Change search
Refine search result
1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 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. Aitomäki, Yvonne
    et al.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Estimating suspended fibre material properties by modelling ultrasound attenuation2006In: Mathematical Modeling of Wave Phenomena: conference on mathematical modeling of wave phenomea, Växjö, Sweden, 14 - 19 August 2005 / [ed] Börje Nilsson; Louis Fishman, Melville, NY: American Institute of Physics (AIP), 2006, p. 250-259Conference paper (Refereed)
    Abstract [en]

    An analytical model for use in the inverse problem of estimating material properties of suspended fibres from ultrasonic attenuation has been developed. The ultrasound attenuation is derived theoretically from the energy losses arising when a plane wave is scattered and absorbed off an infinitely long, isotropic, viscoelastic cylinder. By neglecting thermal considerations and assuming low viscosity in the suspending fluid, we can make additional assumptions that provide us with a tractable set of equations that can be solved analytically. The model can then be to used in inverse methods of estimating material properties. We verify the model with experimentally obtained values of attenuation for saturated Nylon fibres. The experimental results from Nylon fibres show local peaks in the attenuation which are thought to be due to the resonant absorption at the eigenfrequencies of the fibres. The results of the experiments show that the model is sufficiently sensitive to detect differences in different types of Nylon. Applications for suspended fibre characterization can be found in the paper manufacturing industry.

  • 3. Aitomäki, Yvonne
    et al.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Material property estimates from ultrasound attenuation in fibre suspensions2009In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 49, no 4-5, p. 432-437Article in journal (Refereed)
    Abstract [en]

    An investigation of a new method for measuring fibre material properties from ultrasonic attenuation in a dilute suspension of synthetic fibres of uniform geometry is presented. The method is based on inversely solving an ultrasound scattering and absorption model of suspended fibres in water for the material properties of the fibres. Experimental results were obtained from three suspensions of nylon 66 fibres each with different fibre diameters. A forward solution to the model with reference material values is compared to experimental data to verify the model's behaviour. Estimates of the shear and Young's modulus, the compressional wave velocity, Poisson's ratio and loss tangent from nylon 66 fibres are compared to data available from other sources. Experimental data confirms that the model successfully predicts that the resonance features in the frequency response of the attenuation are a function of diameter. Consistent estimated values for the compressional wave velocity and the Poisson's ratio were found to be difficult to obtain but in combination gave values of shear modulus within previously reported values and with low sensitivity to noise. Young's modulus was underestimated by 54% but was consistent and had low sensitivity to noise. The underestimation is believed to be caused by the assumption of isotropic material used in the model. Additional tests on isotropic fibre would confirm this. Further analysis of the model sensitivity and the reasons for the resonance features are required.

  • 4.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Sounding Out Paper Pulp: Ultrasound Spectroscopy of Dilute Viscoelastic Fibre Suspensions Acoustics and Ultrasonics2006Conference paper (Other academic)
    Abstract [en]

    A model of attenuation of ultrasound in fibre suspensions is compared to a model of backscattering pressure from submersed cylinders subjected to a sound wave. This analysis is carried out in the region where the wavelength is of the same order as that of the diameter of the fibre. In addition we assume the cylinder scatterer to have no intrinsic attenuation and the longitudinal axis of the scatterer is assumed to be perpendicular to the direction of propagation of the incident wave. Peaks in the frequency response of both the backscattering pressure, expressed in the form of a form function, and the attenuation are shown to correspond. Similarities between the models are discussed. Since the peaks in the form function are due to resonance of the cylinder, we infer that the peaks in the attenuation are also due to resonance. The exact nature of the waves causing the resonance are still unclear however the first resonance peaks are related to the shear wave and hence the shear modulus of the material. The aim is to use the attenuation model for solving the inverse problem of calculating paper pulp material properties from attenuation measurements. The implications of these findings for paper pulp property estimation is that the supporting fluid could, if possible, be matched to density of that of pulp fibres and that the estimation of material properties should be improved by selecting a frequency range that in the region of the first resonance peaks.

  • 5.
    Aitomäki, Yvonne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Estimating material properties of solid and hollow fibers in suspension using ultrasonic attenuation2013In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 60, no 7, p. 1424-1434Article in journal (Refereed)
    Abstract [en]

    Estimates of the material properties of hollow fibers suspended in a fluid using ultrasound measurements and a simple, computationally efficient analytical model are made. The industrial application is to evaluate the properties of wood fibers in paper pulp. The necessity of using a layered cylindrical model (LCM) as opposed to a solid cylindrical model (SCM) for modeling ultrasound attenuation in a suspension of hollow fibers is evaluated. The two models are described and used to solve the inverse problem of estimating material properties from attenuation in suspensions of solid and hollow polyester fibers. The results show that the measured attenuation of hollow fibers differs from that of solid fibers. Elastic properties estimates using LCM with hollow-fiber suspension measurements are similar to those using SCM with solid-fiber suspension measurements and compare well to block polyester values for elastic moduli. However, using the SCM with the hollow-fiber suspension did not produce realistic estimations. In conclusion, the LCM gives reasonable estimations of hollow fiber properties and the SCM is not sufficiently complex to model hollow fibers. The results also indicate that the use of a distributed radius in the model is important in estimating material properties from fiber suspensions.

