• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.59-67
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• 2018

In this paper, the test facility for coaxial propellers at low Reynolds developed and validated by measured data. The test equipment was designed to measure the hovering performance of propellers according to distances between the upper/lower propellers. Thrust, torque, rotational speed, vibration, and amperage of upper and lower propellers can be measured separately. The data acquisition system was built to collect signals of sensors, and LabVIEW software was used to control the motor and collect the signal. The hover performance tests of single propellers were preceded for the facility validation, and then the performance values of coaxial propellers were measured according to distances and diameter differences between the upper/lower propellers. The results showed that the high efficiency is achieved at 20%~30% distance between the upper propeller and lower one. The configuration that the upper propeller has shorter diameter than the lower one has the highest efficiency than other configuration.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.192-197
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• 2012

In this paper, a non-contact microwave technique was presented to detect the surface crack of the metals. An open-ended coaxial cable line was used as a sensor at 11 GHz, and the reflection coefficients were measured by scanning along the metal surface including artificial surface cracks. A parameter, the K value which was defined as the difference between maximum and minimum reflection coefficients, was measured and used to estimate the crack depth. A linear relationship between the K value and crack depth was found. This study showed that non-contact detection of the surface cracks of metals is possible using the open-ended coaxial line sensor at X-band.

• Journal of Biomedical Engineering Research
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• v.30 no.4
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• pp.333-340
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• 2009

MR compatible coaxial-slot antenna for microwave hyperthermia was developed while its structure and size of each part were determined by computer simulation using finite element method(FEM). Its local heating performance was evaluated using tissue-mimic phantom and swine muscles. 2% agarose gel mixed with 6mM/$\ell$ $MnCl_2$ as a biological tissue-mimic phantom was heated by the proposed antenna driven by a 2.45GHz microwave generator. The temperature changes of the phantom were monitored using multi-channel digital thermometer at the distance of 0mm, 5mm, 10mm and 20mm from the tip center of the antenna. Also muscle tissue of swine was heated for 2 and 5minutes with 50W and 30W of microwave generator powers, respectively, to evaluate the local heating performance of the antenna. MRI compatibility was also verified by acquiring MR images and MR temperature map. MR signals were acquired from the agarose gel phantom using $T2^*$ GRE sequence with 1.5T clinical MRI scanner(Signa Echospeed, GE, Milwaukee, WI, U.S.A.) at Pusan Paik Hospital and were transferred to PC in order to reconstruct MR images and temperature map using proton resonance frequency(PRF) method and laboratory-developed phase unwrapping algorithm. Authors found that it has no severe distortion due to the antenna inserted into the phantom. Finally, we can conclude that the suggested coaxial-slot antenna has an excellent local heating performance for both of tissue-mimic phantom and swine muscle, and it is compatible to 1.5T MRI scanner.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.2
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• pp.107-113
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• 2008

In 22.9[kV]-y distribution systems, underground cables are provided with multiple-point ground in which each coaxial-neutral line of the distribution cable lines(A, B, C phases) is 3-wire common grounded. In the underground cable distribution systems, circulating current flows in the coaxial-neutral lines and its magnitude amounts to about $40{\sim}50[%]$ load currents, even though loads are balanced. Power loss due to the circulating current consequently reaches to about 76[%] total losses occurred in all conductor lines. This power loss provokes additional temperature rise of the underground cable lines and finally results in 20[%] reduction of the current capacity of the cables. This paper presents a new ground method to overcome such a problem. The proposed method eliminates the circulating current flowing in the coaxial-neutral line effectively. Measurement results confirmed from the practical site-test show validity and effectiveness of this research.

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.55-59
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• 2007

Co-based amorphous magnetic wire with a diameter of $125{\mu}m$ and a length of 40 mm was used as an inner conductor of a coaxial cable to construct a magnetic sensor. Sensor characteristics was measured up to 3 GHz with applied up to 60 Oe by using network analyzer. Frequency dependence of impedance for this sensor was very close to the impedance resonant pattern of transmission line and 250 MHz was obtained as a 1/4 wavelength without external magnetic field. Large impedance change was measured in the magnetic field range between 0 Oe and 1 Oe, which was influenced by permeability change of magnetic amorphous wire. Because ${\Delta}Z/{\Delta}H$ value of $300{\Omega}/Oe$ was obtained at 0.1 Oe, this coaxial cable with amorphous wire can be useful as a magnetic sensor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.168-172
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• 2003

