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  • 1.
    Engholm, Marcus
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    A narrowband ultrasonic spectroscopy technique for the inspection of layered structures2006Licentiate thesis, monograph (Other scientific)
  • 2.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ultrasonic Arrays for Sensing and Beamforming of Lamb Waves2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Non-destructive testing (NDT) techniques are critical to ensure integrity and safety of engineered structures. Structural health monitoring (SHM) is considered as the next step in the field enabling continuous monitoring of structures.

    The first part of the thesis concerns NDT and SHM using guided waves in plates, or Lamb waves, to perform imaging of plate structures. The imaging is performed using a fixed active array setup covering a larger area of a plate. Current methods are based on conventional beamforming techniques that do not efficiently exploit the available data from the small arrays used for the purpose. In this thesis an adaptive signal processing approach based on the minimum variance distortionless response (MVDR) method is proposed to mitigate issues related to guided waves, such as dispersion and the presence of multiple propagating modes. Other benefits of the method include a significant increase in resolution. Simulation and experimental results show that the method outperforms current standard processing techniques.

    The second part of the thesis addresses transducer design issues for resonant ultrasound inspections. Resonant ultrasound methods utilize the shape and frequency of the object's natural modes of vibration to detect anomalies. The method considered in the thesis uses transducers that are acoustically coupled to the inspected structures. Changes in the transducer's electrical impedance are used to detect defects. The sensitivity that can be expected from such a setup is shown to highly depend on the transducer resonance frequency, as well as the working frequency of the instrument. Through simulations and a theoretical argumentation, optimal conditions to achieve high sensitivity are given.

    List of papers
    1. Direction of Arrival Estimation of Lamb Waves Using Circular Arrays
    Open this publication in new window or tab >>Direction of Arrival Estimation of Lamb Waves Using Circular Arrays
    2011 (English)In: Structural Health Monitoring, ISSN 1475-9217, E-ISSN 1741-3168, Vol. 10, no 5, p. 467-480Article in journal (Refereed) Published
    Abstract [en]

     Uniform circular arrays (UCAs) with 360 degrees azimuthal coverage are very useful for structural health monitoring (SHM) of large planar structures. Difficulties encountered when working with Lamb waves include their dispersive and multi-modal nature. In this paper three different methods for estimating the direction-of-arrival (DOA) of incoming Lamb waves are compared and verified using simulated and experimental data. The previously proposed phase-mode excitation based beamformer is compared with two high-resolution spectral estimation techniques, the Capon method and the multiple signal classification method (MUSIC). Design consideration and guidelines for UCAs are presented. To experimentally evaluate the performance of the considered DOA methods a prototype array consisting of 16 separate pinducers arranged in a ring was constructed. The array was provided with an analog multiplexer that enabled recording signals received by the individual elements using a digital oscilloscope. The array was used for the reception of ultrasonic pulses sent by broadband piezoelectric transmitters and propagating in an aluminum plate. A selection of simulation and experimental results is presented showing the superior performance of the Capon beamformer.

    Keywords
    array signal processing, adaptive beamforming, guided waves, dispersive waves, multi-modal waves
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-122107 (URN)10.1177/1475921710379512 (DOI)000294287000002 ()
    Available from: 2010-04-07 Created: 2010-04-06 Last updated: 2017-12-12Bibliographically approved
    2. Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves
    Open this publication in new window or tab >>Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves
    2010 (English)In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 57, no 12, p. 2712-2724Article in journal (Refereed) Published
    Abstract [en]

    Lamb waves are considered a promising tool for the monitoring of plate structures. Active arrays employing beamforming techniques enables monitoring large areas of plate structures. Dispersion and multiple propagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on standard beamforming while reducing the effects of dispersion and multiple modes through frequency selectivity and transducer design. This paper presents a minimum variance distortionless response (MVDR) approach for Lamb waves using a uniform rectangular array (URA) and a single transmitter. Theoretically calculated dispersion curves are used to compensate for dispersion. The combination of the MVDR approach and the two dimensional array improves the suppression of interfering Lamb modes. The proposed approach is evaluated on simulated and experimental data and compared to the standard delay-and-sum (DAS) beamformer. It is shown that the MVDR algorithm performs better in terms of higher resolution and better sidelobe and mode suppression capabilities. Known issues of the MVDR approach, such as, signal cancellation in highly correlated environments, and poor robustness, are addressed using methods that have proven effective for the purpose in other fields of active imaging.

