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  • 51. Johansson, Eva-Lena
    et al.
    Benckert, Lars
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase object data obtained from defocused laser speckle displacement2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 16, s. 3229-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An optical technique that is based on defocused digital speckle photography is proposed for the evaluation of phase objects. Phase objects are different kinds of transparent or semi-transparent media that allow light to be transmitted. A phase object inserted in a laser speckle field introduces speckle displacement, from which information about the object may be extracted. It is shown that one may use speckle displacements to determine both the phase gradients and the positions of phase objects. As an illustration the positions and focal lengths of two weak lenses have been derived from defocused laser speckle displacement

  • 52. Kajberg, Jörgen
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Optical method to study material behaviour at high strain rates2000Ingår i: IUTAM Symposium on Field Analysis for Determination of Material Parameters - Experimental and Numerical Aspects: proceedings of the IUTAM Symposium held in Abisko National Park, Kiruna, Sweden, July 31 - August 4, 2000 / [ed] P. Ståhle, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2000, s. 37-49Konferensbidrag (Refereegranskat)
  • 53.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Amer, Eynas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Melander, Emil
    Uppsala University.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Single-shot dual-polarization holography: measurement of the polarization state of a magnetic sample2015Ingår i: SPECKLE 2015: VI International Conference on Speckle Metrology / [ed] Fernando Mendoza Santoyo; Eugenio R. Mendez, SPIE - International Society for Optical Engineering, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper a single-shot digital holographic set-up with two orthogonally polarized reference beams is proposed to achieve rapid acquisition of Magneto-Optical Kerr Effect images. Principles of the method and the background theory for dynamic state of polarization measurement by use of digital holography are presented. This system has no mechanically moving elements or active elements for polarization control and modulation. An object beam is combined with two reference beams at different off-axis angles and is guided to a detector. Then two complex fields (interference terms) representing two orthogonal polarizations are recorded in a single frame simultaneously. Thereafter the complex fields are numerically reconstructed and carrier frequency calibration is done to remove aberrations introduced in multiplexed digital holographic recordings. From the numerical values of amplitude and phase, a real time quantitative analysis of the polarization state is possible by use of Jones vectors. The technique is demonstrated on a magnetic sample that is a lithographically patterned magnetic microstructure consisting of thin permalloy parallel stripes

  • 54.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bergström, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dual-wavelength digital holography: single shot calibration2014Ingår i: Interferometry XVII: Techniques and Analysis, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2014, artikel-id 920305Konferensbidrag (Refereegranskat)
    Abstract [en]

    In an on line shape measurement in disturbed environment, use of many wavelengths in order to avoid phase ambiguity may become a problem as it is necessary to acquire all holograms simultaneously due to environmental disturbances. Therefore to make the shape data available the different holograms have to be extracted from a single recorded image in spectral domain. Appropriate cut areas in the Fourier method are therefore of great importance for decoding information carried by different wavelengths. Furthermore using different laser sources, induces aberration and pseudo phase changes which must be compensated. To insure any phase change is only because of the object shape, calibration is therefore indispensable. For this purpose, effects of uncontrolled carrier frequency filtering are discussed. A registration procedure is applied using minimum speckle displacements to find the best cut area to extract and match the interference terms. Both holograms are numerically propagated to a focus plane to avoid any unknown errors. Deviations between a reference known plate and its measurement are found and used for calibration. We demonstrate that phase maps and speckle displacements can be recovered free of chromatic aberrations. To our knowledge, this is the first time that a single shot dual wavelength calibration is reported by defining a criteria to make the spatial filtering automatic avoiding the problems of manual methods. The procedure is shown to give shape accuracy of 35μm with negligible systematic errors using a synthetic wavelength of 1.1 mm.

  • 55.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bergström, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements2015Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, nr 16, s. 5003-5010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18  mm×18  mm.

  • 56.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bergström, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Single Shot Dual-Wavelength Digital Holography: Calibration Based on Speckle Displacements2014Ingår i: International Journal of Optomechatronics, ISSN 1559-9612, Vol. 8, nr 4, s. 326-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a calibration method which allows single shot dual wavelength online shape measurement in a disturbed environment. Effects of uncontrolled carrier frequency filtering are discussed as well. We demonstrate that phase maps and speckle displacements can be recovered free of chromatic aberrations. To our knowledge, this is the first time that a single shot dual wavelength calibration is reported by defining a criteria to make the spatial filtering automatic avoiding the problems of manual methods. The procedure is shown to give shape accuracy of 35 µm with negligible systematic errors using a synthetic wavelength of 1.1 mm.

  • 57.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dual-wavelength digital holographic shape measurement using speckle movements and phase gradients2013Ingår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 52, nr 10, artikel-id 101912Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new method to measure shape by analyzing the speckle movements in images generated by numerical propagation from dual-wavelength holograms is presented. The relationship of the speckle movements at different focal distances is formulated, and it is shown how this carries information about the surface position as well as the local slope of the object. It is experimentally verified that dual-wavelength holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve the object shape. From a measurement on a cylindrical test object, the method is demonstrated to have a random error in the order of a few micrometers.

