• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.101-102
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• 2012

수중에서는 대기와 달리 매질의 차이로 인하여 통신의 제약이 따르므로 초음파를 이용하여 정보를 송 수신한다. 수중통신을 하기 위해서는 신호를 증폭시키는 전력증폭기와 증폭된 전기 신호를 초음파로 변환시키는 트랜스듀서가 필요하다. 전력증폭기는 선형적인 출력이 보장되어야 하며, 수중에서의 발열과 연료문제로 인하여 높은 효율로 동작하여야 한다. 하지만 기존의 전력증폭기는 인가되는 고정전압과 출력전압의 차이로 인해 손실이 발생하여 효율이 저하된다. 본 논문에서는 수중 통신에 적합한 특성을 가진 APEX사의 Class B push-pull 타입의 MP108A증폭기를 사용하여 선형적인 출력 특성을 보장하며 넓은 대역폭을 갖는 전력증폭기를 구현하고, 실험을 통해 특성을 확인하였다.

• Journal of Oral Medicine and Pain
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• v.33 no.4
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• pp.387-394
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• 2008

Purpose : The purpose of this study was to verify the usefulness and feasibility of ultrasonographic imaging for the detection of the disorders of the surrounding supporting structure such as articular capsule, retrodiscal tissue and related ligaments, osteoarthritic evidence and associated disc displacement at the temporomandibular joint(TMJ) Materials and Methods : 20 patients(40 joints) with periodic lock and crepitations were investigated prospectively using 12 MHz array transducer. Ultrasonographic Imagings were assessed for osteoarthritic surface changes of condyle, extent of disc displacement and disorders of surrounding structures. Ultrasonographic images were compared with clinical investigations, conventional radiography and Dental Computed Tomographic scans. Results : In clinical and conventional radiography, osteoarthritic changes were diagnosed in 8 joints. Ultrasonographically 7 of the 8 osteoarthritic changes were diagnosed correctly. Sensitivity, specificity, and accuracy of ultrasonography in the osteoarthritic detections were 87.5%, 62.5%, and 67.5% respectively. About the detection of disc displacement, disc displacement were diagnosed in 21 joints clinically. Ultrasonographically 19 of the 21 disc displacements were diagnosed correctly. Sensitivity, specificity, and accuracy of ultrasonography in the osteoarthritic detections were 95%, 90%, and 92.5% respectively. when the disorders of supportive structure were figured out, the disorders of supportive structure were diagnosed in 18 joints clinically. Ultrasonographically 1 of the 18 the disorders of supportive structure were diagnosed correctly. Sensitivity, specificity, and accuracy of ultrasonography in the osteoarthritic detections were 5.5%, 4.5%, and 55% respectively. Conclusion : Ultrasonography is an relatively reliable diagnostic tool for the detection of disc displacement and some of osteoarthritic changes. But it's not an insufficient imaging technique for the detection of the disorders of the surrounding structure.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.167-179
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• 2021

In order to characterize the mixing process of confluence for understanding the impacts of a river on the other river, it has been crucial to analyze the spatial mixing patterns for main streams depending on various inflow conditions of tributaries. However, most conventional studies have mostly relied upon hydraulic or water quality numerical models for understanding mixing pattern analysis of confluences, due to the difficulties to acquire a wide spatial range of in-situ data for characterizing mixing process. In this study, backscatters (or SNR) measured from ADCPs were particularly used to track sediment mixing assuming that it could be a surrogate to estimate the suspended sediment concentration. Raw backscatter data were corrected by considering the beam spreading and absorption by water. Also, an optical Laser diffraction instrument (LISST) was used to verify the method of acoustic backscatter and to collect the particle size distribution of main stream and tributary. In addition, image-based spatial distributions of sediment mixture in the confluence were monitored in various flow conditions by using an unmanned aerial vehicle (UAV), which were compared with the spatial distribution of acoustic backscatter. As results, we found that when acoustic backscatter by ADCPs were well processed, they could be proper indicators to identify the spatial patterns of the three-dimensional mixing process between two rivers. For this study, flow and sediment mixing characteristics were investigated in the confluence between Nakdong and Nam river.

