• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.52-62
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• 2002

Electrical characteristics of two types of 20 GHz Push-Push GaAs MESFET dielectric resonator oscillators having Wilkinson and T-junction power combiners for the output stage have been investigated. The Push-Push oscillator for suppressing fundamental frequency 10 GHz and enhancing 20 GHz has been designed and realized in microstrip configuration on 20 mil thick RT-Duroid(${\varepsilon}_r$=2.52) teflon substrate. Two different types of power combiners, T-junction and Wilkinson, have been considered. Whenever one type of the combiners has been adopted for the output circuit, output power, phase noise and fundamental frequency suppression characteristics of the oscillator have been measured. When the Wilkinson power combiner was used, a maximum output power of 5.67 dBm, a phase noise of -105.5 dBc/Hz at an offset frequency of 100 kHz and a fundamental frequency suppression of -29.33 dBc have been measured. When the T-junction power combiner was used, a maximum output power of -1.17 dBm, a phase noise of -102.2 dBc/Hz at an offset frequency of 100 kHz and a fundamental frequency suppression of -17.84 dBc have been measured.

• Journal of the Korean Institute of Educational Facilities
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• v.10 no.4
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• pp.5-20
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• 2003

The purpose of the research on the noise of educational facilities is to build up pleasant environments by minimizing the influence on the students in the school. This study provides fundamental data for acoustic design by measuring, computer simulation and analyzing the room acoustic characteristics of the lecture room in middle school. For measurement on the factors of room acoustic, RT of lecture room and noise reductions depending on various walls of different structures were measured and analyzed. The lecture system being installed and carried out on the normal lecture room was divided into 4 types-employment of multimedia machines, employment of multimedia machines and loud speakers, employment of loud speaker, and existing verbal speaking-and SPL for each type was measured and analyzed. Based on the measured characteristics of acoustic characteristics for normal lecture room, the problems for environment of noise were understood through computer simulation, applications for improvements of performance for each facility were studied, schemes for improvements of performance by using the effects were presented, necessary fundamental data were secured, and schemes to enhance flexibility on the existing facilities of school against changing educational courses were secured.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.51-59
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• 2000

In-cylinder spray flow motion plays an important in the adjustment of mixture preparation with a fundamental spray characteristics and in-cylinder flow field well in direct-injection gasoline engine. In this study, the fundamental spray characteristics such as mean drop size, velocity distribution, spray angle were measured and in-cylinder spray flow motion was visualized in order to optimize intake port, piston top land and combustion chamber shapes in the development stage of mass-produced G야 engine. For these experiments, the PDPA measurements and Mie scattering technique were used for detailed spray characteristics and in-cylinder spray motions were obtained by use of ICCD camera through the single-cylinder optical engine. From the experimental results, the test injector shows a good low-end linearity between the dynamic flow and fuel injection pulse width and the fuel spray of 20mm or less in SMD with good spray symmetry. In addition, the in-cylinder tumble flow has more effect on the homogeneous mixture formation than that of in-cylinder swirl flow at early injection mode and the in-cylinder swirl flow plays a better role of stratified mixture preparation than tumble flow at late injection mode.

• Phonetics and Speech Sciences
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• v.5 no.3
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• pp.55-60
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• 2013

The purpose of this study was to investigate the acoustic characteristics of crying infants according to the communication intents such as hunger and pain in terms of acoustic differences in the fundamental frequency ($F_0$), jitter, shimmer, noise-to-harmonic ratio(NHR), habitual pitch, and intensity. The subjects were 20 healthy, normal infants, less than seven days old, from the city of Seoul and were born after 38 to 42 weeks(full term) of pregnancy. The sound of crying was recorded for three minutes. The crying due to pain was induced by means of the inborn metabolism error test, whereas the crying due to hunger was verified by means of the rooting reflex by waiting for the designated eating time. The results were as follows: (1) the fundamental frequency, noise-to-harmonic ratio(NHR), and intensity of the infants' crying due to pain was higher than that by hunger, showing a significant difference between the mean values. (2) the infants' crying due to hunger and that by pain did not have a significant difference in the mean jitter and shimmer values but both of them were largely outside of the normal threshold values(jitter by 1.04% and shimmer by 3.81%). This study was significant in the sense that it showed the acoustic characteristics of infants' crying from hunger and pain were very different from each other according to the communication intents in terms of the six acoustic parameters.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.613-624
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• 2002