  • 58.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Singh, Alok Kumar
    Institute of Applied Optics, University of Stuttgart.
    Pedrini, Giancarlo
    Institute of Applied Optics, University of Stuttgart.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Full-field 3D deformation measurement: Comparison between speckle phase and displacement evaluation2016Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, nr 27, s. 7735-7743Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to describe a full-field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x,z) and (y,z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from the four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with rigid body movements and phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2 × 10-3 in the measurement of deformation gradients

  • 59.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Shape reconstruction using dual wavelength digital holography and speckle movements2013Ingår i: Optical Measurement Systems for Industrial Inspection VIII, / [ed] Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, SPIE - International Society for Optical Engineering, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    A new technique to measure depth based on dual wavelength digital holography and image correlation of speckle movements is demonstrated. By numerical refocusing of the complex optical field to different focus planes and by measuring the speckle movements caused by a wavelength shift both the object surface position and its local slope can be determined. It is shown how the speckle movement varies linearly with the surface slope, the wavelength shift and the distance of the numerical propagation. This gives a possibility to measure the slope with approximately the same precision as from the interferometric phase maps. In addition, when the object surface is in focus there is no speckle movement so by estimating in what plane the speckle movement is zero the absolute surface position can be measured.

  • 60.
    Kinell, Lars
    et al.
    Luleå tekniska universitet.
    Eriksson, Magnus
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Component forming simulations validated using optical shape measurements2003Ingår i: Optical Measurement Systems for Industrial Inspection III: 23 - 26 June 2003, Munich, Germany / [ed] Wolfgang Osten, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2003, s. 409-419Konferensbidrag (Refereegranskat)
    Abstract [en]

    For validation of forming simulations a methodology, using optical shape measurements, is here presented. In this work, the shape of a sheet metal component with complex geometry is measured using projected fringes. The component in consideration is a closed section steel profile that is formed using a forming tool. The shape is measured using the reduced temporal phase unwrapping scheme and calibration data for the calculation of absolute coordinates in the local coordinate system. Local 3-D coordinates from several measurements of this long object are merged together through a feature based stitching program. To validate the finite-element model, the final shape of the forming simulation is compared to the results from the shape measurements. Since no computer aided design model exists for the formed beam, the features in shape of the measured object are used as references when comparing results

  • 61.
    Kinell, Lars
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Robustness of reduced temporal phase unwrapping in the measurement of shape2001Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 40, nr 14, s. 2297-2303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The predictions of success rate and depth uncertainty for the negative exponential sequence used for temporal phase unwrapping of shape data are generalized to include the effect of a reduced sequence and speckle noise in single-channel and multichannel systems, respectively. To cope with the reduction of the sequence, a scaling factor is introduced. A thorough investigation is made of the performance of this algorithm, called the reduced temporal phase-unwrapping algorithm. Two different approaches are considered: a single-channel approach in which all the necessary images are acquired sequentially in time and a multichannel approach in which the three channels of a color CCD camera are used to carry the phase-stepped images for each fringe density in parallel. The performance of these two approaches are investigated by numerical simulations. The simulations are based on a physical model in which the speckle contrast, the fringe modulation, and random noise are considered the sources of phase errors. Expressions are found that relate the physical quantities to phase errors for the single-channel and the multichannel approaches. In these simulations the single-channel approach was found to be the most robust. Expressions that relate the measurement accuracy and the unwrapping reliability, respectively, with the reduction of the fringe sequence were also found. As expected, the measurement accuracy is not affected by a shorter fringe sequence, whereas a significant reduction in the unwrapping reliability is found as compared with the complete negative exponential sequence

  • 62.
    Larsson, Linda
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Thuvander, Fredrik
    Karlstads Universitet.
    Microscopic 3D displacement field measurements using digital speckle photography2004Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 41, nr 5, s. 767-777Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A technique to measure object shape and 3-D displacement fields in micro-scale is offered by microscopic stereo digital speckle photography. The displacement of the random features that are often present on many engineering surfaces when viewed in a microscope is measured with the system, using image correlation. In this paper the equipment, physical model and calibration routines are described. The technique can be applied for sub-mm sized objects of arbitrary shape for small deformation fields. As a verifying experiment, an in-plane rotation of a flat calibration plate is presented. The expected in-plane errors are shown to be less than 0.1μm and the corresponding out-of-plane errors about three times larger. As a pilot experiment, micro-structural paper expansion is studied, when exposed to humidity. The scaling properties of the microscope as well as the sampling criteria and reliability of the system are discussed in detail

  • 63.
    Lif, J.O.
    et al.
    STFI.
    Fellers, C.
    Söremark, C.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Characterizing the in-plane hygroexpansivity of paper by electronic speckle photography1995Ingår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 21, nr 9, s. J302-J308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A newly developed electronic speckle photographic system is used to investigate the hygroexpansion of paper. By using a spray-paint technique for the creation of the speckle pattern, two applications of the system are demonstrated on different machine-made papers. The first one is the determination of the displacement field after the exposure of a sheet to a moisture change. The second is the determination of hygroexpansion orientation. Lastly, an investigation of the correspondence between hygroexpansion and tensile stiffness orientations determined by an ultrasonic technique is presented.

