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  • 1. Andersson, Angelica
    et al.
    Mohan, N. Krishna
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    TV shearography: quantitative measurement of shear-magnitude fields by use of digital speckle photography2000Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 16, s. 2565-2568Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Digital speckle photography combined with TV shearography is developed for precise measurement of the magnitude of the shear field in a linear shear configuration. As an application the method is implemented to determine the slope-change variations of a three-dimensional object with TV shearography in which the shear magnitude is obtained with the digital speckle photography technique

  • 2.
    Benckert, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Lars
    Molin, Nils-Erik
    Fresnel diffraction of a Gaussian laser beam by polished metal cylinders1990Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 29, nr 3, s. 416-421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A laser beam touching the periphery of a polished cylinder is subjected to both diffraction and reflection. Inthe area where diffracted light and reflected light interact the resulting intensity distribution differs from thepattern predicted by diffraction theory for a sharp edge. The difference increases with cylinder radius. Inthis paper it is shown that a good description of the resulting intensity pattern is obtained by adding thereflected light amplitude to the diffracted amplitude as predicted by the Fresnel-Kirchhoff theory for a sharpedge.

  • 3.
    Benckert, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsson, Mikael
    Molin, Nils-Erik
    Measuring 3-D displacement of a surface using the white light speckle technique1986Inngår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, s. 207-210Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When measuring in plane surface deformation using white light speckle photography, errors will arise if an out of plane displacement is present. Here it is shown that stereoscopic photography resolves this problem and makes the measurement of true in plane displacements possible. A rigid body translation is also introduced to determine unambiguously the direction of the displacement

  • 4.
    Benckert, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsson, Mikael
    Molin, Nils-Erik
    Measuring true in-plane displacements of a surface by stereoscopic white-light speckle photography1987Inngår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 26, nr 2, s. 167-169Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When in-plane surface deformations are measured using white-light speckle photography, errors arise if an out-of-plane displacement is present. Stereoscopic photography resolves this problem and makes possible the measurement of true in-plane displacements. A rigid-body translation is introduced to determine unambiguously the direction of the displacement

  • 5.
    Benckert, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    White light speckle: a non-contact method for the measurement of strain- and velocity fields1985Rapport (Annet vitenskapelig)
  • 6.
    Edlund, G.
    et al.
    Luleå tekniska universitet.
    Wikander, G.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The visualization of modes in a circular cochlear model by hologram interferometry1978Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 59, nr 22, s. 299-303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work has been carried out to study the possibilities of using hologram interferometry to examine the mechanical behavior of the inner ear. The purpose was to make a model of the cochlea with a curved and stiff basilar membrane and to look for both travelling wave and standing wave patterns. The level of excitation is approximately the same as found in actual hearing when scaled to model dimensions and hence much lower than in most previous model studies. Also in contrast to previous studies, curvature effects are investigated

  • 7. Fällström, Karl-Evert
    et al.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    Wåhlin, Anders
    Transient bending waves in plates studied by hologram interferometry1989Inngår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 29, nr 4, s. 378-387Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Propagating bending waves are studied in plates made of aluminum and wood. The waves are generated by the impact of a ballistic pendulum. Hologram interferometry, with a double pulsed ruby laser as the light source, is used to record the out of plane motion of the waves. Elliptic-like fringes visualize differences in wave speed for different directions in the anisotropic plate and circular ones are obtained for the isotropic plate. The experimental data for the isotropic plate compare favorably with analytical results derived from the Kirchhoff-plate equation with a point impact of finite duration. A similarity variable is found when starting conditions are modeled as a Dirac pulse in space and time, that brings new understanding to the importance of specific parameters for wave propagation in plates. A formal solution is obtained for a point force with an arbitrary time dependence. For times much larger than the contact time, the plate deflection is shown to be identical to that from a Dirac pulse applied at the mean contact time. A method for determining material parameters, and the mean contact time, from the interferograms is hence developed.

