• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.342-342
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• 2008

The low temperature sintering and microwave dielectric properties of ceramic/glass composites which were composed of ceramics in the $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ and zinc borosilicate glass/bismuth-zinc borosilicate glass were investigated with a view to applying the microwave dielectrics to low temperature co-fired ceramics. The $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ addition of 5 wt% ZBS and BZBS glass ensured a successful sintering below $900^{\circ}C$. In addition, pyrochlore phase was observed in the all composition. $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ with 5 wt% BZBS glasss demonstrated 70 as the dielectric constant ($\varepsilon_r$), 2,500 GHz as the Q$\times$f value, and -40 ppm/$^{\circ}C$ as TCF.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.10
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• pp.870-875
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• 2002

Ba(Zn$_1$-xCox)TaO$_3$[BZCT] ceramics were Prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of 1450∼1550$\^{C}$ for 5 hr in air. The crystal structure of BZCT ceramics was investigated by the XRD. The microstructure of the specimens were observed by SEM. The structural properties of BZCT specimens were investigated as a function of composition and sintering temperature. All BZCT ceramics sintered over 1550$\^{C}$ were showed a polycrystalline complek perovskite structure without second phases and any unreacted materials. The density of BZCT (70/30) specimen sintered at 1550$\^{C}$ was 6.31g/㎤. In the case of the BZCT(70/30) ceramics sintered at 1550$\^{C}$ for 5 hours, dielectric constant, qualify factor and temperature coefficient of resonant frequency for microwave dielectrics application were a good value of 29, 16,468 at 10㎓ and -4.4 ppm/$\^{C}$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.313-314
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• 2006

$BiNbO_4$ ceramics were sintered under the presence of zinc-borosilicate(ZBS) glass and resultant microwave dielectric properties were investigated with a view to applying the composition to LTCC technology. The addition of 5~20 wt% ZBS glass ensured successful sintering below $900^{\circ}C$. In general, increased addition of ZBS glass increased sinterability and temperature coefficient of resonant frequency(${\tau}_f$), but it decreased the dielectric constant(${\varepsilon}_r$) and quality factor($Q{\times}f_0$) significantly due to the formation of an excessive liquid. The sintered $BiNbO_4$ ceramics at $900^{\circ}C$ with 15 wt% ZBS glass demonstrated 25 in dielectric constant(${\varepsilon}_r$), 3,700 in quality factor($Q{\times}f_0$), and -32 $ppm/{\circ}C$ in temperature coefficient of resonant frequency(${\tau}_f$).

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.8
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• pp.335-339
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• 2002

Ba(Mgl-xCox)TaO3[BMCT] ceramics were prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of 1525~$1625^{\circ}C$ for 5hr. in air. The crystal structure of BMCT ceramics was investigated by the XRD. The microstructure of the specimens were observed by SEM. The Microwave dielectric properties of BMCT specimens were investigated as a function of composition and sintering temperature. All BMCT ceramics sintered over 1575$^{\circ}C$ were showed a polycrystalline complex perovskite structure. The density of BMCT (90/10) specimen sintered at $1575^{\circ}C$ was 7.75g/㎤. As the Co contents decreased, the ordering parameter of B-site in BMCT increased. In the case of the BMCT(90/10) ceramics sintered at $1575^{\circ}C$ for 5 hours, dielectric constant, quality factor and temperature coefficient of resonant frequency for microwave dielectrics application were a good value o( 25, 17, 845 at 10㎓ and +2.4 ppm/${\circ}$, respectively.