  • 64.
    Lindström, John
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Digitala tjänster och system.
    Lejon, Erik
    Gestamp Hardtech AB.
    Kyösti, Petter
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Mecella, Massimo
    University of Sapienza.
    Heutelbeck, Dominic
    FTK.
    Hemmje, Matthias
    FTK.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Birk, Wolfgang
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gunnarsson, Bengt
    Data Ductus AB.
    Towards intelligent and sustainable production systems with a zero-defect manufacturing approach in an Industry4.0 context2019Ingår i: Procedia CIRP, vol 81 / [ed] Edited by Peter Butala, Edvard Govekar, Rok Vrabič, Elsevier, 2019, Vol. 81, s. 880-885Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper addresses intelligent and sustainable production achieved through combination and integration of online predictive maintenance, monitoring of process parameters and continuous quality control of both input materials and output from the process. This enables production systems, within both manufacturing and process industries, to move towards zero-defect manufacturing. Such a zero-defect manufacturing approach allows for earlier identification of problems or issues, which will or already negatively affect the output. The paper outlines the first part of the second cycle of an action research effort at Gestamp HardTech AB in Sweden, whose objective is to keep its position as a world-leading provider of press-hardened vehicle parts. In order to fully implement the zero-defect manufacturing approach, 4-6 action research cycles are expected to be needed in order to iteratively refine the approach. During the first cycle, various methods and solutions for some of the individual issues/problems have been conceptualized, realized and initially tested. The selected design criteria for the action research efforts were: simplicity, low cost, robustness, high-quality output and future-proofing. The result from the research in the second cycle so far is an action plan for the technical change and a set of challenges/problems which need additional investigation.

  • 65. Lycksam, Henrik
    et al.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Digital holographic interferometry in a disturbed environment2007Ingår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 86-Konferensbidrag (Övrigt vetenskapligt)
  • 66. Lycksam, Henrik
    et al.
    Gren, Per
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Digital holographic interferometry in a disturbed environment2006Ingår i: Speckle06: speckles, from grains to flowers ; 13 - 15 September 2006, Nimes, France ; [proceedings] / [ed] Pierre Slangen; Christine Cerruti, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2006, s. 634111-Konferensbidrag (Refereegranskat)
    Abstract [en]

    The problem of environmental disturbances in Digital Holographic Interferometry has been addressed in this investigation. Disturbances may be caused by vibrations, air turbulence or the presence of scattering particles and the effect of them might significantly prevent spread of the technique into a wider area of application. To handle the problem with air turbulence a temporal sequence of an event is analysed and the effect on the motion and phase of the speckles is analysed and described using statistical measures. The effect of the medium will be fed back to the sequence using an adaptive filter and the undisturbed phase evolution estimated. The principle is demonstrated using a heat source placed in between the object and the CCD camera as the disturbance on a simple tilt experiment. The presence of scattering particles is more intriguing and has to be dealt with separately. In this investigation we adopt the technique of low-coherence interferometry to depth-code the holographic images acquired. The seeding of the pulsed Nd:YAG laser source used is shut off that results in a coherence length of about one cm. The paper shows a few preliminary results from a simple wavepropagation experiment.

  • 67.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Gren, Per
    Measurement of spatiotemporal phase statistics in turbulent air flow using high-speed digital holographic interferometry2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 8, s. 1314-1322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We describe a method of measuring spatiotemporal (ST) structure and covariance functions of the phase fluctuations in a collimated light beam propagated through a region of refractive index turbulence. The measurements are performed in a small wind tunnel, in which a turbulent temperature field is created using heated wires at the inlet of the test section. A collimated sheet of light is sent through the channel, and the phase fluctuations across the sheet are measured. The spatial phase structure function can be estimated from a series of images captured at an arbitrary frame rate by spatial phase unwrapping, whereas the ST structure function requires a time resolved measurement and a full three-dimensional unwrapping. The measured spatial phase structure function shows agreement with the Kolmogorov theory with a pronounced inertial subrange, which is taken as a validation of the method. Because of turbulent mixing in the boundary layers close to the walls of the channel, the flow will not obey the Taylor hypothesis of frozen turbulence. This can be clearly seen in the ST structure function calculated in a coordinate system that moves along with the bulk flow. At zero spatial separation, this function should always be zero according to the Taylor hypothesis, but due to the mixing effect there will be a growth in the structure function with increasing time difference depending on the rate of mixing.

