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  • 151.
    Zipser, L.
    et al.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Franke, H.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ultrasound object fields in air reconstructed using digital phase conjugation2002In: Proceedings: 2002 IEEE Ultrasonics Symposium : October 8 - 11, 2002, Forum Hotel, Munich, Germany / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2002, p. 765-768Conference paper (Refereed)
    Abstract [en]

    A scanning laser Doppler vibrometer is used to record 2D ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction using phase conjugation (time reversal) of the object sound field is then performed and the original object field intensity and phase is reconstructed.

  • 152.
    Zipser, Lothar
    et al.
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Franke, Heinz
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Reconstructing two-dimensional acoustic object fields by use of digital phase conjugation of scanning laser vibrometry recordings2003In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 29, p. 5831-5838Article in journal (Refereed)
    Abstract [en]

    scanning laser Doppler vibrometer is used to record two-dimensional ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction by use of phase conjugation (time reversal) of the object sound field is then performed, and the original object field intensity and phase is reconstructed

  • 153.
    Öhman, Johan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    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.
    Polarization-resolved dual-view holographic system for 3D inspection of scattering particles2019In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 58, no 34, p. G31-G40Article in journal (Refereed)
    Abstract [en]

    A novel dual-view polarization-resolved pulsed holographic system for particle measurements is presented. Both dual-view configuration and polarization-resolved registration are well suited for particle holography. Dual-view registration improves the accuracy in the detection of 3D position and velocities, and polarization-resolved registration provides polarization information about individual particles. The necessary calibrations are presented, and aberrations are compensated for by mapping the positions in the two views to positions in a global coordinate system. The system is demonstrated on a sample consisting of 7 μm spherical polystyrene particles dissolved in water in a cuvette. The system is tested with different polarizations of the illumination. It is found that the dual view improves the accuracy significantly in particle tracking. It is also found that by having polarization-resolved holograms, it is possible to separate naturally occurring sub-micrometer particles from the larger, 7 μm seeding particles.

  • 154.
    Öhman, Johan
    et al.
    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.
    Axial Particle Positioning by Wavefront Parameterization using Chebyshev Polynomials and Off-axis Digital Holography2017In: Digital Holography and Three-Dimensional Imaging, Washington: The Optical Society , 2017, article id M4A.3Conference paper (Refereed)
    Abstract [en]

    A particle can be axially positioned where its scattered light has a plane wavefront. The phase anomaly compared to a plane wave is fitted to 3D Chebyshev polynomial, where coefficients correspond to the axial position.

    Download full text (pdf)
    fulltext
  • 155.
    Öhman, Johan
    et al.
    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.
    Identification, tracking, and sizing of nano-sized particles using dual-view polarization-resolved digital holography and T-matrix modeling2020In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 59, no 14, p. 4548-4556Article in journal (Refereed)
    Abstract [en]

    In this paper, we demonstrate how polarization-resolved holography can be used to determine if a particle is spherical or not and to estimate the size information of nanoparticles. The T-matrix method is used to model the scattered light from both spheres and spheroids. A dual-view polarization-resolved imaging system is used in order to obtain polarization ratio angles (β₁,β₂). From the obtained β₁ and β₂, it is possible to estimate whether or not a particle is spherical or not. It is found that non-sphericity only has a minor effect up to around sizes of 120nm, and for that range, a spherical approximation is valid. For larger particles, the orientation influence the polarization response greatly. The size of a non-spherical particle can be estimated from the polarization ratio angles. The upper limit we can estimate unambiguously is around 200nm. Finally, the model is applied to experimental measurements of naturally occurring particles in purified water. From the measurements, it is possible to separate spherical from non-spherical particles and also give a rough estimate of the size.

  • 156.
    Öhman, Johan
    et al.
    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.
    Off-axis digital holographic particle positioning based on polarization-sensitive wavefront curvature estimation2016In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, no 27, p. 7503-7510Article in journal (Refereed)
    Abstract [en]

    Poor axial resolution in holographic particle imaging applications makes particle positioning in 3D space morecomplex since the positions are not directly obtained. In this paper we estimate the axial position of micrometerparticles by finding the location where the wavefront curvature from the scattered light becomes zero. By record-ing scattered light at 90°using off-axis holography, the complex amplitude of the light is obtained. Byreconstruction of the imaged scene, a complex valued volume is produced. From this volume, phase gradientsare calculated for each particle and used to estimate the wavefront curvature. From simulations it is found that thewavefront curvature became zero at the true axial position of the particle. We applied this metric to track an axialtranslation experimentally using a telecentric off-axis holographic imaging system with a lateral magnification ofM1.33. A silicon cube with molded particles inside was used as sample. Holographic recordings are performedboth before and after a 100μm axial translation. From the estimated positions, it was found that the mean dis-placement of particles between recordings was 105.0μm with a standard deviation of 25.3μm.

  • 157.
    Öhman, Johan
    et al.
    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.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Polarization Resolved Dual-View Holographic System for Investigation of Microparticles2019In: OSA Technical Digest (Optical Society of America, 2019), 2019, article id Th2A.5Conference paper (Refereed)
    Abstract [en]

    A dual-view polarization resolved digital-holographic system is presented. The necessary calibration for both polarization and spatial coordinates are outlined. As an example the system is is used to track spherical microparticles in a cuvette.

    Download full text (pdf)
    fulltext
  • 158.
    Öhman, Johan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Österlund, Helene
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Nordqvist, Kerstin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Polarization-Resolved Digital Holographic Measurements of MicroplasticsManuscript (preprint) (Other academic)
    Abstract [en]

    Dual-view digital holography is used to image samples of microplastics. The detection is polarization-resolved and produces, in total, four different intensities, one in each polarization direction on each camera. Ratio angles between all four components are calculated, and differences between the samples are investigated. This paper uses four different samples, particles from rubber tires, plastic bottles, coffee cups, and a reference sample. It is found that the data varies a lot for all samples. But when calculating the correlation coefficients differences between the samples are observed.

1234 151 - 158 of 158
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