  • 8. Fällström, Karl-Evert
    et al.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transient bending waves in anisotropic plates studied by hologram interferometry1989Inngår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 29, nr 4, s. 409-413Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Propagating bending waves are studied in plates made of glass-fiber reinforced polyester. The waves are generated by the impact of a ballistic pendulum. Hologram interferometry, with a double pulsed ruby laser as light source, is used to record the out of plane motion of the waves. The interferograms have an elliptic-like symmetry for an orthotropic plate, while the wave pattern for a symmetric angle-ply reinforced plate has a symmetry about the axes of reinforcements. Experimental data are compared on one hand to analytical results obtained by assuming that the orthotropic plate can be described as if isotropic along the main axes, and on the other hand to numerical results from calculations using the finite-element method. The effective Young's modulus raised to power 1/4 is shown to be an important parameter for the description of the dispersive wave pattern. A defect in the plate alters the wave pattern in the interferograms significantly. This may have technical use.

  • 9. Fällström, Karl-Evert
    et al.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Nondestructive method to determine material properties in orthotropic plates1987Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 8, nr 2, s. 103-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An electronic speckle pattern interferometer (ESPI) is used to determine modes of vibration in rectangular, orthotropic, free-free-plates; that is using a noncontact, nondestructive, optical method. It is shown, using the finite element method (FEM), that each of the first three modes of vibration in rectangular orthotropic plates has a strong dependence upon only one of the main material parameters, namely the in-plane shear modulus and the two Young's moduli, respectively. With this one-variable dependence it is a simple task to determine the effective material parameters. This method has several obvious advantages compared to the use of test bars and it can be extended to give a measure of the damping parameters and probably also be used for production control. Preliminary results are presented and discussed

  • 10. Fällström, Karl-Evert
    et al.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Schedin, Staffan
    Luleå tekniska universitet.
    Wåhlin, Anders
    Mechanical and thermal effects in a steel plate impacted by a focused laser pulse1997Inngår i: Nondestructive Testing and Evaluation, ISSN 1058-9759, E-ISSN 1477-2671, Vol. 13, nr 5, s. 293-307Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A short laser pulse from a 1 J ruby laser is focused at a steel plate. The effect will be that the material surface at the impact point becomes very rapidly heated. Metal vapour leaves the surface at a very high velocity. That is, both a mechanical impulse and local thermal energy are transferred to the plate. The mechanical impulse creates propagating bending waves in the plate, which in turn creates transient sound waves in the surrounding air. The heated spot at the plate surface creates thermal stresses in the plate which give rise to an out-of-plane deformation of the plate. This deformation is added up to the propagating bending waves. These effects are studied in experiments using pulsed holographic interferometry.

  • 11. Granqvist, S.
    et al.
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hertegård, S.
    Speckle photography applied to detect structure displacement in high-speed laryngoscopic recordings2003Konferansepaper (Fagfellevurdert)
  • 12.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Tatar, Kourosh
    Granström, Jan
    Molin, Nils-Erik
    Jansson, E.V.
    Department of Speech, Music and Hearing, Royal Institute of Technology (KTH).
    Laser vibrometry measurements of vibration and sound fields of a bowed violin2006Inngår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, nr 4, s. 635-644Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser vibrometry measurements on a bowed violin are performed. A rotating disc apparatus, acting as a violin bow, is developed. It produces a continuous, long, repeatable, multi-frequency sound from the instrument that imitates the real bow-string interaction for a 'very long bow'. What mainly differs is that the back and forward motion of the real bow is replaced by the rotating motion with constant velocity of the disc and constant bowing force (bowing pressure). This procedure is repeatable. It is long lasting and allows laser vibrometry techniques to be used, which measure forced vibrations by bowing at all excited frequencies simultaneously. A chain of interacting parts of the played violin is studied: the string, the bridge and the plates as well as the emitted sound field. A description of the mechanics and the sound production of the bowed violin is given, i.e. the production chain from the bowed string to the produced tone

