• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2633-2640
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• 2024

The purpose of this study was to investigate the effect of the reflector, surface treatment, and length of scintillation crystals on the performance of a time-of-flight and depth-of-interaction (TOF-DOI) PET detector with a dual-ended readout and to determine the best reflector and surface treatment. Various types of crystal arrays with three different reflectors (ESR, BaSO₄, and Toray), three different lateral surface treatments (all-polished (AP), all-roughened (AR), and partially roughened (PR, three sides polished, and one side roughened)), and two different lengths (20 and 15 mm) were fabricated. The highest light collection efficiency and best energy resolution were achieved using a crystal with a diffuse reflector (BaSO₄ for AP and Toray for AR). In contrast, the best coincidence timing resolution (CTR) was achieved using an AR crystal with a specular reflector (ESR). The best DOI resolution was achieved using an AR crystal with BaSO₄. Moreover, the results measured with the 20 mm long crystals were similar to those measured with the 15 mm long crystals. Therefore, we concluded that the dual-ended readout PET detector employing the crystal with AR lateral surface treatment and ESR was a good candidate for TOF-DOI PET because it provided excellent CTR and adequate DOI resolution.

• Journal of Environmental Science International
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• v.16 no.3
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• pp.255-260
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• 2007

The photocatalytic decolorization of Rhodamine B (RhB) was studied using packed-bed reactor and immobilized $TiO_2/UV$ System. The 20 W UV-A, UV-B and UV-C lamps were employed as the light source. The effect of shape and surface polishing extent of reflector, distance between the reactor and reflector, reactor material were investigated. The results showed that the order of the initial reaction constant with reflector shape was round > polygon > W > rhombus. The optimum distance between the reactor and reflector was 2 cm. The initial reaction constant of quartz reactor was 1.46 times higher than that of tile PVDF reactor.

• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.1-10
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• 1999

In this paper, the design for the shaped offset cassegrain antenna system combined with corrugated feed horn is presented. First, spherical-mode wave theory is applied to the corrugated conical horn and its radiation patterns are investigated. Using the radiation patterns, design data of the corrugated conical horn are obtained by efficiency investigation of horn antenna. When the investigation is completed, the flare angle and length of the corrugated conical horn is determined. Next, the main and sub-reflector is designed using Snellis law and the conservation principle of energy. Then the uniform direction and energy density of the traveling wave at the aperture of the main-reflector is obtained. The maximum size of the main-reflector is determined by investigation of the illumination and spillover efficiency. Finally, the curvature of the main-reflector is modified to satisfy the condition of the uniform phase. From the calculated efficiencies, the designed site of the main-reflector and sub-reflector, system gain of the shaped offset cassegrain antenna has been obtained 40.5dB in Ka-band frequency. It has better characteristics than the result of SABOR with 39dB gain.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.34-39
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• 2015

In this paper, a design of an offset Cassegrain antenna is proposed for Ku and Ka dual-band without increasing the antenna size. For Efficiency of computation and implementation, the frequency selectivity surface (FSS) of reflecting the Ka-band signal and passing the Ku-band is provided for the sub-reflector instead of the main reflector. The proposed FSS hyperboloid sub-reflector is the periodic structure of a unit cell comprising octagon metal rings embedded in the multiple layers. The proposed design is verified for 19 GHz and 45 GHz bands by the use of precise electromagneitc-field simulations.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.3
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• pp.39-44
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• 2007

In this paper, satellite searching and tracking method for the satellite antenna in naval vessels system are proposed. For fast searching satellite, Wide Range Search(WRS) algorithm is proposed where the signal strength of side-lobe is utilized as well as that of main-lobe. Satellite tracking algorithm to stabilize satellite antenna is based on conical-scanning which is accomplished by the use of the sub-reflector located in front of the focus of the reflector. The sub-reflector rotates about a slightly tilted axis by means of a motor and shapes the antenna beam to utilize stabilization. To show the validity of the proposed method, an experimental example is represented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.6
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• pp.515-521
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• 2014