Electrical characteristics of two types of 20 GHz Push-Push GaAs MESFET dielectric resonator oscillators having Wilkinson and T-junction power combiners for the output stage have been investigated and compared. So we have explained that the output power and phase noise properties of the Push-push FET DRO are depending on return loss and isolation characteristics of power combiner at the fundamental and the second harmonic frequencies. A Push-push oscillator for suppressing the fundamental frequency of 10 GHz and enhancing the second harmonic of 20 GHz has been designed and fabricated in microstrip configuration on 20 mil thick RT-Duroid($\varepsilon$$_{r}$ = 2.52) Teflon substrate. Return loss and isolation characteristics of T-junction and Wilkinson have been measured at the fundamental frequency of 10.2 GHz and the second harmonic frequency of 20.5 GHz. At the fundamental frequency, -12 dB return loss and -3.7 dB isolation have been measured for the T-junction power combiner, and -14 dB return loss and -11 dB isolation fur the Wilkinson power combiner. At the second harmonic frequency, -10 dB return loss and -7.5 dB isolation have been obtained for the T-junction power combiner, and -23 dB return loss and -22 dB isolation for the Wilkinson power combiner. As a result, we have confirmed that the oscillator based on the Wilkinson power combiner with better retrun loss and isolation characteristics produces more output power and better phase noise characteristics..

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.217-217
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• 2009

This paper describes the characteristics of polycrystalline 3C-SiC doubly clamped beam micro resonators. The polycrystalline 3C-SiC doubly clamped beam resonators with 60 ~ 100 ${\mu}m$ lengths, $10\;{\mu}m$ width, and $0.4\;{\mu}m$ thickness were fabricated using a surface micromachining technique. Polycrystalline 3C-SiC micro resonators were actuated by piezoelectric element and their fundamental resonant frequency was measured by a laser vibrometer in vacuum at room temperature. For the 60 ~ 100 ${\mu}m$ long cantilevers, the fundamental frequency appeared at 373.4 ~ 908.1 kHz. The resonant frequencies of doubly clamped beam with lengths were higher than simulated results because of tensile stress. Therefore, polycrystalline 3C-SiC doubly clamped beam micro resonators are suitable for RF MEMS devices and bio/chemical sensor applications.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.2
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• pp.91-97
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• 2003

In addition to its strong oxidizing power, the ozone has definite advantages over other commercial oxidants, namely, no undesirable by- products or residues are formed. With growing interest in the improvement of the ozone production in the industrial fields, many types of ozonizer using the electrical discharges have been proposed for the higher efficiency and the higher Performance at atmospheric Pressure. Among them, a superposition of different type discharges has been proposed. Especially, since the improvement for the low efficiency of dc discharge and narrow gap of surface discharge is required, a do and an at voltage are applied to same reaction space (or volume) to increase energy density at the same space. An investigation was focused on the superposition with a dc (streamer) corona and 3 surface discharge. This paper describes the investigation results on fundamental ozone generation characteristics by this superimposed discharge.

• MALSORI
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• v.55
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• pp.61-76
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• 2005

This paper aims to analyze the acoustic effects of vowels produced in a distant-talking environment. The analysis was performed using a statistical method. The influence of gender and speakers on the variation was also examined. The speech data used in this study consist of 500 distant-talking words and 500 normal words of 10 speakers (5 males and 5 females). Acoustic features selected for the analysis were the duration, the formants (Fl and F2), the fundamental frequency and the total energy. The results showed that the duration, F0, F1 and the total energy increased in the distant-talking speech compared to normal speech; female speakers showed higher increase in all features except for the total energy and the fundamental frequency. In addition, speaker differences were observed.

• Proceedings of the Korea Concrete Institute Conference
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• 1990.04a
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• pp.39-44
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• 1990

This experimental study is performed by using artificial lightweight aggregate manufactured in laboratory, and the test results of it are compared with those using foreign materials in respect of design compressive strength, unit weight. The tests on strength characteristics such as bending, splitting tensile strength and on mechanical characteristics including σ-εcurve, elastic modulus, poisson's ratio are performed to provide the fundamental data required for the design. From this study, it is possible to obtain the high-strength concrete having compressive strength of 500 kg/㎠ and unit weight of 1.85-2.0 t/㎥. And also it is recommended that sandlightweight concrete having high specfic strength is more practical for general use.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.7
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• pp.685-692
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• 2009

Vehicle interior noise is the results of numerous sources of excitation. One source involving tire pavement interaction is the tire cavity resonance and the forcing it provides to the vehicle spindle. Using a simplified model for the tire acoustic cavity system only, we formulated finite element equation to predict the fundamental acoustic cavity resonant characteristics inside tire-wheel assembly of undeformed and deformed tire. Combining the finite element analysis with experimental verification, we explained the acoustic characteristics theoretically. Especially, we have shown that the difference between the first two resonant frequencies increases as the deformation of deformed tire increases.