• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.657-662
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• 2013

A size-reduced high frequency mixer designed by adopting artificial dielectric substrate is described in this work. The artificial dielectric substrate is composed by stacking the lower substrate in which a lot of metalized via-holes exist, and upper substrate on which microstrip lines are realized. The effective dielectric constant increases due to the inserted lots of via-holes, and this may be applied to size-reduction of high frequency circuits. In this work, in order to present an application example of size-reduction for active high frequency circuits using the artificial dielectric substrate, a 8GHz single gate mixer is miniaturized and measured. It is described that the basic circuit elements for mixers such as hybrid, low pass filter, and matching networks can be replaced by the artificial dielectric substrate for size-reduction. The final mixer has 55% of size compared to the normal one. The measured average conversion gain is around 3dB which is almost similar result as the normal circuit.

• Journal of Power Electronics
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• v.15 no.1
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• pp.31-38
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• 2015

In this paper, a buck-boost type battery charger is developed for charging battery set with a lower voltage. This battery charger is configured by a rectifier circuit, an integrated boost/buck power converter and a switched capacitors circuit. A boost power converter and a buck power converter sharing a common power electronic switch are integrated to form the integrated boost/buck power converter. By controlling the common power electronic switch, the battery charger performs a hybrid constant-current/constant-voltage charging method and gets a high input power factor. Accordingly, both the power circuit and the control circuit of the developed battery charger are simplified. The switched capacitors circuit is applied to be the output of the boost converter and the input of the buck converter. The switched capacitors circuit can change its voltage according to the utility voltage so as to reduce the step-up voltage gain of the boost converter when the utility voltage is small. Hence, the power efficiency of a buck-boost type battery charger can be improved. Moreover, the step-down voltage gain of the buck power converter is reduced to increase the controllable range of the duty ratio for the common power electronic switch. A prototype is developed and tested to verify the performance of the proposed battery charger.

• Journal of Sericultural and Entomological Science
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• v.14 no.2
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• pp.81-92
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• 1972

Studies on Pathogenicity of Nosema bombycis Naegeli are summarized as follows: 1. The mortality of the parents, Jam 103 and Jam 104, is remarkbly higher than that of the hybrid, Jam 103$\times$Jam 104, whereas there is no difference in the mortality between the parents. 3. In the mortality of the pathogen-concentration, it is increased in order of the following concentrations inoculated, 10$^{8}$ , 10$^{7}$ , 10$^{8}$ and 10$^{5}$ /ml. 3. In the mortality of each instar, it is high in order of 5th, 4th, 3rd, and 2nd instar. 4. In the interaction between the mortalities of the varieties and the concentrations, 1) The mortality shows no differences between the parents and the hybrid in the high concentration of 10$^{8}$ /ml. 2) The mortality of the hybrid is lower than that of the parents in the low concentration of 10$^{5}$ /ml, whereas no difference is found between the parents. 3) The interaction appears at the same level in the middle concentration of 10$^{6}$ /ml to the parents and of 10$^{7}$ /ml to the hybrid. 5. It was pointed out that active immunity depends upon the volume of antigen injection, immunizing period, and injection intervals. In this experiment, it is noticed that the optimum volume of injection is above 20ml and D is the best one of the four treatment (A.B.C.D.). 6. The immune sera indicate such a 12,800 high titer in the indirect method can be obtained from the D immunizing method. Silkworm tissues and N. bombycis spores show self-fluorescence, but it is able to distinguish it from the F.I.T.C. by using the U.V. filter. 7. The midgut epithelium is examined to be the first site of the tissues which are penetrated into and multiplied by the inoculation of the pathogen per os.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.183-184
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• 2013

Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was ＞99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.