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  • 1990-1994  (3)
  • 1850-1859
  • Laser ultrasonics  (2)
  • fracture  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 271-277 
    ISSN: 1573-4862
    Keywords: Laser ultrasonics ; directional ultrasound ; arrays of optical fibers ; thermoacoustic arrays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Some aspects of the generation and detection of ultrasound with laser beams are presented. The objective of the study is (1) to present some experimental results on the generation of ultrasound with an array of optical fibers, (2) to discuss the possibility of generating directional surface waves with acousto-optic scanning in a very narrow frequency band, thus increasing the signal-to-noise ratio, and (3) to discuss the feasibility of the directional detection of ultrasound by using an array of optical fibers as a receiver, also with the goal of increasing the signal-to-noise ratio.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 13 (1994), S. 33-42 
    ISSN: 1573-4862
    Keywords: Laser ultrasonics ; Lamb waves ; Fresnel arrays ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An experimental technique is proposed to analyze and control laser-generated Lamb waves propagating in aluminum plates. The technique consists in forming on the surface of the specimen an array of concentric arc sources by passing the laser beam through a Fresnel lens. The spacing between the illuminated arcs produces a “forcing wavelength” for which only a few specific frequencies (those which satisfy the dispersion relation) can propagate in the sample. Dispersion curves can be obtained by measuring the frequency content of the received signals for a range of wavenumbers. The technique offers a relatively high signal-to-noise ratio because of the narrow-band nature of the method and because of the confocal geometry of the source distribution. Reasonably good agreement is obtained between theoretical and experimental dispersion curves especially for the lower modes, thus showing that the proposed technique may have some potential for some specific applications in laser ultrasonic nondestructive evaluation.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 13 (1994), S. 63-73 
    ISSN: 1573-4862
    Keywords: Concrete ; acoustic emission ; fracture ; damage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The study presented in this paper is placed in the context of the frequency analysis of acoustic emission in concrete. The purpose is to study the ability to identify an acoustic emission event by deducing its spectrum from a detected signal. The identification is carried out progressively so as to separate the various functions involved in the acoustic emission process, and to approach the usual conditions of acoustic emission processing during fracture tests of concrete specimens. Impulses of different forms are generated on the surface of concrete test specimens, and the signals detected are analyzed. The identification of signals takes into account the frequency response of the transducers and the wave attenuation as function of the frequency.
    Type of Medium: Electronic Resource
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