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Benckert, Lars
Publications (10 of 27) Show all publications
Johansson, E.-L., Benckert, L. & Sjödahl, M. (2008). Improving the quality of phase maps in phase object digital holographic interferometry by finding the right reconstruction distance (ed.). Paper presented at . Applied Optics, 47(1), 1-8
Open this publication in new window or tab >>Improving the quality of phase maps in phase object digital holographic interferometry by finding the right reconstruction distance
2008 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, no 1, p. 1-8Article in journal (Refereed) Published
Abstract [en]

Improved quality of phase maps in pulsed digital holographic interferometry is demonstrated by finding the right reconstruction distance. The objective is to improve the optical phase information when the object under study is a phase object and when it is out of focus, leading to low contrast fringes in the phase map. A numerical refocusing is performed by introducing an ideal lens as a multiplication by a phase field in the Fourier domain, and then a region of maximum speckle correlation is found by comparing undisturbed and disturbed sub-images in different refocused imaging planes. After finding the right reconstruction distance, a phase map of high visibility is constructed. By this technique a 30 % reduction of the phase error for a flow of Helium gas and a 50 % reduction of the phase error for a weak thin lens were obtained, which resulted in a significant improvement of the visual appearance of the phase maps.

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-13156 (URN)10.1364/AO.47.000001 (DOI)000252757600001 ()2-s2.0-40749154411 (Scopus ID)c5706960-9762-11dc-ad7f-000ea68e967b (Local ID)c5706960-9762-11dc-ad7f-000ea68e967b (Archive number)c5706960-9762-11dc-ad7f-000ea68e967b (OAI)
Note
Validerad; 2008; 20071120 (evalena)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Johansson, E.-L., Benckert, L. & Sjödahl, M. (2004). Improving optical phase acqusition by numerical refocusing of pulsed TV interferograms (ed.). In: (Ed.), (Ed.), Proceedings of ICEM 12: . Paper presented at International Conference on Experimental Mechanics : 29/08/2004 - 02/09/2004.
Open this publication in new window or tab >>Improving optical phase acqusition by numerical refocusing of pulsed TV interferograms
2004 (English)In: Proceedings of ICEM 12, 2004Conference paper, Published paper (Refereed)
Abstract [en]

In optical measurement situations where holographic interferometry is used the optical phase information maybe poor because of too large object deformation. The speckle pattern displacement must be less than the specklesize in the image plane to obtain high contrast fringes. A phase object that is out of focus in a laser speckle fieldmay give large speckle displacements in comparison to the situation where no phase object is present. Acombination of pulsed TV holography, digital speckle photography and a numerical refocusing technique isshown to improve the optical phase information. A flow of helium gas has been used as a test object. When thegas is out of focus an interferogram of low contrast fringes is obtained, but after refocusing high contrast fringesare obtained. The phase gradients may also be determined from the improved phase data. These phase gradientsare compared to the ones obtained in another way from two speckle displacement fields in two different imagingplanes after numerical refocusing of the speckle fields. The two phase gradients are similar

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-29390 (URN)2dcd4350-bb56-11db-b560-000ea68e967b (Local ID)2dcd4350-bb56-11db-b560-000ea68e967b (Archive number)2dcd4350-bb56-11db-b560-000ea68e967b (OAI)
Conference
International Conference on Experimental Mechanics : 29/08/2004 - 02/09/2004
Note
Godkänd; 2004; 20061026 (cira)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Johansson, E.-L., Benckert, L. & Sjödahl, M. (2004). Phase object data obtained by pulsed TV holography and defocused laser speckle displacement (ed.). Paper presented at . Applied Optics, 43(16), 3235-3240
Open this publication in new window or tab >>Phase object data obtained by pulsed TV holography and defocused laser speckle displacement
2004 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, no 16, p. 3235-3240Article in journal (Refereed) Published
Abstract [en]

Transient events in optically transparent media occur in many engineering applications. Using pulsed TV holography to capture a laser speckle field propagated through an optical disturbance makes it possible to obtain both the position and the phase gradients of the disturbance. The technique depends on the fact that speckles transmitted through an optical disturbance will be displaced by an amount that depends on the relation of the defocus to the object. First the speckle field is captured holographically, without and with disturbance present. Then the recorded fields are numerically refocused in a computer to a number of different focal planes. With a cross-correlation technique a number of speckle displacement fields are obtained, and from them the data about the disturbance are obtained. So far the technique has been shown to work for thin objects

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-6897 (URN)10.1364/AO.43.003235 (DOI)000221717800005 ()2-s2.0-2942538592 (Scopus ID)53a954d0-6f73-11db-962b-000ea68e967b (Local ID)53a954d0-6f73-11db-962b-000ea68e967b (Archive number)53a954d0-6f73-11db-962b-000ea68e967b (OAI)
Note
Validerad; 2004; 20060926 (cira)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Johansson, E.-L., Benckert, L. & Sjödahl, M. (2004). Phase object data obtained from defocused laser speckle displacement (ed.). Paper presented at . Applied Optics, 43(16), 3229-34
Open this publication in new window or tab >>Phase object data obtained from defocused laser speckle displacement
2004 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, no 16, p. 3229-34Article in journal (Refereed) Published
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

