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  • 1.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    3D selektiv avbildning av ljudkällor2007Conference paper (Other academic)
  • 2.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Digital holographic reconstructions of ultrasound from laser vibrometry recordings2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    If sound and noise from an engine, say a lawn mower, is to be reduced, it is of advantage to know from which part of the machine the noise is coming. An interesting medical application for localization of sound sources is optoacoustic imaging of tissue. A localization of the sound source in this case could be an useful tool for an early detection of high blood concentrations around tumors. Besides localization of primary sources, reconstruction of scattered or diffusive reflected fields could be a useful tool for studying opaque materials and objects. This could reveal abnormalities such as cavities or regions of different materials or densities in an object. In this thesis a scanning laser vibrometer is used to make quantitative two-dimensional measurements of ultrasound (US) 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 at 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. These recordings are used for digital reconstruction of the acoustic fields by use of phase conjugation. Both recordings and reconstructions of the sound fields are performed for several wavelengths by tuning the primary US transducer around its resonance frequency. Combining several reconstructions for different wavelengths enhances the depth resolution. This resolution is improved even further by applying a phase filter. It is shown that this reconstruction technique makes possible a very thorough localization of the primary source even for highly scattered US-fields.

  • 3.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Digitala rekonstruktioner av ljudkällor från optiska mätningar av ljudfält2004Conference paper (Other academic)
  • 4.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Measurements of sound fields using laser vibrometry and digital reconstructions of the sound fields2004Conference paper (Other academic)
  • 5.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Scattered ultrasound fields measured by scanning laser vibrometry2003In: SMD 03 : Svenska mekanikdagar : Göteborg 13-15 augusti 2003, Göteborg: Svenska nationalkommittén för mekanik , 2003Conference paper (Other academic)
  • 6.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Selective imaging of sound sources in air using phase-calibrated multiwavelength digital holographic reconstructions2007In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 46, 75801- p.Article in journal (Refereed)
    Abstract [en]

    A method for selective imaging using multiwavelength digital holographic reconstructions and the phase response of a sound source is demonstrated. Several sound measurements, using laser vibrometry, and digital reconstructions are made for several frequencies of the sound field emitted from two ultrasound transducers with different phase characteristics. Adding the reconstructed complex amplitudes together and applying a filter derived from the standard deviation over the phases for the different reconstructions makes possible a selective imaging of primary sources. When the imaging method is calibrated for a certain phase response, only primary sources with that particular phase response are imaged. Other sources and unwanted speckles are efficiently suppressed. The depth resolution obtained is 3 wavelengths.

  • 7.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Selektiv avbildning av primära ljudkällor2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, 35- p.Conference paper (Other academic)
  • 8.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Simuleringar och mätningar av ljudfält från en fiol2005In: Svenska Mekanikdagar 2005, Lund: Lund Institute of Technology , 2005Conference paper (Other academic)
  • 9.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sound source localization from laser vibrometry recordings2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Acoustic holography deals with a typical inverse problem, to obtain the unknown from something that is known. From measurements of sound, most often using microphone arrays, reconstructions of the sound field are made in an attempt to find out what causes the sound. The successfulness of such analyses is highly dependent on the quality of the reconstructed images, where factors like noise and spatial resolution are of importance. Also, when using microphones for measurements of the sound it is inevitable that the sound field is disturbed. Such disturbances will always have an impact on the reconstructions, even though in most cases the effects are negligible. In this thesis laser vibrometry for the purpose of sound measurements has been investigated and evaluated. Since it is an optical method it has the great advantage of allowing the sound to be measured without being disturbed. The 1D quantitative data it provides can be used without any preparation for the 2D numerical propagation of sound fields. Further on, the measurement data can also be used in order to obtain a 2D or 3D tomographic reconstruction of the sound field. A multi-wavelength method is also presented, which efficiently suppresses noise and increases the spatial depth resolution in sound field reconstructions. The sound is measured and reconstructed for several frequencies. When adding these reconstructions they will only add up constructively in positions corresponding to a sound source. This way noise in the resulting image is efficiently suppressed and the information of interest enhanced. Besides this "cleaning" of the image a large improvement of the depth-resolution is also achieved. While the in-plane size of the imaged sound source is diffraction-limited, the spatial depth-resolution can be improved by applying a filter based on the standard deviation calculated over the phase for the different reconstructions. Using this filter, sound sources can be imaged with a depth-size as small as only two wavelengths. Another advantage with this multi-wavelength technique is that it is possible to make a selective imaging of sound sources. When the measured sound originates from several different sound sources, a reconstruction can be made where only sound sources of a specific type are imaged. The other sound sources are treated as noise and are efficiently suppressed. This multi-wavelength method for imaging and localization of sound sources has so far proven to be very efficient and to have a low sensitivity to noise in the measurements.

