• Structural Engineering and Mechanics
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• 제84권2호
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• pp.253-268
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• 2022

Using non-destructive Acoustic Emission (AE) and optical Digital Image Correlation (DIC) methods, the moment-curvature behavior of steel and GFRP bars reinforced concrete beams under flexure was explored in this study. In the tension zone, laboratory studies were carried out on steel-RC and GFRP-RC beams with varying percentages of longitudinal reinforcement ratios of 0.33 %, 0.52%, and 1.11%. The distinct mechanism of cracking initiation and fracture progression of failure in steel-RC and GFRP-RC beams were effectively correlated and picked up using AE waveform characteristics of the number of AE hits and their amplitudes, AE energy as well as average frequency and duration. AE XY event plots and longitudinal strain profiles using DIC gives an online and real-time visual display of progressive AE activity and strains respectively to efficaciously depict the crack evolution and their advancement in steel-RC and GFRP-RC beams. They display a close matching with the micro and macro-cracks visually observed in the actual beams at various stages of loading.

• 대한음성학회지:말소리
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• 제67호
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• pp.149-166
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• 2008

In spoken document retrievals (SDR), subword (typically phonemes) indexing term is used to avoid the out-of-vocabulary (OOV) problem. It makes the indexing and retrieval process independent from any vocabulary. It also requires a small corpus to train the acoustic model. However, subword indexing term approach has a major drawback. It shows higher word error rates than the large vocabulary continuous speech recognition (LVCSR) system. In this paper, we propose an probabilistic slot detection and n-gram based string matching method for phone based spoken document retrievals to overcome high error rates of phone recognizer. Experimental results have shown 9.25% relative improvement in the mean average precision (mAP) with 1.7 times speed up in comparison with the baseline system.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2001년도 추계학술발표논문집 (상)
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• pp.801-804
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• 2001

This article is concerned with automatic segmentation of two adjacent vowels for speech signals. All kinds of transition case of adjacent vowels can be characterized by spectrogram. Firstly the voiced-speech is extracted by the histogram analysis of vowel indicator which consists of wavelet low pass components. Secondly given phonetic transcription and transition pattern spectrogram, the voiced-speech portion which has consecutive vowels automatically segmented by the template matching. The cross-correlation function is adapted as a template matching method and the modified correlation coefficient is calculated for all frames. The largest value on the modified correlation coefficient series indicates the boundary of two consecutive vowel sounds. The experiment is performed for 154 vowel transition sets. The 154 spectrogram templates are gathered from 154 words(PRW Speech DB) and the 161 test words(PBW Speech DB) which are uttered by 5 speakers were tested. The experimental result shows the validity of the method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1014-1017
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• 2007

Sound focusing technologies has been studied for various purposes from early 1990s. As a result, these technologies make us possible to apply in many uses. For example, we can treat tumors using focused ultrasonic waves without surgical knife and communicate in the ocean using time reversal array. Also applications for personal audio system become issues. Recently, as technologies are developing, in some applications, needs for regional focusing become increasing because previously suggested focusing methods, such as phase conjugation, time reversal and inverse filtering, were all about a point focusing. Therefore, studies on regional focusing method are essentially needed. Regional focusing method was firstly mentioned by Choi and Kim in 2002: acoustic contrast control. However, in regional focusing, physical interpretations between control variables and results are still not easy because of its complexity. In this regard, we tried to understand the relations between control variables and results in wavenumber domain and suggested a solution method for regional focusing: wavenumber spectrum matching. We also showed how to make spatially focused sound shape using the suggested method from the simplest case: line focusing.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2400-2413
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• 2019

Doubly-selective (DS) fading channel is often occurred in many orthogonal frequency division multiplexing (OFDM) communication systems, such as high-speed rail communication systems and underwater acoustic (UWA) wireless networks. It is challenging to provide an accurate and fast estimation over the doubly-selective channel, due to the strong Doppler shift. This paper addresses the doubly selective channel estimation problem based on complex exponential basis expansion model (CE-BEM) in OFDM systems from the perspective of distributed compressive sensing (DCS). We propose a novel DCS-based improved sparsity adaptive matching pursuit (DCS-IMSAMP) algorithm. The advantage of the proposed algorithm is that it can exploit the joint channel sparsity information using dynamic threshold, variable step size and tailoring mechanism. Simulation results show that the proposed algorithm achieves 5dB performance gain with faster operation speed, in comparison with traditional DCS-based sparsity adaptive matching pursuit (DCS-SAMP) algorithm.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.5-8
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• 2000

This paper proposes GaN film as a piezoelectric material for SAW(surface acoustic wave) filters. The fabricated GaN SAW filter exhibited a very high velocity of 5800 ㎧and relatively low insertion loss of -9.9 dB without matching circuit. From Smith's equivalent circuit model, the calculated electromechanical coupling factor (K$^2$) was about 4.$\pm$03％. which is larger than those obtained from other thin film piezoelectric materials and allows the realization of wider filter fractional bandwidths.

• 대한전기학회논문지
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• 제41권2호
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• pp.192-198
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• 1992

The electrical properties of the ultrasonic probes and the piezoelectric composite materials with 1-3 connectivity by the extrusion method have been studied. The relative permittivity and piezoelectric coefficient increase linearly as PZT volume% increases and resonance frequency moves to low frequency as the sample thickness increases. The acoustic impedance matching with body and water is better than PZT ceramics' and the reception sensitivity is fine as the thickness thins down.