• Journal of the Korean Society of Radiology
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• v.82 no.4
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• pp.943-947
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• 2021

Chondrolipomas, which are lipomas with chondroid metaplasia, are rare benign soft tissue tumors with no relevant epidemiological reports or radiological information. A limited number of lipomas with osteo/chondroid differentiation have been reported in the literature between 1960 and 2008. Moreover, only few studies have described the radiologic findings of chondrolipomas. Herein, we present a case of chrondrolipoma arising from the left supraclavicular region in a 77-year-old female.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.3-9
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• 2007

With a growing concern about the state of infrastructure worldwide, the demand for the development of reliable nondestructive testing techniques (NDT) is ever increasing. Among possible NDT techniques, microwave method is proven to be effective in fast and non-contact inspection of concrete structures and inclusions inside concrete. It is also found that the microwave method has a potential in detecting the delamination between fiber reinforced polymers (FRP) plate and concrete. On the other hand, ultrasonic method can be another way to find the delamination. In this paper, the research work needed for the development of a reliable microwave method and ultrasonic method is studied in the measurements of concrete specimens reinforced with FRP. Concrete specimens are made with FRP and artificial delamination inside. A microwave measurement system with hom antennas with high center frequency and broad frequency bandwidth are used to image inside concrete specimens for the detection of debonding between concrete and FRP. Also, ultrasonic method is used for the same condition. Both results are compared with each other.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.136-141
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• 2004

A torsional guided wave mode was applied to detect a crack in a pipe. An array of electromagnetic acoustic transduce. (EMAT that can generate and receive torsional guided ultrasound with the frequency of 200kHz was designed and fabricated for testing a pipe of 2.5 inch diameter Artificial notches with various depths were fabricated in a bent feeder pipe mock-up and the detectability was examined from the distance of 2m of the specimen. The axial notches with the depth of 5% of wall thickness were successfully detected by a torsional mode (T(0,1)) generated by the EMAT However, it was found that the depth of defects was not related to the signal amplitude.

• The Journal of the Korea Contents Association
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• v.15 no.8
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• pp.397-407
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• 2015

Concrete is a attractive construction material, however durability problem occur due to steel corrosion, which leads propagation to structural safety problem. The recently developed FRP (Fiber Reinforced Plastic) Hybrid Bar has an engineering merit of both structural steel and FRP. Accelerated corrosion test for RC (Reinforced Concrete) samples with normal steel and FRP Hybriud Bar are performed and their flexural capacity is evaluated. Furthermore UV(Ultrasonic Velocity) measurement is attempted for analysis of variation of UV due to corrosion condition. After corrosion test, there is no significant reduction in RC beam with FRP hybrid bar but 11.5% of reduction in the case of normal steel is evaluated with 3.3% of UV reduction. For commercial production of FRP hybrid bar, bond strength evaluation through long-term submerged corrosion is required.

• The Journal of Korean Orthopaedic Ultrasound Society
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• v.7 no.2
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• pp.120-126
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• 2014

Acromioclavicular (AC) joint cyst is an uncommon presentation around the shoulder joint that is usually associated with chronic rotator cuff pathology and degenerative AC joint arthritis. Understanding the underlying pathophysiology of the shoulder joint is essential for appropriate interpretation of the AC joint cyst, assistance in determining the therapeutic strategy, and prevention of complications after treatment. We present a case of AC joint cyst with an aseptic fistula which was complicated by simple excision for recurred AC joint cyst after multiple aspirations. This case revealed a massive rotator cuff tear involving supraspinatus, infraspinatus, and subscapularis tendon on ultrasonography. We also reviewed the clinical approach and treatment options to be considered for its pathogenesis in the literature.

• Journal of the Korea Society of Computer and Information
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• v.16 no.4
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• pp.23-28
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• 2011

Ultrasound images for the abdominal muscles are complicated enough to have difficulty in interpreting their results. For better interpretation, magnifying the original image is necessary but its magnified image could be deteriorated and suffer from information loss. Thus, in this paper, we propose a magnifying method that reduces the gap between the original image and the magnified one in quality using a fuzzy method with weights for its brightness and interpolation. The proposed method extracts information of pixels in magnified image that have most similar characteristics of the original one by applying fuzzy membership function. In the process, the difference in the brightness between pixels of the magnified image and the original one using bilinear interpolation method and the weight value using the interpolation from multiplied values of four pixels are supplied to the fuzzy membership function. In this experiment, the proposed method reduces the cloudy phenomenon appears commonly compared to the bilinear interpolation method among those qualitative issues of image interpretation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.483-489
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• 2017

An ultrasonic technique was developed to characterize the resonance behavior of a microcantilever operating in a megahertz regime. A high-power ultrasonic pulser and a contact transducer were employed to excite the silicon microcantilever, and a Michelson interferometer was used to obtain the time domain waveform. The natural frequency of the microcantilever was evaluated through the fast Fourier transform of the signal, and a numerical analysis using the finite element method confirmed the measurement data. The present study proposes a novel and facile method to evaluate nanoscale materials and structures with high sensitivity compared to conventional approaches.