    Keywords
    imaging, array processing, adaptive beamforming, Lamb waves, guided waves, structural health monitoring, dispersive waves, multi-modal waves, mode suppression, 2d arrays
    National Category
    Signal Processing
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-122187 (URN)10.1109/TUFFC.2010.1745 (DOI)000285359100012 ()
    Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2018-06-08Bibliographically approved
    3. Imaging and Suppression of Lamb Modes Using Multiple Transmitter Adaptive Beamforming
    Open this publication in new window or tab >>Imaging and Suppression of Lamb Modes Using Multiple Transmitter Adaptive Beamforming
    (English)Manuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    Lamb waves have proven to be very useful for plate inspection since large areas of a plate can be covered from a fixed position. This ability makes them suitable for both inspection and structural health monitoring (SHM) applications. During the last decade research on the use of active arrays in combination with beamforming techniques have shown that a fixed array can be used to perform omni-directional monitoring over a large area of a plate structure. The dispersion and multiple ropagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on conventional, delay-and-sum (DAS) beamforming, while reducing the effects of dispersion and multiple modes through frequency selectivity and transducer design. The paper describes an adaptive beamforming technique using a minimum variance distortionless response beamforming (MVBF) approach for spatial Lamb wave filtering with multiple transmitters-multiple receivers. Dispersion is compensated for using theoretically calculated dispersion curves. Simulations are used for evaluating the performance of the technique for suppression of interfering Lamb modes, both with and without the presence of mode conversion using different array configurations. An aluminum plate with artificial defects is used for the experimental evaluation. A simple simulation model of the plate is used to compare the performance of different sizes of active arrays. The results show that the MVBF approach performs much better in terms of resolution and interfering mode suppression than the widely used standard beamformer.

    Keywords
    imaging, array processing, adaptive beamforming, Lamb waves, guided waves, structural health monitoring, dispersive waves, multi-modal waves, mode suppression, 2d arrays
    National Category
    Signal Processing Control Engineering
    Identifiers
    urn:nbn:se:uu:diva-122188 (URN)
    Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-04-12
    4. Narrowband ultrasonic spectroscopy for NDE of layered structures
    Open this publication in new window or tab >>Narrowband ultrasonic spectroscopy for NDE of layered structures
    2005 (English)In: INSIGHT, the Journal of The British Institute of Non-Destructive Testing, Vol. 47, p. 220-224Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-75944 (URN)
    Available from: 2006-03-10 Created: 2006-03-10 Last updated: 2011-01-11
    5. Designing and evaluating transducers for narrowband ultrasonic spectroscopy
    Open this publication in new window or tab >>Designing and evaluating transducers for narrowband ultrasonic spectroscopy
    2005 (English)In: 2005 IEEE Ultrasonics Symposium, 2005Conference paper, Published paper (Refereed)
    Identifiers
    urn:nbn:se:uu:diva-75987 (URN)
    Available from: 2006-03-10 Created: 2006-03-10 Last updated: 2010-04-07
    6. Designing and evaluating transducers for narrowband ultrasonic spectroscopy
    Open this publication in new window or tab >>Designing and evaluating transducers for narrowband ultrasonic spectroscopy
    2007 (English)In: NDT & E international, ISSN 0963-8695, E-ISSN 1879-1174, Vol. 40, no 1, p. 49-56Article in journal (Refereed) Published
    Abstract [en]

    Introduction of new composite materials in aerospace applications has created a demand for an efficient NDE technique. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered structures. In our previous work we have described the principle of narrowband ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. This paper is concerned with optimizing the NBUS setup consisting of a piezoelectric transducer coupled to a multi-layered structure. Differences in the electrical impedance of a piezoelectric transducer caused by variations of parameters of the inspected structure are estimated using an equivalent circuit model and a finite element analysis. The theoretical analysis presented in the paper results in design guidelines for NBUS transducers.

