• Smart Structures and Systems
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• v.1 no.4
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• pp.355-368
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• 2005

Large and complex structures are being built now-a-days and, they are required to be functional even under extreme loading and environmental conditions. In order to meet the safety and maintenance demands, there is a need to build sensors integrated structural system, which can sense and provide necessary information about the structural response to complex loading and environment. Sophisticated tools have been developed for the design and construction of civil engineering structures. However, very little has been accomplished in the area of monitoring and rehabilitation. The employment of appropriate sensor is therefore crucial, and efforts must be directed towards non-destructive testing techniques that remain functional throughout the life of the structure. Fiber optic sensors are emerging as a superior non-destructive tool for evaluating the health of civil engineering structures. Flexibility, small in size and corrosion resistance of optical fibers allow them to be directly embedded in concrete structures. The inherent advantages of fiber optic sensors over conventional sensors include high resolution, ability to work in difficult environment, immunity from electromagnetic interference, large band width of signal, low noise and high sensitivity. This paper brings out the potential and current status of technology of fiber optic sensors for civil engineering applications. The importance of employing fiber optic sensors for health monitoring of civil engineering structures has been highlighted. Details of laboratory studies carried out on fiber optic strain sensors to assess their suitability for civil engineering applications are also covered.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.506-513
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• 2021

The durability and safety of reinforced concrete structures significantly depend on the reinforcement conditions, concrete cover thickness, cracks, and concrete strength. There are two ways to accurately determine the information on reinforcing bars embedded in concrete - the local destructive method and the non-destructive rebar detection test. In general, the non-destructive rebar detection tests, such as the electromagnetic wave radar method, electromagnetic induction method, and radiation method, are adopted to avoid damage to the structural elements. The moisture content and temperature of concrete affect the dielectric constant, which is the electrical property of concrete, and cause interference in the non-destructive rebar detection test results. Therefore, in this study, the effects of the electromagnetic wave radar method and electromagnetic induction method have been analyzed according to the temperature and surface moisture content of concrete. Due to the technological advancement and development of equipment, the average error rate was less than 5% in the specimens at 24℃, irrespective of their operating principles. Among the tested methods, the electromagnetic induction method showed very high accuracy. The electromagnetic wave radar method indicated a relatively small error rate in the dry state than in the wet state, and exhibited a relatively high error rate at high temperatures. It was confirmed that the error could be reduced by applying the electromagnetic wave radar method when the temperature of the probe was low and in a dry state, and by using the electromagnetic induction method when the probe was in a wet state or at a high temperature.

• Current Photovoltaic Research
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• v.5 no.2
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• pp.55-58
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• 2017

We investigated the influences of dielectric thin film coating on the optical characteristics of c-Si wafers with nanocone (NC) arrays using finite-difference time-domain (FDTD) simulations. Dielectric thin films on high-refractive-index surface can lower optical reflection and reflection dips appear at the wavelengths where destructive interference occurs. The optical reflection of the NC arrays was lower than that of the dielectric-coated planar wafer in broad wavelength range. Remarkable antireflection effects of the NC array could be attributed to beneficial roles of the NCs, including the graded refractive index, multiple reflection, diffraction, and Mie resonance. Dielectric thin films modified the optical reflection spectra of the NC arrays, which could not be explained by the interference alone. The optical properties of the dielectric-coated NC arrays were determined by the inherent optical characteristics of the NC arrays.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.69-72
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• 2013

In long-range ultrasonic testing, a phased array probe composed of multiple identical transducers with an uniform interval of one quarter wavelength is usually used for the transmission or reception directivity control. This paper shows that the propagation directions of individual echoes can be identified in real time by displaying the inputs of a process for summing the constitution reception signals after compensating the phase difference due to the transducer interval, together with the output of the process. A constructive interference of the constitution echoes indicates a forward direction echo propagating along an intended direction while a destructive interference implies a reverse direction echo propagating along the direction opposite to the intended one.