• The Korean Journal of Ceramics
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• v.2 no.2
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• pp.111-113
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• 1996

Dielectric properties at microwave frequency region of the five-layered compound $Ba_5Nb_4O_{15}$ prepared by the conventional solid state reaction method were investigated. $Ba_5Nb_4O_{15}$ has excellent microwave dielectric characteristics; ${\varepsilon}_r$=38, Q=7500 at 10 GHz, and ${\tau}_l$=+50 ppm/K. Since this compound has a high dielectric constant, high Q and sufficiently stable characteristics, it is useful for the applications at microwave frequencies.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.583-590
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• 1997

The effects of Mn2O3 and Y2O3 additives on the microstructure and dielectric properties of Sr(Zr, Ti)O3 have been investigated. Powders with Sr(Zr1-xTix)O3(0$\leq$x$\leq$0.1) composition were prepared by the conventional solid state processing from commercial TiO2 and precipitation-processed ZrO2. The powders containing sintering additives of Mn2O3 and Y2O3 were compacted and then sintered at 1,55$0^{\circ}C$ for 4 h to get>97% relative density. Mn2O3 suppressed the grain growth and Y2O3 enhanced the density of sintered body. The oxidation state of Mn ions were determined by a chemical wet method and EPR spectroscopy. Mn ions were present as Mn2+ and Mn4+ in SrZrO3, while as Mn3+ and Mn4+ in Ti-substituted Sr(Zr, Ti)O3. With the substitution of Ti, the lattice parameters of SrZrO3 decreased and its dielectric constant increased with remarkable decrease in Q value. The dielectric constant of Sr(Zr, Ti)O3 was in the range of 30 to 40, Q values 1,200~5,400 at 6 GHz and temperature coefficient of resonant frequency -67~100 ppm/K.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.249-252
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• 2003

The microwave dielectric properties of $0.7Mg_4Ta_2O_9-0.3TiO_2$ ceramics were investigated. All samples were prepared by the conventional mixed oxide method. The structural properties were investigated with sintering temperature by X-ray Diffractor meter. According to. the X-ray diffraction patterns of the $0.7Mg_4Ta_2O_9-0.3TiO_2$ ceramics, major phase of the hexagonal $Mg_4Ta_2O_9$ were appeared. In the case of $0.7Mg_4Ta_2O_9-0.3TiO_2$ ceramics sintered at $1400^{\circ}C$, dielectric constant, quality factor and temperature coefficient of resonant frequency were 11.72, 126,419GHz, $-31.82ppm/^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.240-246
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• 2000

The microwave dielectric properties of the complex perovskite (Pb0.5Ca0.5)(Fe0.5Ta0.5)O3 ceramics were investigated with the porosity and the dielectric mixing rule. Assuming that the specimens were mixtures of real dielectrics and pores, with 3-0 connectivity, the ionic polarizabilities modified by Maxwell's equation were more close to the theoretical values rather than those modified by Wiener's equation in porous specimens. The theoretical dielectirc loss were obtained with the infrared reflectivity spectra from 50 to 4000cm-1, which were calculated by Kramers-Kronig analysis and classical osciallator model. The relative tendency of dielectric loss calculated from the theoretical value and Maxwell's equation in the specimens with different porosities was in good agreement with the one by the post resonant method.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2315-2317
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• 2005

In this paper, an iterative method to model the electromagnetic heating of electrically large lossy dielectrics is presented. Frequency domain finite element (FEM) solutions of the wave equation are determined for the lossy inhomogeneous dielectric as the material properties are change with temperature and time. The power absorbed from microwave losses is applied to a finite element time domain (FETD) calculation of the heat diffusion equation. Time steps appropriate for updating the piecewise material properties in the wave equation and the time stepping of the heat equation are presented. The effects of preheating and source frequency are investigated.

• Journal of Biosystems Engineering
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• v.32 no.4
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• pp.237-246
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• 2007

In this study, the microwave free-space transmission technique was used to measure the dielectric property of powdered food at microwave frequencies. The sample holder was designed and fabricated to transmit the microwave signals ranging from 1 to 15GHz. From the microwave propagation theory the equation expressing the dielectric property of powdered food was derived and validated by standard dielectrics. The dielectric property of powdered food such as wheat flour, coffee powder and milk powder was measured and analyzed. In the uniform range of bulk density of material, the real parts of permittivity of the food samples increased with the increase of moisture content, bulk density and temperature of the samples. The propagation properties such as attenuation and phase shift increased linearly as the moisture density of the food samples increased. As a measuring frequency of the moisture content, the X-band was recommended.