  • 13.
    Isaksson, Anna
    et al.
    Luleå tekniska universitet.
    Saldner, Henrik
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Influence of enclosed air on vibration modes of a shell structure1995Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 187, nr 3, s. 451-466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experiments show that enclosed air in a thin walled structure affects some modes of vibration significantly. Air coupling between vibrating sides of the structure cannot (always) be neglected and frequencies cannot be predicted if calculations are performed as if in a vacuum. As a first attempt to include the enclosed air in a FE model of a violin body, the elastic properties of the air are modelled as a set of one dimensional non-interacting elastic members (columns of air) connecting opposite sides of the orthotropic shell structure. This admittedly oversimplified (but easy to formulate) model must be used with great care, since it neglects the three-dimensional wave behaviour of the enclosed air. A lower limit of allowed frequencies is that which corresponds to a wavelength in air which is much greater than a characteristic length of the object. For the violin this lower limit is less than about 600 Hz. Optical modal analysis of the real, physical, violin model has been performed by using electronic holography. Calculated modes of vibration are compared with experimental ones. For the lowest eigenmodes a good agreement between measured and calculated frequencies is reached despite the simple air model used. Modal shapes remain surprisingly unaffected. For some engineering calculations the simple one-dimensional model might be used.

  • 14. Jansson, E
    et al.
    Moral, Alonso
    Frydén, L.
    Niewczyk, B.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Runnemalm, Anna
    Saldner, Henrik
    Wåhlin, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    On the acoustical function of the violin1997Inngår i: 25. Congresso nazionale : Perugia, 21-23 maggio 1997 : atti / Associazione italiana di acustica, 1997Konferansepaper (Fagfellevurdert)
  • 15.
    Jansson, Erik V.
    et al.
    Kungliga tekniska högskolan, KTH.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Optical modal analysis compared to modal analysis with digital electronic equipment1988Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 84, nr 1, s. 136-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hologram interferometry and speckle interferometry have introduced powerful tools for "optical modal analysis." The vibration amplitudes at a single frequency are recorded simultaneously for all points of a surface. The excitation position and frequency are adjusted to give a normal mode by watching the vibration patterns in real time. In the common modal analysis with digital electronic equipment, the vibrations of a single point as a function of time are recorded for all frequencies simultaneously via the impulse response. Impulse responses for a large number of points are measured, analyzed, and recalculated to extract the normal modes. Investigations of two modes of a complicated object (a violin) using both methods showed differences. The position of the dominating antinodes agreed, but the distribution of the vibration amplitudes and especially the nodal lines did not always agree. The differences seem to depend mainly on methods. The differences imply that great cautiousness is motivated in interpreting unknown vibration modes of objects with complicated structures and boundaries. The real time observation with the optical modal analysis offers hereby advantages

