• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.774-780
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• 2009

This paper proposes a transmitted power saving method for underwater acoustic sensors considering the acoustic wave propagation characteristic that propagation loss increases more rapidly in higher frequency band. In the proposed scheme, sensor nodes are divided into a few groups based on the distance between sink node and the sensor node, and each group uses its own frequency band. The node group with longer distance uses lower frequency and the node group with shorter distance uses higher frequency. By means of such a distance-dependent frequency allocation, all sensor nodes are able to maintain a certain target signal-to-noise ratio (SNR), but also save transmitted power. In addition, the optimum size of node group is obtained, and also a frequency allocation algorithm is proposed accordingly. Numerical results show that the proposed scheme saves transmitted power by more 10 dB comparing non-grouping methods.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.465-475
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• 2004

This paper is the first part of the study on the development of a smart active layer (SAL) sensor, which consists of two parts. In this first part, the theory and concept of the SAL sensor is investigated, which is designed for the detection of elastic waves caused by internal cracks and damages in structures. For the development SAL sensor, (i) the basic theory of elastic waves was studied, (ii) the feasible study of the SAL as an elastic waves detection sensor using the finite element analysis (FEA) with respect to a piezoceramic disc was performed. (iii) the comparison of performances between some piezoceramic sensors and a commercial acoustic emission (AE) sensor was accomplished to ensure the applicability by the experimental means, such as a pencil lead break test. Also, the conceptional study for the SAL sensor, which can be utilized for the effective detection and locating of defects by the arrangement of regularly distributed sensors, was discussed.

• Smart Structures and Systems
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• v.8 no.3
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• pp.321-341
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• 2011

Acoustic emission (AE) monitoring was conducted for mortar specimens under three types of static loading patterns (cubic-splitting, direct-shear and pull-out). Each of the applied loading patterns was expected to produce a particular fracture process. Subsequently, the AEs generated by various fracture or damage processes carried specific information on temporal micro-crack behaviors of concrete for post analysis, which was represented in the form of detected AE signal characteristics. Among various available characteristics of acquired AE signals, frequency content was of great interest. In this study, cement-based piezoelectric sensor (as AE transducer) and home-programmed DEcLIN monitoring system were utilized for AE monitoring on mortar. The cement-based piezoelectric sensor demonstrated enhanced sensitivity and broad frequency domain response range after being embedded into mortar specimens. This broad band characteristic of cement-based piezoelectric sensor in frequency domain response benefited the analysis of frequency content of AE. Various evaluation methods were introduced and employed to clarify the variation characteristics of AE frequency content in each test. It was found that the variation behaviors of AE frequency content exhibited a close relationship with the applied loading processes during the tests.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.214-221
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• 2019

In this paper, a temperature dependent acoustic receiving characteristics of underwater acoustic sensor is studied by theoretical and experimental investigations. Two different types (low mid frequency sensor and high frequency sensor) of underwater acoustic sensors are designed with different configuration of baffle and conditioning plate. The temperature dependent characteristics of the acoustic sensors are investigated within the temperature range from $-2^{\circ}C$ to $35^{\circ}C$. The material properties of the piezoelectric ceramics, molding and baffle, which are the primary materials of the acoustic sensors, are measured with temperature change. The temperature dependent RVS (Receiving Voltage Sensitivity) characteristics of the acoustic sensors are simulated by using the measured material properties. The RVS changes of the acoustic sensors are measured by changing temperature in the watertank where the acoustic sensors are installed. The measured and the simulated data show that the temperature dependent characteristics of the acoustic sensors are mainly dependent for the sound speed changes of the molding material.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.3
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• pp.190-198
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• 2013

In order to predict acoustic pressure distributions by exterior incident wave at Cylindrical Hydrophone Array (CHA) sensor's positions, acoustic pressure analysis is performed by using beam tracing method. Beam tracing method is well-known of reliable pressure analysis methods at high-frequency range. When an acoustic noise source is located at the center of rectangular room, acoustic pressure analysis is performed by using both beam tracing method and Power Flow Boundary Element Method (PFBEM). By comparing with results of beam tracing method and those of PFBEM, the accuracy of beam tracing method is verified. We develop the CHA pressure analysis program by verified beam tracing method. The developed software is composed of model input, sensor array creator, analysis option, solver and post-processor. We can choose a model option of 2D or 3D. The sensor array generator is connected to a sonar which is composed of center position, bottom, top and angle between sensors. We also can choose an analysis option such as analysis frequency, beam number, reflect number, etc. The solver module calculates the ray paths, acoustic pressure and result of generating beams. We apply the program to 2D and 3D CHA models, and their results are reliable.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.147-152
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• 2012