  • 68.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Gren, Per
    Mätningar av spatiotemporal statistik i ett turbulent luftflöde med höghastighets digital holografisk interferometri2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 60-Konferensbidrag (Övrigt vetenskapligt)
  • 69. Lycksam, Henrik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Leblanc, James
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wiener filtering of interferometry measurements through turbulent air using an exponential forgetting factor2008Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, nr 16, s. 2971-2978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of imaging through turbulent media has been studied frequently in connection with astronomical imaging and airborne radars. Therefore most image restoration methods encountered in the literature assume a stationary object, e.g., a star or a piece of land. In this paper the problem of interferometric measurements of slowly moving or deforming objects in the presence of air disturbances and vibrations is discussed. Measurement noise is reduced by postprocessing the data with a digital noise suppression filter that uses a reference noise signal measured on a small stationary plate inserted in the field of view. The method has proven successful in reducing noise in the vicinity of the reference point where the size of the usable area depends on the degree of spatial correlation in the noise, which in turn depends on the spatial scales present in the air turbulence. Vibrations among the optical components in the setup tend to produce noise that is highly correlated across the field of view and is thus efficiently reduced by the filter. © 2008 Optical Society of America.

  • 70.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Öhman, Marcus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    High-speed interferometric measurement and visualization of the conversion of a black liquor droplet during laser heating2012Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 50, nr 11, s. 1654-1661Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Black liquor is a mix of organic and inorganic materials that is left after the kraft pulping process. In a modern pulp mill the pulping chemicals and the energy in the black liquor is recovered and used in the pulping cycle by burning the black liquor in a recovery burner. An alternative to the recovery boiler is to gasify the black liquor to produce an energy rich synthesis gas that can be upgraded into synthetic fuels or chemicals. Characterization of black liquor has mostly been done under conditions that are relevant for recovery boilers but the conditions in a gasifier differ significantly from this. In particular the droplets are much smaller and the heating rates are much higher. This paper presents an optical interferometric technique that has the potential to produce data under relevant conditions for gasification. In the paper, results are measured at atmospheric conditions and with relatively low heating rate. However, the method can be applied also for pressurized conditions and at heating rates that are only limited by the frame rate of the digital camera that is used to capture the transient event when the droplets are heated. In the paper the dynamic properties of the gas ejected from and the swelling during conversion of a single droplet are measured

  • 71. Miroshnikova, N.
    et al.
    Yalukova, O.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sarady, Istvan
    Study of the interaction mechanism between different materials and pulses from CO2-and Nd:YAG-lasers using Digital Speckle Photography2004Ingår i: Laser-assisted micro- and nanotechnologies 2003, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2004Konferensbidrag (Refereegranskat)
  • 72. Miroshnikova, N.
    et al.
    Yalukova, O.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sarady, Istvan
    Study of the interaction mechanisms between different materials and pulses from CO2- and Nd:YAG-lasers using digital speckle photography2004Ingår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 5506, s. 42-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulsed irradiation from CO2- and Nd:YAG lasers focused on the front side of different plates produces nearly instantaneous surface changes on the rear side of the plate. The responses of the materials depend on physical parameters such as pulse energy and duration, photon energy, the absorption and mechanical characteristics of the target material. The equipment built up for visualization of these phenomena consists of a cw. He-Ne laser, a digital CCD camera and a fast computer. The analysis is done using Digital Speckle Photography (DSP). Using focused and defocused laser speckle patterns, DSP enables measurement of in-plane strain fields, Brownian motion and residual micro-structural changes in the material caused by a laser pulse. Results are obtained at the frame rate of the digital camera and allow the creation of animated real-time or "movie" sequences. Results from CO2- and Nd:YAG pulse interaction on Al2O3 ceramics and steel plates will be presented. The Brownian motion during the relaxation phase is more or less localized to the impacted area for both materials and both wavelengths but the relaxation times differ significantly. Steel also exhibits some residual material changes and doesn't recover completely while Al2O3 returns to its initial state some time after the impact

  • 73.
    Miroshnikova, Natalia
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sarady, Istvan
    Percussion hole drilling of metals with a fourth-harmonic Nd:YAG laser studied by defocused laser speckle correlation2005Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 44, nr 17, s. 3403-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Defocused speckle correlation is introduced as a tool for measuring the response in metal sheets during percussion laser drilling. For this procedure the fourth-harmonic Nd:YAG wavelength (266 nm) was used in pulsed mode. The method provides a cost-efficient and robust alternative to speckle interferometry for the study of the small deformations that appear during laser processing. The accuracy was shown to be of the order of a few tens of microradians for the tilt component that is measured, which translates to a few nanometers in deflection when the component is spatially integrated. In the measurements, deflections in the form of craters as large as 50 nm were detected on the back sides of silver and copper sheets. The diameters of the craters were 300 μm in the silver and 150 μm in the copper sheet; the output diameter of the hole was ~5 μm