  • 16. Jansson, E.V.
    et al.
    Fryden, L.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hansen, C.
    Niewczyk, B.
    Influence of top and back plate stiffness on low frerquency modes of a violin1997Inngår i: Acoustics - High Tatras '97: proceedings of the 31st international acoustical conference, Zvolen: TU Zvolen , 1997Konferansepaper (Fagfellevurdert)
  • 17. Jansson, E.V.
    et al.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Fundamental violin acoustics related to quality2002Inngår i: Proceedings of the 32nd International Acoustical Conference: European Acoustics Association (EAA) Symposium "Acoustics Banská Štiavnica 2002" ; September 10 - 12, 2002, Slovakia, Zvolen: TU Zvolen , 2002Konferansepaper (Fagfellevurdert)
  • 18.
    Jansson, E.V.
    et al.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    On tuning of free violin plates1989Inngår i: C A S Journal, ISSN 1053-7694, Vol. 1, nr 3, s. 27-30Artikkel i tidsskrift (Fagfellevurdert)
  • 19.
    Jansson, E.V.
    et al.
    Kungliga tekniska högskolan, KTH.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Saldner, Henrik O.
    Luleå tekniska universitet.
    On eigenmodes of the violin: electronic holography and admittance measurements1994Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 95, nr 2, s. 1100-1105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present experimental investigation, using recently assembled advanced electro-optical equipment for vibration analysis of three violins, was conducted to seek answers to three questions. A general or global question: Which parts of the violin body are vibrating the most? And two questions related to tonal quality: Are basic low-frequency vibration modes of a musically superior instrument different from those of an inferior violin? Can some special vibration properties be found to support the ``bridge hill?'' Optically obtained vibration modes were recorded as well as frequency responses in the form of admittance measurements. The investigation showed that the vibration modes found earlier are representative both for the inferior violin and the musically superior instruments, although discrepancies can be seen, both in eigenmode shapes and admittance responses. The experimental results are also in quite good agreement with published results of the modal analysis of a violin. Further, the experimental results indicate that the transversal vibrations are mainly within the plates, but at low frequencies, the vibrations of the edges and of the ribs can be large and in-plane as well as transversal. At higher frequencies, the transversal vibration amplitudes are small at the plate edges and larger inside. The top plate tends to have the largest amplitude of vibrations. In the 2.5-kHz range the violin with the most clear ``bridge hill'' tends to have the largest vibrations of the plates.

  • 20. Lindberg, B.
    et al.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, E.V.
    Kungliga tekniska högskolan, KTH.
    Experiments with transient waves in a violin bridge1994Inngår i: C A S Journal, ISSN 1053-7694, Vol. 2, nr 6, s. 24-27Artikkel i tidsskrift (Fagfellevurdert)
  • 21.
    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 measurement2000Inngår i: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 10, nr 2, s. 147-159Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 22.
    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 deformations2000Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 4, s. 573-577Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 23.
    Mohan, N. Krishna
    et al.
    Indian Institute of Technology, Madras.
    Saldner, Henrik O.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Combined phase stepping and sinusoidal phase modulation applied to de-sensitized TV holography1996Inngår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 7, s. 712-715Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many TV holography techniques use phase stepping between frames. In vibration studies, sinusoidal phase modulation extends the use of these techniques. A simple technique is presented to combine phase stepping and phase modulation (bias vibration) on a single mirror. It is applied to a de-sensitized TV holographic (DTV) configuration for quantitative evaluation of the large vibration amplitudes.

  • 24.
    Mohan, Nandigana K
    et al.
    Indian Institute of Technology.
    Saldner, Henrik
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Recent applications of TV holography and shearography1996Inngår i: Laser Interferometry VIII: Applications, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 1996Konferansepaper (Fagfellevurdert)
    Abstract [en]

    TV holography is used to measure the components of the deformation vector, whereas TV shearography is used to obtain the derivatives of the displacement components. In this paper, we highlight a novel approach to split the CCD into two parts which enables to extract entirely different information from a single experimental configuration. A holo-shearography configuration provides simultaneous measurement of out-of-plane displacement and its slope change in real time. Similarly a holo-comparative configuration multiplexes an out-of-plane displacement configuration and a comparative interferometric configuration. Few experimental results using both these configurations are presented. In addition TV holography is implemented for vibration studies on an Indian classical musical instrument--Veena. The preliminary studies on a model veena are demonstrated

  • 25.
    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 analysis2000Inngår 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, 2000Konferansepaper (Fagfellevurdert)
  • 26. Mohan, N.K.
    et al.
    Saldner, Henrik
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Electronic shearography applied to static and vibrating objects1994Inngår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 108, nr 4-6, s. 197-202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An optical shearography configuration is presented which can be used for the measurement of slope change for static and vibrating objects in real time. Displacement and vibration amplitude fields are extracted from the shear data, which is an useful property in noise environments. In a Michelson interferometer set-up the two arms are provided with a phase-shift mirror and a bias modulation mirror to carry out the numerical evaluation of the measured deformation. Experimental results for an edge- clamped aluminium plate are presented

  • 27. Mohan, N.K.
    et al.
    Saldner, Henrik O.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Electronic speckle pattern interferometry for simultaneous measurement of out-of-plane displacement and slope1993Inngår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 18, nr 21, s. 1861-1863Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An optical configuration is presented for simultaneous measurement of out-of-plane displacement and slope change in electronic speckle pattern interferometry. Experimental results for a rectangular plate clamped along the edges and loaded at the center are presented.