This paper dealt with the frequency component analysis of acoustic signals produced by corona and series-arc discharges as a diagnostic technique for closed-switchboards. Corona and series-arc discharge were simulated by a needle-plane electrode and an arc generator specified in UL1699, respectively. Acoustic signal was detected by a wideband acoustic sensor with a frequency bandwidth of 4 Hz~100 kHz (-3 dB). We analyzed frequency spectrums of the acoustic signals detected in various discharge conditions. The results showed that acoustic signals mainly exist in ranges from 30 kHz to 60 kHz. From the experimental results, an acoustic detection system which consists of a constant current power supply (CCP), a low noise amplifier (LNA) and a band pass filter was designed and fabricated. The CCP separates the signal component from the DC source of acoustic sensor, and the LNA has a gain of 40 dB in ranges of 280 Hz~320 kHz. The high and the low cut-off frequency are 30 kHz and 60 kHz, respectively. We could detect corona and series-arc discharges without any interference by the acoustic detection system, and the best frequency is considered in ranges of 30 kHz~60 kHz.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.398-400
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• 1995

In this Study, the Electrostatic Coutour Distribution in Polymer Electret Acoustic Sensor is calculated using Finite Element Method. As a result, the Electrostatic Countour Distribution is visualized and the design modification could be processed.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.117-122
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• 2006

Modernized GNSS such as new GPS signals updated GLONASS and coming Galileo promises higher quality and higher reliability for users. Powerful technologies such as Internet, ubiquitous network technology and sensor network has been used to promote a safe and more secure lifestyle. This report describes experimental trials to combine these technologies namely GPS and Sensor Network into a high-performance system. GPS is used to enlarge the communication range, resolving the service area limitations, as a wider service area is required at shore areas compared to urban area. GPS position datum is also used as primary network routing information to get practical Sensor Network. Another application is the under water Sensor Network. Accurate GPS position and time are used to establish stable and high reliability underwater acoustic Sensor Network. This paper describes the background of the project 'Harbor area Marine Ubiquitous Sensor Network', preliminary consideration and testing. Radio and acoustic communication is the main focus of this preliminary experiment.

• Composites Research
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• v.17 no.4
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• pp.61-67
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• 2004

Nondestructive damage sensitivity on single-basalt fiber/epoxy composites was evaluated by micromechanical technique and acoustic emission (AE). Piezoelectric lead-zirconate-titanate (PZT), polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer were used as AE sensor, respectively. In single-fiber composite, the damage sensing with different sensor types were compared to each other. Piezoelectric PVDF polymer sensor was embedded in and attached on the composite, whereas PZT sensor was only attached on the surface of specimen. In case of embedded polymer sensors, responding sensitivity was higher than that of the attached case. It can be due to full constraint inside specimen to transfer elastic wave coming from micro-deformation. For both the attached and the embedded cases, the sensitivity of P(VDF-TrFE) sensor was almost same as that of conventional PVDF sensor.

• Transactions of Materials Processing
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• v.18 no.2
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• pp.144-149
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• 2009

Recently, the monitoring technology of machining process is very important to improve productivity and quality in manufacturing filed. Such monitoring technology has been performed to measurement using vibration signal, acoustic emission signal and tool dynamometer. However, micro machining is limited small-scale parts machining because micro tool is very small and weakness to generate signal in micro machining process. Therefore, this study has efficient sensing technology for real monitoring system in micro machine that is proposed to supplement a disadvantage of single-sensor by multi sensor. From experimental result, it was evaluated tool wear and cutting situation according to repetitive slot cutting condition and changing cutting condition, and it was performed monitoring spindle rpm and condition according to compare acceleration signal with current signal.