• The Journal of the Acoustical Society of Korea
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• v.20 no.3
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• pp.83-90
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• 2001

Conventional SAW duplexer filters employ a 1/4 wavelength transmission line, which causes difficulty in fabrication of the strip line on the package. Its manufacturing process is also complicated, because it needs integrating process of the separate transmitting filter, receiving filter and isolation circuits. This paper concerns development of a new structure of the duplexer filter that has all the transmitting filter, the receiving filter and the isolation circuit as a one chip device. For composition of the duplexer, we design the component SAW ladder filters and the isolation network consisting of lumped inductor and capacitor elements. Performance of the whole duplexer is optimized by the nonlinear multivariable minimization of a proper target function, and the result is compared with that of commercial filters.

• The Journal of the Acoustical Society of Korea
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• v.19 no.4
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• pp.107-114
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• 2000

This work is aimed to develop a new type of the Push-Pull ultrasonic transducer that can provide higher sound pressure level and simpler internal structure than conventional types. The driving part of the newly designed transducer is positioned in the middle of the cylinder, and its optimum geometry is determined by using the FEM package, ANSYS. Through FEM model analysis, the effects of all of its geometrical variables such as transducer length, transducer radius, and the edge shape of the end cap have been examined, and the results have led to the optimum geometry. The newly designed transducer has been found to give better performance than that of traditional ones.

• The Science & Technology
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• v.29 no.11 s.330
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• pp.75-78
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• 1996

비디오 카세트 리코더(VCR)가 등장한 1970년대 이래 가장 중요한 가전제품이 마침내 가을바람과 함께 우리 옆에 모습을 드러내기 시작했다. 오랫동안 고대하던 디지털 비디오 디스크는 영화관 수준의 품질을 가진 영상과 스트레오 음향을 우리에게 낯익은 오디오 콤팩트 디스크(CD)와 닮은 디스크에 실어 우리 안방극장에 제공한다. 한쪽에 4.7기가바이트씩의 용량을 가진 한장의 DVD는 '바람과 함께 사라지다' 정도의 길이를 가진 고화질의 영화 한편을 수록할 수 있다. DVD는 음악, 영화, 게임 그리고 다른 멀티미디어 패키지를 저장할 수 있다. 그래서 거추장스런 종래의 비디오카세트는 물론 레이저디스크, 오디오, CD 그리고 심지어는 오늘날 출시되는 신형 컴퓨터 4대중 3대꼴로 내장된 씨디롬도 결국은 DVD 앞에서 무릎을 꿇고 말 것이라고 생각하는 사람들이 많다.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.470-478
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• 2015

A heuristic method treating a layered ocean bottom in a ray modeling is to use the plane wave reflection coefficient for multiple-layered structure, named an one-layer assumption in this paper. We examine the validity of one-layer assumption in the case of two-layered ocean bottom, and obtain a simple inequality condition depending on the sound speed ratio, the ratio of layer thickness to source-receiver range, and the grazing angle of first reflected ray. From this inequality condition, it is shown that an one-layer assumption can be applicable to ray propagation problems at mid frequencies. Finally, numerical experiments are performed in the ocean environment similar to the East Sea in Korea. Incoherent transmission loss is calculated by the geometrical beam model with the plane wave reflection coefficient for multiple-layered ocean bottom and compared with the result of SNUPE 2.0, which is a parabolic equation package developed in Seoul National University.

• The Journal of the Acoustical Society of Korea
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• v.15 no.5
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• pp.99-106
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• 1996

The noise of a compressor is a major contributor to overall noise radiated from the refrigerator. The major source of the noise is radiated by the vibration of the compressor shell. In this study, to identify the dynamic characteristics of compressor shell, a compressor shell is divided into several components and these are analyzed with a commercial FEM(Finite Element Method) package such as MSC/NASTRAN. Using substructure synthesis method, the dynamic characteristics of the total system is identified. The coherence of each component to the total system is computed by using strain and kinetic energy. To increase the frequency of the first resonance mode which is most effective mode to the noise of the compressor shell, the improving strategy of dynamic characteristics is suggested by changing mass and stiffness of the coherence component to the first mode.

• Journal of IKEEE
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• v.26 no.3
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• pp.396-400
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• 2022

In this study, an ICT-based underwater communication monitoring device for underwater structures is implemented based on lifting fixture that transport human bodies found on the seabed to sea level. The lifting fixture is packaged with a retback, sideback, and cartridge that injects air. Monitoring systems are developed in a mobile manner in a portable structure. The underwater ultrasonic sensor signal is supplied using a USB port, and the O/S consists of Linux. For the underwater communication dong test, a measurement test was conducted in real time from 6m to 40m in depth on the east coast. The ultrasonic sound sensor is converted to 2,400 bps to verify the transmission error according to the duality. The communication speed of sensor to monitoring is 115,200 bps, and the speed of communication from controller to receiver is 2,400 bps. In the commercialization stage of the lifting device, it is easy to develop a low-end type and the compatibility is wide.