• 수산해양기술연구
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• 제34권1호
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• pp.85-95
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• 1998

어종의 식별을 위한 수중음향학적 정보를 수집하는 데 사용하기 위한 광대역 초음파 변환기를 개발할 목적으로 저주파용 Tonpilz형 초음파 변환기를 설계, 제작하고, 이 변환기의 음향 방사면에 $Al_2O_3$와 epoxy 수지를 서로 혼합하여 생성한 복합재료층과 폴리우레탄 수지로서 제작한 음향 정합층을 각각 직렬 접착시킨 복합구조 초음파 변환기의 광대역 주파수 특성에 대하여 분석, 고찰한 결과를 요약하면 다음과 같다. 1) Tonpilz형 transducer (head mass : 알류미늄 / 두께 22.0 mm, tail mass : 황동 / 두께 15.0 mm )의 음향 방사면에 두께 7.0 mm의 $Al_2O_3$와 epoxy 수지로서 생성한 복합재료층의 두께 18.0 mm의 폴리우레탄 수지로서 제작한 정합층을 직열접착한 복합 구조 초음파 변환기의 - 3 dB점에 대한 하한 및 상한 주파수 범위는 35.0~42.3 kHz (${\Delta}f=7.3 kHz)$이었고, 이 주파수 구간에 있어서의 송파전압감도의 최대치는 135.7 dB re $1\;{\mu}Pa/V$ 이었다. 2) Tonpilz형 transducer (head mass : 알류미늄 / 두께 23.0 mm, tail mass : 황동 / 두께 15.0 mm )의 음향 방사면에 두께 11.0 mm의 $Al_2O_3$와 epoxy 수지로서 제작한 복합재료층과 두께 15.8.0 mm의 폴리우레탄 수지로서 제작한 정합층을 직열접착한 복합 구조 초음파 변환기의 - 3 dB점에 대한 하한 및 상한 주파수 범위는 35.5~41.73 kHz (${\Delta}f=6.2 kHz)$이었고, 이 주파수 구간에 있어서의 송파전압감도의 최대치는 136.3 dB re $1\;{\mu}Pa/V$ 이었다. 3) 본 연구에서 시작한 복합구조 초음파 변환기에 chirp 신호(펄스 폭 4 ms, 중심주파수 40 kHz, 대역폭 40 kHz)를 인가하고, 수중방사음역에 있어서의 시간응답특성을 조사한 결과, 그 응답특성은 송신전압감도의 주파수특성과 매우 잘 일치하는 경향을 나타내었다. 이상의 결과로부터 본 연구에서 설계, 제작한 이중정합층을 갖는 복합구조 초음파 변환기는 단순구조의 Tonpilz형 초음파 변환기와 비교하여 비록 송파전압감도에 있어서는 약 5 dB 정도의 음향출력의 손실이 불가피하지만, 그 대신 주파수 대역폭을 약 5 재 정도 확대시킬 수 있는 장점이 있기 때문에 이 넓은 주파수 대역을 효과적으로 활용하면 어종식별을 위한 음향산란신호를 정량적으로 수집 및 평가하는 것이 가능하다고 판단된다.

• 한국음향학회지
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• 제20권5호
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• pp.69-75
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• 2001

본 연구에서는 일반적인 1, 2단자쌍 회로망의 임피던스 정합회로를 간단하고 빠르게 구할수 있는 새로운 방법을 제시하였다. 먼저 임피던스 정합 대상인 1단자쌍 또는 2단자쌍 회로망에 인덕터와 캐패시터의 조합으로 이루어진 임의의 L-회로망 형태의 정합회로가 포함된 전체 회로망 구조를 설정하고, 이 구조에 대한 전송행렬을 계산한 뒤에 회로망 양단의 부하저항 조건을 적용하여 전체 회로망의 입출력 임피던스를 구하였다. 이 식으로부터 정합용 소자의 정확한 값을 연립방정식을 이용하여 계산하였다. 본 연구의 타당성을 검증하기 위해 CDMA(code division multiple access)용 소자로 널리 사용되는 중간주파수 대 역 withdrawal 가중형 SAW필터 에 본 연구에서 제시한 방법을 적용하여 임피던스 정합 전후의 특성변화를 시뮬레이션과 실험을 통하여 확인하였다. 그 결과 85.38 MHz의 중심주파수에서 비대역폭이 1.2％ 삽입손실이 29 dB, VSWR (voltage standing wave ratio)이 80인 필터를 본 연구방법을 이용하여 정합한 경우에 각각의 성능이 1.8％, 9 dB, 3으로 향상됨을 시뮬레이션과 실험을 통해 확인하였다. 본 연구결과는 SAW (surface acoustic wave) 디바이스의 정합에 매우 용이하게 이용될 수 있을 뿐만 아니라 다른 형태의 1, 2단자쌍 회로망의 임피던스 정합에도 널리 사용될 수 있다.

• 한국위성정보통신학회논문지
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• 제12권1호
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• pp.101-106
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• 2017

In this paper, we present Emergency exit signs are installed to provide escape routes or ways in buildings like shopping malls, hospitals, industry, and government complex, etc. and various other places for safety purpose to aid people to escape easily during emergency situations. In case of an emergency situation like smoke, fire, bad lightings and crowded stamped condition at emergency situations, it's difficult for people to recognize the emergency exit signs and emergency doors to exit from the emergency building areas. This paper propose an automatic emergency exit sing recognition to find exit direction using a smart device. The proposed approach aims to develop an computer vision based smart phone application to detect emergency exit signs using the smart device camera and guide the direction to escape in the visible and audible output format. In this research, a CAMShift object tracking approach is used to detect the emergency exit sign and the direction information extracted using template matching method. The direction information of the exit sign is stored in a text format and then using text-to-speech the text synthesized to audible acoustic signal. The synthesized acoustic signal render on smart device speaker as an escape guide information to the user. This research result is analyzed and concluded from the views of visual elements selecting, EXIT appearance design and EXIT's placement in the building, which is very valuable and can be commonly referred in wayfinder system.