• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.323-329
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• 2003

In this paper, the method of material constants extraction in a thin-film bulk acoustic resonator(FBAR) using a genetic algorithm(GA) is proposed. The material constants are extracted from the input impedance of a FBAR by a GA optimizer. The characteristics of the FBAR input impedance affected by the material constants were studied to decide the fitness function for GA. As a result, the fitness was estimated by the series- and parallel -resonance frequencies and the FBAR bandwidth, as determined from the input impedance of the FBAR. A flowchart for the GA and a procedure fur the proposed extraction method are explained in detail, and the results of the material constants extraction are presented.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.333-336
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• 2021

Oxide YBCO bulk superconductors are manufactured using the melt process. Because seed crystal growth method utilizes a slow-spreading layer-by-layer reaction, a long-term heat treatment is required to manufacture a single-crystal specimen of several cm. In this study, the melt process method was applied to compensate for the shortcomings of the seed crystal growth method. The thickness of the upper and lower pellets of the YBCO bulk was molded to 40 mm, and YBCO superconductor was produced by heat treatment. The measurement results of capture magnetism was in line with the literature. This results in a relationship that the higher the growth of Y211 particle in the YBCO, the higher the superconducting properties. We analyzed the YBCO superconductor, focusing on the Y₂BaCuO₅ particle distribution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.94-97
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• 2003

This study uses ZnO thin film as a piezoelectric material and Pt as bottom electrode for FBAR (film bulk acoustic resonator) device. ZnO thin film and Pt were deposited by RF-magnetron sputtering method. ZnO thin film and Pt were oriented to c-axis. Top electrode Al was deposited by thermal evaporation. The membrane was formed of bulk micromachining. The FBAR was evaluated by XRD, SEM and electrical characterization. The resonant frequency was measured by HP 8753C Network Analyzer. A fabricated FBAR device exhibited a resonant frequency of 700 MHz ~ 1.5 GHz. When bottom electrode and top electrode thickness were fixed, the resonant frequency was increased as decreasing ZnO thin film thickness.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.432-435
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• 2020

The elasticity tensor for water may be employed to model the fully saturated porous material. Mostly water is assumed to be incompressible with a bulk modulus, however, the upper and lower bounds of off-diagonal components of the elasticity tensor of porous materials filled with water are violated when the bulk modulus is relatively high. In many cases, the generalized Hill inequality describes the general bounds of Voigt and Reuss for eigenvalues, but the bounds for the component of elasticity tensor are more realistic because the principal axis of eigenvalues of two phases, matrix and water, are not coincident. Thus in this paper, for anisotropic material containing pores filled with water, the bounds for the component of elasticity tensor are expressed by the rule of mixture and the upper and lower bounds of fully saturated porous materials are violated for low porosity and high bulk modulus of water.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.6
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• pp.461-465
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• 2021

A diffusion heat treatment process for YBa₂Cu₃O_7-y bulk superconductor in a Gd₂O₃ powder was attempted. As a result of measuring the critical temperature of the superconducting bulk, there was no change in the superconducting transition temperature as the Gd particles diffused into the YBa₂Cu₃O_7-y lattice, resulting in dense microstructure. As a result of measuring the critical current, the critical current density (J_c) of the superconducting bulk having treated by the Gd thermal diffusion treatment at 0 T increased to 3×10⁴ A/cm² at 0 T, which was higher than that of the superconducting bulk without thermal diffusion treatment. The surface magnetic force of the superconducting bulk with Gd thermal diffusion treatment was observed at the center of the superconducting bulk with the maximum trapped magnetic force (Hmax) of 1.51 kG. This result means that the Gd thermal diffusion treatment contributes to improving the critical current density Jc of YBa₂Cu₃O_7-y, and it is believed that Gd particles migrating into the superconducting bulk through thermal diffusion either fill the surface pores of YBa₂Cu₃O_7-y superconductors or act as a flux pinning center.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.214-215
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• 2003

• Journal of the Korean Society of Clothing and Textiles
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• v.38 no.3
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• pp.397-403
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• 2014