  • 6. Bucht, Thore
    et al.
    Kjellmert, Bo
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Experimentell metodik1995 (ed. 5)Book (Other (popular science, discussion, etc.))
  • 7.
    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.

  • 8.
    Delsing, Jerker
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    van Deventer, Jan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Eliasson, Jens
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, Jonny
    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.
    Sandin, Fredrik
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Concepts and Architecture for a Thumb-Sized Smart IoT Ultrasound Measurement System2016In: IEEE Ultrasonic Symposium 2016, Piscataway, NJ: IEEE conference proceedings, 2016Conference paper (Refereed)
    Abstract [en]

    This paper presents the technology concepts for a “thumb”-sized self-contained ultrasonic IoT measurement sys- tem. An overall architecture is proposed, and key elements are discussed with solutions using existing technology, thus arguing that realization is possible with the current technology.

    Such an ultrasonic IoT measurement system is constrained by its size and available energy, although it requires at least decent computational and communication resources. Because streaming data from such a device is not advisable from an energy viewpoint, there is a need for resource efficient (energy, memory and computational power) data analysis.

    An architecture with the following parts as well as some implementation details and performance data are proposed here:

    • Energy supply, battery and super capacitor

    • Transducer excitation achieving almost zero electrical losses

    • Event detection sensor interface

    • Data aggregation using sparse approximation and learned

      feature dictionaries, adapted to resource constrained em-

      bedded systems

    • IoT communication protocols and implementations enabling

      event -based communication and System of Systems integra- tion capabilities

      The optimization of system level performance requires each subsystem to be optimized for the specific measurement situation taking into account the subsystem interdependencies. This can be performed using a combined electrical and acoustical model of the system. Here, the model allowing electronic and acoustic co-simulation using SPICE is an important tool bridging the electronic and acoustic domains. 

  • 9.
    Hamfelt, Jesper
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Gustafsson, Jonas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    van Deventer, Jan
    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.
    Häggström, Fredrik
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    A passive Barkhausen noise sensor for low-power applications2016In: 2016 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, Piscataway, NJ: IEEE Communications Society, 2016, p. 280-284, article id 7520374Conference paper (Refereed)
    Abstract [en]

    This paper proposes a passive Barkhausen noise sensor design suitable for low power applications. The sensor uses a permanent magnet and the relative motion between itself and a measured specimen instead of the conventional method that uses a fixed sensor and an alternating magnetic field. Since this novel design is passive, the sensor is well suited for low power applications and could potentially be used in e.g. A condition monitoring system integrated into a rolling element bearing. Proof of concept testing has been performed showing that the proposed sensor produces similar results as conventional Barkhausen noise sensors when applied to specimens being cyclically loaded until failure in a rotating bending rig. The results imply that material fatigue detection using the Barkhausen noise can be performed with the proposed sensor at a fraction of the energy cost compared to a conventional sensor. This warrants future research into the development of the proposed sensor, its advantages, disadvantages, and functionality

  • 10.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Design of high-intensity ultrasound reactor2017In: IEEE International Ultrasonics Symposium, IUS, Piscataway, NJ: IEEE Computer Society, 2017, article id 8092948Conference paper (Refereed)
    Abstract [en]

    Design and optmiziation of ultrasonic reactors are important objectives in sonochemical processing. The recent expansion of the use of ultrasonic reactors in various research projects all faces the problem of scaling up laboratory results for industrial use. A traditional ultrasonic reactor usually has several issues, such as low effectiveness and complex and unstable system performance, which all are unfavorable for efficient sonochemical processing. This study adresses these issues and investigates a new flow type ultrasonic reactor designed to generate transient cavitation as the main source for ultrasound for sonochemical processing. This study proposes the principle of the flow type ultrasonic reactor design to generate transient cavitation. The objective of this work is to design an ultrasonic reactor with a new geometry. The idea is to improve process efficiency based on resonance enhanced ultrasound controlled cavitation

  • 11.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Design of a high-intensity ultrasound reactor2017Conference paper (Refereed)
    Abstract [en]

    Design, and optimization of ultrasonic reactors are important objectives in sonochemical processing. The recent expansion of the use of ultrasonic reactors in various research areas all faces the problem of scaling up from laboratory results to industrial purposes. A traditional ultrasonic reactor usually has several issues, such as low effectiveness as well as complex and unstable system performance, which all are unfavorable for efficient sonochemical processing. This study addresses these issues and investigates a new flow type ultrasonic reactor designed to generate transient cavitation as the main source for ultrasound. Some important factors like pressure, material, flow and geometry are considered in the design. Numerical optimization as well as experimental investigations are performed to reach an optimized, energy-efficient and controlled ultrasound cavitation reactor. Results from numerical modeling are used for acoustic optimization of the reactor, which is driven with three transducers mounted radially in the reactor wall with 120° spacing. The final reactor is excited with dual frequencies a total of 9 sonotrodes. The reactor is intended to be used in studies of pre-treatment of cellulose fibers aiming at developing an alternative, energy efficient fibrillation process and for ultrasound leaching of minerals.

