• Journal of Electrical Engineering and Technology
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• v.8 no.4
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• pp.856-862
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• 2013

A cavity-backed two-arm spiral antenna for partial discharge diagnosis is presented. The proposed antenna consists of a two-arm Archimedean spiral, a tapered microstrip balun as spiral antenna feed, and a ring-shaped absorber-loaded cavity. The Archimedean spiral antenna is designed for the operating frequency band of 0.3 GHz to 1.5 GHz and fed by the tapered microstrip balun. The cavity is utilized to transform the bidirectional beam into a unidirectional beam, thereby enhancing gain. The ring-shaped absorber is stacked in the cavity to reduce the reflected waves from the cavity wall. The proposed antenna is designed and simulated using CST Microwave Studio. A prototype of the proposed antenna is likewise fabricated and tested. The measured radiation patterns are directional to the positive z-axis, and the measured peak gain is 8.13 dBi at a frequency of 1.1 GHz.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.227-232
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• 2021

In this paper, the narrow-band characteristic, which is the disadvantage of the existing the PD sensor, was improved by transforming the sensor shape into a trapezoidal shape to improve the characteristics of the dipole-shaped conventional PD(Patial Discharge) sensor. In addition, by applying a cavity structure, which is a structure that can fundamentally block the electromagnetic wave signal from the outside as it is used for an external sensor, it is a partial discharge sensor that takes advantage of the structural advantages of low cost and convenience of installation. As a result of the experiment, it was shown that there is a broadband characteristic of about 70.5%(1.59~3.32GHz) at the center frequency of 2.45GHz, and the broadband characteristic was confirmed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.2
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• pp.237-244
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• 2016

This paper, presents the characteristics of electromagnetic fields radiated from a pole-transformer. The cylindrical cavity is used to measure electromagnetic fields radiated from a pole-transformer when partial discharge occures inside the pole-transformer. The theoretical analysis is conducted by a finite difference time domain (FDTD) method. As a result, frequency characteristics of the radiated electromagnetic waves emitted from the inside the cavity to the outside through the 1st and 2nd bushings could be observed for the configuration of the cylindrical cavity with a radiation window. The frequency characteristics of electromagnetic field are also studied according to the enclosure structure of the cylindrical cavity. To verify the theoretical analysis, computed results are compared to experimental results.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.88-98
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• 2014

A supercavitation is modern technology that can be used to reduce the frictional resistance of the underwater vehicle. In the process of reaching the supercavity condition which cavity envelops whole vehicle body, a vehicle passes through transition phase from fully-wetted to supercaviting operation. During this phase of flight, unsteady hydrodynamic forces and moments are created by partial cavity. In this paper, analytical and numerical investigations into the dynamics of supercavitating vehicle in transition phase are presented. The ventilated cavity model is used to lead rapid supercavity condition, when the cavitation number is relatively high. Immersion depth of fins and body, which is decided by the cavity profile, is calculated to determine hydrodynamical effects on the body. Additionally, the frictional drag reduction associated by the downstream flow is considered. Numerical simulation for depth tracking control is performed to verify modeling quality using PID controller. Depth command is transformed to attitude control using double loop control structure.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.89-94
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• 2012

In this paper, a UHF cavity-backed spiral antenna for partial discharge diagnosis is proposed. The proposed antenna consists of two-arm Archimedean spiral, a cavity, and a balun for feeding. The spiral antenna is designed for 0.3-1.5 GHz operating frequency. Two spiral arms of the proposed antenna are fed by a microstrip tapered-balun. In order to enhance the gain, the cavity is located in the back side of the spiral pattern. The proposed antenna is designed and simulated using CST Microwave Studio. The designed antenna is also fabricated and tested to validate performance. The measured radiation patterns are directional to the +z-axis and measured peak gain is 9.92 dBi.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.412-422
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• 2012

Air lubrication techniques for frictional drag reduction on ships have been proposed by numerous researchers since the 19th century. However, these techniques have not been widely adopted as questions persist about their drag reduction performance beyond the laboratory, as well as energy and economic cost-benefit. This paper draws on data from the literature to consider the suitability of air lubrication for large ocean going and U.S. Great Lakes ships, by establishing the basic energy economic calculations and presenting results for a hypothetical air lubricated ship. All the assumptions made in the course of the analysis are clearly stated so that they can be refined when considering application of air lubrication to a specific ship. The analysis suggests that, if successfully implemented, both air layer and partial cavity drag reduction could lead to net energy savings of 10 to 20%, with corresponding reductions in emissions.