In this study, various types of Jumchi Hanji were made to develop shroud materials as a new use for Hanji. The properties of Hanji (basis weight, thickness, apparent density, bulk, tensile strength, wet tensile strength, elongation ratio, tear strength, bursting strength, and folding endurance) are measured. In all cases, Jumchi Hanji had a higher thickness, lower apparent density and higher bulk than Hanji because pores in the intervals of mulberry fiber are composed of bulk. So, it is considered to carry a value as a textile material. As for the results of the strength analysis of Jumchi Hanji, Jumchi technique enhances 25% of elongation ratio, which is regarded the most important role in textiles and 35% of bulk. Moreover, it was shown that it enhanced overall strength. In conclusion, it implies the possibility of applying it as a shroud material. Jumchi Hanji is thought to have enough potential to be developed as a material to carry the characteristics of Hanji in the textile market.

• Transactions of the Society of Information Storage Systems
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• v.2 no.3
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• pp.189-195
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• 2006

Bragg detuning effect if, one of the serious problems if the photopolymer is used for the recording material of holography memories. And the critical reasons of that are known as the bulk refractive index change and shrinkage of recording material. However, the trials for analyzing the effect are mainly on the K-sphere and biased on the transmission hologram. So, we approached Bragg detuning effect numerically and applied the method to the transmission holograms and the reflection holograms all together. We simulated it with MATLAB. As a result, the bulk refractive index change causes+Bragg detuning effect on the transmission holograms and the reflection holograms. But the shrinkage leads to+Bragg detuning effect on the transmission hologram and-Bragg detuning effect on the reflective hologram. Compared to experimental result, the bulk refractive index change(${\fallingdotseq}4{\times}10^{-4}$) and the ratio of shrinkage to the thickness of the material(${\fallingdotseq}1.67{\times}10^{-3}$) could be matched with Bragg detuning effect on the transmission hologram and the reflection hologram.

• Journal of Powder Materials
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• v.21 no.4
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• pp.301-306
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• 2014

Titanium alloys are extensively used in high-temperature applications due to their excellent high strength and corrosion resistance properties. However, titanium alloys are problematic because they tend to be extremely difficult-to-cut material. In this paper, the powder synthesis, spark plasma sintering (SPS), bulk material characteristics and machinability test of hybrid $Ti_2AlC$ ceramic bulk materials were systematically examined. The bulk samples mainly consisted of $Ti_2AlC$ materials with density close to theoretical value were synthesized by a SPS method. Random orientation and good crystallization of the $Ti_2AlC$ was observed at $1100^{\circ}C$ for 10 min under SPS sintering conditions. Scanning electron microscopy results indicated a homogeneous distribution and nano-laminated structure of $Ti_2AlC$ MAX phase. The hardness and electrical conductivity of $Ti_2AlC$ were higher than that of Ti 6242 alloy at sintering temperature of $1000^{\circ}C{\sim}1100^{\circ}C$. Consequently, the machinability of the hybrid $Ti_2AlC$ bulk materials is better than that of the Ti 6242 alloy for micro-EDM process of micro-hole shape workpiece.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.1
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• pp.70-73
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• 2023

To improve superconductor properties, the size of the crystal grains of the superconductor should be adjusted, the amount of electricity flowing through the superconductor should be increased, and the superconductor should be designed to withstand external magnetic fields. It is necessary to control the microstructure so that many flux pinning centers are developed inside the superconductor so that defects are generated physically or chemically, and the micro secondary phase for trapped magnetic flux must be dispersed inside the superconductor. In order to measure the superconducting magnetic force of the superconducting bulk in a simplified manner, the superconducting magnetic force was analyzed using an Nd-Fe-B permanent magnet of 3.80 kG. In particular, by delaying the growth of partially melted Y₂BaCuO₅ particles, we devised a plan to refine Y₂BaCuO₅ particles to effectively improve superconducting magnetic force, and analyzed superconducting magnetic force in a single crystal YBa₂Cu₃O_7-y superconducting bulk using a gauss meter. The melted superconducting bulk traps 80% or more of the applied magnetic field, and can be used as a bulk magnet of high magnetic field magnetization applicable to electric power equipment.