• 한국인터넷방송통신학회논문지
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• 제17권2호
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• pp.191-197
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• 2017

스마트폰의 사용이 보편화됨에 따라 스마트폰을 이용한 다양한 응용서비스가 개발되고 있으며, 추가적인 장치없이 음향 신호를 이용하여 데이터를 송수신하거나 위치를 측정하는 기술이 활발하게 개발되고 있다. 그러나 스마트폰 장치의 한계로 음향 주파수의 선택에 한계가 있고, 음향신호 발생 장치의 전자회로의 비선형성으로 인해 인간이 감지할 수 있는 음향신호 잡음이 발생하는 문제가 있다. 따라서 시끄러운 소리가 나므로 실용화에 어려움이 있다. 본 논문에서는 인간이 감지하는 음향 신호의 크기 측정 방법을 제안하고, 이에 따라 여러 가지 음향 신호를 비교 분석함으로써 음향 통신 및 위치측정 시스템 개발시에 비가청 음향 신호 설계에 활용하도록 한다.

• 소음진동
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• 제8권6호
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• pp.1137-1143
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• 1998

This paper describes the method to measure of the vibrational power transmitted from the vibration source to the supporting structure in the horizontal direction. Generally, it is impossible to measure horizontal forces at the coupling points. However. the vibrational Power transmitted in the horizontal direction can be measured by using indirect method that is based on the mechanical impedance and velocities at the coupling points. We proposed the method to estimate the vibrational power when the vibration source and supporting structure cannot be separated. In this paper. the vibrational power transmitted in the horizontal direction is also estimated by using this method. The estimated and measured results of the mobilities at the coupling point and vibrational power in the horizontal direction are compared. It is shown that the estimated results agree well with the measured results. For the supporting structure with multiple coupling points, the other coupling points should be considered for measuring the vibrational power transmitted through one coupling points. We examine the effects of other coupling points and measure the vibrational power without considering the other coupling points.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1995년도 춘계학술대회논문집; 전남대학교, 19 May 1995
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• pp.196-201
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• 1995

The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

• Transactions on Electrical and Electronic Materials
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• 제10권6호
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• pp.222-226
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• 2009

The objective of this study is to share multimedia contents included in existing digital devices and to solve the problems of an increase in installation fees and non-environmentally friendly interiors. This study designed a new digital signal transmitter and receiver using power line transmission and HDMI in order to solve the problems in the existing systems. The transmitter and receiver designed in this study used an AD9867BCPZ PLC chip in which the transmission came from digital signals originating in a PC, and the system architecture was configured so that the outputs signals were connected to a TV from the receiver. The experiment was implemented by adding a Video Test Generator, a USBPre external sound card, and Smaart Live 6 for analyzing the characteristics of the configured system. In the video test results, it was verified that communication was actively implemented, and the image quality showed a constant level from the measurement of the captured video. In the case of the sound, it was verified that more than 90% of the sound signals were normally transmitted and received from the examination of their phases and magnitudes. Thus, the performance of the system designed in this study was verified, which leads to the resolution of some of the problems found in current digital devices.

• 제어로봇시스템학회논문지
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• 제11권9호
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• pp.774-780
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• 2005

For the accurate inspection of the resources and space in the ocean, the method of locating the measurement equipments in the seafloor and retrieving these equipments later after a certain period of time. is generally used. In this method, the reliability of retrieving measurement equipments is very important. In our proposed remotely-controlled acoustic release system, an underwater ultrasonic wave recognition algorithm by which we can recognize the sound signal without the influence of disturbances due to underwater environment changes is developed, and a battery is used for the reduction of electric power consumption. we show the effectiveness of our proposed system through experimental results.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1994년도 FIFTH WESTERN PACIFIC REGIONAL ACOUSTICS CONFERENCE SEOUL KOREA
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• pp.704-709
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• 1994

The insertion loss is the measured change in power flux at a specified receiver, when the acoustic transmission path between it and the source is modified by the insertion of silencer element. Such measurements have clear and valid physical meaning particularly if the source impedance remains while the transmission path is altered. When the invarient condition is satisfied, the insertion loss is given by the ratio of the acoustic pressure in upstream to that in downstream of the silencer, and that of the particle velocity. The measurement is consisted of using an adaptation of the two microphone method to obtain the complex amplitude of the sound in upstream tube as well as in downstream tube of the silencer. Examples of the data, reduced and presented in terms of the pressure ratio and particle speed ratio, are compared with the theoretical calculations.

• 한국음향학회지
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• 제40권3호
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• pp.241-246
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• 2021

현재 라우드스피커 시스템은 다양한 입력 채널 및 앰프를 포함하는 액티브 스피커로 변화하고 있다. 이러한 액티브 스피커의 경우 기존 패시브 스피커 혹은 유닛 단품 측정 표준인 IEC 60268-5 만으로 측정이 불가능한 경우가 많다. 본 논문은 IEC한국 대표로 IEC60268-21 표준을 제정하면서 새롭게 정의한 아날로그, 디지털 입력 및 유선, 무선 입력 채널을 가지고 다양한 제어 기능을 가진 파워 앰프를 내장한 액티브 스피커 측정 표준에 대해 상세하게 알아보고자 한다.

• 동력기계공학회지
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• 제11권3호
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• pp.35-40
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• 2007

Leak would happen because of the damage of high temperature and high-pressure valve in nuclear power plant. condition based prevention maintenance is essential by using the suitable method based on local condition. Energy loss prevention can prevent from an accurate test, Local actually and ability. The methods of test for high energy fluid leak at present are analysis of ${\Delta}T$, AE(Acoustic Emission) analysis, and thermal image. The result for test of secondary system in nuclear power plant Unit reveals that the AE occurred clearly in leakage situation, but thermal image didn't occur. It is identified that leak is occurred when the orifice located front and back of valve operates. It shows that making a impatient judgment by using the single method if it is leakage is containing uncertainty. So we think that using the Multi-Measuring method is more sound judgment than single-measuring method.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권5호
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• pp.258-263
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• 2004

The purpose of this experiment is to modify diagnosis criterion of isothermal relaxation current(IRC) measurement equipment which is using for distribution cable diagnosis. We're using this system for several years in the field instead of DC leakage current measurement and lots of cables were replaced. But we have to investigate on the reliability of this equipment for our cables because we didn't carried out condition assessment of extracted cables after field diagnosis by this equipment. It is important thing for cable maintenance. If the replacement criterion is improper we can not prevent failures or will waste budget on account of replacement of the sound cables. In this paper we selected field installed cables and injected silicone fluid to the cables for insulation rehabilitation. In order to prove reliability of the diagnosis equipment we compared diagnosis results and AC breakdown strength according to operating time after silicone treatment. This is the results of the field test for 1 year.

• 한국유체기계학회 논문집
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• 제2권4호
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• pp.57-64
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• 1999

The prediction method of the performance and aerodynamic noise from a sirocco fan was developed and compared with measured data. To predict the performance of the sirocco fan, the well-known slip coefficients and various loss models were tested and applied to forward curved sirocco impellers. Using loss models proposed for both impeller and casing, the predicted performance characteristics were in good agreement with measured ones by an ANSI test plenum. Various scaling models for aerodynamic noise from the sirocco fan were evaluated and tested against measured power levels in terms of flow coefficient. It was shown that the turbulent broadband sound power from the sirocco fan can be modeled successfully by trailing edge noise.