  • 12.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Design of a high-intensity ultrasound reactor2017In: IEEE International Ultrasonics Symposium, IUS, Piscataway, NJ: IEEE Computer Society, 2017, article id 8091660Conference paper (Refereed)
    Abstract [en]

    Design, and optimization of ultrasonic reactors are important objectives in sonochemical processing. The recent expansion of the use of ultrasonic reactors in various research areas all faces the problem of scaling up from laboratory results to industrial purposes. A traditional ultrasonic reactor usually has several issues, such as low effectiveness as well as complex and unstable system performance, which all are unfavorable for efficient sonochemical processing. This study addresses these issues and investigates a new flow type ultrasonic reactor designed to generate transient cavitation as the main source for ultrasound. Some important factors like pressure, material, flow and geometry are considered in the design. Numerical optimization as well as experimental investigations are performed to reach an optimized, energy-efficient and controlled ultrasound cavitation reactor. Results from numerical modeling are used for acoustic optimization of the reactor, which is driven with three transducers mounted radially in the reactor wall with 120° spacing. The final reactor is excited with dual frequencies a total of 9 sonotrodes. The reactor is intended to be used in studies of pre-treatment of cellulose fibers aiming at developing an alternative, energy efficient fibrillation process and for ultrasound leaching of minerals

  • 13.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Shankar, Vijay
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Acoustic design principles for energy efficient excitation of a high intensity cavitation zone2019In: Proceedings of the 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019: ICA 2019, 9 - 13 September / [ed] Martin Ochmann, Aachen, Germany, 2019, p. 948-955Conference paper (Other academic)
    Abstract [en]

    Energy-efficient process intensification is a key aspect for a sustainable industrial production. To improve energy conversion efficiency high intensity cavitation is a promising method, especially in cases where the material to be treated is valuable and on the micro meter scale. Transient collapsing cavitation bubbles gives powerful effects on objects immersed in fluids, like cellulose fibers, mineral particles, enzymes, etc. The cavitation process needs optimization and control, since optimal conditions is multivariate challenge. This study focuses on different design principles to achieve high intensity cavitation in a specific volume in a continuous flow. This study explores some potential design principles to obtain energy efficient process intensification. The objective is to tune several different resonance phenomena to create a powerful excitation of a flowing suspension (two-phase flow and cavitation bubbles). The reactor is excited by sonotrodes, connected to two coupled resonant tube structures, at the critical frequency. Finally cavitation bubbles are initiated by a flow through a venturi nozzle. The acoustically optimised reactor geometry is modelled in Comsol Multiphysics®, and excited by dedicated ultrasound signals at three different frequencies. The effect of the high intensity cavitation is experimentally evaluated by calorimetric method, foil tests and degree of fibrillation on cellulose fibers.

  • 14.
    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.

  • 15.
    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.

  • 16.
    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.

  • 17.
    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.

  • 18.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Photoacoustic techniques applied in pulp quality measurements2011Conference paper (Refereed)
    Abstract [en]

    The pulp and paper industry is constantly striving to increase product quality and lowering the production costs. These efforts requires new or improved measurement techniques that either performs better than existing techniques or determines process parameters that at present cannot be determined. In the presented study we review a new photoacoustic technique that may have an impact in these matters. The photoacoustic technique is presented for two basic settings. The first is based on the effect that light absorbed in the fibre suspension generates sound through a thermoelastic energy transformation process. The sound wave, while propagating through the suspension, is distorted and attenuated by the fibres and thus inherently carries information about the suspension. The acoustic wave propagation is described mathematically and the model is used in an inverse manner to determine properties of the suspension and of the fibres, such as the fibre material elastic properties. The second setting includes monitoring of the scattered light intensity as well as its time-of-flight through the suspension. By combining the optical measurements and measurements of acoustic attenuation and speed of sound we have found that the combination can be used to give a good estimate of the total mass fraction as well as fiber and fines mass fractions. The proposed photoacoustic technique has potential to become a valuable tool for pulp and paper manufacturers enabling production of a more consistent product quality and further develop the understanding of the fiber elastic properties impact on the finished product.

  • 19.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Time dependent flow around spherical particles and in porous media1990Licentiate thesis, comprehensive summary (Other academic)
  • 20.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ultrasonic measurement technology for characterization of pulp fibre suspensions1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the papermaking industry, there is a need for sensors to measure the properties of the fibre suspension that determine important parameters in the finished paper. This lack of on-line sensors hampers the development of advanced process control strategies. Ultrasonic measurement techniques might become useful tool for on-line measure of fibre properties. In general, an acoustic wave, propagating through a suspension, inherently carries information about the physical properties of the suspended material. The presented thesis deals with the fundamental physical processes that governs the propagation of ultrasonic waves in dilute suspensions of paper pulp fibres and water. It also presents a simulation tool capable of simulating all components of a pulse-echo, ultrasonic measurement system, including measurement cell and the fluid under investigation. Experiments are performed in a custom-built measurement cell for low intensity, ultrasonic, pulse-echo measurements. It is investigated both theoretically and experimentally how macroscopic, measurable quantities as speed of sound and attenuation of the ultrasonic pulse are affected by fibre mass fraction, fibre geometry and the physical properties of the fibre material. This knowledge could be applied in using ultrasound to evaluate elastic, or other properties, of fibres in a fibre suspension.

