• Smart Structures and Systems
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• v.12 no.2
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• pp.97-119
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• 2013

This paper presents numerical and experimental results on the use of guided waves for structural health monitoring (SHM) of crack growth during a fatigue test in a thick steel plate used for civil engineering application. Numerical simulation, analytical modeling, and experimental tests are used to prove that piezoelectric wafer active sensor (PWAS) can perform active SHM using guided wave pitch-catch method and passive SHM using acoustic emission (AE). AE simulation was performed with the multi-physic FEM (MP-FEM) approach. The MP-FEM approach permits that the output variables to be expressed directly in electric terms while the two-ways electromechanical conversion is done internally in the MP-FEM formulation. The AE event was simulated as a pulse of defined duration and amplitude. The electrical signal measured at a PWAS receiver was simulated. Experimental tests were performed with PWAS transducers acting as passive receivers of AE signals. An AE source was simulated using 0.5-mm pencil lead breaks. The PWAS transducers were able to pick up AE signal with good strength. Subsequently, PWAS transducers and traditional AE transducer were applied to a 12.7-mm CT specimen subjected to accelerated fatigue testing. Active sensing in pitch catch mode on the CT specimen was applied between the PWAS transducers pairs. Damage indexes were calculated and correlated with actual crack growth. The paper finishes with conclusions and suggestions for further work.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.675-687
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• 2010

Structural Health Monitoring (SHM) is the science and technology of monitoring and assessing the condition of aerospace, civil and mechanical infrastructures using a sensing system integrated into the structure. Impedance-based SHM measures impedance of a structure using a PZT (Lead Zirconate Titanate) patch. This paper presents a low-power wireless autonomous and active SHM node called Autonomous SHM Sensor 2 (ASN-2), which is based on the impedance method. In this study, we incorporated three methods to save power. First, entire data processing is performed on-board, which minimizes radio transmission time. Considering that the radio of a wireless sensor node consumes the highest power among all modules, reduction of the transmission time saves substantial power. Second, a rectangular pulse train is used to excite a PZT patch instead of a sinusoidal wave. This eliminates a digital-to-analog converter and reduces the memory space. Third, ASN-2 senses the phase of the response signal instead of the magnitude. Sensing the phase of the signal eliminates an analog-to-digital converter and Fast Fourier Transform operation, which not only saves power, but also enables us to use a low-end low-power processor. Our SHM sensor node ASN-2 is implemented using a TI MSP430 microcontroller evaluation board. A cluster of ASN-2 nodes forms a wireless network. Each node wakes up at a predetermined interval, such as once in four hours, performs an SHM operation, reports the result to the central node wirelessly, and returns to sleep. The power consumption of our ASN-2 is 0.15 mW during the inactive mode and 18 mW during the active mode. Each SHM operation takes about 13 seconds to consume 236 mJ. When our ASN-2 operates once in every four hours, it is estimated to run for about 2.5 years with two AAA-size batteries ignoring the internal battery leakage.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.641-659
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• 2010

Structural Health Monitoring (SHM) gradually becomes a technique for ensuring the health and safety of civil infrastructures and is also an important approach for the research of the damage accumulation and disaster evolving characteristics of civil infrastructures. It is attracting prodigious research interests and the active development interests of scientists and engineers because a great number of civil infrastructures are planned and built every year in mainland China. In a SHM system the sheer number of accompanying wires, fiber optic cables, and other physical transmission medium is usually prohibitive, particularly for such structures as offshore platforms and long-span structures. Fortunately, with recent advances in technologies in sensing, wireless communication, and micro electro mechanical systems (MEMS), wireless sensor technique has been developing rapidly and is being used gradually in the SHM of civil engineering structures. In this paper, some recent advances in the research, development, and implementation of wireless sensors for the SHM of civil infrastructures in mainland China, especially in Dalian University of Technology (DUT) and Harbin Institute of Technology (HIT), are introduced. Firstly, a kind of wireless digital acceleration sensors for structural global monitoring is designed and validated in an offshore structure model. Secondly, wireless inclination sensor systems based on Frequency-hopping techniques are developed and applied successfully to swing monitoring of large-scale hook structures. Thirdly, wireless acquisition systems integrating with different sensing materials, such as Polyvinylidene Fluoride(PVDF), strain gauge, piezoresistive stress/strain sensors fabricated by using the nickel powder-filled cement-based composite, are proposed for structural local monitoring, and validating the characteristics of the above materials. Finally, solutions to the key problem of finite energy for wireless sensors networks are discussed, with future works also being introduced, for example, the wireless sensor networks powered by corrosion signal for corrosion monitoring and rapid diagnosis for large structures.

