1. Articles in category: NDE/NDT

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    1. Electromagnetic analysis for optical coherence tomography based through silicon vias metrology

      Electromagnetic analysis for optical coherence tomography based through silicon vias metrology

      This paper reports on progress in the analysis of time-domain optical coherence tomography (OCT) applied to the dimensional metrology of through-silicon vias (TSVs), which are vertical interconnect accesses in silicon, enabling three-dimensional (3D) integration in microelectronics, and estimates the deviations from earlier, simpler models. The considered TSV structures are 1D trenches and circular holes etched into silicon with a large aspect ratio. As a prerequisite for a realistic modeling, we work with spectra obtained from reference interferograms measured at a planar substrate, which fully includes the dispersion of the OCT apparatus. Applying a rigorous modal approach, we estimate the differences ...

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    2. Measurement of granule layer thickness in a spouted bed coating process via optical coherence tomography

      Measurement of granule layer thickness in a spouted bed coating process via optical coherence tomography

      In this work a recently developed in-line measurement technique for monitoring of coating thickness was applied to a spray-coating process in a three-dimensional prismatic spouted bed. The layer thickness was quantified with an optical coherence tomography (OCT) sensor positioned in front of the observation window of the process chamber. The time-dependent layer thickness was measured directly and in real-time from the OCT images, with no chemometric calibration being needed. To validate the obtained data, additional off-line OCT measurements were performed with optical particle size measurements and micro–computed tomography (micro-CT). The off-line measurements were conducted with representative samples extracted at ...

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    3. Optical properties of human milk

      Optical properties of human milk

      With human milk being the most important source of infant nutrition, the protection and support of breastfeeding are essential from a global health perspective. Nevertheless, relatively few objective methods are available to investigate human milk composition and lactation physiology when a mother experiences breastfeeding problems. We argue that optics and photonics offer promising opportunities for this purpose. Any research activity within this new application field starts with a thorough understanding on how light interacts with human milk. Therefore, the aim of this study was to investigate the full set of optical properties for human milk and the biological variability therein ...

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    4. Optical coherence tomography in forensic sciences: a review of the literature

      Optical coherence tomography in forensic sciences: a review of the literature

      Optical coherence tomography (OCT) is an interferometric imaging technique that has revolutionized clinical ophthalmology since the first half of the 1990’s. Despite this approach being successfully employed in ophthalmology and having great potential in forensic cases, its use in different forensic fields appears to be quite limited. In this review we reviewed the scientific literature regarding the application of OCT in forensic science and legal medicine from 1995 to 2019. Our research showed the usefulness of this approach for the study of coronary injuries, postmortem ocular changes, forensic entomology, and several other applications of specific forensic interest (the study ...

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    5. Application of optical coherence tomography for improved in-situ flaw detection in nylon 12 selective laser sintering (Thesis)

      Application of optical coherence tomography for improved in-situ flaw detection in nylon 12 selective laser sintering (Thesis)

      Despite significant advances made since the inception of selective laser sintering (SLS), many of the same problems identified by early researchers including high part porosity, inadequate surface finish, and part strength uncertainty persist today. Because of these challenges, quality validation and improved process control continue to be identified as critical areas of improvement in industry roadmaps. To address these issues, an optical coherence tomography (OCT) sensor is investigated for feasibility of use in in-situ flaw detection in SLS. Benchtop OCT imaging of nylon in solid, liquid, and resolidified phases revealed subsurface imaging through liquid and resolidified nylon material was possible ...

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    6. How to Measure Coating Thickness of Tablets: Method Comparison of Optical Coherence Tomography, Near-infrared Spectroscopy and Weight-, Height- and Diameter Gain

      How to Measure Coating Thickness of Tablets: Method Comparison of Optical Coherence Tomography, Near-infrared Spectroscopy and Weight-, Height- and Diameter Gain

      Film coating of pharmaceutical dosage forms, such as tablets and pellets, can be used to tailor the drug release profile. With that regard, a uniform coating thickness of a single tablet (intra-tablet), all tablets (inter-tablet) and subsequent batches (inter-batch) is crucial. We present a method comparison between in-line (optical coherence tomography and near-infrared spectroscopy) and well-established off-line (height-, weight- and diameter-gain) approaches to determining the coating thickness of tablets. We used single tablets drawn during a commercial coating process. Comparing the low intra- and high inter-tablet coating variability indicated that the tablets had a broad distribution of spray zone passes ...

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    7. Laser cleaning of paintings: in situ optimization of operative parameters through non-invasive assessment by optical coherence tomography (OCT), reflection FT-IR spectroscopy and laser induced fluorescence spectroscopy (LIF)

      Laser cleaning of paintings: in situ optimization of operative parameters through non-invasive assessment by optical coherence tomography (OCT), reflection FT-IR spectroscopy and laser induced fluorescence spectroscopy (LIF)

      Nowadays the use of laser technology as a highly precise tool for the cleaning of paintings is gaining ground. The development of a non-invasive analytical protocol aimed at thorough assessment of the treated surfaces and real time monitoring of the laser cleaning action is thus becoming imperative. This ensures that no side effects (e.g. discoloration, darkening, blackening) will occur on the painting surfaces due to laser ablation. In the present study the potential of the combined use of optical coherence tomography (OCT) and reflection FT-IR spectroscopy for in situ non-invasive assessment of laser cleaning procedures has been investigated on ...

