• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.5
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• pp.1028-1048
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• 2011

The relation of multicast transmission and directional antennas is an open problem that has been debated for a long period of time. In this paper, we propose a group-aware multicast scheme of efficient multicast communication using the directional antennas for 60GHz millimeter wave wireless networks. For this purpose, we first derive the relation among beamwidth, distance between devices and most suitable data rate in the 60GHz frequency-based wireless network. In addition, for the dynamic beamforming of multicast communication, the x and y coordinates of any point with sender device at the center is generated, and a best-chosen group is deduced based on the Euclidean distance. Then the most suitable data rate for the group is obtained using the law of cosine. Using the Standard IEEE 802.11ad MAC protocol as an example, extensive simulation results demonstrate that the proposed scheme outperforms the existing multicast communication schemes with directional antennas under different situations.

• Journal of the Korean Society of Visualization
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• v.11 no.3
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• pp.12-16
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• 2013

The impact and spreading behaviors of silicon dioxide nanoparticle colloidal suspension droplets were quantitatively visualized using a high-speed imaging system. Millimeter-scale droplets were generated by a syringe pump and a needle. Droplets of different velocity were impacted on a non-porous solid surface. Images were consecutively recorded using a CMOS high-speed camera at 5000 fps (frames per second) for millimeter-scale droplets. Temporal variations of droplet diameter, velocity and maximum spreading diameters were evaluated from the sequential images captured for each experimental condition. Effects of Reynolds number, Weber number, and particle concentration were investigated experimentally.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.112-117
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• 2012

This paper presents a new stopper mechanism for precision stage by using the Piezoelectric element actuator. The new stage including a new stopper mechanism has the precision positioning mechanism that was been developed for generation displacements with nanometer accuracy and a millimeter dynamic range simulataneouly. The stage is composed not of the mechanical two stopper but of only one Piezoelectric element actuator. The characteristics for the new stage and the stopper have been evaluated experimentally. As the results, we can know that the linearity error characteristics of stage is 30nm in the $20{\mu}m$ measurement range. In addition, the experimental results are confirmed the possibility of the movement in millimeter range.

• Journal of Electrical Engineering and Technology
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• v.5 no.3
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• pp.497-502
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• 2010

In this paper, the O-mode ultrashort-pulse reflectometry (USPR) millimeter-wave signals that propagate into the plasma and cover a frequency bandwidth of 33-158 GHz are examined numerically using MATLAB. Two important processes are involved in the computation: the propagation of the USPR impulse signal through a waveguide and the frequency up-conversion using millimeter-wave mixers. These mixers are limited to intermediate frequency signals that are less than 500 mV; thus, it is necessary to disperse the impulse signal into a chirped waveform using the waveguide. The stationary phase method is utilized to derive a closed-form formula for a chirped waveform under the assumption that the USPR impulse is Gaussian. In the process of frequency up-conversion, the chirped waveform is mixed with the mixer LO signal, and the lower frequency components of the RF signal are removed using high pass filters.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.135-138
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• 2003

The circular cavity resonator which can measure the dielectric properties of dielectrics in the V-band($50GHz{\sim}75GHz$) frequency range was designed and fabricated. Exciting and detecting of the resonator is peformed by WR15 rectangular waveguides using Bethe's small hole coupling. The GaAs plate sample was used for the verification of the performance of the fabricated circular cavity resonator. In the measurement of GaAs single crystal using that resonator, the resonant frequency of the dominant $TE_{011}$ mode, the permittivity and $Q{\times}f_0$ were measured as 53.29GHz, 12.87 and 138,000, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.6
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• pp.128-135
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• 1996

This paper proposes a high precision measurement technique to obtain the height of gage block with a few millimeter height. The proposed technique is consisted of two steps : In the first step, laser position transducer and electric micrometer are adopted to obtain a coarse value of the height of gage block, and then, in the second step, heterodyne laser interferometry is adopted to acquire the precision value. A new kind of phase detector is constructed in the low cost for the heterodyne interferometer and its linearity with ${\pm}1%$ is confirmed by experiment. Also measurement error factors due to enviroments are discussed and methodology to reduce such errors is proposed. Preliminary experiments are carried out for the gage blocks of as high as a few millimeter.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.5
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• pp.617-624
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• 2007

This paper presents a novel quadstable monolithic mechanism (QsMM) which provides four stable equilibrium positions within its operation range. The quadstable mechanism has been realized from the use of both X- and Y-directional bistable structures which use curved snapping beams. A millimeter-scale brass mechanism was fabricated by ultra-precision milling to test the quadstability and the displacement-load behavior, and the prototype clearly demonstrated four distinct stable positions in its millimeter-scale planar operation. We discuss the design concept, finite element simulation for static and transient responses, fabrication by ultra-precision milling, and experimental measurement of the proposed quadstable mechanism.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.3
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• pp.248-258
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• 1997

The analytical solutions of the Fraunhofer Diffraction(FD) theory and the principle for measurement of the dispersion relation of plasma wave is presented. Especially, the method for measurement of low-frequency wave is discussed. The wavenumbers of the density fluctuations are obtained from the curve fitting between the expremental FD profile and theoretical one for each frequency component. In measurement of the wavenumber of the low -frequency region, the information of the wavenumber is easily obtained from the ratio of the intensity at = 0 to the intensity at =0.5. The millimeter wave FD apparatus was designed to measure low-frequency density fluctuations. The determined wavenumbers are in the range of =0.1~ 1.0cm. Thus, the millimeter wave FD method was shown to be useful for the measurement of low-frequency density fluctuations, which are impossible to be measured by using a convention. Thomson scattering. The obtained dispersion relations will be useful information for plasma waves.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.151-157
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• 2000

The ITU-R model for cross-polarization, which is accurate enough in real rainfall environments, is proposed in this paper. By comparing this with measurement data and the ITU-R model, we have also derived a prediction model for rain cross-polarization applicable upto millimeter wave band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1264-1268
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• 2003

In this paper, we have designed the duplexer using non-radiative dielectric(NRD) guide in millimeter wave band. The designed duplexer is composed of two stepped-impedance filters and T-junction. Stepped-impedance filters we designed with an equivalent circuit model of evanescent waveguide and the T-junction is optimized to minimize return loss of -20 dB or more. The characteristics of duplexer show good agreements with the expected results.