• Journal of the Institute of Electronics Engineers of Korea TE
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• v.42 no.2
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• pp.23-28
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• 2005

This study was to suggest the propagation path loss and predictive model of propagation path analysis in order to apply the frequency in the millimeter-wave band to the real time inter-vehicle communication system. This study was to suppose the case of inter-vehicle communication on the one-way two-lanes road in the big cites with a lot of traffic jams in order to analyze the effect by the reflected wave of multipath. As a simulation of suggested model, it found out that the propagation path by the reflected wave was about 0.1[m]$\sim$5.1[m] longer than the one by the direct wave during the transmission of 100[m] wave direct path. Also, as a result of comparing the propagation path loss, the loss would be about -0.8[dB]$\sim$-4.2[dB] larger in case of wall reflection and -0.8[dB]$\sim$-1[dB] vehicle reflection. From the result above, this researcher found out that the path loss of reflected wave produced by the walls was about -3.2[dB] larger than the path loss produced by the adjacent vehicles.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.8
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• pp.709-716
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• 2016

In this paper, A duplexer module with temperature-insensitive electrical characteristics was proposed for remote wireless communication system. Duplexer modules are required to have performances of low insertion loss, high isolation between transmitted band and received band, harmonic suppression as well as high power durability in the system for transmitting guided information to missile flying a free space on the ground. The proposed duplexer module are consist of transmission bandpass filter and receiving bandpass filter which are connected to common antenna port, planar coupler for output power monitoring and low pass filter for harmonic attenuation of power amplifier and coaxial cavity resonator. The material and dimensions of the resonator are determined for minimum frequency shift by temperature variation using 3D EM simulation. The measured results of the prototype showed a good agreement with the simulation results, and it should be well applied not only for guided weapon systems but also for any other communication systems such as remote radio head.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.2
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• pp.86-94
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• 1996

In the life management safety evaluation of constructs base on a fracture mechanics, the size of defect is the very important parameter. ICFPD (Induced Current Focusing Potential Drop)technique has been developed for detecting and sizing of defects that exist not only on surface but also inside and interior of structural components. The principle of this technique is to induce a focusing current at an exploration region by a straight induction wire through which an alternating current (AC)flows that has constant amplitude and frequency. The potential distributed on the surface of metallic material is measured by potential pick-up pins that are settled on the probe. In this paper, this NDI technique was applied to the evaluation of surface cracks and blind cracks in plate specimens. The results of this study show that in the case of surface crack, the distribution of potential drop is varied with the inched angle of surface crack, and the potential drops in the crack region and the crack edge region are varied with the inclined angle and depth of crack. The distribution of potential drop for the blind crack is distingulished from that for the surface crack, and the potential drop in the crack region is varied with the depth of crack.

• 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.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.4
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• pp.25-31
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• 1994

A system for EMAT, which generates ultrasound by electro-magnectic forces and performs nondestructive testing in noncontact, was established. By linking it with a 3 axis scanning system and a data acquisition and processing system the automation of EMAT testing was attempted. A EMAT sensor was fabricated and the directivity pattern of it was measured. To be suitable automation, it has a transmitter and a receiver in one case and the main beam direction of it can be controlled by the frequency of driving signal. A program which controls the EMAT system, the 3 axis scanner and the data acquisition and processing system was developed. It also processes acquired data and displays the processing results. IBM-PC/AT compatible PC was used as main controller and the stratage of the program is emulation of real devices on the PC monitor. To provide the performance of the established EMAT system, two aluminium blocks containing artificial flaws and a welded aluminium block were tested. The result of the tests were satisfactory.

• Composites Research
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• v.23 no.5
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• pp.22-29
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• 2010

This paper describes the evaluations of tension-compression fatigue characteristics and life for glass fiber/epoxy laminate composite applied to railway bogie to reduce weight. Test samples of tension-compression fatigue were composed of glass fiber/epoxy 4-harness woven laminate composites with different stacking sequence of warp-direction, fill-direction and ${\pm}45^{\circ}$-direction. The tension-compression fatigue test was conducted with stress ratio (R) of -1 and frequency of 5Hz. Goodman diagram were used to evaluate the fatigue characteristics and life of glass fiber/epoxy 4-harness satin woven laminate composite. Anti-buckling jig was designed to prevent buckling of specimen under compression load. The test results showed that the fatigue characteristics of glass fiber/epoxy 4-harness satin woven laminate composite with stacking sequence of warp-direction had a good performance in comparison with that of SM490 used to conventional metal railway bogie.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1193-1199
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• 2010

Spot welding is the primary method of joining sheet metals in the automotive industry. As automobiles are subjected to fatigue loading, some spot welds may fracture before the whole system has failed. This local fracture of spot welds may lead to change in the dynamic response and consequently affect fatigue behavior of an automobile. Therefore, this change in dynamic response should be taken into consideration to assess the fatigue life of structures subjected to spectrum loading, such as automobiles. In this study, vibration fatigue analysis was performed by taking into consideration the change in the dynamic response due to accumulated damage at spot-welded parts. Fatigue tests were carried out on tensile-shear spot-welded specimens under constant amplitude loading condition. And the fatigue life of spot welds under spectrum loading was predicted using vibration fatigue analysis method based on finite element analysis.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.1
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• pp.23-30
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• 1997

Recently high frequency ultrasonic transducers to employ polyvinylidene fluoride(PVDF) or polyvinylidene fluoride trifluoroethylene P(VDF-TrFE) have been used to detect small flaws in immersion testing. The detection field depending on the water path between the transducer and a specimen and the path in a tested specimen was measured using a PVDF transducer with nominal frequency 80MHz. Also, C-scan and B-scan were performed for the specimens made of Cr-Ni steel with the artificial flaws, the flat-bottom holes with diameter ranging from $50{\mu}m$ to $560{\mu}m$ at 12mm depth. As the result, the flaws with diameter larger than $280{\mu}m$ were detected, but the flaws with the ratio of diameter to wavelength smaller than about 0.48 were not detected. That the smaller flaws could not be detected was attributed to the attenuation of high frequency components in the steel specimens.

• Journal of the Korean Wood Science and Technology
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• v.38 no.6
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• pp.457-462
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• 2010

Sound absorption capability and bending strength of laminated ship-building plywood waste of maple and melanti wood were estimated. Sound absorption coefficients of wood had been measured by the two microphone transfer function method and bending strength examined by three point loading. The maximum strength in bending of laminated ship-building plywood waste of maple and melanti wood were 534 and 414 kgf/$cm^2$, respectively. The sound absorption coefficients of laminated ship-building plywood waste were higher than mongolian oak and fiber board, well used construction material. Especially, in the case of laminated ship-building plywood waste of melanti wood, average sound absorption coefficient was about 0.25. It was surmised that the laminated ship-building plywood waste can be used as interior materials because of its good mechanical and sound absorption properties.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.425-433
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• 2001

A correlation between fatigue damage and acousto-ultrasonic (AU) parameters has been obtained from signals acquired during fatigue loading of the single-lap joints of a carbon-fiber reinforced plastic (CFRP) laminates and A16061 plate. The correlation showed an analogy to those representing the stiffness reduction $(E/E_0)$ of polymer matrix composites by the accumulation of fatigue damage. This has been attributed to the transmission characteristics of acoustic wave energy through bonded joints with delamination-type defects and their influence on the change of spectral content of AU signals. Another correlation between fatigue cycles and the spectral magnitude of acoustic emission (AE) signals has also been found during the final stage of fatigue loading. Both AU and AE can be applied almost in real-time to monitor the evolution of damage during fatigue loading.