  • 21.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ultrasonic wave attenuation and phase velocity in a paper-fibre suspension1997In: Proceedings: 1997 IEEE Ultrasonics Symposium, October 5 - 8, 1997, Toronto Marriott Eaton Centre, Ontario, Canada : an international sympo / [ed] S. C. Schneider; M. Levy; B. R. McAvoy, Piscataway, NJ: IEEE Communications Society, 1997, Vol. 1, p. 841-844Conference paper (Refereed)
    Abstract [en]

    An ultrasonic pulse-echo technique has been used to investigate whether ultrasonic wave attenuation and phase velocity can be employed to measure fiber mass fraction in a paper fibre suspension. Attenuation and phase velocity has been determined using Fourier transform and cross-correlation techniques. Measurements have been carried out in the frequency range from 250 kHz to 3 MHz. The mass fraction of dispersed fibres varied between 0% to 1.0%. It has been shown that the attenuation varies linearly with fibre mass fraction, and that attenuation is proportional to frequency. Phase velocity is found to correlate weakly with fibre mass fraction, and is also independent of frequency, in the range covered. It is concluded that mass fraction of fibres in a paper fibre suspension can be measured via its attenuation of ultrasonic pulses

  • 22.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Sokas, Kestutis
    Speed of sound measurements in humid air using an ultrasonic flow meter2003In: Proceedings, XVII IMEKO World Congress: June 22 – 27, 2003, Dubrovnik, Croatia, 2003, p. 1650-1653Conference paper (Refereed)
    Abstract [en]

    This paper presents results from experiments using an ultrasonic gas flow meter measuring the speed of sound in air at varying air velocities, humidities and temperatures. The meter utilises the sing-around technique. The transducers in the meter are silicon-based ultrasonic transducers with a centre frequency of 800 kHz. In order to investigate the performance of the flow meter it was tested in a novel gas flow facility connected to a calibration facility for flow meters used for liquids. The Reynolds’ numbers for the investigated flow velocities ranged from 0 to 3,2·104, the relative humidity varied from 40% to 80% RH and the temperature varied from 20°C to 46°C. It was found that the experimentally measured speed of sound corresponded well with the speed of sound obtained from theory. It is also concluded that the flow meter could potentially be used in determining the relative humidity in flowing air at atmospheric pressures using speed of sound and temperature measurements.

  • 23.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Delsing, Jerker
    Sokas, Kęstutis
    Speed of sound measurements in gas-mixtures at varying composition using an ultrasonic gas flow meter with silicon based transducers2003Conference paper (Refereed)
    Abstract [en]

    This paper concerns speed of sound measurements performed in three different gas mixtures at constant temperature and pressure while the concentration of the gases was varied. The performed experiments used an ultra sonic, sing-around, gas flow meter equipped with silicon based transducers. The center frequency of the transducers was 800 kHz. Speed of sound was measured in mono-, di- and triatomic gases: argon (Ar), oxygen (O2) and carbon dioxide (CO2), in either air or nitrogen (N2) as a background gas. The gas under investigation was mixed with the background gas in a test chamber and the concentration of the gas under examination was varied between 0% and 100%. A gas chromatograph was used in order to accurately determine the composition of the gas mixture. The experiments show that measured speed of sound, as a function of gas composition, agrees with the speed of sound obtained from theory. The achieved data also show that the speed of sound measurements was performed with low standard deviation. Thus, one can conclude that this type of ultrasonic gas flow meter is well suited in determining gas concentration in a binary gas mixture as well as flow velocity. The technique could be of value in both industrial and medical applications.

  • 24.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Niemi, Jan
    Aitomäki, Yvonne
    Ultrasonic methods in determining elastic material properties of fibres in suspension2008In: 2007 IEEE Ultrasonics Symposium proceedings: New York City, NY, USA, 28 - 31 October 2007, Piscataway, NJ: IEEE Communications Society, 2008, p. 46-49Conference paper (Refereed)
    Abstract [en]

    The presented study concerns the application of the pulse-echo ultrasound measurement technique in determining the elastic properties of fibres suspended in water. The two kinds of fibre materials are investigated, nylon 6/6 fibres and softwood pulp fibres. The fibre mass fraction was 0.5% for nylon and ranges from 0% up to 1% for softwood pulp. The ultrasonic measurements are performed in the frequency range of 2-11 MHz. It is shown that the velocity dispersion of the ultrasound is small for each suspension sample. In obtaining the fibres longitudinal Young's modulus two methods are used, one based on phase velocity and one based on acoustic attenuation. It is found that both methods gives reasonable estimates of the longitudinal Young's modulus for nylon 6/6. For pulp fibres the determined Young's modulus is overestimated in comparison with earlier findings.

