• Journal of Magnetics
• /
• v.3 no.2
• /
• pp.64-67
• /
• 1998

Microwave absorbing properties of ferrite-epoxy composite (absorbing layer) attached on the carbon fiber polymer composite (reflective substrate) are analyzed on the basis of wave propagation theory. A modified equation for wave-impedance-matching at the front surface of absorbing layer including the effect of electrical properties of the quasi-conducting substrate is proposed. Based on this analysis, the frequency and layer dimension that produce zero-reflection can be estimated from the intrinsic material properties of the obsorbing layer and the substrate. It is demonstrated that the microwave reflectivity of carbon fiber composite has a strong influence on the microwave absorbance of front magnetic layer.

• Journal of the Korean Ceramic Society
• /
• v.34 no.8
• /
• pp.843-853
• /
• 1997

The effect of dopant on microwave dielectric properties of (1-x)MgTiO3-xCaTiO3 ceramics, known to be used as microwave dielectric resonators for global positioning system and personal communication system, has been analyzed in terms of variations in defect concentrations and microstructural features with its addition. The addition of dopants was revealed to result in a significant change in the microstructure as well as defect concentration of the ceramics. For instance, the quality factor is proportional to sintered density of the ceramics by inversely proportional to grain size as well as vacancy concentration. Accordingly, it is believed that the dopant effect on the microwave dielectric properties should be separately analyzed with either microstructural change or the change in vacancy concentration.

• Korean Journal of Food Science and Technology
• /
• v.26 no.6
• /
• pp.696-703
• /
• 1994

The purpose of this study was to investigate the gelatinization properties of potato starch heated with microwave. Two types of potato starches were prepared; In group A raw potato starch was heated with microwave and in group B potato starch was isolated from potato heated with microwave. Both groups were exposed to the microwave energy in a 560W, 2,450 MHz oven for 60, 120, 180 and 300 seconds. Gelatinization behaviour by DSC made a few differences according to the ratio of starch to water. As the microwave heating time took longer, gelatinization temperature and gelatinization $enthalpy({\bigtriangleup}H_1)$ were decreased in and melting $enthalpy({\bigtriangleup}H_2)$ was increased in group A. Whereas they were increased in group B. In both groups, maximum viscosity in gelatinization by Brabender amylogram was decreased by microwave heating. Then the peak of the maximum viscosity was shifted to higher temperature and cold viscosity was slightly increased. In group A, viscosity in gelatinization and light transmittance by NaOH was increased in initial stage and gel volume in gelatinization by KSCN was decreased. On the other hand, in group B, viscosity by alkali was slightly decreased, but light transmittance by NaOH was almost never changed. Gel volume is decreased like group A.

• Journal of the Korean Ceramic Society
• /
• v.47 no.2
• /
• pp.163-168
• /
• 2010

Effects of compositions on the microwave dielectric properties of the MgO-$TiO_2$ system were investigated as a function of the molar ratio of MgO to $TiO_2$ ($0.9{\leq}MgO/TiO_2\;(x){\leq}1.2$). With the compositional changes, secondary phases of $MgTi_2O_5$ and $Mg_2TiO_4$ were also detected along with $MgTiO_3$. Microwave dielectric properties of the specimens were dependent on the types of phases developed in the sintered specimens. A single phase of $MgTiO_3$ showed a dielectric constant (K) of 18.2, a quality factor (Qf) of 198,000 GHz, and a temperature coefficient of resonant frequency (TCF) of $-51\;ppm/^{\circ}C$. However, the dielectric properties of the specimens with a secondary phase of $MgTi_2O_5$ (K=19.9, Qf=48,000 GHz) and/or $Mg_2TiO_4$ (K=15.6, Qf=56,000 GHz) were worsened. Dependence of the microwave dielectric properties on the secondary phase of the MgO-$TiO_2$ system was also discussed in terms of dielectric mixing rules.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.11a
• /
• pp.492-494
• /
• 2002

The fundamental principles of the operation of microwave discharges that are used to convert microwave energy to broad spectrum visual light are known. In this paper, emission dependance of microwave discharges in mixture content of sulfur with noble gases was studied. It is shown that the excitation of this gaseous mixture is carried out in two phases: (1) ionization of noble gas atoms by a microwave field and (2) the consequent maintenance of slightly ionized nonequilibrium plasma by the field. These two processes have essentially various thresholds for the microwave pump. The purpose of this work is to investigate spectral properties of the high frequency discharges in a mixture sulfur vapors with noble gases.