  • 74.
    Miroshnikova, Natalia V.
    et al.
    Luleå tekniska universitet.
    Yalukova, O. M.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sarady, Istvan
    Study of mechanisms by which the radiation of powerful pulsed CO2 and Nd:YAG lasers acts on various materials, using the method of digital speckle photography2004Ingår i: Journal of optical technology (Print), ISSN 1070-9762, E-ISSN 1091-0786, Vol. 71, s. 514-519Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a method of digital speckle photography that can be used to study the mechanisms by which powerful radiation from pulsed CO2 and Nd:YAG lasers acts on various materials. Rough-surfaced plates made from aluminum oxide and steel were used as experimental samples. The results of the experiments are presented in the form of three-dimensional graphs that clearly display the characteristics and dynamics of the processes being studied.

  • 75.
    Mohan, N. Krishna
    et al.
    Indian Institute of Technology.
    Andersson, A.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    Optical configurations in TV holography for deformation and shape measurement2000Ingår i: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 10, nr 2, s. 147-159Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent years, TV holography is extensively implemented for determination of deformation and surface shape of diffusely reflecting surfaces. Such investigations are of primary importance in many applications, because these physical parameters are related to the functionality, integrity and performance of the engineering objects. In this paper, a new approach for determination of deformation and surface shape using simple optical configurations is presented. Description of each configuration, theory of fringe formation and the measuring sensitivity are discussed. Experimental results using four frame phase shifting technique are illustrated.

  • 76.
    Mohan, N. Krishna
    et al.
    Indian Institute of Technology.
    Andersson, Angelica
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    Optical configuration for TV holography measurement of in-plane and out-of-plane deformations2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 4, s. 573-577Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel TV holography method is proposed for parallel evaluation of in-plane and out-of-plane deformation fields. The method permits a trade-off between in-plane and out-of-plane measuring sensitivity. A four-exposure, four-frame phase shifting technique is used in the experiments; the experimental results for an aluminum specimen subjected to both rotation in its own plane and a bending couple load at the center are presented

  • 77.
    Mohan, Nandigna Krishna
    et al.
    Indian Institute of Technology, Madras.
    Andersson, Angelica
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    Fringe formation in a dual beam symmetric illumination-observation TV holography system: an analysis2000Ingår i: Laser interferometry X / [International Conferences on Laser Interferometry X, held as part of SPIE's International Symposium on Optical Science and Technology 2000], 31 July - 1 August 2000, San Diego, USA, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2000Konferensbidrag (Refereegranskat)
  • 78.
    Mohan, N.K.
    et al.
    Indian Institute of Technology.
    Svanbro, Angelica
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    Dual-beam symmetric illumination-observation TV holography system for measurements2001Ingår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 40, nr 12, s. 2780-2787Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Leendertz dual-beam symmetric illumination-normal observation arrangement is widely employed for real time evaluation of in-plane displacement components as well as surface shape. Instead of observing along the optical axis, we have examined the Leendertz arrangement by observing the scattered light along the direction of the illumination beams, and imaged it as two separate images onto the photo sensor of a CCD camera. The interferometer is a combination of two channels, each of which measures independently and simultaneously the information pertaining to either the in-plane displacement component of a deformation vector, or the surface relief variation of a three-dimensional object. In addition, a summary of possible measurements that can be carried out from the present arrangement is also highlighted. Experimental results using a four-frame phase shifting technique are illustrated

  • 79. Molin, Nils-Erik
    et al.
    Sjödahl, Mikael
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andersson, A.
    Luleå tekniska universitet.
    Digital speckle photography combined with speckle interferometry2001Ingår i: Second International Conference on Experimental Mechanics, 29 November - 1 December 2000, Singapore, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2001Konferensbidrag (Refereegranskat)
  • 80. Molin, Nils-Erik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Andersson, A.
    Luleå tekniska universitet.
    Digital speckle photography combined with speckle interferometry2000Ingår i: Proceedings of the IOP Applied Optics and Opto-Electronics Conference: Loughborough, 2000, IOP Publishing Ltd , 2000Konferensbidrag (Refereegranskat)
  • 81. Molin, Nils-Erik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Svanbro, Angelica
    Speckle photography combined with speckle interferometry2004Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 41, nr 4, s. 673-686Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By combining speckle interferometry (SI) measurements with speckle photography, the fringe visibility can be kept high despite the presence of a large bulk or rotating motion of the object. This combined technique improves the usability and measuring range of both pulsed and phase-stepped Sl-methods. This paper reviews the theory of fringe formation in Sl and shows some recent applications of this combined technique

  • 82. Molin, Nils-Erik
    et al.
    Svanbro, Angelica
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Combined digital speckle photography (DSP) and interferometry2001Ingår i: Second international conference on experimental mechanics, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2001Konferensbidrag (Refereegranskat)
    Abstract [en]

    A general problem in optical metrology is to measure a deformation field when this field is added to a translation or a rotational motion. Methods like Speckle Photography (SP) do handle large rigid body motions but the results might be of too poor accuracy to resolve the deformation field. Interferometric methods on the other hand might measure the deformation field but the bulk motion makes the fringes disappear. By combining Digital Speckle Photography, Dsp, (also called digital correlation) with Speckle Interferometry, SI, (also called ESPI, DSPI, TV holography, pulsed TV holography) or with shearography (TV shearography) such measuring situations can be mastered.

