Bolívar, P. Haring
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Bolívar, P. Haring
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Publication Access status: Metadata only , Defect Detection in Bidirectional Glass Fabric Reinforced Thermoplastics Based on 3-D-THz ImagingNon-homogeneous, bi-directional glass fabric reinforced thermoplastic (GFRT) composites are used in the automobile industry to produce economic and environmentally friendly vehicles. Despite the fact that GFRT materials have superior mechanical characteristics and lower manufacturing cost compared with traditional materials, they are prone to significant deformation and defect emergence during the forming/manufacturing of parts from prefabricated laminates. Some defects, especially hidden ones like delamination and consolidation defects, can significantly reduce the mechanical properties of the final parts. It is essential to use 3D non-destructive testing (NDT) technology to detect and identify such hidden defects. This research investigates the ability of 3D THz imaging to detect hidden defects (i.e., delamination and consolidation) in GFRT composite materials. Frequency modulated continuous wave (FMCW) technique is used to generate 3D-THz cross-sectional images. Non-defective and defective samples with a thickness of 1.5mm have been measured with two 3D THz imaging systems operating in the frequency range from 238 to 316GHz and from 499 to 733 GHz. In addition, a simulation of the reflected FMCW spectrum is presented to analyze the measurements and intercompare the performance of the two imaging systems. A systematic analysis in a large sample set demonstrates that a delamination defect with a thickness of 125μm as well as a consolidation defect with a difference in thickness less than 0.4mm can be successfully detected by the 700-GHz imaging system.Source Type:Article5 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Dye-sensitized solar cell: Effect of light on N3 dye/BMII electrolyte based architectureThis study evaluates the photovoltaic performance of Dye-Sensitized Solar Cells (DSSCs) for varied light conditions. The focus of this work is on exploring the experimental characteristics of a thin-film solar cell composed of ITO/TiO2/N3 Dye and BMII electrolyte molecules/Pt/ITO. A meticulous investigation is conducted to understand the impact of different illumination intensities on the efficiency of these solar cells. In the experiments, the power conversion efficiencies (PCE) of the device reached 7.61 % with a maximum open-circuit voltage (Voc) of 0.67 V under 100 mW/cm2 AM 1.5 solar irradiance. The morphology of the TiO2 nanopArticles that have been synthesized for the DSSC were analyzed by Ultraviolet-visible Spectrometry, X-Ray Diffractometry, as well as Scanning Electron Microscopy and Atomic Force Microscopy investigations. Electrochemical impedance spectroscopy (EIS) parameters and Nyquist plot showed that charge transfer and DSSC are important for the equivalent circuit structure. The results of this study allow optimizing the performance of future DSSCs for sustainable energy systems.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Graphene-Based Optoelectronic Mixer Device for Time-of-Flight Distance Measurements for Enhanced 3D Imaging ApplicationsA large and growing number of applications benefit from innovative and powerful 3D image sensors. Graphene photodetectors can achieve 3D sensing functionalities by intrinsic optoelectronic frequency mixing due to the nonlinear output characteristics of the sensor. In first proof of principle distance measurement demonstrations, we achieve modulation frequencies of 3.1 MHz, signal-to-noise ratios of ∼40 dB, distance detection up to at least 1 m, and a mean accuracy of 25.6 mm. The scalable More than Moore detector approach enables geometrical fill factors close to 100% and can easily complement powerful functionalities by simple back-end integration on top of CMOS electronics.Source Type:Article - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , High Responsivity and Ultra-Low Detection Limits in Nonlinear a-Si:H p-i-n Photodiodes Enabled by PhotogatingPhotodetectors operating at the wavelength in the visible spectrum are key components in high-performance optoelectronic systems. In this work, massive nonlinearities in amorphous silicon p-i-n photodiodes enabled by the photogating are presented, resulting in responsivities up to 744 mA/W at blue wavelengths. The detectors exhibit significant responsivity gains at optical modulation frequencies exceeding MHz and a more than 60-fold enhanced spectral response compared to the non-gated state. The detection limits down to 10.4 nW/mm 2 and mean signal-to-noise ratio enhancements of 8.5 dB are demonstrated by illuminating the sensor with an additional 6.6 µW/mm 2 red wavelength. Electro-optical simulations verify photocarrier modulation due to defect-induced field screening to be the origin of such high responsivity gains. The experimental results validate the theory and enable the development of commercially viable and complementary metal oxide semiconductor (CMOS) compatible high responsivity photodetectors operating in the visible range for low-light level imaging and detection.Source Type:Article6 - Some of the metrics are blocked by yourconsent settings
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Publication Access status: Metadata only , Interdigitated terahertz metamaterial sensors: design with the dielectric perturbation theory(2024); ; ; ; Designing terahertz sensors for highly sensitive detection of nanoscale thin films and a few biomolecules poses a substantial challenge but is crucial for unlocking their full potential in scientific research and advanced applications. This work presents a strategy for optimizing metamaterial sensors in detecting small quantities of dielectric materials. The amount of frequency shift depends on intrinsic properties (electric field distribution, Q -factor, and mode volume) of the bare cavity as well as the overlap volume of its high-electric-field zone(s) and the analyte. Guided by the simplified dielectric perturbation theory, interdigitated electric split-ring resonators (ID-eSRRs) are devised to significantly enhance the detection sensitivity compared with eSRRs without interdigitated fingers. ID-eSRR’s fingers redistribute the electric field, creating strongly localized enhancements, which boost analyte interaction. The periodic change of the inherent antiphase electric field reduces radiation loss, leading to a higher Q -factor. Experiments with ID-eSRR sensors operating at around 300 GHz demonstrate a remarkable 33.5 GHz frequency shift upon depositing a 150 nm SiO 2 layer as an analyte simulant, with a figure of merit improvement of over 50 times compared with structures without interdigitated fingers. This rational design offers a promising avenue for highly sensitive detection of thin films and trace biomolecules.Source Type:Article5 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Preparation and Characterization of Transferable Encapsulated Dye-Sensitized Solar CellsThe increasing demand for sustainable energy as a means to combat the impact of climate change is addressed via a novel concept in the present work. Herein presented are developed transferable encapsulated dye-sensitized solar cells, canonically “solar capsules”, for photovoltaic applications on alternative surfaces, such as facades. The solar capsule assembly houses all the components necessary for photovoltaic energy conversion, enclosed within a semiconductor nanotubular array, making them truly unique in their construction. This capsule-style unit enables an easy transfer and draft onto a wide range of materials and surfaces for photovoltaic functionalization and applications. This type of dye-sensitized solar cell typically consists of transferred solar capsules and two additional electrodes. The design and construction of solar capsules means they have a high economic viability as they can seamlessly be up-scaled using commercially established techniques such as anodization and subsequent functionalization. This work demonstrates a working model of such transferable solar capsules by fabricating TiO2 nanotubes that are functionalized via facile dip- and spin-coating techniques in a wet lab at ambient conditions. These prototypes are characterized in bulk and are thoroughly investigated at the nanoscale for information on the chemical distribution of the constituents, as they may be influenced during the manufacturing process.Source Type:Article4