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Linz, Austria

Ramer G.,Vienna University of Technology | Kasberger J.,RECENDT GmbH | Brandstetter M.,Vienna University of Technology | Saeed A.,Johannes Kepler University | And 2 more authors.
Applied Physics B: Lasers and Optics | Year: 2014

We present the design and fabrication of a single-mode slab waveguide structure for mid-infrared spectroscopy optimized for broadband coupling. The sensor uses grating couplers for robust off-axis coupling and a silicon nitride guiding layer for mechanical robustness. An external cavity quantum cascade laser-based transmission method is introduced for characterizing the structure's broadband coupling behavior. Light from an external cavity quantum cascade laser with a spectral range of 0.5 μm around 6 μm was coupled into the waveguide without the need for moving parts. First spectra taken with this sensor are presented. © 2013 Springer-Verlag Berlin Heidelberg.

Cernuda C.,Johannes Kepler University | Lughofer E.,Johannes Kepler University | Suppan L.,Kompetenzzentrum Holz GmbH | Roder T.,Lenzing AG | And 4 more authors.
Analytica Chimica Acta | Year: 2012

In viscose production, it is important to monitor three process parameters in order to assure a high quality of the final product: the concentrations of H 2SO 4, Na 2SO 4 and Z nSO 4. During on-line production these process parameters usually show a quite high dynamics depending on the fiber type that is produced. Thus, conventional chemometric models, which are trained based on collected calibration spectra from Fourier transform near infrared (FT-NIR) measurements and kept fixed during the whole life-time of the on-line process, show a quite imprecise and unreliable behavior when predicting the concentrations of new on-line data. In this paper, we are demonstrating evolving chemometric models which are able to adapt automatically to varying process dynamics by updating their inner structures and parameters in a single-pass incremental manner. These models exploit the Takagi-Sugeno fuzzy model architecture, being able to model flexibly different degrees of non-linearities implicitly contained in the mapping between near infrared spectra (NIR) and reference values. Updating the inner structures is achieved by moving the position of already existing local regions and by evolving (increasing non-linearity) or merging (decreasing non-linearity) new local linear predictors on demand, which are guided by distance-based and similarity criteria. Gradual forgetting mechanisms may be integrated in order to out-date older learned relations and to account for more flexibility of the models. The results show that our approach is able to overcome the huge prediction errors produced by various state-of-the-art chemometric models. It achieves a high correlation between observed and predicted target values in the range of [0.95,0.98] over a 3 months period while keeping the relative error below the reference error value of 3%. In contrast, the off-line techniques achieved correlations below 0.5, ten times higher error rates and the more deteriorate, the more time passes by. © 2012 Elsevier B.V.

Veres I.A.,University of Bristol | Veres I.A.,RECENDT GmbH | Smith R.A.,University of Bristol | Pinfield V.J.,Loughborough University
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2015

In this study, modeling approaches for porosity in layered media are presented and compared. First, an effective-medium model is used to account for the frequencydependent attenuation of the elastic waves. The effective-medium model is based on a single-scattering approach, i.e., it neglects multiple-scattering effects. Then, the effective-medium model is compared in time-domain finite element simulations. The numerical model allows the study of the scattering of the elastic waves on randomly distributed spherical cavities and also accounts for multiple-scattering effects. The models are compared to investigate the validity of the effective-medium model approach. The calculated reflected laminate responses and transmission spectra from the two models show a good agreement. © 2014 IEEE.

Cernuda C.,Johannes Kepler University | Lughofer E.,Johannes Kepler University | Marzinger Wolfgang W.,I RED Infrarot Systeme GmbH | Kasberger J.,RECENDT GmbH
Chemometrics and Intelligent Laboratory Systems | Year: 2011

In polyetheracrylat (PEA) production, it is important to monitor three process parameters in order to assure a high quality of the final product: hydroxyl (OH) number, viscosity and acidity (acid number). Due to the high resolution and high sensitivity, it has been shown in the past that the Fourier transform near infrared (FTNIR) process spectrum measurements can be used to obtain spectra with precise content information about these process parameters. In order to perform an automatic supervision and to reduce the (off-line, laboratory) analysis effort of experts and operators of these substances, chemometric quantification models have to be used. In this paper, we investigate the usage of a specific type of fuzzy systems, so-called Takagi-Sugeno fuzzy systems, for calibrating the chemometric models. This type of model architecture supports the usage of piecewise local linear predictors, being able to model flexibly different degrees of non-linearities implicitly contained in the mapping between NIR spectra and reference values. The training of these models is conducted by an evolving clustering method (adding new local linear models on demand) and a local (weighted) least squares estimation of the consequent parameters, and connected with a wavelength (dimensionality) reduction mechanism. Results on a concrete data set show that it can outperform state-of-the-art calibration methods as well as support vector regression as alternative non-linear model. © 2011 Elsevier B.V.

Passler K.,University of Graz | Nuster R.,University of Graz | Gratt S.,University of Graz | Burgholzer P.,RECENDT GmbH | And 2 more authors.
Biomedical Optics Express | Year: 2010

A dual mode scanning acoustic microscope is investigated, yielding simultaneously images with optical and acoustical contrast. Short laser pulses are used to excite acoustic waves in a sample for the photoacoustic imaging mode. At the same time the pulses irradiate a conical target generating limited diffraction acoustic waves (X-waves) for large depth of field ultrasound imaging. For photoacoustic as well as for ultrasound imaging a focusing, ring shaped detector is applied. First phantom experiments demonstrate the possibility to acquire data for both imaging modes in a single scan, by separating images due to their different time of flight. © 2010 Optical Society of America.

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