  • 28.
    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 measurements2001Inngår i: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 40, nr 12, s. 2780-2787Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 29.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A pulsed TV-holography system: development and some results1998Inngår i: International Conference on Applied Optical Metrology: 8 - 11 June 1998, Balatonfüred, Hungary, SPIE - International Society for Optical Engineering, 1998, s. 148-153Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In TV holography (also called ESPI or DSPI), temporal phase stepping is a common method. It allows quantitative evaluation of high quality interferograms of quasi-static events and of harmonic vibrations. To study transient and rapid events, pulsed lasers with pulses of short duration (about 25 ns) are instead employed. This 'freezes' most mechanical and acoustic events, such as propagating transient bending waves and acoustic fields. A recently developed pulsed TV holography system allows all-electronic recording and evaluation of interferograms. Two object state recordings are captured on subsequent frames using a CCD-camera connected to a PC computer. The time separation can be set from 20 microseconds to 700 microseconds using a double pulsed ruby laser. Phase maps are calculated and unwrapped to give 3D-plots of the deformation or pressure fields. Recordings of bending wave propagation in plates and transient sound fields in air will illustrate the system performance.

  • 30.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Applications of whole field interferometry in mechanics and acoustics1999Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 31, nr 2, s. 93-111Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A description is given of fringe formation in holographic interferometry, in electronic speckle pattern interferometry, in electro-optic or TV holography and for a newly developed system for pulsed TV-holography. A numerical example, which simulates the equations describing the different techniques, is included. A strain measuring system using defocused digital speckle photography is described. Experiments showing mode shapes of musical instruments, transient bending wave propagation in beams and plates as well as sound pressure fields in air are included

  • 31.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hologram interferometry as a tool to investigate transient waves in mechanics1989Inngår i: SSecond International Conference on Holographic Systems, Components, and Applications: 11 - 13 September, Bath, UK, London: Institution of Engineering and Technology, 1989Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Hologram interferometry was introduced in 1965 by Powell and Stetson. With a double pulsed ruby laser as light source, this technique is a very competitive tool for the study of transient events like the propagation of bending waves in plates and shells, to visualize shock waves in phase objects like air or water or just to record nice double exposure holograms of modes of vibration in optical modal analysis. In the following a number of experiments to visualize wave propagation in solids and liquids are presented

  • 32.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Optical Methods for Acoustics and Vibration Measurements2014Inngår i: Springer Handbook of Acoustics, New York: Encyclopedia of Global Archaeology/Springer Verlag, 2014, s. 1139-1163Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Modern optical methods applicable to vibration analysis, monitoring bending-wave propagation in plates and shells as well as propagating acoustic waves in transparent media such as air and water are described. Field methods, which capture the whole object field in one recording, and point measuring (scanning) methods, which measure at one point (small area) at a time (but in that point as a function of time), will be addressed. Temporally, harmonic vibrations, multi-frequency repetitive motions and transient or dynamic motions are included. Interferometric methods, such as time-average and real-time holographic interferometry, speckle interferometry methods such as television (TV) holography, pulsed TV holography and laser vibrometry, are addressed. Intensity methods such as speckle photography or speckle correlation methods and particle image velocimetry (PIV) will also be treated.