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.9-15
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• 2001

The total pressure and partial pressure of small cavity for flat panel display have been successfully measured by using an ultra-high vacuum chamber with mass spectrometer. The total pressure in the panel was in the range of $10^{-6}$ Torr and the major partial pressure affecting increase in total pressure were those of Ar, $CH_4$and He. The baking temperature during evacuation process was very important for high-vacuum package, the total pressure and partial pressure of $CH_4$ were decreased as the increase of baking temperature.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.38-46
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• 2008

Studies on cavitation instabilities of hydrofoils and cascades are reviewed to obtain fundamental understandings of the instabilities observed in turbopump inducers. Most of them are based on the stability analysis of two-dimensional inviscid cavitating flow. The most important finding of the analysis is that the cavitation instabilities depend only on the mean cavity length. For a hydrofoil, the characteristic length is the chord length and partial/transitional cavity oscillation occurs with shorter/longer cavity than 75% of the chord length. For cascades, the characteristic length is the blade spacing and various modes of instabilities are predicted when the mean cavity is longer than 65% of the spacing. In the last part, rotating choke is shown to occur when the cavity becomes longer than the spacing.

• Journal of the Korean Society of Visualization
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• v.11 no.2
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• pp.46-54
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• 2013

Study of the wave structure and shear layer in the vicinity of a wall mounted cavity is done by time averaged colour schlieren and time resolved instantaneous shadowgraph technique in an M=1.7 flowfield. Effect of change of cavity width on flow structure is investigated by using constant length to depth (L/D) ratio cavity models with varying length to width (L/W) ratio of 0.83 to 4. The time averaged shock wave structure was observed to change with change in cavity width. Dependence of the shock angle at the leading edge on the shear layer width is also evident from the images obtained. Unsteadiness in the flow field in terms of shear layer dynamics and quasi steady nature of shock waves was evident from the images obtained during instantaneous shadowgraph experiments. Apart from the leading and trailing edge shocks, several other waves and flow features were observed. These flow features and the associated physical phenomena are discussed in details and presented in the paper.

• Radiation Oncology Journal
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• v.37 no.4
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• pp.259-264
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• 2019

Purpose: Accurate localization of the lumpectomy cavity during accelerated partial breast radiation (APBR) is essential for daily setup to ensure the prescribed dose encompasses the target and avoids unnecessary irradiation to surrounding normal tissues. Three-dimensional ultrasound (3D-US) allows direct visualization of the lumpectomy cavity without additional radiation exposure. The purpose of this study was to evaluate the feasibility of 3D-US in daily target localization for APBR. Materials and methods: Forty-seven patients with stage I breast cancer who underwent breast conserving surgery were treated with a 2-week course of APBR. Patients with visible lumpectomy cavities on high quality 3D-US images were included in this analysis. Prior to each treatment, X-ray and 3D-US images were acquired and compared to images from simulation to confirm accurate position and determine shifts. Volume change of the lumpectomy cavity was determined daily with 3D-US. Results: A total of 118 images of each modality from 12 eligible patients were analyzed. The average change in cavity volume was 7.8% (range, -24.1% to 14.4%) on 3D-US from simulation to the end-of-treatment. Based on 3D-US, significantly larger shifts were necessary compared to portal films in all three dimensions: anterior/posterior (p = 7E-11), left/right (p = 0.002), and superior/inferior (p = 0.004). Conclusion: Given that the lumpectomy cavity is not directly visible via X-ray images, accurate positioning may not be fully achieved by X-ray images. Therefore, when the lumpectomy cavity is visible on US, 3D-US can be considered as an alternative to X-ray imaging during daily positioning for selected patients treated with APBR, thus avoiding additional exposure to ionizing radiation.