1. Articles in category: NDE/NDT

    1-24 of 364 1 2 3 4 ... 14 15 16 »
    1. Comparison of laser triangulation, phase shift triangulation and swept source optical coherence Tomography for nondestructive inspection of objects with micrometric accuracy

      Comparison of laser triangulation, phase shift triangulation and swept source optical coherence Tomography for nondestructive inspection of objects with micrometric accuracy

      We compare the performance of laser triangulation, phase shift triangulation and swept source optical coherence tomography (SSOCT) for quantitative nondestructive inspection. Measurement accuracies of these three optical 3D imaging techniques can be reduced to a few tens of micrometers or less, making it possible to locate and geometrically characterize defects at the micrometric scale. We consider surfaces with different optical properties and we discuss the ability of these techniques to reconstruct the surface profiles. For opaque surfaces, the three techniques provide very similar results. For semi-transparent and transparent surfaces, the accuracy achieved by SSOCT relies on the capability of detecting ...

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    2. Terahertz continuous wave system using phase shift interferometry for measuring the thickness of sub-100-μm-thick samples without frequency sweep

      Terahertz continuous wave system using phase shift interferometry for measuring the thickness of sub-100-μm-thick samples without frequency sweep

      A terahertz continuous wave system is demonstrated for thickness measurement using Gouy phase shift interferometry without frequency sweep. One arm of the interferometer utilizes a collimated wave as a reference, and the other arm applies a focused beam for sample investigation. When the optical path difference (OPD) of the arms is zero, a destructive interference pattern is produced. Interference signal intensity changes induced by the OPD changes can be easily predicted by calculations. By minimizing the difference between the measured and the calculated signal against the OPD, the thicknesses of sub-100-μm-thick samples are determined at 625 GHz.

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    3. Sub-surface imaging of soiled cotton fabric using full-field optical coherence tomography

      Sub-surface imaging of soiled cotton fabric using full-field optical coherence tomography

      In the laundry industry, colorimetry is a common way to evaluate the stain removal efficiency of detergents and cleaning products. For ease of visualization, the soiling agent is treated with a dye before measurement. However, it effectively measures the dye removal rather than stain removal, and it cannot provide depth-resolved information of the sample. In this study, we show that full-field (FF) optical coherence tomography (OCT) technique is capable of measuring the cleaning effect on cotton fabric by imaging the sub-surface features of fabric samples. We used a broadband light-emitting diode (LED) source to power the FF-OCT system that achieves ...

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      Mentions: Yalin Zheng
    4. Feature Of The Week 04/28/2019: Real-Time High-Resolution Mid-Infrared OCT

      Feature Of The Week 04/28/2019: Real-Time High-ResolutionMid-Infrared OCT

      The potential for improving the penetration depth of optical coherence tomography systems by using light sources with longer wavelengths has been known since the inception of the technique in the early 1990s. Nevertheless, the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region, resulting in slow acquisition, low sensitivity, and poor axial resolution. In this work, a mid-infrared spectral-domain optical coherence tomography system operating at a central wavelength of 4 µm and an axial resolution of 8.6 µm is demonstrated. The system produces two-dimensional cross-sectional images ...

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    5. Process control and quality assurance in remote laser beam welding by optical coherence tomography

      Process control and quality assurance in remote laser beam welding by optical coherence tomography

      Remote laser beam welding significantly outperforms conventional joining techniques in terms of flexibility and productivity. This process benefits in particular from a highly focused laser radiation and thus from a well-defined heat input. The small spot sizes of high brilliance laser beam sources, however, require a highly dynamic and precise positioning of the beam. Also, the laser intensities typically applied in this context result in high process dynamics and in demand for a method to ensure a sufficient weld quality. A novel sensor concept for remote laser processing based on optical coherence tomography (OCT) was used for both quality assurance ...

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    6. Inline weld depth measurement for high brilliance laser beam sources using optical coherence tomography

      Inline weld depth measurement for high brilliance laser beam sources using optical coherence tomography

      As a result of the rapidly growing importance of applications in electro mobility that require a precisely defined laser weld depth, the demand for inline process monitoring and control is increasing. To overcome the challenges in process data acquisition, this paper proposes the application of a novel sensor concept for deep penetration laser beam welding with high brilliance laser sources. The experiments show that optical coherence tomography (OCT) can be used to measure the weld depth by comparing the distance to the material surface with the distance to the keyhole bottom measured by the sensor. Within the presented work, the ...

