• 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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.1
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• pp.1-11
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• 2000

A low frequency, high power hydroacoustic transducer with 7 tonpilz piston elements assembled in a circular array suitable for marine application, such as the transmission of underwater information and the development of new fisheries resources in the deep sea zone was designed. A modified Mason's model was applied to monitor and to simulate the transducer behavior at each step during the fabrication. The in air, and in water constructed tonpilz transducer was tested experimentally and numerically by changing the size and the type of the material for head, tail and acoustic window. Also, the developed transducer was excited by pulse signals and the received waveform was analyzed. The resonance peaks in the transmitting voltage response(TVR) of a single tonpilz element without housing were observed at 11.33kHz in air and 10.93kHz in air and 10.93 kHz in water, respectively, with the overall electrical-acoustic efficiency of 43.7%. The value of TVR of single tonpilz element with aluminum housing in water was 129.87dB re 1 $\mu$Pa/V at 12.25 kHz with the frequency bandwith of 2.15 kHz and half beam angle of 30.2$^{\circ}$at -3dB.The resonance peaks in the transmitting voltage response of the 7 element circular transducer were observed at 11.50 kHz in air and 11.45 kHz in water, respectively. The value of TVR in water 144.84 dB re 1$\mu$Pa/V at 11.5kHz with the frequency bandwith of 4.25 kHz and the half beam angle of $22.3^{\circ} $ at -3dB.Reasonable agreement between the experimental measurements and the theoretical predictions for the directivity patterns, TVRs and the impedance characteristics of the designed transducer was achieved.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.8
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• pp.710-717
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• 2015

In this paper, we design an array antenna structure based on a patch ESPAR(Electronically Steerable Parasitic Array Radiator) antenna with three elements for reliable communication in high-speed railway wireless communication. The ESPAR antenna consists of the active element with a single RF-chain and the parasitic elements surrounding an active element. The ESPAR antenna is capable of beamforming by adjusting the reactance of the parasitic element. We propose a vertical array antenna structure based on the patch ESPAR antenna and simulate it according to the change of the number of antennas and the distance between antenna rows. The simulation results show that we can get the maximum beam gain and highest directivity when the distance between antenna rows is ${\lambda}$.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.11
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• pp.1050-1056
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• 2015

In this paper, we use the characteristics of electromagnetic waves underwater attenuation for estimating linear distance between a transmitting node and receiving node, and research underwater vertical plane attenuation model for constructing the underwater localization system. The underwater localization of 2 dimensional with the plane attenuation model in the horizontal plane (H-plane) was proposed previous research. But for the 3 dimensional underwater localization, the additional vertical plane (E-plane) model should be considered. Because the horizontal plane of omnidirectional antenna has the same attenuation tendency in x-y plane according to the distance, whereas in vertical plane shows an irregular pattern in x-z plane. For that reason, in the vertical plane environment, the attenuation should be changed by the position and inclination. Hence, in this paper the distance and angle between transmitting and receiving node are defined using spherical coordinate system and derive an antenna gain pattern using half power beam width (HPBW). The HPBW is called a term which defines antenna's performance between isotropic and other antennas. This paper derives omnidirectional antenna's maximum gain and attenuation pattern model and define vertical plane's gain pattern model using HPBW. Finally, experimental verifications for the proposed underwater vertical plane's attenuation model was executed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.3
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• pp.318-325
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• 2019

As satellite communication technology with high efficiency and spatiality evolves, demands of customer for efficient and effective satellite broadcasting services are increasing due to interval reduction of the between satellites, and the limited radio-frequency spectrum resources. Recently, research on antenna that it possible to simultaneously receive multiple signal from various satellites while holding maintain the same number of previous reception channels by using the single reflector has been ongoing. It is necessary to be able to simultaneously receive signals from various satellites in order to maintain the same number of previous reception channels. We suggest a multiband antenna which can be simultaneously and independently receiving Ku band and Ka band satellite broadcasting signals transmitted by three adjacent satellites. We have designed and simulated using commercial design tools TICRA CHAMP and CST MWS to meet the target specifications. It appears that the antenna has -10 dB return loss, and more than 40 dBi directivity gain in Ku band and Ka band respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.6
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• pp.63-70
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• 2012

This paper discussed on the directive gain improvement method of the U-type ultra wide-band(UWB) planar patch antenna model with CPW feeding. For directive gain improvement, the U-type printed patch antenna model with CPW feeding is reconstructed as a microstrip structure by adding a reflection plane with aperture slot. The reflection coefficient of the reconstructed antenna is less than -6.5 dB(VSWR < 3.3) to the characteristic impedance of $50.08{\Omega}$ and showed the directive radiation patterns with the directive gain of 7.5 dBi ~ 10.1 dBi, the front-back ratio of 17.8 dB ~ 28.7 dB and the range of -3dB radiation angle over ${\pm}30^{\circ}$ to the main beam direction of ${\theta}=0^{\circ}$.

• Journal of IKEEE
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• v.2 no.2 s.3
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• pp.194-199
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• 1998

In the atmospheric wireless optical communication system, the low power transmission can be accomplished by the high directivity of laser beam. But, the transmitted optical signal undergoes the serious influences by the atmospheric effects like absorption, scattering, and turbulence because the transmission channel is the atmospheric space. In this paper, therefore, we obtain the link equation for an atmospheric wireless optical LOS communication link under the atmospheric effects and find the repeaterless transmission length to estimate the system performance through the computer simulation. From the results of the computer simulation, we present the transmission length that is possible to transmit without a repeater at given data rates and know that data rate is decreased rapidly when the transmission length is increased slightly at given bit error rate.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.3
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• pp.207-212
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• 2005

Dual frequency acoustic pinger(AP) was manufactured to reduce study effect by long-term use of developed single frequency AP to prevent cetacean bycatch. Directivity characteristic of transducer was the omnidirectional pattern which showed less than ${\pm}3dB$ the change range of sensitivity on the beam pattern of right and left. Source power level(SPL) was 1384311pa with epoxy window before casing however after casing 1170B11Pa at sea. Dual frequency Af was tested to identify the avoidance behavior of bottlenose dolphin by its working. However the efficiency of dual frequency AP about the study effect was verified experiment repeatedly using single and dual frequency AP.

• Journal of the Korean Chemical Society
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• v.39 no.1
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• pp.14-22
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• 1995

This paper is concerned with the design of optimal surface heating patterns that result in focusing acoustic energy inside a subsurface target volume at a specified target time. The surface of the solid is heated by an incident laser beam which gives rise to shear and compressional waves propagating into the solid. The optimal heating design process aims to achieve the desired energy focusing at the target with minimal laser power densities and minimal system disturbance away from the target. The optimality conditions are secured via the conjugated gradient method and by the finite element method along with using the half-space Green's function matrix. Good quality energy focusing is achived with the optimal designs reflecting the high directivity of the photothermally generated shear wave patterns.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.3
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• pp.559-567
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• 1999

A piezoelectric flextentional sonar transducer has been simulated using a coupled FE-BEM. The dynamics of the sonar transducer is modelled in three dimensions and is analyzed with external electrical excitation conditions. Different results are available such as steady-state displacement modes, underwater directivity patterns, resonant frequencies, bandwidths, quality factors, output acoustic powers and transmitting voltage responses. It is shown that the present barrel-stave sonar transducer of the piezoelectric material produces flextentional displacements which could be related with higher output power, lower quality factor and more omnidirectional beam pattern than other types of sonar transducers. The results of the present sonar transducer modelling are also compared with those of a commercial package such as ATILA.