• Korean Journal of Food Science and Technology
• /
• v.35 no.2
• /
• pp.222-228
• /
• 2003

Optimum extraction conditions for yield, browning color, electron-donating ability, nitrite-scavenging effect, total polyphenol content, and tyrosinase-inhibitory activity of Flammulina velutipes were determined using response surface methodology through central composite design. Yield of F. velutipes was affected by ethanol concentration, and browning color improved more with the increase of ethanol concentration than microwave power. Nitrite-scavenging effect was improved with increasing ethanol concentration and decreasing microwave power. Electron-donating ability and total polyphenol content were improved with increasing ethanol concentration and microwave power. Tyrosinase-inhibitory effect increased more with decrease in microwave power than with ethanol concentration. The optimal range of extraction conditions for effective component of F. velutipes were $47.21{\sim}76.05$ watt of microwave power, $10.25{\sim}43.56%$ of ethanol concentration, and 5.72 min of extraction time.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.5
• /
• pp.577-583
• /
• 2017

A series of microwave waste tire pyrolysis experiments were conducted using a lab-scale batch reactor to delineate the effects of microwave ouput power on the pyrolysis behavior of waste tire. As results of experiments, it was found that as the microwave output power was increased from 1.22 kW/kg to 2.26 kW/kg, the reaction temperature and oil yield increased significantly and the required time and microwave power consumption decreased remarkably, respectively. With increased power consumption, the content of the fixed carbon of pyrolysis residue increased.

• Journal of electromagnetic engineering and science
• /
• v.15 no.2
• /
• pp.82-88
• /
• 2015

The magnetron, a vacuum tube, is currently the usual high-power microwave power source used for microwave heating. However, the oscillating frequency and output power are unstable and noisy due to the low quality of the high-voltage power supply and low Q of the oscillation circuit. A heating system with enhanced reliability and the capability for control of chemical reactions is desired, because microwave absorption efficiency differs greatly depending on the object being heated. Recent studies on microwave high-efficiency power amplifiers have used harmonic processing techniques, such as class-F and inverse class-F. The present study describes a high-efficiency 100 W GaN-HEMT amplifier that uses a harmonic processing technique that shapes the current and voltage waveforms to improve efficiency. The fabricated GaN power amplifier obtained an output power of 50.4 dBm, a drain efficiency of 72.9%, and a power added efficiency (PAE) of 64.0% at 2.45 GHz for continuous wave operation. A prototype microwave heating system was also developed using this GaN power amplifier. Microwaves totaling 400 W are fed from patch antennas mounted on the top and bottom of the microwave chamber. Preliminary heating experiments with this system have just been initiated.

• Journal of Biosystems Engineering
• /
• v.40 no.3
• /
• pp.250-260
• /
• 2015

Purpose: Dual cylindrical microwave chambers equipped with an ohmic heating tube were designed and fabricated to maximize the electric field strength for expeditious heat treatment of particulate foods. Methods: The efficacy of the combination heater was investigated by simulating the electric field distribution by using COMSOL Multiphysics software. Results: All components of the designed microwave heating unit were suitable for transmitting maximal microwave power to the load. The simulated electric field distribution implied that single-mode microwave heating would be sufficient for the steady generation of a highly localized heating zone in the cavity. During impedance matching, the calculated reflection coefficient ($S_{11}$) was small, possibly implying minimal power loss and wave reflection in the designed microwave heating chamber. Conclusions: This study demonstrates the possibility of concentrating the microwave power at the centerline for a single-frequency microwave, for thermal treatment of multiphase foods without attenuating the microwave power.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.53 no.3
• /
• pp.180-187
• /
• 2004

A conventional power supply of a microwave oven has a 60Hz transformer and high voltage capacitor(HVC). Though it is very simple and has low cost, it has several problems such as large size, heavy weight and low efficiency To improve these problems, various high frequency inverter type power supply have been investigated and developed in recent years. But these cost is higher than the conventional one due to additional control circuit, fast switching devces. In this paper, a novel pulse power supply for microwave oven using high frequency transformer embedded HVC(High Voltage Capacitor) is proposed for down-sizing, cost reduction and efficient improvement. To verify the effectiveness of the proposed transformer, an equivalent circuit of transformer embedded HVC is derived and it's characteristic is described. And the validity of the proposed pulse power supply embedded HVC-high frequency transformer is shown by simulations and experiments accroding to various operating conditions.

