Development of a Data Fusion-Based Multi-Sensor System for Hybrid Sheet Molding Compound

In den letzten Jahren ist die Produktion von faserverstärkten Kunststoffen stetig gestiegen. Ein Teil davon ist das glasfaser-verstärkte Sheet Molding Compound (SMC), welches sich durch seine günstigen Herstellkosten und einfache Verarbeitung auszeichnet. Allerdings weist dieses Material schlechte mechanische Eigenschaften auf, welche eine Anwendung für Strukturbauteile verhindert. Um diesem Nachteil entgegen zu wirken, wird das diskontinuierliche Glasfaser-SMC lokal mit kontinuierlichem Carbonfaser-SMC verstärkt. Dadurch können die Vorteile des günstigen und leicht zu verarbeitenden Glasfaser-SMC mit den sehr guten mechanischen Eigenschaften von Carbonfaser-SMC in Faserrichtung kombiniert werden. Die Kombination dieser beiden Werkstoffe kann bereits in einem frühen Produktionsschritt zu einer Vielzahl an möglichen Defekten wie beispielsweise Delamination, Falten oder Winkelabweichungen führen. Um keine weiteren wertschöpfenden Maßnahmen an defekten Bauteilen durchzuführen, muss die Qualitätssicherung bereits in einem frühen Prozessstadium durchgeführt werden. Die zu entdeckenden Fehler werden in außen- und innenliegende Defekte unterteilt. Da kein System verfügbar ist, um alle relevanten Defekte zu detektieren, wird pro Defektklasse ein Messsystem benötigt. Zudem erstreckt sich der Anwendungsbereich neben dem Halbzeug auch auf das ausgehärtete Bauteil. Das Laserlichtschnittsystem und die aktive Thermografie, in Form der Puls-Phasen-Thermografie, haben sich als geeignet erwiesen. Beide Systeme werden zunächst einzeln untersucht und für den vorliegenden Anwendungsfall angepasst. Dabei ist es möglich die Puls-Phasen-Thermografie methodisch zu einer Tiefenauswertung weiterzuentwickeln. Des Weiteren werden Fehler nicht nur detektiert, sondern auch definiert. Anschließen werden die beiden Systeme in einem Multisensorik-System zusammengeführt. Mit Hilfe der Datenfusion sind eine Auswertung von außen- und innenliegenden Defekten, sowie die Ermittlung von geometrischen Zusammenhängen zwischen einzelnen Defekten möglich. Durch den Aufbau eines Schichtmodells wird zusätzlich eine benutzerfreundliche Auswertung ermöglicht, welche dem Anwender schnell einzelne Schichten aufzeigen kann. Mit der Ermittlung der Messunsicherheit des Multisensorik-Systems wird die Güte aufgezeigt

Modeling of second-harmonic generation in periodic nanostructures by the Fourier modal method with matched coordinates

We present an advanced formulation of the Fourier modal method for analyzing the second-harmonic generation in multilayers of periodic arrays of nanostructures. In our method, we solve Maxwell’s equations in a curvilinear coordinate system, in which the interfaces are defined by surfaces of constant coordinates. Thus, we can apply the correct Fourier factorization rules as well as adaptive spatial resolution to nanostructures with complex cross sections. We extend here the factorization rules to the second-harmonic susceptibility tensor expressed in the curvilinear coordinates. The combination of adaptive curvilinear coordinates and factorization rules allows for efficient calculation of the second-harmonic intensity, as demonstrated for one- and two-dimensional periodic nanostructures

From dark to bright: First-order perturbation theory with analytical mode normalization for plasmonic nanoantenna arrays applied to refractive index sensing

We present a first-order perturbation theory to calculate the frequency shift and linewidth change of photonic resonances in one- and two-dimensional periodic structures under modifications of the surrounding refractive index. Our method is based on the resonant state expansion, for which we extend the analytical mode normalization to periodic structures. We apply this theory to calculate the sensitivity of bright dipolar and much darker quadrupolar plasmonic modes by determining the maximum shift and optimal sensing volume

Unveiling Photodeactivation Pathways for a New Iridium(III) Cyclometalated Complex