    Keywords
    Narrowband ultrasonic spectroscopy, Transducer design, Layered materials
    National Category
    Computer and Information Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-13355 (URN)10.1016/j.ndteint.2006.07.006 (DOI)000242411700007 ()
    Available from: 2008-01-22 Created: 2008-01-22 Last updated: 2018-01-12Bibliographically approved
  • 3.
    Engholm, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves2010In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 57, no 12, p. 2712-2724Article in journal (Refereed)
    Abstract [en]

    Lamb waves are considered a promising tool for the monitoring of plate structures. Active arrays employing beamforming techniques enables monitoring large areas of plate structures. Dispersion and multiple propagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on standard beamforming while reducing the effects of dispersion and multiple modes through frequency selectivity and transducer design. This paper presents a minimum variance distortionless response (MVDR) approach for Lamb waves using a uniform rectangular array (URA) and a single transmitter. Theoretically calculated dispersion curves are used to compensate for dispersion. The combination of the MVDR approach and the two dimensional array improves the suppression of interfering Lamb modes. The proposed approach is evaluated on simulated and experimental data and compared to the standard delay-and-sum (DAS) beamformer. It is shown that the MVDR algorithm performs better in terms of higher resolution and better sidelobe and mode suppression capabilities. Known issues of the MVDR approach, such as, signal cancellation in highly correlated environments, and poor robustness, are addressed using methods that have proven effective for the purpose in other fields of active imaging.

  • 4.
    Engholm, Marcus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Stepinski, Tadeusz
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Designing and evaluating transducers for narrowband ultrasonic spectroscopy2005In: 2005 IEEE Ultrasonics Symposium, 2005Conference paper (Refereed)
  • 5.
    Engholm, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signal Processing.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signal Processing.
    Designing and evaluating transducers for narrowband ultrasonic spectroscopy2007In: NDT & E international, ISSN 0963-8695, E-ISSN 1879-1174, Vol. 40, no 1, p. 49-56Article in journal (Refereed)
    Abstract [en]

    Introduction of new composite materials in aerospace applications has created a demand for an efficient NDE technique. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered structures. In our previous work we have described the principle of narrowband ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. This paper is concerned with optimizing the NBUS setup consisting of a piezoelectric transducer coupled to a multi-layered structure. Differences in the electrical impedance of a piezoelectric transducer caused by variations of parameters of the inspected structure are estimated using an equivalent circuit model and a finite element analysis. The theoretical analysis presented in the paper results in design guidelines for NBUS transducers.

  • 6.
    Engholm, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Direction of Arrival Estimation of Lamb Waves Using Circular Arrays2011In: Structural Health Monitoring, ISSN 1475-9217, E-ISSN 1741-3168, Vol. 10, no 5, p. 467-480Article in journal (Refereed)
    Abstract [en]

     Uniform circular arrays (UCAs) with 360 degrees azimuthal coverage are very useful for structural health monitoring (SHM) of large planar structures. Difficulties encountered when working with Lamb waves include their dispersive and multi-modal nature. In this paper three different methods for estimating the direction-of-arrival (DOA) of incoming Lamb waves are compared and verified using simulated and experimental data. The previously proposed phase-mode excitation based beamformer is compared with two high-resolution spectral estimation techniques, the Capon method and the multiple signal classification method (MUSIC). Design consideration and guidelines for UCAs are presented. To experimentally evaluate the performance of the considered DOA methods a prototype array consisting of 16 separate pinducers arranged in a ring was constructed. The array was provided with an analog multiplexer that enabled recording signals received by the individual elements using a digital oscilloscope. The array was used for the reception of ultrasonic pulses sent by broadband piezoelectric transmitters and propagating in an aluminum plate. A selection of simulation and experimental results is presented showing the superior performance of the Capon beamformer.

  • 7.
    Engholm, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Using 2-D Arrays for Sensing Multimodal Lamb Waves2010In: Conference on Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2010 San Diego, CA, MAR 08-11, 2010 / [ed] Shull PJ, Diaz AA, Wu AF, 2010, Vol. 7649Conference paper (Refereed)
    Abstract [en]

    Monitoring structural integrity of large planar structures requires normally a relatively dense network of uniformly distributed ultrasonic sensors. A 2-D ultrasonic phased array with all azimuth angle coverage would be extremely useful for the structural health monitoring (SHM) of such structures. Known techniques for estimating direction of arriving (DOA) waves cannot efficiently cope with dispersive and multimodal Lamb waves (LWs). In the paper we propose an adaptive spectral estimation technique capable of handling broadband LWs sensed by 2-D arrays, the modified Capon method. Performance of the technique is evaluated using simulated multiple-mode LWs, and verified using experimental data.

