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  • 1.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Linder, Tomas
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Light scattering in cellulose nanofibre suspensions: Model and experiments2016In: Computers in Chemistry Proceeding from ACS National Meeting San Diego: Proceeding from ACS National Meeting San Diego, American Chemical Society (ACS), 2016, p. 122-, article id CELL 235Conference paper (Other academic)
    Abstract [en]

    Here light scattering theory is used to assess the size distribution in a suspension of cellulose as it is fibrillated from micro-scaled to nano-scaled fibres. A model based on Monte carlo simulations of the scattering of photons by different sizes of cellulose fibres was used to predict the UV-IF spectrum of the suspensions. Bleached cellulose hardwood pulp was tested and compared to the visually transparent tempo-oxidised hardwood cellulose nanofibres (CNF) suspension. The theoretical results show that different diameter size classes exhibit very different scattering patterns. These classes could be identified in the experimental results and used to establish the size class dominating the suspension. A comparison to AFM/microscope size distribution was made and the results indicated that using the UV-IF light scattering spectrum maybe more reliable that size distribution measurement using AFM and microscopy on dried CNF samples. The UV-IF spectrum measurement combined with the theoretical prediction can be used even at this initial stage of development of this model to assess the degree of fibrillation when processing CNF.

  • 2.
    Carlson, Johan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Birk, Wolfgang
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Martinsson, Pär-Erik
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Håkansson, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Castano, Miguel
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Linder, Tomas
    Projekt: SCOPE Norra2011Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    SCOPE Norra är ett samarbetskonsortium för forskning och utveckling tillsammans med massa- och pappersindustrin i Norrbotten och Västerbotten. Projektet koordineras av centrumbildningen ProcessIT Innovations.Inom SCOPE Norra pågår ett flertal delprojekt, uppdelat på ett antal fokusområden.Huvudfinansiär för konsortiet är Tillväxtverket genom medel från EU:s strukturfonder.

  • 3.
    Linder, Tomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Light Scattering in Fiber-based Materials: a foundation for characterization of structural properties2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Deeper knowledge of light propagation in fiber-based materials is fundamental in order to understand their optical appearance as well as for industrial applications. Light scattering measurements are appropriate in handling dynamic industrial environments and can provide information regarding structural properties. In general, on-line property measurements are best utilized by establishing an understanding of the underlying physics and using that knowledge in an optimal way to determine the parameters or properties sought after. Light scattering is affected by numerous parameters such as size, shape, concentration and refractive index of the scattering particles as well as the waveleng th of the incident source. In addition, anisotropic light diffusion in media which have a directional-dependency, such as structured fiber-based materials, are neither well understood nor well investigated.By approximating cellulose fibers as infinitely long, straigth cylinders it is possible to use an analytical solution to Maxwell’s equations to describe the scattering characteristics such as phase functions and scattering efficiency. This makes it possible to utilize both the wave nature of light and structural properties of the fiber network when modelling multiple light scattering. The developed model solves the radiative transfer equation numerically using theMonte Carlo method resulting in a description of multiple scattering in a sphere-cylinder media.The results show that scattering media consisting of infinite long, straigth, homogeneous or hollow cylinders scatter light very differently as compared with a media consisting of spherical particles. Both scattered intensity and the degree of depolarization are affected by a strong forward scattering behavior observed for cylindrical particles. This strong forward scattering behavior was also found to enhance lateral scattering in paper, and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. A strong relationship between anisotropic diffusion and to degree of in-plane fiber orientation was also observed using both measurements and simulations. In conclusion, it was found that the approximation of cellulose fibers as infinitely long, straigth cylinders is reasonable when modelling scattering in paper. The findings indicate that parameters such as geometrical properties, particle composition, fiber orientation and fiber orientation variations can be measured by monitoring scattered light intensity. The obtained knowledge provides a base for further development of on-line sensing techniques that meet industrial requirements. Since the theory is general, it is likewise relevant and applicable to other areas of material science where imaging or remote sensing techniques are of interest.