• Korean Journal of Remote Sensing
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• v.37 no.6_1
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• pp.1599-1610
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• 2021

The natural environment and local ecosystem change depending on various factors, but among them, the change in water temperature is one of the major factors affecting the surrounding environment in the river ecosystem. However, research on water temperature change have not been actively conducted to date compared to the effect of water temperature on the river environment. Therefore, this study intends to study the change in water temperature from 2015 to 2021 through the change in the area of winter ice in the Hongcheon River. Optical satellite images were classified by referring to the field survey results, and the SAR satellite imagestried to overcome the limitations of the input data by using the GLCM texture analysis method. After verifying the accuracy of all images used, the calculated monthly average ice area was compared with the temperature data of the adjacent AWS. It was found that there is a correlation between water temperature and ice area, and the results of this study can be used to study environmental changes in small-scale rivers that are difficult to access or do not have systems in place.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.307-309
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• 2016

This paper present about the system for sensing and controlling a wireless power transfer system using bluetooth protocol in robot, healthcare, smart-grid, and autonomous car. Recently a variety of applications using the Internet of Things (Internet of Things) and machine to machine (Machine to Machine) have been raised in many industries. To do this, it requires the fusion technology which is constituted with control, computing and networking. Embedded system is centered existing control system and Cyber Physical System(CPS) is the systems which was converged of a computing technologies using a wired or wireless network. CPS was adopted in the future government-led technology in the United States and Europe and is being pursued in cooperation with institutes, industries, and academia. In this paper, we implement and describe a technique for controlling the system for transmitting power wirelessly by sensing method using the matching of CPS technology concepts.

• Korean Journal of Remote Sensing
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• v.38 no.6_4
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• pp.1911-1923
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• 2022

The availability of high-resolution satellite images provides precise information without direct observation of the research target. Korea Multi-Purpose Satellite (KOMPSAT), also known as the Arirang satellite, has been developed and utilized for earth observation. The machine learning model was continuously proven as a good classifier in classifying remotely sensed images. This study aimed to compare the performance of the support vector machine (SVM) model in classifying the land cover of the Delaware River port area on high and medium-resolution images. Three optical images, which are KOMPSAT-2, KOMPSAT-3A, and Sentinel-2B, were classified into six land cover classes, including water, road, vegetation, building, vacant, and shadow. The KOMPSAT images are provided by Korea Aerospace Research Institute (KARI), and the Sentinel-2B image was provided by the European Space Agency (ESA). The training samples were manually digitized for each land cover class and considered the reference image. The predicted images were compared to the actual data to obtain the accuracy assessment using a confusion matrix analysis. In addition, the time-consuming training and classifying were recorded to evaluate the model performance. The results showed that the KOMPSAT-3A image has the highest overall accuracy and followed by KOMPSAT-2 and Sentinel-2B results. On the contrary, the model took a long time to classify the higher-resolution image compared to the lower resolution. For that reason, we can conclude that the SVM model performed better in the higher resolution image with the consequence of the longer time-consuming training and classifying data. Thus, this finding might provide consideration for related researchers when selecting satellite imagery for effective and accurate image classification.

