• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.20-26
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• 2012

The objective of this study is to assess plastic deformation in aluminium alloy by acoustic nonlinearity of laser-generated surface waves. A line-arrayed laser beam made by high-power pulsed laser and mask slits is utilized to generate the narrowband surface wave and the frequency characteristics of laser-generated surface waves are controlled by varying the slit opening width and slit interval of mask slits. Various degrees of tensile deformation were induced by interrupting the tensile tests so as to obtain aluminum specimens with different degrees of plastic deformation. The experimental results show that the acoustic nonlinear parameter of a laser-generated surface wave increased with the level of tensile deformation and it has a good correlation with the results of micro-Vickers hardness test and electron backscatter diffraction (EBSD) test. Consequently, acoustic nonlinearity of laser-generated surface wave could be potential to characterize plastic deformation of aluminum alloy.

• Korean Journal of Optics and Photonics
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• v.23 no.5
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• pp.211-216
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• 2012

We report a resonance fiber Bragg sensor interrogation based on a Fourier domain mode-locking (FDML) laser. The FDML laser is constructed based on a conventional ring laser cavity configuration with fiber Fabry-Perot tunable filter (FFP-TF). There are two sensor parts which are composed with two FBGs inside the laser cavity. Each sensor part provides a separate laser cavity for the FDML laser. The resonance frequencies of the laser cavities are 46.687 kHz and 44.340 kHz, respectively. We applied a static and a dynamic strain on the FBG sensor system. The slope coefficients of the measured relative wavelength shift and relative time interval from the static strain are found to be $0.61pm/{\mu}{\epsilon}$ and $0.8ns/{\mu}{\epsilon}$, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.1
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• pp.37-46
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• 2003

The transient responses on arbitrarily interconnected digital transmission lines are analyzed by an efficient node discretization technique. Since the proposed node discretization technique offers an efficient means to discretize transmission lines, the transient waveform at any position on the arbitrarily interconnected lines is easily predicted. Dispersive microstrip multiconductor transmission lines arbitrarily connected are analized for generality. The derivation of frequency-dependent equivalent circuit elements of coupled transmission lines have been carried out by the spectral domain approach(SDA). The effects of variations of excited pulse width on the crosstalks of the high-speed microstrip coupled-lines are also investigated. It has been well known that the crosstalk spike level is monotonously increased when the coupling length and effective permittivity of substrate are increased. In this paper, it is found that the variations of crosstalk level are not further monotonous as shortening the exciting pulse width toward several picosecond. The results are verified by the generalized S-parameter technique.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.12
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• pp.46-53
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• 2003

This paper describes a new linear operational transconductance amplifier (OTA) and its application to the 9th-order Bessel filter. To improve the linearity of the OTA, we employ a mobility compensation technique. The combination of the triode and the subthreshold region transistors can compensate the mobility reduction effect and make the OTA with a good linearity. The proposed OTA shows $\pm$0.32% Gm variation over the input range of $\pm$0.8-V. The total harmonic distortion (THD) was lower than -60-㏈. The 9th-order Bessel filter has been designed using a 0.35-${\mu}{\textrm}{m}$ n-well CMOS process under 3.3-V supply voltage. It shows the cutoff frequency of 8-MHz and the power consumption of 65-mW.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.705-712
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• 2001

In this paper, a new type of aperture coupled microstrip patch antenna with tilted-beam based on the principal of the dipole yagi antenna is proposed and investigated experimentally. Its configuration is composed by 3 types of patches; reflector, driver, and director. Tilted beam patterns are effected by many parameters as those of dipole yagi antenna; sizes of the patches, gaps between the patches, characteristics of the substrates, feeding method and etc. Therefore, in this paper, the effects of varying design parameters of this antenna are studied with a goal of enhancing the gain and tilting the beams. A microtrip patch antenna with tilted beam based on performance trade-offs is designed and fabricated. Measured and simulated results for return loss and radiation patterns are presented. It has 45$^{\circ}$ tilted beam and very close to simulation beam pattern at resonant frequency, 2.58 GHz.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.11
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• pp.1047-1052
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• 2016

