , quasi-MFISFET (Metal-Ferroelectric-Insulator-Semiconductor FET) devices are fabricated using PLZT(10/30/70), PLT(10), PZT(30/70) thin film and their drain current properties are investigated. It is found that the drain current of quasi-MFISFET is directly influenced by the polarization strength of ferroelectric thin fan. Also, when the gate voltages are ${\pm}5\;and\;{\pm}10V$, the memory windows are 0.5 and 1.3V, respectively. It means that the memory window is changed with the variation of coercive voltage generated by the voltage applied on ferroelectric thin film. The electric field and the leakage current with time delay of PLZT(10/30/70) thin lam are measured to investigate the retention property of MFISFET device. Some material parameters such as current density constant, $J_{ETO}$, electric field dependent factor K and time dependent factor m are obtained. The variation of charge density with time is quantitatively analyzed by using the material parameters.