  • 8.
    Engholm, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Olofsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Imaging and suppression of Lamb modes using adaptive beamforming2011In: Smart materials and structures (Print), ISSN 0964-1726, E-ISSN 1361-665X, Vol. 20, no 8, p. 1-13Article in journal (Refereed)
    Abstract [en]

    Lamb waves have proven to be very useful for plate inspection because large areas of a plate can be covered from a fixed position. This capability makes them suitable for both inspection and structural health monitoring (SHM) applications. During the last decade, research on the use of active arrays in combination with beamforming techniques has shown that a fixed array can be used to perform omni-directional monitoring of a plate structure. The dispersion and multiple propagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on conventional, delay-and-sum (DAS) beamforming, while reducing the effects of multiple modes through frequency selectivity and transducer design. The paper describes an adaptive beamforming technique using a minimum variance distortionless response beamforming (MVBF) approach for spatial Lamb wave filtering with multiple-transmitter-multiple-receiver arrays. Dispersion is compensated for by using theoretically calculated dispersion curves. Simulations are used for evaluating the performance of the technique for suppression of interfering Lamb modes, both with and without the presence of mode conversion using different array configurations. A simple simulation model of the plate is used to compare the performance of different sizes of active arrays. An aluminum plate with artificial defects is used for the experimental evaluation. The results show that the MVBF approach performs a lot better in terms of resolution and suppression of interfering modes than the widely used standard beamformer.

  • 9.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Advanced beamforming of 2D arrays for structural health monitoring using Lamb waves2010In: 5th European Workshop on Structural Health Monitoring 2010, Sorrento, Italien, 2010Conference paper (Refereed)
  • 10.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signal Processing.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signal Processing.
    Design of piezoelectric transducers for health monitoring of composite aircraft structures2007In: Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2007 / [ed] Wu HF; Diaz AA; Shull PJ, 2007, p. OG531-OG531Conference paper (Refereed)
    Abstract [en]

    Composite structures have become a significant part of modern lightweight aircrafts. Contrary to the aluminum panels such structures are susceptible to catastrophic failure without noticeable forewarnings. One possible way of preventing catastrophic failures is integrating health monitoring systems in the critical composite structures of the aircraft. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered composite structures. In our previous works we have described the principle of narrow-band ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. It has been proven that the NBUS method is capable of detecting both artificial disbonds and real impact defects in carbon fiber composites.' In this paper we present design guidelines for optimizing narrow-band electromechanical impedance (NBE/MI) sensors that are to be integrated with a monitored composite structure. The NBE/MI sensor takes the form of a piezoelectric element bonded to the monitored structure. Parameter variations in the inspected structure result in the respective variations of the electrical impedance (admittance) of the piezoelectric sensor. Relation between the state of the inspected structure and the sensor's admittance is estimated using the network representation. Conclusions concerning the proper choice of the operating frequencies suitable for various structures are presented.

  • 11.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. Signals and systems.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. Signals and systems.
    Narrowband ultrasonic spectroscopy for inspecting multilayered aerospece structures2006Conference paper (Refereed)
  • 12.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    On the development and testing of a uniform circular array for structural health monitoring of planar structures2008In: Proceedings of the 4th European Workshop on Structural Health Monitoring, Krakow, Polen, 2008Conference paper (Refereed)
  • 13.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Piezoelectric circular array for structural health monitoring using plate waves2009In: 7th International Workshop on Structural Health Monitoring, Stanford, CA, 2009Conference paper (Refereed)
  • 14.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Structural health monitoring of composite structures for temperature varying applications2007Conference paper (Refereed)
  • 15.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uniform circular array for structural health monitoring of composite structures2008In: HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2008 / [ed] Kundu, T, 2008, p. A9352-A9352Conference paper (Refereed)
    Abstract [en]

    Phased array with all-azimuth angle coverage would be extremely useful in structural health monitoring (SHM) of planar structures. One method to achieve the 360 degrees coverage is to use uniform circular arrays (UCAs). In this paper we present the concept of UCA adapted for SHM applications. We start from a brief presentation of UCA beamformers based on the principle of phase mode excitation. UCA performance is illustrated by the results of beamformer simulations performed for the narrowband and wideband ultrasonic signals. Preliminary experimental results obtained with UCA used for the reception of ultrasonic signals propagating in an aluminum plate are also presented.

  • 16.
    Stepinski, Tadeusz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Engholm, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Olofsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Inspection of copper canisters for spent nuclear fuel by means of ultrasound, copper characterization, FSW monitoring with acoustic emission and ultrasonic imaging.2009Report (Other academic)
1 - 16 of 16
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