  • 33.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Optical methods in acoustics2002Inngår i: Proceedings of the 32nd International Acoustical Conference: European Acoustics Association (EAA) Symposium "Acoustics Banská Štiavnica 2002" ; September 10 - 12, 2002, Slovakia, Zvolen: TU Zvolen , 2002Konferansepaper (Fagfellevurdert)
  • 34.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transient bending waves in plates, pipes and shells studied by pulsed hologram interferometry1992Inngår i: Laser in der Technik: Vorträge des 10. Internationalen Kongresses Laser 91 = Laser in engineering / [ed] Wilhelm Waidelich, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1992, s. 3-7Konferansepaper (Fagfellevurdert)
  • 35.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transient sound fields in air from impacted structures, visualised with pulsed TV holography1997Inngår i: Acoustics - High Tatras '97: proceedings of the 31st international acoustical conference, Zvolen: TU Zvolen , 1997Konferansepaper (Fagfellevurdert)
  • 36.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transient wave fields in mechanics and acoustics measured by pulsed holographic interferometry1995Inngår i: Proceedings of the 15th International Congress on Acoustics: Trondheim, Norway, 26-30 June 1995, Trondheim: Tapir Akademisk Forlag, 1995Konferansepaper (Fagfellevurdert)
  • 37.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Visualization of sound fields with application to musical instruments2003Inngår i: Proceedings of SMAC 03: Stockholm Music Acoustics Conference, August 6-9, 2003 / [ed] Roberto Bresin, Stockholm: Kungl. Tekniska Högskolan , 2003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Modern optical measuring methods have the advantage of being contact less, non-disturbing and whole field methods. They often are quantitative and they present "pictures". In the following some modern optical, holographic, speckle and interferometric methods that visualize and measure vibrations and sound fields of musical instruments are presented and discussed

  • 38.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Visualizing instrument vibrations and sound fields2002Inngår i: C A S Journal, ISSN 1053-7694, Vol. 4, nr 5, s. 21-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A review is given of recent applications of modern optical techniques to visualize structural vibrations and sound fields in musical instruments. The advantage of optical techniques in this context is that they give an image of the measured quantity without disturbing the measurements. The techniques considered are usually referred to as TV holography (also called Digital or Electronic Speckle Pattern Interferometry, abbreviated ESPI or DSPI), phase modulated TV holography, pulsed TV holography (pulsed holographic interferometry) and scanning Laser Doppler Vibrometry (LDV).

  • 39.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Fällström, Karl-Evert
    Wåhlin, Anders
    On Bending Wave Propagation and Thermal Deformation of Laser Impacted Plates1995Inngår i: Proceedings of the International Symposium on Advanced Technology in Experimental Mechanics '95: ATEM '95, 1995Konferansepaper (Fagfellevurdert)
  • 40.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Holmgren, Mats
    Luleå tekniska universitet.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jansson, Erik
    Department of Speech Communication and Music Acoustics, KTH.
    Eigenmodes of av violin body1990Inngår i: Proceedings / Nordic Acoustical Meeting 90 - NAM 90: 11-13, 1990 Luleå, Sweden / [ed] Ulrik Sundbäck, Luleå: CENTEK , 1990, s. 421-428Konferansepaper (Fagfellevurdert)
  • 41.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, E.V.
    Kungliga tekniska högskolan, KTH.
    Transient wave propagation in wooden plates for musical instruments1989Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 85, nr 5, s. 2179-2184Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transient bending waves in three wooden plates are studied. A rectangular flat spruce plate (from a guitar top plate) and two arched violin plates (of spruce and maple, respectively) are impacted by a small ballistic pendulum. The impact point is at the center of the guitar plate and the bridge position of the violin plates. A sequence of holographic interferograms of the events is recorded using a double pulsed ruby laser as the light source. The holographic setup is a standard one. The elliptical shape of the interference fringes shows that wood is strongly anisotropic. The shape of the propagating pulse changes with time, which shows the dispersive behavior of bending waves in plates. A solution of the isotropic Euler plate equation for a flat plate is compared to experimental results of the guitar plate, assuming that this description is adequate along the main axes of this orthotropic plate. The shape of the propagating wave pattern and the elliptical rather than circular shape of the violin imply an interesting coincidence