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    7. Effect of solvent lamination on roll-to-roll hot-embossed PMMA microchannels evaluated by optical coherence tomography

      Effect of solvent lamination on roll-to-roll hot-embossed PMMA microchannels evaluated by optical coherence tomography

      Manufacturing of microfluidic based diagnostic devices requires small tolerances and uniform quality to guarantee reliable and repeatable test results. This work describes characterization of morphological changes that occur to a hot embossed PMMA microfluidic channel after solvent lamination with a PMMA lid. A non-contact cross-sectional analysis of the lidded microfluidic device was performed by optical coherence tomography (OCT). The solvent induced morphology change led to a porous structure in bottom corners of hot-embossed channels, which allowed a fluid to absorb in the material. The measurements of solvent diffusion showed faster diffusion rate at the corners of the channel, in which ...

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    8. Novel approach for weld depth determination using optical coherence tomography measurement in laser deep penetration welding of aluminum and steel

      Novel approach for weld depth determination using optical coherence tomography measurement in laser deep penetration welding of aluminum and steel

      The optical coherence tomography (OCT) is a measuring technology which is well-established in medical engineering since the early 1990s. More recently, the technology found its way into laser materials processing where it is used for seam tracking and inspection and also for monitoring and control of deep-penetration laser welding. In this work, deep-penetration laser welding of aluminum and steel using an OCT-system for in-process monitoring of the weld depth was investigated. It is shown that statistical data processing is mandatory to extract the actual keyhole depth. Therefore, two different measures, percentile filtering and considering the frequency distribution of the OCT-data ...

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    9. Partially coherent radar unties range resolution from bandwidth limitations

      Partially coherent radar unties range resolution from bandwidth limitations

      It is widely believed that range resolution, the ability to distinguish between two closely situated targets, depends inversely on the bandwidth of the transmitted radar signal. Here we demonstrate a different type of ranging system, which possesses superior range resolution that is almost completely free of bandwidth limitations. By sweeping over the coherence length of the transmitted signal, the partially coherent radar experimentally demonstrates an improvement of over an order of magnitude in resolving targets, compared to standard coherent radars with the same bandwidth. A theoretical framework is developed to show that the resolution could be further improved without a ...

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    10. Low-bandwidth radar technology provides improved detection of objects

      Low-bandwidth radar technology provides improved detection of objects

      Radar technologies were originally designed to identify and track airborne military targets. Today they're more often used to detect motor vehicles, weather formations and geological terrain. Until now, scientists have believed that radar accuracy and resolution are related to the range of frequencies or radio bandwidth used by the devices. But a new Tel Aviv University study finds that an approach inspired by optical coherence tomography (OCT) requires little to no bandwidth to accurately create a high-resolution map of a radar's surrounding environment. "We've demonstrated a different type of ranging system that possesses superior range resolution and ...

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    11. Towards characterization of bacterial colonies and biofilms: an approach based on swept source optical coherence tomography

      Towards characterization of bacterial colonies and biofilms: an approach based on swept source optical coherence tomography

      The continuous development of microorganism colonies may lead to the development of biofilms. The ability to observe bacterial layers in real time using Optical Coherence Tomography (OCT) can be beneficial for cross-sectional growth studies of bacterial biofilms. A new mathematical model has been developed and utilized to calculate the backscattering optical properties of sample and estimate the necessary parameters. The spectroscopic based analytical method has been successfully demonstrated for characterization of different bacterial colonies and biofilms. The results were verified with conventional ‘Gram staining’ method. The proposed analytical method has potential to monitor realtime growth kinetics of bacteria. The quantities ...

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      Mentions: Raju Poddar
    12. A non-invasive investigation of Egyptian faience using a long wavelength optical coherence tomography (OCT) at 2um

      A non-invasive investigation of Egyptian faience using a long wavelength optical coherence tomography (OCT) at 2um

      Egyptian faience is a non-clay ceramic semi-transparent material, formed of a quartz core and alkalilime glaze with some cases exhibiting an interaction layer between them. Several possible glazing methods have been identified. Previous investigations have tried to identify the glazing technique by using the microstructure images obtained from polished sections using scanning electron microscope (SEM). Such techniques require sampling which is not feasible on museum collections. Optical Coherence Tomography (OCT) is a non-invasive 3D imaging technique, that produces virtual crosssections of transparent and semi-transparent materials. Liang et al. (2012a) investigated the feasibility of using OCT to non-invasively investigate microstructures of ...