  • 25.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Niemi, Jan
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Investigation of the photoacoustic signal dependence on laser power2008In: Advanced Laser Technologies 2007: Proceedings of the Advanced Laser Technologies 2007 Conference / [ed] Ivan A. Shcherbakov; Risto Myllylä; Alexander V. Priezzhev; Matti Kinnunen; Vladimir I. Pustovoy; Mikhail Y. Kirillin; Alexey P. Popov, SPIE - International Society for Optical Engineering, 2008, p. 70220C-Conference paper (Refereed)
    Abstract [en]

    In this study we have focused on exploring the photoacoustic signal generated by laser induced dielectric breakdown process in pure water, under normal conditions. In this case the dielectric breakdown will lead to a formation of a shock wave. We investigated the relation between pulse energy and amplitude, group velocity and power spectrum of the shock wave. Also, the threshold for dielectric breakdown is estimated. A pulsed, high power Nd:YAG laser with λ = 532 nm and a pulse duration of 12 ns was used. The laser pulse energy ranges from 0.1 mJ to 7.4 mJ. Only photoacoustic signals generated from dielectric breakdown was considered. We found that the amplitude and the average group velocity of the shock wave correlates to the laser pulse energy. The frequency contents of the photoacoustic signal changes due to both non-linear behaviour and dissipative effects. We estimated the dielectric breakdown threshold to be 0.44 × 1011Wcm-2.

  • 26.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Rehbinder, Göran
    Luleå tekniska universitet.
    Propagation of pressure perturbations in a layer of a porous medium1990Report (Other academic)
  • 27.
    Löfqvist, Torbjörn
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Rehbinder, Göran
    Transient flow towards a well in an aquifer including the effect of fluid inertia1993In: Applied Scientific Research: an international journal on the applications of fluid dynamics, ISSN 0003-6994, E-ISSN 2212-0939, Vol. 51, no 3, p. 611-623Article in journal (Refereed)
    Abstract [en]

    Transient propagation of weak pressure perturbations in a homogeneous, isotropic, fluid saturated aquifer has been studied. A damped wave equation for the pressure in the aquifer is derived using the macroscopic, volume averaged, mass conservation and momentum equations. The equation is applied to the case of a well in a closed aquifer and analytical solutions are obtained to two different flow cases. It is shown that the radius of influence propagates with a finite velocity. The results show that the effect of fluid inertia could be of importance where transient flow in porous media is studied.

  • 28. Niemi, Jan
    et al.
    Aitomäki, Yvonne
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ultrasonic measurements and modelling of attenuation and phase velocity in pulp suspensions2005In: 2005 IEEE Ultrasonics Symposium: 18 - 21 September 2005, Rotterdam, the Netherlands, Piscataway, NJ: IEEE Communications Society, 2005, Vol. 2, p. 775-779Conference paper (Refereed)
    Abstract [en]

    In the manufacturing process of paper the mass fraction and material properties of the fibres in the pulp suspension are important for the quality of the finished product. This study presents two different methods of pulp characterisation. The first is based on phase velocity, which we use to investigate the composition of the pulp. Here a method is presented where the optimal number of circular shifts within the sampling window of the signal is determined which gives, in a weakly dispersive medium, a continuous phase spectrum and minimizes the likelihood of discontinuities within the bandwidth. Hence, the ambiguity in phase unwrapping is avoided. The results from phase velocity measurements show that the phase velocity weakly increases with increasing amount of fines in the suspension. The dispersion is caused by the fibres and it correlates with fibre mass fraction. The second method is based on attenuation and is used to characterise the wood fibres. The results of the attenuation experiments show that it is possible to inversely calculate wood fibre properties by fitting the model to the experimental data, if the fibre diameter distribution is known. However, the accuracy of these calculation is difficult to determined and more work in this area is required.

  • 29. Niemi, Jan
    et al.
    Carlson, Johan E.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Joint estimation of fibers and fines concentration in paper pulp suspensions using a combined optical and acoustic technique2010In: 2009 IEEE Ultrasonics Symposium: Rome, Italy, 20 - 23 September 2009, Piscataway, NJ: IEEE Communications Society, 2010, p. 1191-1194Conference paper (Refereed)
    Abstract [en]

    This paper presents a method for joint estimation of fiber and fines mass fractions (i.e. pulp consistency) in paper pulp suspension. The technique is based on a combination of optical and ultrasonic measurements. The link between measured quantities and the mass fractions is established through Partial Least-Squares Regression (PLSR). The method is evaluated with experiments on unbleached softwood pulp for a total mass fraction of fibers and fines ranging from 0.6% to 0.54%. The results show that we are able to accurately predict both the fiber and fines mass fractions using the proposed technique. We also show that the performance is increased by combining the two techniques compared to using them by themselves.