The effects of injection conditions on the droplet sizes resulting from the disintegration of a liquid jet by a fast annular gas stream have been investigated using PDPA. The gas/liquid momentum ratio M = $\rho$$_{g}$ $U_{g}$$^2$/$\rho$$_1$ $U_1$$^2$ and Weber number We = $\rho$$_{g}$ $g^2$ $D_1$/$\sigma$ are selected as key parameters in atomization of shear coaxial spray from the fluid mechanics standpoint. It is revealed that SMD( $D_{32}$) varies inversely with gas/liquid momentum ratio(M), whereas Weber number(We) has little effect on the droplet sizes as gas velocities increase. It is found that gas/liquid momentum ratio is more dominant factor controlling the breakup and atomization process of shear coaxial spray. Finally, an empirical correlation between SMD and injection conditions(i.e. gas/liquid momentum ratio M and Weber number We) is proposed based on the experimental results.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.1-8
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• 2017

In order to analyze combustion characteristics of methane-oxygen diffusion flame in a model combustor, combustion experiments were carried out under various spray conditions of propellant scrutinizing combustion stability limit and flame shapes. As the propellant approached the theoretical equivalence ratio condition, a stable detached flame was observed even under high oxygen Reynolds number. And the length of the visible flame increased and the lift-off distance of the flame exhibited a tendency toward decrease. Due to the swirl effect of the propellant by the swirl-coaxial injector, a wide and short flame was produced. Thus, it may be appropriate to employ the swirl-coaxial injector in thrusters having a limited physical dimension.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.5
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• pp.223-228
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• 2018

In this paper the water sensor using a coaxial cavity resonator is designed and manufactured. The water sensor which can sense water drop linearly has been constructed with voltage controlled oscillator(VCO), coaxial cavity resonator, RF switch, RF detector, A/D converter, DAC and micro controller. The operating frequency range of the designed water sensor is from 2.5GHz to 3.2GHz and the input voltage and current source are 24[V/DC] and 1[A]. The designed sensor circuit includes VCO, RF switch, RF detector which varies the frequency characteristics of the devices in the high frequency of 3GHz. And so we should correct the error of the frequency characteristics of those devices in the sensor circuit. To do this, we make the reference path which switches the signals to the RF detector directly without sending it to the resonator. According to the result of simulation and measurement, we can see that there is 0-50MHz difference between simulated resonator frequency and manufactured resonator frequency.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.739-742
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• 2002

The supersonic, dual, coaxial jet impinging upon a vertical flat plate has recently been applied to a variety of industrial manufacturing processes, since it has several advantages over a conventional supersonic impinging jet. In the present study, experimentation is carried out to investigate the effects of the impinging angle of the annular flow and the design Mach number on the flow field formed over the vertical flat plate. A convergent-divergent nozzle is used to obtain the inner jet flow, its design Mach number being changed between $1.0\;and\;2.0$. The outer annular nozzle has a constant area of the Mach number of 1.0, and its impinging angle of $0^{\circ}\;and\;20^{\circ}$. The primary jet pressure ratio is changed in the range from 6.0 to 10.0 and for the annular flow, the assistant jet pressure ratio is changed from 1.0 to 4.0. The distance between the dual, coaxial nozzle and flat plate is also changed. Detailed pressure measurements are conducted along the axis of the jet and on the flat plate as well. The impinging coaxial Jet flows are visualized using the Schlieren and Shadow optical methods. The results show that the flow field on the plate is not strongly dependent only on the primary and assistant pressure ratios but also the impinging angle of the annular nozzle.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.2
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• pp.70-77
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• 2003

In this paper, analysis and measurement on coaxial connecter designed for packaging of microwave and micro strip transition structure are carried out. Even though researches on optimization of various kinds of transition structures have been conducted actively; however, the range of the application was very limited since they have been focused mainly on improvement of specific transmission line. Therefore, in this paper, we tried to analyze three kinds of substrates of which dielectric constants are 2,5,10 and are commercially used nowadays. Besides, we have confirmed reliability of FEM analysis, extracted equivalent circuit of transition area, found out factors determining extracted physical values, and made proof of electromagnetic variations for optimum characteristics. In addition, transition structure showing optimized characteristics on the basis of dielectric and microstrip structure was proposed. We reckon that the result of this research will apply with effect to transition design in microwave packaging development.