• 한국소음진동공학회논문집
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• 제25권6호
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• pp.440-446
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• 2015

Acoustic signal is emitted from a vessel and received by a cylindrical array sensor at some distance from the vessel. Acoustic signal is the source for a cylindrical array sensor which is designed to detect the acoustic signal. Cylindrical array sensors seldom have an ideal hydrodynamic shape and are not sufficiently robust to survive without some protection and they are normally housed in a sonar dome. Reflected signals by some structure inside a sonar dome make unwanted signals. Therefore, an acoustic baffle is used to minimize unwanted signals. The performance of the acoustic baffles can be determined from the acoustic numerical analysis at the design stage. In this study, finite element method was used to analyze the acoustic field around the cylindrical array sensor and baffle effects. The baffle performance can be defined the echo reduction. To show the baffle performance, the specimens were made for pulse tube test and echo reductions were measured during the test. In this paper, the effect of echo reduction of the acoustic baffle was discussed.

• 한국가스학회지
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• 제4권1호
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• pp.9-15
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• 2000

원통형 톨루엔 저장탱크의 구조결함을 조사하기 위하여 음향방출시험을 수행하였다. 원통형 저장탱크는 고장력강으로 제작되었으며, 최근에 저장탱크의 하부 1 및 2단은 전면 보수되었다. 음향방출은 최대설계하중의 $75{\~}84\%$ 레벨영역에서 하중절차에 따라 실시간으로 모니터링 되었다. 시험결과는 순수 음향방출뿐만 아니라 유사 음향방출특성도 보여준다. 밸브잡음으로 판단되는 유사 방출들은 하중과는 무관하게 밸브잠금과정에서 과도적으로 발생되었다. 충수과정에서 발생된 순수 음향방출들은 결함에 기인하며, $75{\~}84\%$의 시험하중영역에서는 성장을 하지 않는 것으로 평가되었다. 이 결함들은 활성센서들을 중심으로 수행된 방사선시험을 통하여 용접균열과 기공인 것으로 밝혀졌다.

• 한국음향학회지
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• 제35권5호
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• pp.403-409
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• 2016

전방향 센서를 이용하는 선배열 센서의 경우, 음원의 방향이 원추각의 형태로 결정되어지므로 좌 우 구분모호성이 발생한다. 이러한 문제를 해결하기 위해 운용적인 방법과 센서 배열의 구조적인 방법에 대한 연구가 진행되었다. 최근에는 음향 벡터 센서 기반의 연구가 이루어지고 있으며, 본 논문에서는 음향 벡터 센서 기반의 빔형성 기법에서 발생하는 센서 배열의 뒤틀림에 따른 좌 우 구분 성능에 대하여 분석하였다. 음향 벡터 센서는 하나의 전방향 센서와 세 개의 지향성 센서로 구성되며, 세 개의 지향성 센서는 서로 수직 방향의 속도성분을 측정한다. 이때 센서 배열의 뒤틀림에 따른 지향성 센서 축의 정보가 정확하지 않으면 잘못된 방향의 신호를 인가하여 빔형성 기법의 성능저하가 나타난다. 따라서 센서 배열의 뒤틀림에 따른 좌 우 구분 성능저하를 분석하고 보상을 통한 빔형성 기법의 성능향상을 확인하였다.

• Journal of Computing Science and Engineering
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• 제6권1호
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• pp.40-50
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• 2012

Increase in the number of older people due to demographic changes poses great challenges to the social healthcare systems both in the Western and as well as in the Eastern countries. Support for older people by formal care givers leads to enormous temporal and personal efforts. Therefore, one of the most important goals is to increase the efficiency and effectiveness of today's care. This can be achieved by the use of assistive technologies. These technologies are able to increase the safety of patients or to reduce the time needed for tasks that do not relate to direct interaction between the care giver and the patient. Motivated by this goal, this contribution focuses on applications of acoustic technologies to support users and care givers in ambient assisted living (AAL) scenarios. Acoustic sensors are small, unobtrusive and can be added to already existing care or living environments easily. The information gathered by the acoustic sensors can be analyzed to calculate the position of the user by localization and the context by detection and classification of acoustic events in the captured acoustic signal. By doing this, possibly dangerous situations like falls, screams or an increased amount of coughs can be detected and appropriate actions can be initialized by an intelligent autonomous system for the acoustic monitoring of older persons. The proposed system is able to reduce the false alarm rate compared to other existing and commercially available approaches that basically rely only on the acoustic level. This is due to the fact that it explicitly distinguishes between the various acoustic events and provides information on the type of emergency that has taken place. Furthermore, the position of the acoustic event can be determined as contextual information by the system that uses only the acoustic signal. By this, the position of the user is known even if she or he does not wear a localization device such as a radio-frequency identification (RFID) tag.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.457-462
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• 2007