  • 83.
    Morris, A.
    et al.
    E.ON UK, Power Technology, Ratcliffe-on-Soar, Nottingham.
    Kourmpetis, M.
    Department of Mechanical Engineering, Imperial College London.
    Dear, I.D.
    School of Engineering and Design, Brunel University, Uxbridge.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dear, J.P.
    Department of Mechanical Engineering, Imperial College London.
    Optical strain monitoring techniques for life assessment of components in power generation plants2007Ingår i: Proceedings of the Institution of mechanical engineers. Part A, journal of power and energy, ISSN 0957-6509, E-ISSN 2041-2967, Vol. 221, nr 8, s. 1141-1152Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The current paper presents the ongoing development of a combination of two methods for monitoring creep strain in mechanical components of electrical power generation plants. This is to obtain, during plant shut-down maintenance periods, needed data to assess the remaining life of installed steam pipes and other components. Related to this research, but not reported on in the current paper, is the development of monitoring for detection of the onset of fatigue and other failure processes in wind turbine generator blades. The auto-reference creep management and control (ARCMAC) system uses precision optics and a charge-coupled device (CCD) camera for uniaxial and biaxial strain measurement. Digital image correlation (DIC) is employed to obtain strain distribution data about the ARCMAC point-to-point monitored sites. These and other systems are being developed to obtain a more comprehensive range of life assessment data. This is mostly for assessing longevity of steam pipes and other components in power stations that are subject to demanding and hostile operational environments. These permanently installed monitoring systems need to be rugged to withstand the demanding heat and mechanical forces to which they are subjected and of a compact design so they can be sited in difficult-to-access locations. This is one of the advantages of the combined ARCMAC and DIC system that is further being developed. These systems are essential for cost-effective management of power plant operation and maintenance and for achieving reliable continuity of service.

  • 84.
    Morris, A.
    et al.
    E.ON UK, Nottingham.
    Puri, A.
    Imperial College London.
    Maharaj, C.
    Imperial College London.
    Kourmpetis, M.
    Imperial College London.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dear, J.P.
    Imperial College London.
    Predicting lifetimes of components in power station engineering plant2007Ingår i: Energy Materials, ISSN 1748-9237, Vol. 2, nr 2, s. 89-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today, there is increasing demand for power station plant to be operated cost effectively and to reliably maintain required electrical supply. This requires minimising the risk of having to shut-down the plant for emergency repairs. Of paramount importance, is plant operating integrity and well prepared and executed maintenance programmes. This paper reports on the recent developments to the Auto-Reference Creep Management & Control (ARCMAC) system used by E.ON UK. This includes achieving biaxial strain measurement with increased resolution and the employment of Digital Image Correlation

  • 85.
    Morris, A.
    et al.
    E.ON UK.
    Puri, A.
    Imperial College London.
    Maharaj, C.
    Imperial College London.
    Kourmpetis, M.
    Imperial College London.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dear, J.P
    Imperial College London.
    Predicting lifetimes of components in power station engineering plant2007Ingår i: Baltica VII: management and maintenance for power plants, Helsinki-Stockholm-Helsinki, 12-14 June, 2007. / [ed] Juha Veivo; Pertti Auerkari, VTT Building and Transport , 2007, Vol. 1, s. 70-82Konferensbidrag (Refereegranskat)
    Abstract [en]

    Today, there is increasing demand for power station plant to be operated cost effectively and to reliably maintain required electrical supply. This requires minimising the risk of having to shut-down the plant for emergency repairs. Of paramount importance, is plant operating integrity and well prepared and executed maintenance programmes. This paper reports on the recent developments to the Auto-Reference Creep Management & Control (ARCMAC) system used by E.ON UK. This includes achieving biaxial strain measurement with increased resolution and the employment of Digital Image Correlation (DIC).

  • 86.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Fotoakustisk holografisk avbildning av kolbaserade absorbenter i en vävnadsfantom2011Konferensbidrag (Refereegranskat)
  • 87.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Photoacoustic holographic imaging of absorbers embedded in silicone2011Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, nr 17, s. 2551-2558Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Light absorbing objects embedded in silicone have been imaged using photoacoustic digital holography. The photoacoustic waves were generated using a pulsed Nd:YAG laser, λ=1064 nm, and pulse length=12 ns. When the waves reached the silicone surface, they were measured optically along a line using a scanning laser vibrometer. The acoustic waves were then digitally reconstructed using a holographic algorithm. The laser vibrometer is proven to be sensitive enough to measure the surface velocity due to photoacoustic waves generated from laser pulses with a fluence allowed for human tissue. It is also shown that combining digital holographic reconstructions for different acoustic wavelengths provides images with suppressed noise and improved depth resolution. The objects are imaged at a depth of 16.5 mm with a depth resolution of 0.5 mm.