• Journal of the East Asian Society of Dietary Life
• /
• v.20 no.3
• /
• pp.423-432
• /
• 2010

In order to streamline bread making process that is time-consuming in regard to the characteristics of process, this study focused on microwave irradiation to dough and raising its temperature to monitor potential variations of dough properties and bread quality, and also examined optimum irradiation time to deduce effective ways for streamlining bread making process. According to analyze dough properties depending on microwave irradiation time, it was found that microwave heat (MWH) 2 showed the highest specific volume and oven spring of all and the lowest hardness (i.e. the highest softness). Moreover, MWH 2 scored the highest points in overall preference under sensory characteristics. As a result, it found that 80-second heating of 700 g bread dough, when exposed to microwave irradiation, contributed to the highest quality of bread.

• Journal of Navigation and Port Research
• /
• v.29 no.2
• /
• pp.147-150
• /
• 2005

We suggest a cast Alnico magnet as a new microwave absorber. The proposed Alnico microwave absorber shows advanced microwave absorption properties of 24 dB at 13.3 GHz for the thicknesses of 1 mm We also investigated the effects of the carbon, which qjfects strongly to microwave absorption in Alnico magnet microwave absorbers. Central frequency shifts toward lower frequency with increasing Alnico content which is related to the frequency to show tan 8 > 1. Also, we investigated the sample thickness dependence on the microwave absorption properties.

• The Korean Journal of Ceramics
• /
• v.4 no.4
• /
• pp.352-355
• /
• 1998

Dense $ Pb(Zr, Ti)O_3(PZT)/Al_2O_3$ nanocomposites were prepared by the 28 GHz microwave heating method and conventional electric furnace sintering. Electrical and mechanical properties of the composites were investigated. The fracture strength of the PZT composites with 0.1vol% $Al_2O_3$ was significantly improved in both sintering methods. Smaller grain size and effective reinforcement of the PZT matrix by the second phase were considered to be responsible for the excellent fracture strength. Planar electromechanical coupling factor Kp of the composites sintered by 28GHz microwave heating was higher than that of the materical prepared by the conventional route. It seemed that the control of the reaction between PZT and $Al_2O_3$ by the microwave rapid sintering resulted in the high piezoelectric properties.

• Journal of the Korean Ceramic Society
• /
• v.35 no.11
• /
• pp.1197-1202
• /
• 1998

To check the possibility for microwave sintering of MLCC(multi layer ceramic capacitor) the tape cast-ed BaTiO3 thick films in zirconia insulation box were sintered by the domestic microwave oven. Microwave sintered samples had higher density lower porosity than coventionally sintered ones. but they didn't show Z5U electrical properties due to short sintering time about 15 minutes.

• Journal of the Korean Wood Science and Technology
• /
• v.23 no.3
• /
• pp.73-82
• /
• 1995

Black locust trees(Robinia pseudo-acacia L.) are growing widely in Korea and have been used to get honey and animal feed, but they have seldom been used as manufacturing materials. This study was carried out to evaluate the possibility of using black locust as bent-wood furniture materials. Softening methods were steaming and micro-wave heating. The specimens of 15${\times}$15${\times}$350mm were all air-dried. For softening, specimens were steamed at 100$^{\circ}C$ for 7 min, or microwave heated for 35 seconds. It is known that microwave heating softens wood much faster than steaming. The bending processing conditions are showed in Table 7. The minimum solid-bending radii of black locust were 40mm for steaming and 150mm for micro-wave heating, respectively. In conclusion the steamed black locust, showed very good solid bending properties, but the bending properties of micro-wave heated black locust were not sufficient for bent-wood furniture.