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    8. Developments in Contact Lens Imaging: New Applications of Optical Coherence Tomography

      Developments in Contact Lens Imaging: New Applications of Optical Coherence Tomography

      Optical coherence tomography (OCT) is a high-speed and non-contact optical imaging technology widely used for noninvasive cross-sectional imaging of biological objects. Two main OCT technologies have been developed: time domain and Fourier domain technologies. The latter can be further divided into spectral domain OCT, which uses a broadband light source and a spectrometer as a detector, and swept source OCT, which employs a quickly-rotating laser source. Advances in OCT technology have made it one of the most helpful devices in ophthalmic practice. Fourier OCT has revolutionized imaging of the posterior segment of the eye, as well as of anterior structures ...

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    9. Microscopic glass blowing used to make tiny optical lenses

      Microscopic glass blowing used to make tiny optical lenses

      Inserting air into hot glass to form a bubble has been used to make glass objects since Roman times. In new work, researchers apply these same glass blowing principles on a microscopic scale to make specialized miniature cone-shaped lenses known as axicons. Axicons are used to shape laser light in a way that is beneficial for optical drilling, imaging and creating optical traps for manipulating particles or cells. These lenses have been known for more than 60 years, but their fabrication, especially when small, is not easy. "Our technique has the potential of producing robust miniature axicons in glass at ...

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    10. Subsurface and Layer Intertwined Template Protection Using Inherent Properties of Full-Field Optical Coherence Tomography Fingerprint Imaging

      Subsurface and Layer Intertwined Template Protection Using Inherent Properties of Full-Field Optical Coherence Tomography Fingerprint Imaging

      The emergence of Full Field-Optical Coherence Tomography (FF-OCT) for fingerprint imaging has shown it’s ability in addressing and solving the drawbacks of traditional fingerprinting solutions such as spoofing attacks, low accuracy for abraded fingerprint. With the availability of multiple internal fingerprints (from subsurface captured at different depths), it is also essential to consider the aspects of ideal biometrics where the privacy of the fingerprint data is preserved. In this work, we propose a new framework for fingerprint template protection, highly customized to FF-OCT by exploring the interplay between subsurface. As a first of it’s kind work attempting template ...

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    11. 3D Printer Powered by Machine Vision and Artificial Intelligence

      3D Printer Powered by Machine Vision and Artificial Intelligence

      Objects made with 3D printing can be lighter, stronger, and more complex than those produced through traditional manufacturing methods. But several technical challenges must be overcome before 3D printing transforms the production of most devices. ADVERTISEMENT Commercially available printers generally offer only high-speed, high-precision, or high-quality materials. Rarely do they offer all three, limiting their usefulness as a manufacturing tool. Today, 3D printing is used mainly for prototyping and low-volume production of specialized parts. Now Inkbit, a startup out of MIT, is working to bring all of the benefits of 3D printing to a slew of products that have never ...

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      Mentions: Inkbit
    12. Differentiating Generic versus Branded Pharmaceutical Tablets Using Ultra-High-Resolution Optical Coherence Tomography

      Differentiating Generic versus Branded Pharmaceutical Tablets Using Ultra-High-Resolution Optical Coherence Tomography

      Optical coherence tomography (OCT) has recently been demonstrated as a powerful tool to image through pharmaceutical film coatings. Majority of the existing systems can, however, resolve film coatings for thickness greater than 10 µm. Here we report on an ultra-high-resolution (UHR) OCT system, with 1 µm axial and 1.6 µm lateral resolutions, which can resolve thin coatings at approximately 4 µm. We further demonstrate a novel application of the system for differentiating generic and branded suppliers of paracetamol tablets.

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      Mentions: Yalin Zheng
    13. Non-Invasive Morphological Characterization of Rice Leaf Bulliform and Aerenchyma Cellular Regions Using Low Coherence Interferometry

      Non-Invasive Morphological Characterization of Rice Leaf Bulliform and Aerenchyma Cellular Regions Using Low Coherence Interferometry

      Non-invasive investigation of rice leaf specimens to characterize the morphological formation and particular structural information that is beneficial for agricultural perspective was demonstrated using a low coherence interferometric method called swept source optical coherence tomography (SS-OCT). The acquired results non-invasively revealed morphological properties of rice leaf, such as bulliform cells; aerenchyma, parenchyma, and collenchyma layer; and vascular bundle. Beside aforementioned morphologic characteristics, several leaf characteristics associated with cytological mechanisms of leaf rolling (leaf inclination) were examined for the pre-identification of inevitable necrosis and atrophy of leaf tissues by evaluating acute angle information, such as angular characteristics of the external bi-directional ...

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    14. 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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    15. 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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    16. 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
    17. 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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    18. 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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    19. 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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    20. 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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    21. 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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    22. 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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    23. 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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