  • 10.
    Olsson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Three-dimensional selective imaging of sound sources2009In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 48, no 3Article in journal (Refereed)
    Abstract [en]

    A technique for 3-D selective imaging of sound sources is described analytically and demonstrated experimentally. One-dimensional recordings of the acoustic field is measured using laser vibrometry. By applying digital holographic and tomographic algorithms to the acquired 1-D data, the full 3-D complex amplitude is reconstructed. The use of multiple frequencies in the spectral content of the acoustic field gives a number of advantages: higher spatial resolution, less noise in the reconstructed image, less sensitivity to noise in the measurements, and the possibility to perform selective imaging. Theory for all three steps-the measurement of sound using light, numerical propagation of waves, and finally the tomographic reconstruction in the process are given. In the experiment, the positions of three ultrasound sources are accurately determined and two different types of transducers are distinguished from each other. This multiwavelength technique could show to be a useful addition to optoacoustic imaging.

  • 11.
    Olsson, Erik
    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.
    Inferometrisk mätning av optoakustiska tryckvågor genererade i blod2009Conference paper (Other academic)
  • 12.
    Olsson, Erik
    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.
    Fotoakustisk holografisk avbildning av kolbaserade absorbenter i en vävnadsfantom2011Conference paper (Refereed)
  • 13.
    Olsson, Erik
    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.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Photoacoustic holographic imaging of absorbers embedded in silicone2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 17, 2551-2558 p.Article in journal (Refereed)
    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.

  • 14.
    Olsson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Sjödahl, Mikael
    Photoacoustic waves generated in blood studied using pulsed digital holography2010In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, no 16, 3053-3058 p.Article in journal (Refereed)
    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

  • 15. Olsson, Erik
    et al.
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    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 vibrometry2003In: 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, 717-727 p.Conference paper (Refereed)
    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

  • 16.
    Olsson, Erik
    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.
    3D Selective imaging of sound sources in air from 1D laser vibrometry measurements2009In: Digital Holography and Three-Dimensional Imaging: OSA Technical Digest (CD), Optical Society of America, 2009, JTuB6Conference paper (Refereed)
    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.

  • 17. Olsson, Erik
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Zipser, Lothar
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction2006In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 45, no 1Article in journal (Refereed)
    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

  • 18.
    Olsson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Tatar, Kourosh
    Sound field determination and projection effects using laser vibrometry2006In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 10, 2843-2851 p.Article in journal (Refereed)
    Abstract [en]

    Sound measurements using laser vibrometry have the advantage that field measurement can be obtained through scanning. It is a non-contact method that provides both qualitative and quantitative information. However, it must be noted that the measurement is an integral along the path of the probing beam. Some effects of this projection are investigated both through measurements and calculations. The sound field calculations are made from measured surface vibrations and they are in good agreement with the measured sound field. The calculations show that the projections very much depend on parameters such as integral depth, or probing depth, and the orientation of the sources. In addition to this, the calculated, or measured, amplitude experiences an enhancement which depends on the wavelength and the distance from the sound source. This enhancement can even result in increasing amplitude with distance. Even though this makes the quantitative data obtained not trustworthy, it is a benefit for the qualitative results which become clearer.

  • 19.
    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, 235-241 p.Article 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.

  • 20.
    Sjödahl, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Tatar, Kourosh
    Olsson, Erik
    Laser metrology in experimental mechanics2005In: 10th NOLAMP Conference: the 10th Nordic Laser Materials Processing Conference, 17-19 August 2005, Luleå Sweden / [ed] Alexander Kaplan, Luleå: Luleå tekniska universitet, 2005, 41-52 p.Conference paper (Refereed)
  • 21.
    Sjödahl, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Amer, Eynas
    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.
    Depth resolution of phase gradients using pulsed digital holography2010In: Biomedical optics (BIOMED): digital holography and three-dimensional imaging (DH) ; April 11 - 14, 2010, Miami, Florida, USA ; technical digest, Washington, DC: Optical Society of America, 2010Conference paper (Refereed)
    Abstract [en]

    technique to gain depth information from a single pair image-plane Digital Holographic recording of a transient phase object positioned between a diffuser and an imaging system has been demonstrated

  • 22.
    Sjödahl, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olsson, Erik
    Amer, Eynas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Depth-resolved measurement of phase gradients in a transient phase object field using pulsed digital holography2009In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 48, no 34, H31-H39 p.Article in journal (Refereed)
    Abstract [en]

    A technique to gain depth information from an image-plane digital holographic recording of a transient phase object positioned between a diffuser and an imaging system is demonstrated. The technique produces telecentric reconstructions of the complex amplitude throughout the phase volume using numerical lenses and the complex spectrum formulation of the diffraction integral. The in-plane speckle movements as well as the phase difference between the disturbed field and a reference field are calculated in a finite number of planes using a cross-correlation formulation. It is shown that depth information about in-plane phase gradients can be determined in two planes using reconstructed speckle fields from four different depths. In addition, the plane of optimum reconstruction for calculating the phase difference with maximum contrast is detected from the technique. The method is demonstrated on a measurement of a laser ablation process.