• Food Science and Preservation
• /
• v.9 no.4
• /
• pp.385-390
• /
• 2002

Functional activities of Lyophyllum ulmarium microwave-assisted extracts under different conditions including electron donating ability, tyrosinase inhibition activity and nitrite scavenging effect were examined. Total polyphenol content increased as increasing microwave power up to 90 W in the water extracts. Electron donating ability increased with microwave power up to 90 W in 50% ethanol extract and 99% ethanol extract. Tyrosinase inhibition activity and nitrite scavenging effect in the extract increased as microwave power increased during extraction. Total polyphenol content increased as extending extraction time up to 5 min in the water extract. But the highest electron donating ability and tyrosinase inhibition activity was obtained after 10 min extraction. Significantly higher total polyphenol content and electron donating ability were found in the water extract whereas greater tyrosinase inhibition activity and nitrite scavenging effect were observed in 99% ethanol extract. The maxium nitrite scavenging effect was found at pH 1.2 and decreased as pH increased.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.32 no.4
• /
• pp.574-580
• /
• 2003

Optimal extraction conditions for yield, browning color, electron donating ability, nitrite scavenging effect, total polyphenol content and tyrosinase inhibitory activity of Lyophyllum ulmarium were determined by using response surface methodology (RSM) through the central composite design. The extraction yield of Lyophyllum ulmarium was effected by ethanol concentration and browning color was improved with the increase of ethanol concentration than microwave power. The nitrite scavenging effect was improved with the increase of ethanol concentration and decrease of microwave power The electron donating ability, browning color, tyrosinase inhibitory activity and total polyphenol content were improved with the increase in ethanol concentration and microwave power. The optimal ranges of extraction conditions for effective components of Lyophyllim ulmarium were predicted as 60.05~102.75 watt of microwave power, 53.20~64.01% of ethanol concentration and 7.77 min of extraction time.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.10
• /
• pp.1477-1482
• /
• 2012

This paper deals with a new variable microwave power distributor and a connector between a deck plate and a input power waveguide for indoor microwave wireless power transmission. We design a new type connector built in the 3-stage coaxial line structure, and calculate the return loss of the connector at 2.45GHz. Newly designed connector shows the excellent return loss performance less than -30dB at the operating frequency of 2.45GHz. And we show a power distributor in which the dividing ratio of the power is controlled mechanically by three rotary fins. The distributor can control the dividing power from 4.5% to 58% with the variance of 5% output power. The experimentally tested results of the distributor are good agreement with the simulation within the return loss of 1%.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.6
• /
• pp.792-797
• /
• 2013

In a indoor microwave power distribution system, matching-type power dividing switch is proposed and designed with a various power dividing ratio. A matching coaxial cable probe is used behind the output probe for the reflecting power absorption. Reflecting characteristics of the matching coaxial cable probe are calculated by analyzing the S-parameter of this structure. Newly proposed matching-type switch shows a very low return loss less than -30dB at the operating frequency of 2.45GHz with a dividing power ratio of 50.2%. The simulated results by use of 3-stage power divider shows a good agreement with the theoretical estimation for the various combination of the different switching ratio.

• Journal of Biosystems Engineering
• /
• v.37 no.6
• /
• pp.385-397
• /
• 2012

Purpose: Drying characteristics of sawdust was studied under batch mode using lab scale microwave dryer. The objective of this study was to investigate the effect of material load and microwave output power on drying characteristics of sawdust. Methods: Material load and microwave output power were varied from 23 to 186 g and 530 to 370 W respectively. Different kinetic models were tested to fit the drying rates of sawdust. Similarly, the activation energy was calculated by employing the Arrhenius equation. Results: The drying efficiency increased considerably, whereas the specific energy consumption significantly decreased with increase in material load and microwave output power. The cumulative energy efficiency increased by 9%, and the specific energy consumption decreased by 8% when the material load was increased from 23 to 186 g. The effective diffusivity increased with decrease in material load and increase in microwave output power. The previously published model gave the best fit for data points with $R^2$ and RMSE values of 0.999 and 0.01, respectively. Conclusions: The data obtained from this study could be used as a basis for modeling of large scale industrial microwave dryers for the pellet production.