  • 88.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sjödahl, Mikael
    Photoacoustic waves generated in blood studied using pulsed digital holography2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 16, s. 3053-3058Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We studied photoacoustic waves using pulsed digital holography. The acoustic waves were generated in a reindeer blood target by absorption of an IR laser pulse, λ=1064 nm and pulse length=12 ns. The acoustic pressure waves were then imaged in water using a second collimated laser pulse at λ=532 nm2 μs after the first IR pulse. Quantitative information on acoustic wave properties such as three-dimensional shape and pressure distribution was calculated by applying the inverse Radon transform on the recorded projection. The pressure pulse had a flat and sharp front parallel with the blood surface, which indicates that the pressure was generated at the blood surface. The generated pressure was proportional to the laser fluence with the proportionality constant equal to 1.8±0.3 cm-1. According to existing data, the proportionality constant should be 1.4 cm-1 for oxygenated human blood, which made our calculations probable

  • 89. Olsson, Erik
    et al.
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Zipser, Lothar
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Franke, Heinz
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Scattered ultrasound fields measured by scanning laser vibrometry2003Ingår i: Optical Measurement Systems for Industrial Inspection III: 23 - 26 June 2003, Munich, Germany / [ed] Wolfgang Osten, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2003, s. 717-727Konferensbidrag (Refereegranskat)
    Abstract [en]

    A scanning laser Doppler vibrometer is used to make quantitative measurements of 2D ultrasound fields in air. The laser light traverses the measurement volume to and from a rigid reflector and determines the velocity of the change in optical path length, which with constant geometry only depends on the changes in index of refraction. Assuming adiabatic conditions, the refractive index rate is proportional to the sound pressure rate and quantitative measures of the sound field are possible to achieve. The emitted or scattered ultrasound being measured origins from a source or object outside the recording area. Using phase conjugation the sound field is then digitally reconstructed outside the recording area, and the reconstructed phase and intensity reveals the location of the source or object. The combination of several such reconstructions of ultrasound fields of different wavelengths, so called wavelength scanning, provides an intensity map that very accurately gives the position of the source. This opens many new possibilities to study hidden or unknown sound sources or scattering objects

  • 90.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D Selective imaging of sound sources in air from 1D laser vibrometry measurements2009Ingår i: Digital Holography and Three-Dimensional Imaging: OSA Technical Digest (CD), Optical Society of America, 2009, artikel-id JTuB6Konferensbidrag (Refereegranskat)
    Abstract [en]

    Digital holographic and tomographic reconstruction algorithms have been used for imaging of sound sources. Making the tomographic reconstruction first produces images with higher quality. Higher resolution and selective imaging is obtained by using multiple frequencies.

  • 91. Olsson, Erik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Zipser, Lothar
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction2006Ingår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 45, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multifrequency digital holographic reconstructions of primary sound sources embedded in scattering media are demonstrated. The sound field is measured with a scanning laser Doppler vibrometer (LDV) and broadening of the spectral content of the sound source is achieved by tuning the primary ultrasound (US) transducer around its resonance frequency. The results show that combining the complex amplitudes from the different frequency reconstructions results in a reduced susceptibility to multiple scattered sound and makes possible a quite thorough localization of the primary sound source. The depth resolution obtained is 11 US frequencies. This depth sensitivity is improved even further to only 2.8 wavelengths by applying a filter determined from the standard deviation over the phases

  • 92.
    Paulsson, Lars
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kato, Jun-ichi
    Optical Engineering Laboratory, The Institute of Physical and Chemical Research, RIKEN!, Wako.
    Yamaguchi, Ichirou
    Optical Engineering Laboratory, The Institute of Physical and Chemical Research, RIKEN!, Wako.
    Temporal phase unwrapping applied to wavelength-scanning interferometry2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 19, s. 3285-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate the use of temporal phase unwrapping in combination with wavelength-scanning interferometry. Two unwrapping strategies are considered: fitting to a reversed exponential sequence and complex Fourier-transform ranging. Measurement of a 10-μm step by use of an external-cavity laser diode is discussed

  • 93.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bergström, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dual-wavelength holographic shape measurement with iterative phase unwrapping2011Ingår i: Optical Measurement Systems for Industrial Inspection VII / [ed] Peter H. Lehmann; Wolfgang Osten; Kay Gastinger, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2011, s. 80820B-Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to measure the shape of a large number of identical components in a manufacturing industry we propose a method where digital holography is used to capture an image of the object and then the shape of the object is achieved by using information from the CAD-model. The holographic recording of the object is done using dual wavelengths giving a synthetic wavelength of about 400 μm. This gives a phase map where the phase intervals represent a depth distance on the object of about 0.2 mm. To find the shape of the object the phase map has to be unwrapped. Since the surface contains discontinuities we use information from the CAD-model of the measured object and unwrap the phase iteratively. The result becomes a digital point representation of the measured surface that can either be used just as a description of the object shape or as a way to describe how well the object has been manufactured compared to the CAD-model. The measurement process that is proposed is adapted for on-line purposes; hence it is fast and reliable.

