• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.369-373
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• 2000

This paper describes a design for microstrip EMC cross dipole array antenna with circular polarization. To realize the wide bandwidth and circular polarization, the electromagnetic-coupled cross dipole is used. To obtain the uniform aperture illumination, offset technique for array is adopted. In 20-element array design, the calculated axial ratio and gain are about 0.1 dB and 9.9 dBi at 12GHz, respectively. The frequency characteristics of a fabricated 20-element array antenna are measured. The calculated results agree well with the measured ones.

• Journal of the Korean Physical Society
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• v.73 no.12
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• pp.1904-1907
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• 2018

We designed a depth-encoding positron emission tomography (PET) detector by using a bottom and side readout method with a cross-arranged scintillator array. To evaluate the characteristics of the novel detector module, we used the DETECT2000 simulation tool to perform the optical photon transport in the crystal array. The detector module consists of an $M(column){\times}N(row)$ cross-arranged crystal array composed of M/3 sub-arrays consisting of $N{\times}3$ crystals. The second column of the sub-array is arranged perpendicular to the first and the third columns. The crystal is optically coupled to the crystals of the other columns; however, the surfaces between the crystals in the same column are treated as reflectors. A $6{\times}5$ crystal array consisting of two sub-arrays was considered for proof of concept. The two multi-pixel photon counter (MPPC) arrays are coupled to the bottom and one side of the crystal array, respectively. The x-y position is determined by the bottom MPPC array, and the side MPPC array gives depth information. All pixels in the x-y plane and the z direction were clearly distinguished.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.1
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• pp.50-57
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• 2001

This paper describes a design for the circularly polarized microstrip EMC cross dipole array antenna with the wide bandwidth. To realize the characteristics of wide bandwidth and circular polarization, the electromagnetic-coupled cross dipole element is proposed. The optimum design parameters of a circularly polarized EMC cross dipole element are calculated by the FDTD and the Ensemble. To obtain the uniform aperture illumination of electric field in an array, offset technique that the cross dipole elements are alternatively arranged on center of the microstrip feed line is adopted. In 20-element array design, the calculated axial ratio and gain are about 0.1dB and 9.9 dBi at 12 GHz, respectively, The frequency characteristics of a fabricated 20-element array antenna are measured. The calculated results agree well with the measured ones.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.1
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• pp.11-17
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• 2020

This study proposes a novel structure for the cross-eye, one of the representative jamming techniques of monopulse sensors. The proposed jammer tranceivers are composed of multi-channels with phased array antenna. We named this structure PRCJ(Phased array Retrodicetive Cross-eye Jammer). In this structure, formulas for calculating cross-eye gain and distance error are derived. We compare the properties of PRCJ with two-element retrodiredtive cross-eye jammer(TRCJ). PRCJ can achieve higher J/S because this structure can steer the spatially combined jamming signal in the direction of the incident monopulse signal. Because of the multiple channels in the phased array, it also increases the degree of freedom of channel matching. Finally, We preform a statistical analysis of the cross-eye gain according to the amplitude and phase errors. From this results, It has been found that PRCJ can get higher cross-eye gain than TRCJ.

• Nuclear Engineering and Technology
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• v.38 no.1
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• pp.69-80
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• 2006

Fluid-elastic instability in an air-water two-phase cross-flow has been experimentally investigated using two different arrays of straight tube bundles: normal square (NS) array and rotated square (RS) array tube bundles with the same pitch-to-diameter ratio of 1.633. Experiments have been performed over wide ranges of mass flux and void fraction. The quantitative tube vibration displacement was measured using a pair of strain gages and the detailed orbit of the tube motion was analyzed from high-speed video recordings. The present study provides the flow pattern, detailed tube vibration response, damping ratio, hydrodynamic mass, and the fluid-elastic instability for each tube bundle. Tube vibration characteristics of the RS array tube bundle in the two-phase flow condition were quite different from those of the NS array tube bundle with respect to the vortex shedding induced vibration and the shape of the oval orbit of the tube motion at the fluid-elastic instability as well as the fluid-elastic instability constant.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1118-1124
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• 2023

Experimental study on the fluidelastic instability (FEI) of a curved tube bundle in single phase downward cross flow is investigated for the design qualification and analysis input preparation of helical coiled steam generator tubing. A 6×9 normal square curved tube array with equal and different vertical/horizontal pitch-to-diameter ratio was under-tested up to 6 m/s in term of gap flow velocity to measure the critical velocity for FEI. The critical velocity for FEI was measured at the turning point from the vibration amplitude plot along the gap flow velocity. Our test results were compared with straight tube results and published data in the design guideline. The applicability of the current design guidelines to a curved tube bundle is also assessed. We found that introducing frequency difference in a curved tube array increases the critical velocity for fluidelastic instability.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1
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• pp.56-61
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• 2002

In piezoelectric ultrasonic linear array transducers widely used for diagnosis, the cross talk caused by the structural cross-coupling between adjacent elements inside the transducer affects the probe performance in a significant manner. In this study, we constructed a finite element model of a piezoelectric ultrasonic transducer, and analyzed its cross talk level with respect to the shape of and materials inside the kerf, The results of this work can be utilized in optimal design of the transducers for medical diagonosis and treatment as well as W applications.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.124-132
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• 2009

Experiments have been performed to investigate fluid-elastic instability of tube bundles, subjected to twophase cross flow. Fluid-elastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and the threshold flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.310-316
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• 2019

Fluidelastic instability is a key issue in steam generator tube bundles subjected in cross-flow. With a low flow velocity, a large amplitude vibration of the tube observed by many researchers. However, the mechanism of this vibration is seldom analyzed. In this paper, the mechanism of cross-flow effects on fluidelastic instability of tube bundles was investigated. Analysis reveals that when the system reaches the critical state, there would be two forms, with two critical velocities, and thus two expressions for the critical velocities were obtained. Fluidelastic instability experiment and numerical analysis were conducted to obtain the critical velocity. And, if system damping is small, with increases of the flow velocity, the stability behavior of tube array changes. At a certain flow velocity, the stability of tube array reaches the first critical state, a dynamic bifurcation occurs. The tube array returns to a stable state with continues to increase the flow velocity. At another certain flow velocity, the stability of tube array reaches the second critical state, another dynamic bifurcation occurs. However, if system damping is big, there is only one critical state with increases the flow velocity. Compared the results of experiments to numerical analysis, it shows a good agreement.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3
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• pp.208-216
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• 2003

In one dimensional linear array type piezoelectric ultrasonic transducers widely used for medical diagnosis, the acoustic cross talk caused by the structural acoustic coupling between the adjacent piezoelectric elements reduces significantly their performance. In the study, we have proposed an acoustic wall to reduce the acoustic cross talk by wave propagation through the surface the transducer which can not be prevented by conventional kerf and have analyzed using a finite element method the acoustic cross talk level with respect to the shape, size and materials of the acoustic wall mounted on a convex one dimensional piezoelectric ultrasonic transducer. We expect that the simulated results provide us with a valuable information to make an optimized design of the way type ultrasonic transducer minimizing the acoustic cross talk level.