  • 42.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jansson, Erik V.
    Royal Institute of Technology.
    Parameters of violin plates and their influence on the plate modes1988Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 83, nr 1, s. 281-291Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noncontact measuring methods and numerical calculations are used in a study of musical instruments. First, a simple method to determine the material parameters of a blank to a violin plate is presented. Eigenmodes of rectangular free-free violin wooden blanks are determined using optical nondestructive methods, Chladni patterns, or tapping. Assuming orthotropic material, the first three eigenmodes for such a blank are calculated using the finite element method (FEM). It is shown that the frequency of each eigenmode depends on separate elastic parameters. With this one variable dependence, it is a simple task to determine effective material parameters for quarter-cut standard wooden blanks when the frequencies and mass are known. Second, the violin maker's problem with the influence of material and geometrical parameters on the vibration modes is investigated. Numerical models and corresponding real violin plates are made from the spruce and the maple blanks. Good agreement between calculated and experimentally obtained plate modes is found. Calculations with a 10% variation in each parameter are thereafter used to give information about the influence of overall plate thickness variation, of local thickness variations, of changes in arch-height, and of material parameters. Third, boundary conditions for the plates when glued to the ribs are examined in a pilot experiment.

  • 43.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Saldner, Henrik
    Jansson, E.V.
    Eigenmodes and electronic holography on three violins1994Inngår i: SMAC 93: proceedings of the Stockholm Music Acoustics Conference July 28-August 1, 1993 / [ed] Anders Friberg, Stockholm: Royal Swedish Academy of Music , 1994Konferansepaper (Fagfellevurdert)
  • 44.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Schedin, Staffan
    Jansson, E.V.
    Gren, Per
    Transient response of the violin body when impacted at the bridge and at the strings1997Inngår i: ISMA'97, Institute of Acoustics , 1997Konferansepaper (Fagfellevurdert)
  • 45. 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 interferometry2001Inngår i: Second International Conference on Experimental Mechanics, 29 November - 1 December 2000, Singapore, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2001Konferansepaper (Fagfellevurdert)
  • 46. 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 interferometry2000Inngår i: Proceedings of the IOP Applied Optics and Opto-Electronics Conference: Loughborough, 2000, IOP Publishing Ltd , 2000Konferansepaper (Fagfellevurdert)
  • 47. 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 interferometry2004Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 41, nr 4, s. 673-686Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 48. 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 interferometry2001Inngår i: Second international conference on experimental mechanics, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2001Konferansepaper (Fagfellevurdert)
    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.

  • 49.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wåhlin, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Jansson, Erik V
    Kungliga tekniska högskolan, KTH.
    Transient wave response of the violin body revisited1991Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 90, nr 4, s. 2192-2195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this investigation, the dispersive, transient wave propagation field of the top plate of a complete violin excited by a mechanically induced pulse at the top of the bridge is presented. A similar investigation has previously been made for excitation parallel with the top plate and is now completed with excitation perpendicular to the plate. From presented interferograms, it is seen that the top plate initially deforms in a nonsymmetric two-pole with centers at the two bridge feet. Shortly thereafter the two poles (valleys) are joined into one, but after 0.30 ms the displacement is still nonsymmetric with maximum motion at the bridge foot closest to the excitation point. From the measurements it can be concluded that for excitation parallel with the top plate, the plate between the f-holes acts mainly as a dipole, but with excitation perpendicular the same part acts mainly as a monopole. Thus the excitation of the top plate when playing the violin depends on the angle of the bow in relation to the top plate and should influence the tone character

  • 50.
    Molin, Nils-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wåhlin, Anders
    Jansson, E.V.
    Luleå tekniska universitet.
    Transient wave response of the violin body1990Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 88, nr 5, s. 2479-2481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at the f-holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments

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