• Korean Journal of Materials Research
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• v.17 no.5
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• pp.239-243
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• 2007

The evaluation and comparison have been made for the EMI noise which was included in the signal from the sensors in the acoustic emission testing for the bottom plate of ground tank at full. The EMI signal has been classified into two types. One is the signal with very short AE count, and this signal possibly can be filtered by front end filter setting of the channel count with low level of 4 and high level of $10^8$. The other EMI signal occurred from CH 1, CH 3 and CH 10, and had high and constant duration with high energy and count (maximun duration > $10^5\;{\mu}s$), and has characteristic gradient of accumulation amplitude distribution. This signal should be removed in the AE signal evaluation by filtering, because this may affect to the total gradient.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.65-74
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• 2021

A key factor that governs the wave interferences of a submerged body is the dimensionless Froude number. Computational Fluid Dynamics (CFD) is used to describe the resistance force coefficients and the generated waves of two SUBOFF submarine models. Grid independence studies are performed on two cases, totally and shallowly submerged cases, with four sets of computing meshes. The highest peaks are marked by red points at given wavelengths, a line is fitted to those points with a least-squares approximation, and the half wake angle at multiple Froude numbers is defined between the fitted line and the centerline of the free surface. The results show that when the depth of the target is 1.1D, constructive interferences occur at Fn = 0.3 and 0.5, while destructive interference occurs at Fn = 0.35 with distortion of the waveform. The half wake angle is less than 19.47° because of the interference between the bow and stern wave systems.

• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.103-109
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• 2015

In an amplitude-splitting interferometer, a beam splitter divides an input beam into two parts, which are superposed after propagating along separate paths, producing an interference effect. We have investigated the phase relation between the reflected and transmitted light waves at BS's made of lossless dielectric stacks. If we define the phases with proper reference planes, a definite phase relation exists, irrespective of the detailed structure of the layers in the BS. Although this results from the generalized Stokes relations, we have verified it numerically for two representative BS's with symmetric and asymmetric layer structures respectively. When we applied the phase relation to interferometers, we could determine the superposition state of the output beam (either constructive or destructive interference) for a general BS, and could verify that the light's energy was conserved.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.373-379
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• 2006

Vibration-based structural health monitoring is one of non-destructive evaluation (NDE) techniques for civil infrastructures. This paper presents a novel fiber optic accelerometer system to monitor civil engineering structures and a successful application of the novel sensor system for measuring ambient vibration of a real building structure. This sensor system integrates the Moire fringe phenomenon with fiber optics to achieve accurate and reliable measurements. The sensor system is immune to electromagnetic (EM) interference making it suitable for difficult applications in such environments involving strong EM fields, electrical spark-induced explosion risks, and cabling problems, prohibiting the use of conventional electromagnetic accelerometers. A prototype sensor system has been developed, together with a signal processing software. The experimental studies demonstrated the high-performance of the fiber optic sensor system. Especially, the sensor was successfully used for monitoring a real building on UCI (University of California Irvine, USA).

• The Journal of the Acoustical Society of Korea
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• v.11 no.1E
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• pp.56-63
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• 1992

The poblem of active oise control has been analysed using a adaptive signal processing technique. In this methods, the adaptive signal processor or model predicts the primary sound wave travelling along the acoustic plant and generates the secondary source 180° out of phase which attempts to attempts to attenuate the undesired noise by destructive interference. In the solutions presented here, acoustic propagation delay is considered as a part of the model which used the FIR filter. The effects of error path and auxiliary path transfer functioin are anayzed and a new on=-line technique for error path modeling, adaptive delayed inverse modeling is presented. In this study, using these new concepts, our system can more reduce the noise level in duct to 5dB-15dB than only using LMS algorithm system.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.199-204
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• 2008

The generation of axisymmetric Lamb waves and interaction with wall thinning (corrosion) defects in hollow cylinders are simulated using the finite element method. Guided wave interaction with defects in cylinders is challenged by the multi-mode dispersion and the mode conversion. In this paper, two longitudinal, axisymmetric modes are generated using the concept of a time-delay periodic ring arrays (TDPRA), which makes use of the constructive/destructive interference concept to achieve the unidirectional emission and reception of guided waves. The axisymmetric scattering by the wall thinning extending in full circumference of a cylinder is studied with a two-dimensional FE simulation. The effect of wall thinning depth, axial extension, and the edge shape on the reflections of guided waves is discussed.