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      Mentions: Haida Liang
    13. Statistical evaluation method to determine the laser welding depth by optical coherence tomography

      Statistical evaluation method to determine the laser welding depth by optical coherence tomography

      A statistical filtering method to determine the depth of laser-welded seams from signals recorded by means of optical coherence tomography (OCT) is proposed and discussed. The measured data points are initially classified into noise and significant data by means of a noise probability, which was defined based on the normalized Poisson distribution. A percentile filter is then applied to the significant data to obtain the depth of the weld seam. It is shown that the depth determined by this approach corresponds to the real seam depth, as obtained from longitudinal sections, to within an average error of less than 5 ...

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    14. Frustrated total internal reflection fingerprint detector

      Frustrated total internal reflection fingerprint detector

      The device provides an optical coherence tomography system; a first bank of light emitting diodes emitting light centered about a first wavelength; a second bank of light emitting diodes, emitting light centered about a second wavelength; a prism, said prism including a first surface transmissive of the wavelength of the probe beam of the optical coherence tomography system, and a second surface which is also transmissive of the wavelength of the probe beam, and where the second is surface coated from a first edge to a midpoint so to be reflective of light at the first wavelength and transmissive of ...

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    15. Focus Tracking System for Femtosecond Laser Machining using Low Coherence Interferometry

      Focus Tracking System for Femtosecond Laser Machining using Low Coherence Interferometry

      We designed a real time, single-laser focus tracking system using low coherence properties of the machining femtosecond laser itself in order to monitor and correct the sample position relative to the focal plane. Using a Michelson Interferometer, the system collects data arising from part of the beam backscattered at the ablation spot. The data is analyzed by a custom software for position correction (employing an XYZ automated translation stage). With the focus tracking enabled we were able to etch channels with a stable cross-section profile on a bovine tooth with relief amplitude tens of times greater than the Rayleigh length ...

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      Mentions: Marcus P. Raele
    16. Microscale light management and inherent optical properties of intact corals studied with optical coherence tomography

      Microscale light management and inherent optical properties of intact corals studied with optical coherence tomography

      Coral reefs are highly productive photosynthetic systems and coral optics studies suggest that such high efficiency is due to optimized light scattering by coral tissue and skeleton. Here, we characterize the inherent optical properties, i.e. the scattering coefficient, μ s , and the anisotropy of scattering, g , of eight intact coral species using optical coherence tomography (OCT). Specifically, we describe light scattering by coral skeletons, coenoarc tissues, polyp tentacles and areas covered by fluorescent pigments (FP). Our results reveal that light scattering between coral species ranges from μ s = 3 mm −1 ( Stylophora pistillata ) to μ s = 25 mm −1 ( Echinopora lamelosa ) . For ...

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    17. Distributed gas detection utilizing Fourier domain optical coherence based absorption spectroscopy

      Distributed gas detection utilizing Fourier domain optical coherence based absorption spectroscopy

      In this study, a new method called Fourier domain optical coherence based absorption spectroscopy (FD-OCAS) is proposed for distributed gas detection for the first time. Mach-Zehnder interferometer based quasi-distributed structure is developed for proof-concept demonstration and experimental verification. Optical interference happens between reference arm and sensing arms of the constructed Mach-Zehnder interferometer. Different sensing arms coded with different fiber lengths contribute different frequency components in ultimate interference signals. Fourier transform is used to separate each frequency to identify different sensing arms, realizing distributed detection. The amplitudes of Fourier transform are related to the gas absorption levels in corresponding sensing arms ...

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    18. In-situ monitoring and quantification of fouling development in membrane distillation by means of optical coherence tomography

      In-situ monitoring and quantification of fouling development in membrane distillation by means of optical coherence tomography

      Fouling formation in membrane distillation limits process stability and could cause besides wetting a rapid flux decrease making the process inefficient. Process performance is conventionally assessed by flux monitoring. Optical Coherence Tomography (OCT) enables in-situ visualization and quantification of fouling layers dominated by scaling in a fully operated direct contact membrane distillation system (DCMD). This study presents an innovative methodology for 3D dataset analysis allowing for the detection and quantification of predominant scaling on the membrane surface. Defined fouling parameters permit a correlation between process performance indicators, especially flux decrease and quantified fouling layer coverage. Additionally, structural information about the ...