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-8102 (URN)10.1364/AO.43.003229 (DOI)000221717800004 ()2-s2.0-2942539080 (Scopus ID)68dda540-6f73-11db-962b-000ea68e967b (Local ID)68dda540-6f73-11db-962b-000ea68e967b (Archive number)68dda540-6f73-11db-962b-000ea68e967b (OAI)
Note
Validerad; 2004; 20060926 (cira)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Johansson, E.-L., Benckert, L. & Sjödahl, M. (2003). Evaluation of phase objects by pulsed TV holography and defocused speckle displacement (ed.). In: (Ed.), Wolfgang Osten (Ed.), Optical Measurement Systems for Industrial Inspection III: 23 - 26 June 2003, Munich, Germany. Paper presented at Optical Measurement Systems for Industrial Inspection : 23/06/2003 - 26/06/2003 (pp. 556-561). Bellingham, Wash.: SPIE - International Society for Optical Engineering
Open this publication in new window or tab >>Evaluation of phase objects by pulsed TV holography and defocused speckle displacement
2003 (English)In: 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, p. 556-561Conference paper, Published paper (Refereed)
Abstract [en]

An optical measurement method is presented for the evaluation of phase objects. Pulsed TV holography in combination with digital speckle photography gives the possibility to study transient events. The phase object is placed in front of a diffuser, on which a CCD camera is focused. Holograms are recorded, with and without the phase object present. The speckle patterns are reconstructed and transformed to different imaging planes using a phase field for propagation. Speckle displacement fields are then calculated for the different imaging planes, which visualise the change of refractive index or phase gradients caused by the phase object. Together with the phase information in the hologram even more information is obtained. A flow of helium gas and a positive weak lens are used as phase objects in two test experiments

Place, publisher, year, edition, pages
Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2003
Series
Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X ; 5144
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-26898 (URN)10.1117/12.500582 (DOI)000184287300061 ()2-s2.0-0141720415 (Scopus ID)028d7c50-bb56-11db-b560-000ea68e967b (Local ID)819450146 (ISBN)028d7c50-bb56-11db-b560-000ea68e967b (Archive number)028d7c50-bb56-11db-b560-000ea68e967b (OAI)
Conference
Optical Measurement Systems for Industrial Inspection : 23/06/2003 - 26/06/2003
Note
Validerad; 2003; 20120123 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-07-10Bibliographically approved
Johansson, E.-L., Benckert, L. & Gren, P. (2003). Particle image velocimetry (PIV) measurements of velocity fields at an organ pipe labium (ed.). In: (Ed.), Roberto Bresin (Ed.), Proceedings of SMAC 03: Stockholm Music Acoustics Conference, August 6-9, 2003. Paper presented at Stockholm Music Acoustics Conference : 06/08/2003 - 09/08/2003. Stockholm: Kungl. Tekniska Högskolan
Open this publication in new window or tab >>Particle image velocimetry (PIV) measurements of velocity fields at an organ pipe labium
2003 (English)In: Proceedings of SMAC 03: Stockholm Music Acoustics Conference, August 6-9, 2003 / [ed] Roberto Bresin, Stockholm: Kungl. Tekniska Högskolan , 2003Conference paper, Published paper (Refereed)
Abstract [en]

A pilot experiment is presented that measures velocity fields in two planes at a blown organ pipe labium for a fundamental tone at 260 Hz. The sound pressure is also measured at the same time as the velocity fields are registered. This makes it possible to follow the change of the velocity field as the sound pressure varies with time. The methods used are stereoscopic particle image velocimetry (PIV) and two-dimensional particle image velocimetry. The difference between the methods is that the first one measures three velocity components by use of two CCD cameras and the second one measures two velocity components with one camera. A double pulsed Nd:YAG laser is used as illuminating source. It gives short light pulses (~13 ns) necessary to resolve the quite high air velocity (~10 m/s). Results show that it is possible to follow a travelling vortex at the organ pipe labium in time as the sound pressure changes. The stereoscopic measurements show that the velocity fields are three-dimensional. The measurements have shown to be repeatable.