In this paper, we propose the CSLR(: Complementary Single Loop Resonators)-loaded inset fed patch antenna with a conducting reflector to improve the radiation patterns. Reflector of the proposed antenna is located below about ${\lambda}_0/4$ from the ground plane of the patch, the size is about two times of the patch. The proposed antenna is designed and fabricated on the substrate which has a dielectric constant and thickness with 2.5 and 0.787 mm, respectively. Simulation results are obtained by using the HFSS, 3D EM Solver based Finite Element Method(: FEM). The resonant frequency and matching characteristics of the antenna with reflector are substantially the same as when there is no change in the antenna without reflector, it is confirmed that radiation patterns are significantly improved by the reflector.

• Journal of Navigation and Port Research
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• v.38 no.6
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• pp.623-627
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• 2014

In recent years, wireless communication technologies in human body have received an increasing attention and the research on an antenna that can be worn also has been actively conducted. In this paper, an wearable antenna that can receive GPS signal frequency is proposed. The antenna was manufactured by using a copper polyester fabric with thickness of 0.08mm as a radiator and a ground plate, and a goatskin with thickness of 0.7mm as dielectric substrate. Cutting edges placed in diagonal direction of square patch in order to obtain a circular polarization characteristic, and the conductive cloth and leather was laminated by using a conductive epoxy. First, goatskin dielectric constant was obtained through the simulation and measurement of resonance frequency of the three square patch antennas with different size. On the basis of the results, an antenna operating in the GPS band was designed and the performance of the antenna was validated by making the experiment. The change of the characteristic of the antenna that is located on the shoulder parts of the clothing and wearing person were measured. And it was confirmed that the reception sensitivity has a similar level as compared to the commercially produced ceramic GPS antenna.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1184-1191
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• 2009

In order to reduce the download around the Smart UAV(SUAV) at Transition mode, flow control using synthetic jet has been performed. Many of the complex tilt rotor flow features are captured including the leading and trailing edge separation, and the large region of separated flow beneath the wing. Based on the results of part 1 of the present work, synthetic jet is located at 0.01c, $0.95c_{flap}$ and it is operated with the non-dimensional frequency of 0.5, 5 to control the leading edge and trailing edge separation. Consequently, download is substantially reduced compared to with no control case at transition mode using leading edge jet only. The present results show that the overall flight performance and stability of the SUAV can be remarkably improved by applying the active flow control strategy based on synthetic jet.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.247-254
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• 2004

We introduce a new space-time signal processing scheme that uses both transmitter diversity technique and transmitter beamforming technique for code-division multiple access (CDMA) systems. Over complex Gaussian Rayleigh channel, the introduced scheme achieves the diveristy gain through the transmitter diversity technique. and the SNR gain by th transmitter beamforming technique. Bit error rate (BER) analyses are given to each of the three cases in which the transmitter diversity scheme, the transmitter beamforming scheme and the introduced scheme are used, in the slowly varying Rayleigh frequency nonselective fading channel. The Monte-Carlo simulation results are shown to match to the analytic results. When the channels between distant antennas are independent, analytic results show that the introduced scheme achieves the lowest $E_{b/}$ $N_{0}$ at target BER 10$^{-6}$ . When the channels between distant antennas are correlated, analytic and simulation results show that the introduced scheme is more robust to the change of channel correlation.n.

• Journal of the Korean Magnetics Society
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• v.13 no.6
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• pp.246-250
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• 2003

The electromagnetic properties of Ni$\_$0.8/Zn$\_$0.2/Fe$_2$O$_4$ having stable characteristics in high frequency range were investigated as functions of Bi$_2$O$_3$, CaO contents. Power loss increased in proportion to the amount of Bi$_2$O$_3$ up to 0.3 wt％ and decreased over 0.3 wt％. Also, permeability increased with Bi$_2$O$_3$ contents. The lowest power loss and highest resonance frequency were obtained to the specimens added Bi$_2$O$_3$ of 0.7wt％ and CaO of 0.3 wt％ due to creation of resistivity layers in the grain boundaries originated by the solid solution of Bi$_2$O$_3$ and CaO.