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    19. Nondestructive Measurement of Conformal Coating Thickness on Printed Circuit Board with Ultra-high Resolution Optical Coherence Tomography

      Nondestructive Measurement of Conformal Coating Thickness on Printed Circuit Board with Ultra-high Resolution Optical Coherence Tomography

      Conformal coating (CC) is widely used to protect printed circuit board (PCB) from corrosion, mould growth and electrical failures. To ensure an effective protection, the thickness of the conformal coating layer needs to be well controlled. However, to date, the coating thickness is usually measured in a destructive way under microscopes. In this study, we proposed to use optical coherence tomography (OCT) to measure the CC thickness nondestructively. Specifically, to obtain a good accuracy in thickness measurement, we constructed a spectral domain OCT (SD-OCT) with ultra-high axial resolution to image the CC layer in three dimensions, and developed an image ...

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    20. Elucidation of microstructural changes in leaves during senescence using spectral domain optical coherence tomography

      Elucidation of microstructural changes in leaves during senescence using spectral domain optical coherence tomography

      Leaf senescence provides a unique window to explore the age-dependent programmed degradation at organ label in plants. Here, spectral domain optical coherence tomography (SD-OCT) has been used to study in vivo senescing leaf microstructural changes in the deciduous plant Acer serrulatum Hayata . Hayata leaves show autumn phenology and change color from green to yellow and finally red. SD-OCT image analysis shows distinctive features among different layers of the leaves; merging of upper epidermis and palisade layers form thicker layers in red leaves compared to green leaves. Moreover, A-scan analysis showed a significant (p < 0.001) decrease in the attenuation coefficient ...

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      Mentions: Wen-Chuan Kuo
    21. Cake formation of bidisperse suspensions in dead-end microfiltration

      Cake formation of bidisperse suspensions in dead-end microfiltration

      The evolution of the cake during dead-end microfiltration of different compositions of bidisperse feeds was investigated using network modeling and three-dimensional (3D) optical coherence tomography (OCT) imaging. The foulant particles were latex of two different sizes (namely, 3 and 5 μm) and the membrane was polycarbonate track-etched with nominal diameter of 2 μm. The results from the network model indicate that (i) the deposition of the smaller particles on the non-porous area was reduced by the presence of larger particles, whereas that of the larger particles was not affected by the concentration of the smaller ones; and (ii) monodisperse small ...

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    22. A Micro-Tomographic Insight into the Coating Systems of Historical Bowed String Instruments

      A Micro-Tomographic Insight into the Coating Systems of Historical Bowed String Instruments

      Musical instruments are tools for playing music, but for some of them—made by the most important historical violin makers—the myths hide the physical artwork. Ancient violin-making Masters developed peculiar construction methods and defined aesthetic canons that are still recognizable in their musical instruments. Recently, the focus of scientific investigations has been set on the characterization of materials and methods used by the ancient violin makers by means of several scientific approaches. In this work, the merits of synchrotron radiation micro-computed tomography and optical coherence tomography (OCT) for the investigation of complex coatings systems on historical bowed string musical ...

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    23. Adaptation Assessment of Three Bonded Resin Restorations at the Cavity Floor Using Cross-Polarization Optical Coherence Tomography

      Adaptation Assessment of Three Bonded Resin Restorations at the Cavity Floor Using Cross-Polarization Optical Coherence Tomography

      Objective: The aim of the study was to compare the composite adaptation of three systems by using cross-polarization optical coherence tomography (CP-OCT). Background data: Most polymer-based restorations suffer from polymerization shrinkage that affects the interfacial seal. This shrinkage cannot be detected by conventional X-ray methods. Optical coherence tomography was proved to be a reliable non-invasive imaging tool to examine biological structures and biomaterials at micron scale. Methods: Twenty-four cylindrical class-V cavities were prepared on the buccal surfaces of the extracted human molars. After cavity preparation, samples were randomly divided into three groups ( n  = 8) according to the restoration system: one-step ...

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      Mentions: Turki Bakhsh
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