  • 4.
    Linder, Tomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Light scattering in pulp and paper2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pulp and paper industry of today is facing a highly competitive market where manufacturers are constantly seeking ways to reduce costs as well as to improve product specifications and quality. On-line quality control is one of many areas being actively developed, from the wood delivered to the plant to the fibers in the finished product. In general, on-line property measurements are best utilized by establishing an understanding of the underlying physics and using that knowledge in an optimal way to determine the parameter or property sought for. One specific area of development is to determine fiber orientation in a paper sheet. The fiber orientation is set by the production Process and is an important parameter since it defines e.g. strength and Optical properties of the paper. In the paper mill today, improvements can be made if the fiber orientation could be determined on-line and in real time. One way of doing this is to use non-contact, full-optical techniques to determine the light scattering pattern in a paper sheet. The objective of this work is to determine the properties of light scattering in paper and how this knowledge could be utilized in extracting information on the properties of paper.A numerical model utilizing light scattering in a sphere-cylinder medium is presented. The simulated medium can represent scattering in both wood pulp and paper. Wood fibers are represented as long, straight cylinders and smaller particles, like fines, are represented as small spherical particles. Scattering from fibers are determined by an analytical solution of Maxwell’s equations for scattering on infinitely long cylinders. The small spherical particles are described by Mie theory. Fibers can have random orientation as in the case of pulp, or aligned orientation as in paper. The layer-like anisotropic microstructure in paper is considered in the model. The model also employ the Stokes-Mueller formalism for the scattering particles, making the state of polarization possible to track.The effects of varying volume concentration and size of the scattering components on reflection, transmission and polarization of the incident light are investigated. The findings on the differences in depolarization and its spatial distribution opens for techniques that enables the relative proportions of fibers and fines in pulp to be determined.For aligned fiber structures it is shown both theoretically and experimentally that spatially resolved reflectance and transmittance exhibits directional dependence. This information could possibly be used in a robust, rapid and cheap device for on-line characterization in the paper production process.

  • 5.
    Linder, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Anisotropic light propagation in paper2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 500-506Article in journal (Refereed)
    Abstract [en]

    We investigate anisotropic light propagation in paper using both a theoretical model and experiments. The theoretical model utilizes the Monte Carlo method to solve the photon transport equation numerically. It is assumed that wood fibres are represented by infinitely long, homogeneous and straight cylinders. The layer-like microstructure and anisotropic orientation of the fibres is considered in the model. The conical scattering by cylindrical objects, the wood fibres, is argued as the main source of anisotropic scattering. Simulations revealed that laterally resolved transmittance exhibits directional dependence. Experiments on light transmitted through a standard kraft liner product confirmed that light in fact do propagate more in the machine direction than in the cross direction. Reasonably good agreement was obtained between experimentally and numerically obtained iso-intensity patterns.

  • 6.
    Linder, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Monte Carlo simulation of photon transport in a randomly oriented sphere-cylinder scattering medium2011In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 105, no 3, p. 659-664Article in journal (Refereed)
    Abstract [en]

    A Monte Carlo simulation tool for simulating photon transport in a randomly oriented sphere-cylinder medium has been developed. The simulated medium represents a paper pulp suspension where the constituents are assumed to be mono-disperse micro-spheres, representing dispersed fiber fragments, and infinitely long, straight, randomly oriented cylinders representing fibers. The diameter of the micro-spheres is considered to be about the order of the wavelength and is described by Mie scattering theory. The fiber diameter is considerably larger than the wavelength and the photon scattering is therefore determined by an analytical solution ofMaxwell’s equation for scattering at an infinitely long cylinder. By employing a Stokes–Mueller formalism, the software tracks the polarization of the light while propagating through the medium. The effects of varying volume concentrations and sizes of the scattering components on reflection, transmission and polarization of the incident light are investigated. It is shown that not only the size but also the shape of the particles has a big impact on the depolarization.