In this paper, we designed axis-displaced Gregorian antenna by using Ray-tracing method. This antenna improves gain, VSWR by rotating the axis of the sub-reflector to get rid of E-field wave returned from sub-reflector to feed horn. Therefore it reduce the sub-reflector size and the volume of antenna. This method is used to track the propagation path for radiation pattern of feed horn from feed horn to sub-reflector, main-reflector and air. We get E-field distribution of this antenna aperture and calculate antenna radiation pattern and optimize the antenna performance. The Ray-tracing Method was verified because the gain, radiation patterns, side lobe level, beam width and return loss of the designed antenna are very similar to CST simulation result and a measured result of the fabricated antenna.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1668-1670
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• 2012

In this paper, a satellite array antenna operates at 12.2GHz~12.75GHz was designed and fabricated. The lowest height and high gain electrical beam tilt was obtained by applying backed slot and sub-reflector widening the distance between the patch and the GND. The simulation and measurement showed good agreements, the electrical beam tilt was $10^{\circ}$, the gain was 26.5dBi, the VSWR was less than 3:1 and the return loss was less than -15dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.4
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• pp.344-350
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• 2009

This paper proposes a hybrid antenna with novel beam steering scheme. The antenna have a cassegrain structure composed of two reflectors. The main reflector is designed for high gain performance using parabola curvature, and the sub-reflector is plate and can be rotated by ${\pm}3^{\circ}$. Thus proposed antenna can steer a antenna beam using the inclination of sub-reflector. A feed array composed of 20 elements is adapted as a feeder for electrical beam steering, and the antenna can be possible to steer the beam by the feed array with sub-reflector. Proposed antenna was fabricated to be operated in Ka-band(30.085$\sim$30.885 GHz) for TX and K-band(20.355$\sim$21.155 GHz), which are the operation frequencies of the Korean satellite, Mugunhwa, to provide satellite multi-media service to vehicles. By the performance test, it can be known that the antenna has minimum gain of 47 dBi for TX and 44.4 dBi for TX and can steer the beam by ${\pm}2^{\circ}$ with sub-reflector.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.5
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• pp.429-436
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• 2012

In concert halls and auditoriums, acoustic reflector and stage enclosure is one of the main factors on the room and stage acoustic characteristics. As a stage enclosure and acoustic reflector honey comb based light-weight reflector is widely used, because it is easy to install. However, there was not enough research on the surface density effect on room and stage acoustics. In this study, sound absorption coefficient tests on three kinds of wooden acoustic reflectors with different surface density were conducted. Surface density of acoustic reflector was changed from 11 kg/$m^2$ to 41 kg/$m^2$. For the low frequency excitation, sub-woofer was used with omnidirectional loud-speaker simultaneously. From the experiments, it was found that sound absorption coefficient below 250 Hz band was decrease by the increment of surface density. In order to check the influence of the surface density on room and stage acoustic parameters, room acoustic simulation was conducted with sound absorption coefficients, which were tested in reverberation chamber. By the increment of surface density of acoustic reflector, RT(reverberation time) and EDT(early decay time) were increased. Also, ST(stage support) was improved in low frequency bands.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.85-90
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• 2008

In this paper, we studied on dual reflector adjusted to monopulse antenna system. As a result, when the efficiency of main reflector is more than 70%, The size of reflector is 30 wavelength of maximum frequency and minimum frequency gain is 37.9dBi, and Maximum frequency gain is 38.6dBi. Also, when a radius is D and Focus-distance is $F_e$, a scheme for efficiency improvement of Sub Reflector is to increase the Focus-distance to Diameter Ratio. In this case, Cross polarization in Far field improved and spherical spreading loss in circumference of reflector reduced. The influence of Radiation pattern followed by the side displacement of feed antenna(at $x_sy_s$) is decreased, it is confirmed that performance of scanning is improved.