We report the synthesis and characterization of a neutral heteroleptic IrIII complex bearing 6-fluoro-2-phenylbenzo[d]thiazole as cyclometalating ligand and (Z)-6-(9H-carbazol-9-yl)-5-hydroxy-2,2-dimethylhex-4-en-3-one as ancillary ligand. The photodeactivation mechanisms have been elucidated through extensive density functional theory (DFT) calculations. The active role of metal-centered (3MC) triplet excited states in the nonradiative deactivation pathways is, for first time, confirmed in such complexes

Formation of chiral fields in a symmetric environment

Chiral fields, i. e., electromagnetic fields with nonvanishing optical chirality, can occur next to symmetric nanostructures without geometrical chirality illuminated with linearly polarized light at normal incidence. A simple dipole model is utilized to explain this behavior theoretically. Illuminated with circularly polarized light, the chiral near-fields are still dominated by the distributions found for the linear polarization but show additional features due to the optical chirality of the incident light. Rotating the angle of linear polarization introduces more subtle changes to the distribution of optical chirality. Using our findings, we propose a novel scheme to obtain chiroptical far-field response using linearly polarized light, which could be utilized for applications such as optical enantiomer sensing

Analytical normalization of resonant states in photonic crystal slabs and periodic arrays of nanoantennas at oblique incidence

We present an analytical formulation for the normalization of resonant states at oblique incidence in one- and two-dimensional periodic structures with top and bottom boundaries to homogeneous space, such as photonic crystal slabs and arrays of nanoantennas. The normalization is validated by comparing the resonant state expansion using one and two resonant states with numerically exact results. The predicted changes of resonance frequency and linewidth due to perturbations of refractive index or geometry can be used to study resonantly enhanced refractive index sensing as well as the influence of disorder. In addition, the normalization is essential for the calculation of the Purcell factor

Tailoring enhanced optical chirality : design principles for chiral plasmonic nanostructures

Electromagnetic fields with strong optical chirality can be formed in the near-field of chiral plasmonic nanostructures. We calculate and visualize the degree of chirality to identify regions with relatively high values. This leads to design principles for a simple utilization of chiral fields. We investigate planar geometries which offer a convenient way to access the designated fields as well as three-dimensional nanostructures which show a very high local optical chirality

Fluorescence lifetime biosensing with DNA microarrays and a CMOS-SPAD imager

Fluorescence lifetime of dye molecules is a sensitive reporter on local microenvironment which is generally independent of fluorophores concentration and can be used as a means of discrimination between molecules with spectrally overlapping emission. It is therefore a potentially powerful multiplexed detection modality in biosensing but requires extremely low light level operation typical of biological analyte concentrations, long data acquisition periods and on-chip processing capability to realize these advantages. We report here fluorescence lifetime data obtained using a CMOS-SPAD imager in conjunction with DNA microarrays and TIRF excitation geometry. This enables acquisition of single photon arrival time histograms for a 320 pixel FLIM map within less than 26 seconds exposure time. From this, we resolve distinct lifetime signatures corresponding to dye-labelled HCV and quantum-dot-labelled HCMV nucleic acid targets at concentrations as low as 10 nM

Oxygen and temperature sensitivity of blue to green to yellow light-emitting Pt(II) complexes

The synthesis and photophysical properties of a series of yellow-green to blue-green emitting heteroleptic, cyclometalated Pt(II)(acac) complexes based on substituted phenylpyridine and tetrahydroquinoline ligands is reported. The luminescence intensities and lifetimes of these compounds were also studied in poly(styrene) films with respect to their responses to oxygen and temperature. Particularly, due to the insensitivity to oxygen quenching, these complexes are promising candidates as inert reference dyes in optical sensors. On the other hand, the Pt(II) complex with 2-(4-bromophenyl)-5,6,7,8-tetrahydroquinoline as C^N ligand, displays a strong temperature quenching effect. The distinct response to temperature was additionally calibrated after incorporation in poly(vinylidene chloride-co-acrylonitrile) serving as oxygen-blocking matrix copolymer. The resulting yellow-green-emitting temperature sensor signifies an interesting alternative to the available mostly red emitting temperature-sensitive probes