  • 30. Niemi, Jan
    et al.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    On a new sensing strategy using a combination of ultrasonic and photoacoustic techniques2006In: Proceedings: 2006 IEEE Ultrasonics Symposium : Vancouver, Canada, 3 - 6 October 2006, Piscataway, NJ: IEEE Communications Society, 2006, p. 1797-1800Conference paper (Refereed)
    Abstract [en]

    The process industry is today aiming for more advanced process control strategies. These strategies rely on quick and accurate sensing of process variables. Considering processes where particles are suspended in a fluid, e.g. paper and pulp industry, there is a need for development of a new or improved in-line sensor technique determining different properties of the particles. In this study we present a sensing strategy where a combination of acoustical and optical measurement techniques is used. For this purpose have we designed and built a measurement cell which utilises the ultrasonic signal generated from an ultrasonic transducer as well as the ultrasonic, or photoacoustic, signal generated using a pulsed laser. The photoacoustic method is using the same transducer as in the transducer based method above. In the transducer based method, the well known pulse-echo technique is used. The pulse is generated by an ultrasonic transducer, travels through the suspension and reflects at a steel reflector. In the photoacoustic method, the ultrasonic transducer receives the ultrasound that is generated when a pulse of laser light is scattered and absorbed in the suspension. The laser beam enters the cell through fused silica windows. The laser beam is crossing the cell orthogonally to the ultrasonic transducer. The photoacoustic signal contains two echoes. The first echo is the acoustic signal which is generated when photons are absorbed by the medium. The second echo is the signal that has been travelling through the suspension and reflected at the steel reflector. The two measurement techniques were tested experimentally in the cell using aqueous suspensions of Nylon 66 fibres. The samples were mixed from fibres of three different diameters 17, 51 and 55 µ m with the length of 1.2mm for the 17µm and 1.5 mm for the 51 and 55µm. The fibres were suspended in distilled and degassed water to mass fractions of 0.12% and 0.25%. Distilled and degassed water was also used as a reference medium when determining the calibration constants for the cell. The photoacoustic signal is generated using a double-pulsed laser having pulse energy of 10 mJ and the laser beam is focused at the centre of the cell. The suspension was pumped around in a closed loop using a peristaltic pump and the temperature of the suspension was monitored during the measurement cycle. The result shows that the signal generated using the transducer based method scales linearly with mass fraction for each type of fibre. The results also show that the photoacoustic signal is sensitive to the number density of scatters in the suspension, i.e. the amplitude of the signal decreases with decreasing fibre diameters. These preliminary results indicate that a combination of these two techniques might be used in resolving the proportion of different particles with different diameter in a suspension.

  • 31.
    Niemi, Jan
    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.
    Wood pulp characterization by a novel photoacoustic sensor2012In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 23, no 8Article in journal (Refereed)
    Abstract [en]

    In this paper we introduce a novel photoacoustic sensing technique that captures a photoacoustic signal excited by a laser light pulse after the light has propagated through a turbid medium. Simultaneously, the ultrasonic sound wave is captured after it has propagated through the same turbid medium. By combining the two signals, more information on the investigated medium can be obtained. Applications can be found in the pulp and paper industry where monitoring wood pulp compositions is of interest. Depending on its origin, pulp suspension contains different compositions of fibres and fibre fragments (fines). Poor control of the pulp composition leads to an unstable process that compromises the production, quality and energy efficiency in the pulp mill. The result shows the feasibility of the photoacoustic sensor in monitoring the mass fractions of fibres and fines in a pulp suspension. The first received echo, corresponding to the light interaction with the sample, showed a stronger correlation to the fines mass fraction compared to fibre mass fraction. The second echo, corresponding to the sound wave interaction with the sample, showed a much stronger correlation to fibre mass fraction than to fines mass fraction. Hence, it is proposed that by combining these two echoes, more information about the pulp suspension could be extracted than from any other sensor built on a single sensing principle.

  • 32.
    Nordlund, Michael
    et al.
    Department of Chemistry - BMC, Uppsala University.
    Bhandary, Sumanta
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Sanyal, Biplab
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Grennberg, Helena
    Department of Chemistry - BMC, Uppsala University.
    Side-selective self-assembly of graphene and FLG on piezoelectric PVDF from suspension2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 7, article id 07LT01Article in journal (Refereed)
    Abstract [en]

    The deposition of few-layer graphene by self-assembly from suspension onto a piezoelectric polymer substrate is presented. The graphene self-assembles with negligible overlap between flakes, and with high selectivity for one of the faces of the substrate, an observation which is discussed and rationalized. A computational study on a model system further confirms the theory and supports the experimental results. The highest obtained degree of surface coverage was estimated to 77%

  • 33.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Comparison of Cavitation Effect in Case of Fixed and Free Fibers in an Ultrasound Beaker2019In: Proceedings of the 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019: ICA 2019, 9 - 13 September / [ed] Martin Ochmann, Aachen, Germany, 2019, p. 8217-8224Conference paper (Other academic)
    Abstract [en]

    In this study, we investigate the impact of high-intensity ultrasound treatment on the mechanical properties of pulp fibers. The pulp fiber samples are sonicated in an acoustically optimised beaker where high-intensity ultrasound is generated using a tuned sonotrode device. The idea is to create a controlled resonance to efficiently enhance the sound pressure in the beaker. Input power is 90Watt. The objective is to define the difference between freely suspended fibers in a beaker compared to keeping fibers in a fixed position. The hypothesis is that fiber treatment at a specific input power will be more efficient in the case when fibers are kept in a high pressure zone. Since the fiber wall is a layered structure, it is likely to delaminate internally which will affect the mechanical properties of the fiber. The effect on fiber properties is verified by measuring the ultrasound attenuation spectra for the treated fibers. The attenuation measurements are based on measurements of a low-intensity ultrasound pulse-echo technique. On a macroscopic scale, changes in the attenuation spectra relates to a change in mechanical properties of the fiber wall, since the suspended fibers more or less retain their diameter and length distributions.

