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Proceedings ArticleDOI

Rapid nondestructive evaluation of defects in GFRP composites using terahertz line scanner

TL;DR: In this paper, a line scanner was used for defect detection in fiber reinforced polymers (GFRP) composites using a 100 GHz source and the total acquisition time for imaging the GFRP sample of dimensions 55× 35 mm2 is 10 s, which is >100 times faster compared to a conventional raster scanning technique.
Abstract: Terahertz (THz) imaging is an attractive alternate to ultrasonic based Non-destructive Evaluation (NDE) especially for Fiber Reinforced Polymers (FRPs) such as Glass FRP (GFRP) composites as the latter demands proximity and additional coupling medium for the best performance. Typically, THz imaging system uses a single emitter-detector configuration employing raster scan method for image acquisition. The image acquisition speed is greatly limited by the speed of the mechanical stages and hence its usage in real-time industrial NDT applications such as in-line quality control has been limited. Alternatively, having an array of detectors will significantly increase the system cost. As an optimal compromise for speed and cost, line scanners are highly desirable. In this work, rapid imaging performance of a THz line scanner has been studied by imaging closely spaced defects in GFRP composites using a 100 GHz source. The total acquisition time for imaging the GFRP sample of dimensions 55× 35 mm2 is 10 s, which is >100 times faster compared to a conventional raster scanning technique. In addition, image deconvolution techniques such as Lucy Richardson and Weiner deconvolution have been adopted to improve the quality of the acquired THz images. The results show that the THz line scanners can successfully be employed for rapid defect detection in GFRP composites.
Citations
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Proceedings ArticleDOI
13 Sep 2021
TL;DR: In this paper, a sequence of image processing steps has been adopted which include (i) Weiner filtering, (ii) Lucy-Richardson deconvolution with the appropriate point-spread function, (iii) histogram based global thresholding of the image.
Abstract: With an increasing trend of anti-social activities and terrorist attacks, there is a persistent demand for rapid and effective security screening systems, particularly in crowded public places such as in metros stations, airports, etc. Nowadays, terahertz (THz) based rapid scanners and cameras are employed as an alternative to the traditional X-ray baggage scanners due to the ability of THz waves to penetrate most nonmetallic materials and low ionizing radiation. Although such rapid THz line scanners and cameras are commercially available, the quality of the THz images acquired with these devices are very poor. This requires advanced image processing techniques to be employed for rapid threat object detection and identification. In this work, a sequence of image processing steps has been adopted which include (i) Weiner filtering, (ii) Lucy-Richardson deconvolution with the appropriate point-spread function, (iii) histogram based global thresholding of the image. This sequence of image processing operations has resulted in refined images thereby enabling rapid threat object detection and identification. This approach may be utilized as a preprocessing step before implementing sophisticated neural networks for automatic threat object detection and classification.

2 citations

References
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Journal ArticleDOI
TL;DR: Aglass fibers reinforced polymer composites have been prepared by various manufacturing technology and are widely used for various applications as mentioned in this paper, however, they are not suitable for the use in medical applications.
Abstract: Glass fibers reinforced polymer composites have been prepared by various manufacturing technology and are widely used for various applications. Initially, ancient Egyptians made containers by glass...

519 citations

Journal ArticleDOI
TL;DR: In this paper, various techniques aimed at detecting potential outliers are reviewed and these techniques are subdivided into two classes, the ones regarding univariate data and those addressing multivariate data.
Abstract: Outliers are observations or measures that are suspicious because they are much smaller or much larger than the vast majority of the observations. These observations are problematic because they may not be caused by the mental process under scrutiny or may not reflect the ability under examination. The problem is that a few outliers is sometimes enough to distort the group results (by altering the mean performance, by increasing variability, etc.). In this paper, various techniques aimed at detecting potential outliers are reviewed. These techniques are subdivided into two classes, the ones regarding univariate data and those addressing multivariate data. Within these two classes, we consider the cases where the population distribution is known to be normal, the population is not normal but known, or the population is unknown. Recommendations will be put forward in each case.

494 citations

Journal ArticleDOI
TL;DR: In this article, transient thermal non-destructive testing (NDT) is used for assessing aircraft composites, which can be used for both reducing manufacturing costs and out-ofservice time of aircraft due to maintenance.

182 citations

Journal ArticleDOI
TL;DR: Terahertz (THz = 1012 Hz) spectroscopy has shown great potential in biomedical research due to its unique features, such as the non-invasive and label-free identification of living cells and medical imaging.
Abstract: Terahertz (THz = 1012 Hz) spectroscopy has shown great potential in biomedical research due to its unique features, such as the non-invasive and label-free identification of living cells and medical imaging. In this review, we summarized the advantages and progresses achieved in THz spectroscopy technology for blood cell detection, cancer cell characterization, bacterial identification and biological tissue discrimination, further introducing THz imaging systems and its progress in tissue imaging. We also highlighted the biological effects of THz radiation during its biological applications and the existing challenges and strategies to accelerate future clinical applications. The future prospects for THz spectroscopy will focus on developing rapid, label-free, and convenient biosensors for point-of-care tests and THz in vivo imaging.

168 citations

Journal ArticleDOI
TL;DR: In this paper, a compact sub-terahertz (THz) imaging system with a 0.2-GHz TUNNETT diode oscillator and its application for non-destructive and harmless inspections of timbers, concrete and ceramic tiles are shown.
Abstract: A compact sub-terahertz (THz) imaging system with a 0.2 THz-band GaAs TUNNETT diode oscillator and its application for non-destructive and harmless inspections of timbers, concrete and ceramic tiles are shown. Sub-THz transmission characteristics of various kinds of woods were investigated. It is shown that wood and concrete show a high transmittance in this frequency range, and that the measured absorption coefficients correlate well with the densities of woods. Then, the invisible grains, knots and diffused water inside the timbers were investigated by sub-THz transmission imaging. It is also shown that the sub-THz wave is a very efficient tool for defect recognition in concrete. Invisible cracks, diffused water and the quality of adhesion of tiles were investigated. It is concluded that the sub-THz wave has shown a high sensitivity in detecting these defects in building blocks.

94 citations