Place, publisher, year, edition, pages
Stockholm: Kungl. Tekniska Högskolan, 2003
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-39704 (URN)e8e5d6c0-bb56-11db-b560-000ea68e967b (Local ID)e8e5d6c0-bb56-11db-b560-000ea68e967b (Archive number)e8e5d6c0-bb56-11db-b560-000ea68e967b (OAI)
Conference
Stockholm Music Acoustics Conference : 06/08/2003 - 09/08/2003
Note
Godkänd; 2003; 20061026 (cira)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Dumortier, L., Dahl, J., Benckert, L. & Kjellström, B. (1999). Evaluation of particle tracking velocimetry for studies of the flow in a boiler furnace (ed.). In: (Ed.), (Ed.), Applied Modelling and Simulation, International conference: . Paper presented at International Conference on Applied Modeling and Simulation : 01/09/1999 - 03/09/1999.
Open this publication in new window or tab >>Evaluation of particle tracking velocimetry for studies of the flow in a boiler furnace
1999 (English)In: Applied Modelling and Simulation, International conference, 1999Conference paper, Published paper (Refereed)
National Category
Energy Engineering Applied Mechanics
Research subject
Energy Engineering; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-39437 (URN)e346c270-b52e-11db-bf94-000ea68e967b (Local ID)e346c270-b52e-11db-bf94-000ea68e967b (Archive number)e346c270-b52e-11db-bf94-000ea68e967b (OAI)
Conference
International Conference on Applied Modeling and Simulation : 01/09/1999 - 03/09/1999
Note
Godkänd; 1999; 20070205 (ysko)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Sjödahl, M., Benckert, L., Molin, N.-E. & Marklund, O. (1999). Optical metrology at Luleå University of Technology, LTU, Sweden (ed.). In: (Ed.), S.G. Pandalai (Ed.), Recent research developments in optical engineering: (pp. 279-293). Paper presented at . Trivandrum: Research Signpost
Open this publication in new window or tab >>Optical metrology at Luleå University of Technology, LTU, Sweden
1999 (English)In: Recent research developments in optical engineering, Trivandrum: Research Signpost, 1999, p. 279-293Chapter in book (Other academic)
Place, publisher, year, edition, pages
Trivandrum: Research Signpost, 1999
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-20522 (URN)59f2a350-bd50-11dd-a7c4-000ea68e967b (Local ID)59f2a350-bd50-11dd-a7c4-000ea68e967b (Archive number)59f2a350-bd50-11dd-a7c4-000ea68e967b (OAI)
Note
Godkänd; 1999; 20081128 (cira)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Huntley, J., Withworth, A., Field, A., Benckert, L., Sjödahl, M., Thesken, J. & Henriksson, A. (1995). High resolution moir photography: application to impact and dynamic fracture on polymers and composites (ed.). In: (Ed.), (Ed.), Impact and dynamic fracture of polymers and composites: papers presented at the ESIS European Symposium on Impact and Dymnamic Fracture of Polymers and Composites, Porto Cervo, Sardinia, Italy. Paper presented at ESIS European Symposium on Impact and Dynamic Fracture of Polymers and Composites : 20/09/1993 - 22/09/1993. : Institution of Mechanical Engineers
Open this publication in new window or tab >>High resolution moir photography: application to impact and dynamic fracture on polymers and composites
Show others...
1995 (English)In: Impact and dynamic fracture of polymers and composites: papers presented at the ESIS European Symposium on Impact and Dymnamic Fracture of Polymers and Composites, Porto Cervo, Sardinia, Italy, Institution of Mechanical Engineers, 1995Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Institution of Mechanical Engineers, 1995
Series
ESIS publication ; 19
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-38993 (URN)d8fe51e0-ffb9-11db-b19d-000ea68e967b (Local ID)d8fe51e0-ffb9-11db-b19d-000ea68e967b (Archive number)d8fe51e0-ffb9-11db-b19d-000ea68e967b (OAI)
Conference
ESIS European Symposium on Impact and Dynamic Fracture of Polymers and Composites : 20/09/1993 - 22/09/1993
Note
Godkänd; 1995; 20070511 (cira)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Melin, L. G., Thesken, J., Nilsson, S. & Benckert, L. (1995). Tensile impact delamination of a cross-ply interface studied by Moire photography (ed.). Paper presented at . Fatigue & Fracture of Engineering Materials & Structures, 18(10), 1101-1114
Open this publication in new window or tab >>Tensile impact delamination of a cross-ply interface studied by Moire photography
1995 (English)In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 18, no 10, p. 1101-1114Article in journal (Refereed) Published
Abstract [en]

Impact induced delamination along a cross-ply interface in carbon fiber/epoxy laminates is studied by high resolution moire photography. The specimens were loaded in a tensile split-Hopkinson bar giving mode I dominated fracture, and a high speed camera captures images during loading and delamination. The resulting moire fringes are analysed to produce full field displacement maps of the area around the loaded and propagating crack tips. The displacement map prior to failure shows good agreement with numerical solutions, calculated using a 3D self-adaptive p-version of the finite element method. The calibrated finite element solutions are then used to give further information about the matrix cracking zone size around the crack tip and the energy release rate. In comparison to quasi-static loading, tensile impact loading was found to increase the failure load and the resulting energy release rates; some physical explanations for this behaviour are discussed. It was concluded that the procedures presented have good potential for further determination of rate dependent material properties in carbon/fiber epoxy composites

National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-6388 (URN)10.1111/j.1460-2695.1995.tb00842.x (DOI)A1995TB82800005 ()2-s2.0-0029388067 (Scopus ID)49e38d00-bb57-11db-b560-000ea68e967b (Local ID)49e38d00-bb57-11db-b560-000ea68e967b (Archive number)49e38d00-bb57-11db-b560-000ea68e967b (OAI)
Note
Godkänd; 1995; 20061026 (cira)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
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