  • 23. Tatar, Kourosh
    et al.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Tomographic reconstruction of 3D ultrasound fields measured using laser vibrometry2007In: Experimental analysis of nano and engineering materials and structures: proceedings of the 13th International Conference on Experimental Mechanics, Alexandroupolis, Greece, July 1-6, 2007 / [ed] Emmanuel Gdoutos, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2007Conference paper (Refereed)
    Abstract [en]

    A method for obtaining the amplitude and phase distribution of an ultrasound field in air, using laser vibrometry and computed tomography, is described. Radiating ultrasound transducers causes pressure variations in the air, which lead to refractive index changes, which in turn can be recorded by the use of interferometric instruments like the laser vibrometer. This point measuring method for the measurement and visualization of sound fields was proposed by Zipser et al. [1, 2]. In order to measure the whole sound field, the laser beam is scanned over the area of interest. With this technique, the absolute phase of the field is obtained directly from the measurements while the amplitude needs some calculations using the Gladstone Dale equation [3]. Moreover, the obtained result using laser vibrometry for sound measurements is an integral of the sound field along the laser light path. The projection effects due to this integral were studied by Olsson and Tatar [4]. In this paper however, the projection property of the measurement method is taken into advantage. Tomographic 3D reconstruction of the sound field is obtained using several projections taken at different angles. The phase and the amplitude distributions of an ultrasound field due to several transducers, emitting at a frequency of 40 kHz, positioned both symmetrically and non-symmetrically are reconstructed.

  • 24. Wahba, Hamdy
    et al.
    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.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Digital holographic microscopy for the study of nano-fibers2013In: Optical Measurement Systems for Industrial Inspection VIII / [ed] Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, SPIE - International Society for Optical Engineering, 2013Conference paper (Refereed)
    Abstract [en]

    The advantages of digital holographic microscopy to record not only the intensity but also the optical phase are employed. The experimental arrangement comprises a Mach-Zehnder type interferometer with a microscopic objective of magnification 100x. The used camera is a 5 Mpixels Allied Vision Guppy Pro F-503 with a pixel pitch of 2.2 μm. The lateral magnification is set to about 200x based on the standard MIL-STD-150A 1951 USAF resolution test target. The dimensions of the aggregated natural cellulose nanowhisker fibers used are in the range of some hundreds of nanometers, which are positioned in the front of the microscopic objective using a 3D translation stage in the object arm of the holographic setup. The recorded off-axis holograms are refocused using the angular spectrum method. The reconstructed complex field is used to calculate optical phase and intensity distributions of the object at different reconstructions depths. The dimensions and orientation of the fibers can be evaluated from the optical field at different depths. Then, the shape and textures along the aggregated natural cellulose nanowhisker fiber can be presented in 3D space. The nano fiber found to have the dimensions of mean width 223 nm, depth 308 nm and length of 8.1 μm. Further, the mean local refractive index of the nano fibers can be calculated (n=1.501).

  • 25.
    Wahba, H.H.
    et al.
    Department of Physics, Faculty of Science, Damietta University, New Damietta City.
    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.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    High resolution digital holographic microscopy for the study of aggregated natural cellulose nanowhisker fibers2015In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 73, 69-74 p.Article in journal (Refereed)
    Abstract [en]

    In this paper, digital holographic (DH) microscopy demonstrates its ability to perform a full characterization of nanofibers. The high resolution and magnification of the presented method to study the nanofibers are tested using standard MIL-STD-150A 1951 USAF resolution test target. In this investigation, aggregated natural cellulose nanowhisker fibers are positioned in the front of the microscopic objective using a 3D translation stage in the object arm of DH setup. The recorded off-axis holograms are refocused using the angular spectrum method. The reconstructed complex field is used to calculate optical phase and intensity distributions of the object at different reconstruction depths. A simple algorithm is used to define the focused image with suitable accuracy. The dimensions and orientation of the fibers can be evaluated from the optical field at different depths. Then, the shape and textures along the aggregated natural cellulose nanowhisker fiber can be presented in a 3D space.

  • 26.
    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, 765-768 p.Conference 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.

  • 27.
    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, 5831-5838 p.Article 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

1 - 27 of 27
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