  • 7.
    Linder, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Coppel, Ludovic G.
    Mittuniversitetet.
    Neuman, Magnus
    Mittuniversitetet.
    Edström, Per
    Mittuniversitetet.
    Lateral light scattering in fibrous media2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 6, p. 7835-7840Article in journal (Refereed)
    Abstract [en]

    Lateral light scattering in fibrous media is investigated by computing the modulation transfer function (MTF) of 22 paper samples using a Monte Carlo model. The simulation tool uses phase functions from infinitely long homogenous cylinders and the directional inhomogeneity of paper is achieved by aligning the cylinders in the plane. The inverse frequency at half maximum of the MTF is compared to both measurements and previous simulations with isotropic and strongly forward single scattering phase functions. It is found that the conical scattering by cylinders enhances the lateral scattering and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. However, it does not fully reach the levels of lateral scattering observed in measurements. It is argued that the hollow lumen of a wood fiber or dependent scattering effects must be considered for a complete description of lateral light scattering in paper.

  • 8.
    Linder, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Wernersson, Erik L.G.
    Centre for Image Analysis, Uppsala University and Swedish University of Agricultural Sciences.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Light scattering in fibrous media with different degrees of in-plane fiber alignment2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 14, p. 16829-16840Article in journal (Refereed)
    Abstract [en]

    Fiber orientation is an important structural property in paper and other fibrous materials. In this study we explore the relation between light scattering and in-plane fiber orientation in paper sheets. Light diffusion from a focused light source is simulated using a Monte Carlo technique where parameters describing the paper micro-structure were determined from 3D x-ray computed tomography images. Measurements and simulations on both spatially resolved reflectance and transmittance light scattering patterns show an elliptical shape where the main axis is aligned towards the fiber orientation. Good qualitative agreement was found at low intensities and the results indicate that fiber orientation in thin fiber-based materials can be determined using spatially resolved reflectance or transmittance.

  • 9.
    Svanström, Erika
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Linder, Tomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Carlson, Johan E.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Combined physical and statistical modeling of laser induced ultrasound signals from thin light absorbing films2013In: 2013 IEEE International Ultrasonics Symposium: [IUS 2013, Prague, Czech Republic; 21 - 25 July 2013, Piscataway, NJ: IEEE Communications Society, 2013, p. 2167-2170Conference paper (Refereed)
    Abstract [en]

    This paper presents a method for predicting the ultrasound pulses generated by thin semi-transparent polymer films, excited by a short laser pulse. The acoustic pressure is first modeled based on the physical properties of the polymer. Partial Least-Squares Regression is then used to link the model pressure to the ultrasound pulses measured by an ultrasound transducer. The uncertainty of the regression is also simulated, showing that the method is robust to noise in the measurements

  • 10.
    Svanström, Erika
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Linder, Tomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Analytical one-dimensional model for laser-induced ultrasound in planar optically absorbing layer2014In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 54, no 3, p. 888-893Article in journal (Refereed)
    Abstract [en]

    Ultrasound generated by means of laser-based photoacoustic principles are in common use today and applications can be found both in biomedical diagnostics, non-destructive testing and materials characterisation. For certain measurement applications it could be beneficial to shape the generated ultrasound regarding spectral properties and temporal profile. To address this, we studied the generation and propagation of laser-induced ultrasound in a planar, layered structure. We derived an analytical expression for the induced pressure wave, including different physical and optical properties of each layer. A Laplace transform approach was employed in analytically solving the resulting set of photoacoustic wave equations. The results correspond to simulations and were compared to experimental results. To enable the comparison between recorded voltage from the experiments and the calculated pressure we employed a system identification procedure based on physical properties of the ultrasonic transducer to convert the calculated acoustic pressure to voltages. We found reasonable agreement between experimentally obtained voltages and the voltages determined from the calculated acoustic pressure, for the samples studied. The system identification procedure was found to be unstable, however, possibly from violations of material isotropy assumptions by film adhesives and coatings in the experiment. The presented analytical model can serve as a basis when addressing the inverse problem of shaping an acoustic pulse from absorption of a laser pulse in a planar layered structure of elastic materials.

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