  • 34.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Comparison of Different Concepts of UltrasoundReactors Using Numerical Simulations2018Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Sonochemical reactors are used for process intensification based on efficientenergy transfer due to ultrasound in order to cause transient cavitation in the medium.Ultrasonic reactors are extensively used for numerous applications due to their differentfeatures. The process of ultrasound cavitation can be defined as generation, growth andviolent collapse of microbubbles under ultrasonic irradiation which can release a highamount of energy in a small volume. The released energy causes a sudden increase intemperature and pressure which thereby can lead to extensive process intensification. Thepresent work deals with the evaluation of two different configurations of ultrasound reactorsusing both numerical modeling and experimental verification. The evaluation is based onprediction of the pressure distribution, verified by foil tests and with calorimetric method.The two reactors were developed to be used for the treatment of cellulose fibers to improveenergy efficiency in the fibrillation process. The goal is to optimize cavitation intensityand minimize the coupling loss factors. The development and evaluation of these two reactorconcepts aim to improve the design methodology for a scalable flow through reactor conceptwith high yield and energy efficiency

  • 35.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Energy Efficient Fibrillation of Cellulose Fibers using an Ultrasound Reactor2019Conference paper (Refereed)
    Abstract [en]

    The pulp and paper industry is in continuous need for energy-efficient production processes. Therefore, there is a focus in reducing electrical energy use in the production of paper.  The most energy demanding processes are related to fibrillation, which in some cases use up to 80% of required electrical power, with a net efficiency of 1%. The presented work focus on ultrasound controlled cavitation in concentrating the processing energy to provide an energy efficient development of cellulose fibers. The objectives are to develop a scalable cavitation reactor to obtain energy-efficient fibrillation of cellulose fibers aiming at reducing the energy use by 50%. Our goal is to develop a methodology based on multiphysic simulation for the design of an alternative refiner based on ultrasound cavitation. The reactor concept is of a flow through type where cavitation bubbles are initiated in the fiber suspension by the pressure release when the pulp flow through a venturi nozzle. The induced cavitation bubbles are collapsed by high intensity ultrasound at resonant frequencies. The collapsing bubbles and their associated shock waves modify the fiber wall properties which enables fibrillation.  Energy efficient fibrillation of cellulose fibers is therefore possible to achieve through an optimized combination of hydrodynamic and ultrasonic controlled cavitation. Initial results shows a positive effect on fiber quality. However, further optimization of process parameters like temperature and static pressure is required.

  • 36.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Shankar, Vijay
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Comparison of Two Different Ultrasound Reactors for the Treatment of Cellulose Fibers2019In: Ultrasonics Sonochemistry, ISSN 1350-4177Article in journal (Refereed)
    Abstract [en]

    The pulp and paper industry is in continuous need for energy-efficient production processes. In the refining process of mechanical pulp, fibrillation is one of the essential unit operations that count for up to 80% of the total energy use. This initial study explores the potential and development of new type of scalable ultrasound reactor for energy efficient mechanical pulping. The developed reactor is of continuous flow type and based on both hydrodynamic and acoustic cavitation in order to modify the mechanical properties of cellulose fibers. A comparison of the prototype tube reactor is made with a batch reactor type where the ultrasonic horn is inserted in the fluid. The pulp samples were sonicated by high-intensity ultrasound, using tuned sonotrodes enhancing the sound pressure and cavitation intensity by a controlled resonance in the contained fluid. The resonant frequency of the batch reactor is 20.8 kHz and for the tube reactor it is 22.8 kHz. The power conversion efficiency for the beaker setup is 25% and 36 % in case of the tube reactor in stationary mode. The objective is to verify the benefit of resonance enhanced cavitation intensity when avoiding the effect of Bjerkenes forces. The setup used enables to keep the fibers in the pressure antinodes of the contained fluid. In case of the continuous flow reactor the effect of hydrodynamic cavitation is also induced. The intensity of the ultrasound in both reactors was found to be high enough to produce cavitation in the fluid suspension to enhance the fiber wall treatment. Results show that the mechanical properties of the fibers were changed by the sonification in all tests. The continuous flow type was approximately 50% more efficient than the beaker. The effect of keeping fibers in the antinode of the resonant mode shape of the irradiation frequency was also significant. The effect on fiber properties for the tested mass fraction was determined by a low-intensity ultrasound pulse-echo based measurement method, and by a standard pulp analyzer