This paper reports on the research which investigates acoustic signals acquired in turning with rough and finish simultaneously. The material is aluminum thin pipe. Two acoustic sensors were set on CNC machine. One was set on the finish bite and the other the rough. Two signals were first analyzed in order to consider how much the acoustic signal from the finish bite was coupled by that from the rough. A simple data collecting system to acquire signals from the finish was then determined because two acoustic signals were little coupled. Second the fundamental experiments were accomplished to study the effects of machine vibration and material state. The signal characteristics due to surface defects were studied from the collected acoustic signal data. The signal analysis was based on real time data, root mean squared average and frequency spectrum by fast fourier transform. As a result, the acoustic signals were made effects by machine condition, material structure. The acoustic signal from the finish bite was closely correlated with surface quality. Two types surface micro defects were then evaluated by the signal characteristics.

• 센서학회지
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• 제19권6호
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• pp.490-496
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• 2010

In this study, in order to overcome the weakness of acoustic field analysis which is generally used for ultrasonic probe performance evaluation, automatic acoustic field measurement system and evaluation parameters were proposed. The comparisons between acoustic field simulation and measured acoustic distribution data of normal and abnormal channels were conducted to evaluate the availability of proposed system and evaluation parameters. First, the impulse response characteristic of sample probe was investigated to classify the normal elements and abnormal elements. And then, normal channels and abnormal channels with abnormal element were chosen. The suggested 12 evaluation parameters were calculated using the acoustic fields of these channels. The availability of proposed automatic acoustic field measurement system and evaluation parameters was confirmed. And the performance evaluation of ultrasonic probe using acoustic field analysis could be easier and faster.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.608-612
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• 2000

Active control of sound radiation(using active structural acoustic control) from a vibrating rectangular plate by a steady-state harmonic point force disturbance is experimentally studied. Control structural input are achieved by two piezoceramic actuators bonded to the surface of the panel. Two accelerometers are implemented as error sensors. Estimated radiated sound signals using vibro-acoustic path transfer function are used as error signals. The vibro-acoustic path transfer function represents system between accelerometers and microphones. The control approach are based on a multi-channel filtered-x LMS algorithm. The results demonstrate that attenuation of sound levels of 3dB, 13dB are achieved.

• 비파괴검사학회지
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• 제23권3호
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• pp.280-284
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• 2003

사용하지 않은 새 금속 압력용기에 대하여, 사용 전 음향방출시험을 수행할 때 장비점검, 탐촉자간 거리, 탐촉자 위치, 전 측정 시스템 점검, 가압방법, 잡음 제거법 및 시험 결과의 평가 등에 대한 절차를 수립하고 현장 응용시험이 수행되었다. 일반적으로 음향방출 시험은 많은 잡음을 포함하는데 시험동안 관찰결과를 기록하여 평가 시 시간 필터링함으로서 잡음을 제거할 수 있었다.

• Smart Structures and Systems
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• 제23권2호
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• pp.173-184
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• 2019

The main objective of this study is to evaluate the true fracture energy and monitor the damage progression in steel fibre reinforced concrete (SFRC) specimens using acoustic emission (AE) features. Four point bending test is carried out using pre-notched plain and fibre reinforced (0.5% and 1% volume fraction) - concrete under monotonic loading. AE sensors are affixed at different locations of the specimens and AE parameters such as rise time, AE energy, hits, counts, amplitude and duration etc. are obtained. Using the captured and processed AE event data, fracture process zone is identified and the true fracture energy is evaluated. The AE data is also employed for tracing the damage progression in plain and fibre reinforced concrete, using both parametric- and signal- based techniques. Hilbert - Huang transform (HHT) is used in signal based processing for evaluating instantaneous frequency of the acoustic events. It is found that the appropriately processed and carefully analyzed acoustic data is capable of providing vital information on progression of damage on different types of concrete.

• Journal of information and communication convergence engineering
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• 제12권1호
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• pp.8-13
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• 2014

We consider the sensor selection problem in large sensor networks where the goal is to find the best set of sensors that maximizes application objectives. Since sensor selection typically involves a large number of sensors, a low complexity should be maintained for practical applications. We propose a geometry-based sensor selection algorithm that utilizes only the information of sensor locations. In particular, by observing that sensors clustered together tend to have redundant information, we theorize that the redundancy is inversely proportional to the distance between sensors and seek to minimize this redundancy by searching for a set of sensors with the maximum average distance. To further reduce the computational complexity, we perform an iterative sequential search without losing optimality. We apply the proposed algorithm to an acoustic sensor network for source localization, and demonstrate using simulations that the proposed algorithm yields significant improvements in the localization performance with respect to the randomly generated sets of sensors.