  • 94.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bergström, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Optisk formmätning för användning on-line i tillverkningsprocesser2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 88-Konferensbidrag (Övrigt vetenskapligt)
  • 95.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Simplified model for light scattering from granular materials with varying moisture content2013Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, nr 17, s. 4006-4012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reflection measurements were performed on dry and moistened sand grains and glass spheres, respectively. A simple model for determining the water content is proposed from looking at the reflection distribution in the plane of incidence. The model is a combination of two sheared cosine-functions and consists of only two parameters. One parameter controls whether the reflection is mainly in the forward or backward direction. The former is true when the water content is high and the latter is true when the material is dry. The other parameter gives an idea of the homogeneity of the material.

  • 96.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase errors due to speckles in laser fringe projection2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 11, s. 2047-2053Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When measuring a three-dimensional shape with triangulation and projected interference fringes it is of interest to reduce speckle contrast without destroying the coherence of the projected light. A moving aperture is used to suppress the speckles and thereby reduce the phase error in the fringe image. It is shown that the phase error depends linearly on the ratio between the speckle contrast and the modulation of the fringes. In this investigation the spatial carrier method was used to extract the phase, where the phase error also depends on filtering the Fourier spectrum. An analytical expression for the phase error is derived. Both the speckle reduction and the theoretical expressions for the phase error are verified by simulations and experiments. It was concluded that a movement of the aperture by three aperture diameters during exposure of the image reduces the speckle contrast and hence the phase error by 60%. In the experiments, a phase error of 0.2 rad was obtained.

  • 97.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sjödahl, Mikael
    Phase errors in speckle reduced laser fringe projection2010Ingår i: Speckle 2010: optical metrology : 13 - 15 September 2010, Florianópolis, Brazil / [ed] Armando Albertazzi Gonçalves, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2010, s. 73871E-Konferensbidrag (Refereegranskat)
    Abstract [en]

    When measuring 3D-shape with triangulation and projected interference fringes it is of interest to reduce the phase error in the fringe pattern. A study has been carried out concerning parameters that will affect the phase error and an analytical expression has been derived. It is concluded that the phase error depends on the speckle contrast, C, and the modulation, M, of the fringes and since the phase in this investigation is determined using the spatial carrier method the phase error also depends on the filtering of the Fourier spectrum. To reduce the phase error this work has been focusing on suppressing the speckle contrast. For this the method with a moving aperture is used; a disk with several apertures is rotated in the aperture plane of the camera lens. To verify the derived expression for the phase error and the method to suppress speckles both numerical simulations and experiments have been performed. In the measurements made it was concluded that after an aperture movement of three aperture diameters the speckle contrast and hence the phase error was reduced by 60 %. A phase error of 0.15 radians was obtained in the experiments, thus approximately 1/40 of a fringe period

  • 98.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sjödahl, Mikael
    Shape measurement with one fringe pattern recording including a digital master2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 14, s. 2622-2629Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a method in which the 3D shape of an object can be measured and compared to the shape of the digital master of the object, e.g., the computer-aided design model. The measurement is done using a stereo camera system and a single projected fringe pattern. Because the digital master is available, i.e., the expected shape is known, only one projection and image recording is necessary; thus, the method becomes fast. The idea in this work is to find homologous points in the cameras, i.e., points corresponding to the same object point, using the object information. An algorithm to find the homologous points is presented and a method to calculate shape is described. Given the ambiguity due to the fact that the phase in the images is wrapped, there is a maximum deviation from the master that can be correctly detected. An analytical expression for this deviation is derived. Results from the shape measurement of an object both with and without deviations from the digital master are also presented. In these measurements, where the measurement volume is approximately 1 dm3 and the fringe period on the object plane is about 1 mm, the accuracy is ≈± 40 μm, and a deviation of max ≈± 1.6mm can be correctly detected.

  • 99.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Incoherent imaging of coherent projection2007Konferensbidrag (Övrigt vetenskapligt)
  • 100.
    Saarela, Juha
    et al.
    Department of Electrical and Information Engineering and Infotech Oulu, University of Oulu.
    Löfqvist, Torbjörn
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ramser, Kerstin
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Olsson, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Detection of laser induced dielectric breakdown in water using a laser doppler vibrometer2010Ingår i: Central European Journal of Physics, ISSN 1895-1082, E-ISSN 1644-3608, Vol. 8, nr 2, s. 235-241Artikel i tidskrift (Refereegranskat)
    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.

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