  • 37.
    Saarela, Juha
    et al.
    Department of Electrical and Information Engineering and Infotech Oulu, University of Oulu.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Detection of laser induced dielectric breakdown in water using a laser doppler vibrometer2010In: Central European Journal of Physics, ISSN 1895-1082, E-ISSN 1644-3608, Vol. 8, no 2, p. 235-241Article in journal (Refereed)
    Abstract [en]

    This study is focused on exploring the feasibility of an all-optic surface scanning method in determining the size and position of a submerged, laser generated, optoacoustic source. The optoacoustic effect was here generated when the absorption of a short electromagnetic pulse in matter caused a dielectric breakdown, a plasma emission flash and a subsequent acoustic wave. In the experiment, a laser pulse with l = 1064 nm and 12 ns pulse length was aimed at a volume of deionized water. When the laser beam was focused by a f = 16 mm lens, a single dielectric breakdown spot occurred. When a f = 40 mm was used several breakdowns in a row were induced. The breakdowns were photographed using a double shutter camera. The acoustic wave generated by the dielectric breakdowns were detected at a point on the water surface using a laser Doppler vibrometer (LDV). First, the LDV signal was used to calculate the speed of sound with an accuracy of 10 m/s. Secondly, the location and length of the dielectric breakdown was calculated with an accuracy of 1 mm. The calculated position matched the breakdown location recorded by a camera. The results show that it is possible to use LDV surface measurements from a single spot to determine both the position and length of the OA source as well as the speed of sound in the medium. Furthermore, the LDV measurements also show a secondary peak that originates from the OA source. To unravel the origin and properties of this interesting feature, further investigations are necessary.

  • 38.
    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.

  • 39.
    Svanström, Erika
    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.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    On laser-induced ultrasound generated in a thin semi-transparent layered polymer structure2012In: Photons Plus Ultrasound: Imaging and Sensing 2012 / [ed] Alexander A. Oraevsky; Lihong V. Wang, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2012Conference paper (Refereed)
    Abstract [en]

    We investigate laser-induced ultrasound generated in a plane semi-transparent layered polymer structure. The scope is to study relations between generated ultrasound, as e.g. amplitude, and centre frequency and bandwidth of its frequency spectrum, and properties of the polymer layers, like thickness and absorption. This knowledge can then be used when designing polymer film based, semi-transparent ultrasonic devices specifically for photoacoustic applications. The experimental study is set-up as a factorial experiment with a completely randomised design. In the experiments, the light source is a pulsed Nd:YAG laser. As absorber, a semi-transparent, non-conductive polymer film in a plane layered structure of one or more layers on a glass substrate is used. The frequency spectra of the generated ultrasound spans 2 to 20 MHz, which is recorded by a broadband PVDF ultrasonic transducer. The results show that an increased thickness of the polymer layer structure relate to a lower center frequency and a lower bandwidth, and that an increased optical absorption and a decreased layer structure thickness is related to a higher ultrasound amplitude.

  • 40.
    Törmänen, Matti
    et al.
    Department of Electrical Engineering, 90014 University of Oulu.
    Niemi, Jan
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Myllylä, Risto
    Department of Electrical Engineering, 90014 University of Oulu.
    Pulp consistency determined by a combination of optical and acoustical measurement techniques2006In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 4, p. 695-702Article in journal (Refereed)
    Abstract [en]

    In this study, methods based on ultrasonic attenuation and optical time-of-flight measurements are used simultaneously in determining both the fibres and fines mass fractions, respectively, of a cellulose pulp fibre suspension. The optical measurements are done by a laser radar and the acoustical measurements are based on ultrasonic attenuation measurements in a pulse-echo set-up. Two kinds of long-fibre fractions are studied, thermo-mechanical pulp and chemical softwood pulp. Fibre and fines mass fraction ranges are 0.25–1.0% and 0–0.75%, respectively. The results show that the fibres are the predominant source for absorption and scattering of ultrasonic waves and are thus mainly contributing to the attenuation of ultrasound in the pulp. It is also found that the fines are the predominant source for optical scattering and fines are thus mainly contributing to the propagation delay of the light pulse in the laser radar set-up. By combining the ultrasonic attenuation and the optical time-of-flight measurements, it is shown that the mass fraction of fines and the mass fraction of fibres in a pulp sample could be determined, respectively.

  • 41.
    van Deventer, Jan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Löfqvist, Torbjörn
    Delsing, Jerker
    PSpice simulation of ultrasonic systems2000In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 47, no 4, p. 1014-1024Article in journal (Refereed)
    Abstract [en]

    The usage of electrical analogies for the simulation of wave generation and propagation in ultrasound transducers is well established. In this paper a PSpice approach that includes the temperature and frequency dependency of the transducer performance is proposed. The analogy between acoustic wave propagation and wave propagation in an electric transmission line is given. Further ways to deduce temperature and frequency dependencies are discussed. The simulation approach is applied to a pulse-echo setup for the determination of speed of sound and attenuation in liquids and solids. Experiments and simulations are made for three temperatures and in the frequency range 1-12 MHz using water, glycerine, and polymers (PMMA and PEEK) as test samples. Comparison shows a good agreement between simulation and experiments. Results for glycerine indicates that the available attenuation models for high viscosity liquids is inappropriate

1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf