• International Journal of Safety
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• v.7 no.2
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• pp.17-22
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• 2008

Recent developments in contactless, air-coupled sensing of seismic and ultrasonic waves in concrete structures are presented. Contactless sensing allows for rapid, efficient and consistent data collection over a large volume of material. Two inspection applications are discussed: air-coupled impact-echo scanning of concrete structures using seismically generated waves, and air-coupled imaging of internal damages in concrete using ultrasonic tomography. The first application aims to locate and characterize shallow delamination defects within concrete bridge decks. Impact-echo method is applied to scan defected concrete slabs using air coupled sensors. Next, efforts to apply air-coupled ultrasonic tomography to concrete damage imaging are discussed. Preliminary results are presented for air-coupled ultrasonic tomography applied to solid elements to locate internal defects. The results demonstrate that, with continued development, air-coupled ultrasonic tomography may provide improved evaluation of unseen material defects within structures.

• Smart Structures and Systems
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• v.17 no.1
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• pp.31-43
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• 2016

Applications of ultrasonic tomography to concrete structures have been reported for many years. However, practical and effective application of this tool for nondestructive assessment of internal concrete condition is hampered by time consuming transducer coupling that limits the amount of ultrasonic data that can be collected. This research aims to deploy recent developments in air-coupled ultrasonic measurements of solids, described in Part 1 of this paper set, to concrete in order to image internal inclusions. Ultrasonic signals are collected from concrete samples using a fully air-coupled (contactless) test configuration. These air coupled data are compared to those collected using partial semi-contact and full-contact test configurations. Two samples are considered: a 150 mm diameter cylinder with an internal circular void and a prism with $300mm{\times}300mm$ square cross-section that contains internal damaged regions and embedded reinforcement. The heterogeneous nature of concrete material structure complicates the application and interpretation of ultrasonic measurements and imaging. Volumetric inclusions within the concrete specimens are identified in the constructed velocity tomograms, but wave scattering at internal interfaces of the concrete disrupts the images. This disruption reduces defect detection accuracy as compared with tomograms built up of data collected from homogeneous solid samples (PVC) that are described in Part 1 of this paper set. Semi-contact measurements provide some improvement in accuracy through higher signal-to-noise ratio while still allowing for reasonably rapid data collection.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.70-79
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• 2020

The main objective of this research to develop an IoT based wireless contactless ultrasonic system (ICUS) and its application to concrete structure. The developed system consists of 16 mems, 2Mhz digitizer, amplifying circuit, FPGA, and wifi module, enabling to measure leaky surface waves from concrete specimens without physical coupling process and wires. Multi-channel analysis is performed to improve the accuracy of data analysis, and the velocity of leaky surface waves and acoustics are derived. Field inspection of railroad concrete sleepers is conducted to evaluate the performance of the system and to compare the results with conventional ultrasonic pulse velocity (UPV). As a result of the field inspection, UPV was limited to evaluate damages. This is because crack pattern of railroad sleepers is parallel to ultrasonic ray path and accessibility of the railroad at the field is disadvantageous to contact-based UPV. On the other hand, ICUS possibly detect the damages as reduction of dynamic modulus by up to 59% compared to non-damaged specimen.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.24-24
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• 2022

토양 수분은 육상 생태계를 지배하는 핵심 변수로 널리 간주되어 왔다. 따라서 토양 수분을 모니터링하고 추정하는 것은 수문, 농업, 생화학적, 및 기후 역학을 평가하는 데 필수적이다. 그러나 최대 토양 접촉을 요구하는 기존의 토양 수분 모니터링 방법은, 토양 교란을 최소화하여 토양의 고유 특성을 보전하지 못하는 한계가 있다. 이 문제를 극복하기 위해 본 연구에서는 비접촉 초음파 시스템을 이용하여 토양 수분을 평가 방법을 개발하였다. 이 시스템은 공기-토양 조인트 절반 공간에서 누설 레일리파(Rayleigh wave)를 측정하도록 설계되었다. 토양 수분의 변화에 대한 누설 레일리파의 측정은 통제된 실험 설계에서 모래, 실트, 점토와 같은 세 가지 토양 유형에서 평가하였다. 본 연구 결과에서 세 가지 토양 사례 모두, 누설 레일리파의 에너지와 토양 수분 사이에 밀접한 관계가 있음을 보였다. 그러나 모래에서 얻은 동적 매개변수의 특성은 실트 및 점토의 특성과 다른 형태를 보였다. 이러한 결과는 미세한 토양 입자와 대조적으로 굵은 토양 입자는 증발 과정에서 감소된 토양 강도로 설명될 수 있다. 관측된 누설 레일리파에서 얻은 동적 매개변수를 기반으로 토양 수분을 평가하기 위해 랜덤 포레스트 모형을 이용하였다. 예측된 토양 수분의 정확도는 모든 데이터 및 토양 유형에 관계없이 높은 정확도를 보였다(R² ≥ 0.98, RMSE ≤ 0.0089 m³ m^-3). 즉, 본 연구에서는 레일리파가 토양 교란 없이 토양 수분 변화를 지속적으로 평가할 수 있는 큰 잠재력을 가지고 있음을 보여주었다.