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  • 1
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    Quantitative broadband ultrasonic backscatter - An approach to nondestructive evaluation in acoustically inhomogeneous materials (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The use of a broadband backscatter technique to obtain the frequency dependence of the longitudinal-wave ultrasonic backscatter coefficient from a collection of scatterers in a solid is investigated. Measurements of the backscatter coefficient were obtained over the range of ultrasonic wave vector magnitude-glass sphere radius product between 0.1 and 3.0 from model systems consisting of dilute suspensions of randomly distributed crown glass spheres in hardened polyester resin. The results of these measurements were in good agreement with theoretical prediction. Consequently, broadband measurements of the ultrasonic backscatter coefficient may represent a useful approach toward characterizing the physical properties of scatterers in intrinsically inhomogeneous materials such as composites, metals, and ceramics, and may represent an approach toward nondestructive evaluation of these materials.
    Keywords: ACOUSTICS
    Type: Journal of Applied Physics; 52; Feb. 198
    Format: text
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  • 2
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    Kramers-Kronig relationship between ultrasonic attenuation and phase velocity (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Kramers-Kronig relations linking the attenuation and dispersion are presented for a linear acoustic system. These expressions are used as a starting point to derive approximate, nearly local expressions relating the ultrasonic attenuation at a specific frequency to the local frequency derivative of the phase velocity (i.e., dispersion). The validity of these approximate relationships is demonstrated in several acoustic systems exhibiting substantially different physical properties.
    Keywords: ACOUSTICS
    Type: Acoustical Society of America; vol. 69
    Format: text
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  • 3
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    Excitation of a Helmholtz resonator by a turbulent boundary layer (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A turbulent boundary layer on the fuselage of a glider is used to excite a Helmholtz resonator whose openings are comparable in size to the turbulent eddies in the boundary layer. The resonator was excited at both the Helmholtz frequency and a standing wave frequency. The level of the resonator response and the response frequency are the major results. A shift in the response frequency, compared to acoustic excitation, indicates an interaction of turbulent and acoustic motions and a modification of the orifice end correction. A strong excitation phenomenon occurs when the resonator and boundary layer are tuned, in which case turbulent eddies of about the orifice diameter in size flow past the orifice and impose a frequency equal to one of the resonant frequencies of the resonator.
    Keywords: ACOUSTICS
    Type: Acoustical Society of America; vol. 58
    Format: text
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  • 4
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    Ultrasonic dispersion (delta V/V) determined from mechanical resonance frequency shifts (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: With standing wave ultrasonic techniques, small changes in phase velocity which result from changes in some external parameter (e.g., temperature or magnetic field) have traditionally been determined by observing shifts in the mechanical resonance frequency of a composite resonator. Some previous investigators have assumed that the fractional change in velocity is equal to the fractional change in frequency. Substantially improved formulas for determining the dispersion are presented and one of these is shown to be much more accurate than all previous approximations. The results of simulated and actual experiments over wide ranges of dispersion, transducer loading parameter, and frequency are analyzed in order to compare the errors inherent in the various approximations.
    Keywords: ACOUSTICS
    Type: NASA-CR-142244 , Ultrasonics Symp.; Jan 01, 1974; St Louis, MO; United States
    Format: application/pdf
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  • 5
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    Optimizing signal-to-error ratio in standing wave ultrasonic measurements (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Standing wave ultrasonic techniques for the measurement of very small changes in acoustic attenuation and phase velocity are discussed. Enhanced sensitivity to these small changes was achieved by making the specimen part of a composite ultrasonic resonator. It was found that a point of maximum sensitivity on the response of such an ultrasonic resonator need not coincide with a point of maximum signal-to-error ratio. A model is presented and analyzed which takes into account error due to long term (low frequency) noise effects such as gain drifts and dc level shifts. This model yields a quantitative value for the signal-to-error ratio in which the signal is defined as the ideal change in the monitored response and the error as the difference between the experimentally measured change and the signal. The specific frequency dependent forms for the ultrasonic response and the sensitivity enhancement factor were used to predict the operating point on a mechanical resonance corresponding to maximum signal-to-error ratio.
    Keywords: ACOUSTICS
    Type: NASA-CR-142243
    Format: application/pdf
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  • 6
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    General relationships between ultrasonic attenuation and dispersion (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: General relationships between the ultrasonic attenuation and dispersion are presented. The validity of these nonlocal relationships hinges only on the properties of causality and linearity, and does not depend upon details of the mechanism responsible for the attenuation and dispersion. Approximate, nearly local relationships are presented and are demonstrated to predict accurately the ultrasonic dispersion in solutions of hemoglobin from the results of attenuation measurements.
    Keywords: ACOUSTICS
    Type: Acoustical Society of America; vol. 63
    Format: text
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  • 7
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    Ultrasonic dispersion determined from mechanical resonance frequency shifts (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: With standing wave ultrasonic techniques, small changes in phase velocity which result from changes in some external parameter (e.g., temperature or magnetic field) have traditionally been determined by observing shifts in the mechanical resonance frequency of a composite resonator. Some previous investigators have assumed that the fractional change in velocity is equal to the fractional change in frequency. We discuss quantitatively the errors involved in such an approach, showing that it leads to substantial inaccuracies when the loading effect of the transducer(s) cannot be neglected. Substantially improved formulas for determining the dispersion are presented and one of these is shown to be much more accurate than all previous approximations. The results of simulated and actual experiments over wide ranges of dispersion, transducer loading parameter, and frequency are analyzed in order to compare the errors inherent in the various approximations.
    Keywords: ACOUSTICS
    Type: Ultrasonics Symposium; Nov 11, 1974 - Nov 14, 1974; Milwaukee, WI
    Format: text
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