• Korean Journal of Remote Sensing
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• v.38 no.5_1
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• pp.545-557
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• 2022

This study used high-resolution satellite images and supervised classification technique based on machine learning method in order to detect the areas affected by wildfires in the demilitarized zone (DMZ) where direct access is difficult. Sentinel-2 A/B was used for high-resolution satellite images. Land cover map was calculated based on the SVM supervised classification technique. In order to find the optimal combination to classify the DMZ wildfire damage area, supervised classification according to various kernel and band combinations in the SVM was performed and the accuracy was evaluated through the error matrix. Verification was performed by comparing the results of the wildfire detection based on satellite image and data by the wildfire statistical annual report in 2020 and 2021. Also, wildfire damage areas was detected for which there is no current data in 2022. This is to quickly determine reliable results.

• Smart Structures and Systems
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• v.29 no.2
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• pp.301-309
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• 2022

Protective coatings are most widely used anticorrosive structures for steel structures. The corrosion under the coating damages the host material, but this damage is completely hidden. Therefore, a field-applicable under-coating-corrosion visualization method has been desired for a long time. Laser ultrasonic technology has been studied in various fields as an in situ nondestructive inspection method. In this study, a comparative analysis was carried out between a guided-wave ultrasonic propagation imager (UPI) and pulse-echo UPI, which have the potential to be used in the field of under-coating-corrosion management. Both guided-wave UPI and pulse-echo UPI were able to successfully visualize the corrosion. Regarding the field application, the guided-wave UPI performing Q-switch laser scanning and piezoelectric sensing by magnetic attachment exhibited advantages owing to the larger distance and incident angle in the laser measurement than those of the pulse-echo UPI. Regarding the corrosion visualization methods, the combination of adjacent wave subtraction and variable time window amplitude mapping (VTWAM) provided acceptable results for the guided-wave UPI, while VTWAM was sufficient for the pule-echo UPI. In addition, the capability of multiple sensing in a single channel of the guided-wave UPI could improve the field applicability as well as the relatively smaller size of the system. Thus, we propose a guided-wave UPI as a tool for under-coating-corrosion management.

• Korean Journal of Remote Sensing
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• v.40 no.3
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• pp.307-316
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• 2024

On January 1, 2024, an earthquake with a moment magnitude of 7.5 occurred on the Noto Peninsula in Japan. The earthquake caused significant surface displacement on the Noto Peninsula. The surface displacement is measured by global navigation satellite system (GNSS) base stations, but there are limitations in obtaining information in areas where base stations do not exist. Therefore, in this study, we aim to determine the horizontal land surface displacement across the Noto Peninsula using offset tracking, which can detect rapidly occurring displacement. As a result of analyzing the Noto Peninsula using the offset tracking technique, it was found that more horizontal surface displacement occurred in the northwest region than in the northeast region of the Noto Peninsula, where the epicenter was located, and the surface displacement value reached a maximum of 2.9 m. The results of this study can be used to calculate surface displacement values in areas where surface displacement data are not available through ground GNSS base stations.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.219-224
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• 2011

In this study, a piezoelectric smart sensor that can be embedded inside of concrete structures is developed to investigate the early stage of concrete curing. A waterproof coating is used to protect the piezoelectric sensor from moistures of concrete mixture. Also, a mortar case is utilized to encapsulate the sensor to protect it from impact loads. To estimate the strength of concrete, a self-sense guided-wave actuated sensing technique is applied. In the guided wave, its velocity is varied according to the mechanical properties of concrete such as modulus of elasticity. Because modulus of elasticity directly affects the strength of concrete, the guidedwave's velocity also affects the concrete strength development. To verify the feasibility of using the proposed approach, the smart sensor was embedded into a 100MPa concrete cylinder and the self-sense guided wave is continuously measured throughout the curing process. The measurements showed that the propagation time (TOF) of the measured guided waves gradually decreased as the curing age increased. Especially, at the early age of the curing process, the variation of the TOF was very significant. Furthermore, the results showed that there is a linear relationship between the TOF of the self-sense guided waves and the strength of concrete existed. It is safe to conclude that the proposed approach can be used very effectively in monitoring of the strength development of high strength concrete structures.