Ultrasonic scattering

SMT-2022 Effect of ultrasonic scattering on inspection of austenitic welds Or. M. Bieth Inadtuto for Advarteed Materlala... 

Achenbach, J. D. (1987). Flaw characterisation by ultrasonic scattering methods. In Solid mechanics research for quantitative non-destructive evaluation (ed. J. D. Achenbach and Y. Rajapakse), pp. 67-81. Nijhoff, Dordrecht. [264]... 

Attempts have also been made to include the effects of droplet flocculation in ultrasonic scattering theory [63]. 

At measunng point A where there is no Teflon sheet, the time-domain waveform reveals only one reflection from the bottom surface of the CFRP sample, and its power spectrum shows a decrease in the higher-frequency component above 20 MHz, as shown in Fig. 35a. The decrease is probably caused by ultrasonic scattering by the multilayered structure of CFRP cloth, since the half-wavelength at 20 MHz is about 75 pm, which is comparable to the thickness of CFRP cloth (70 pm). 

Ultrasonic Scattering from Emulsions during Depletion Flocculation... 

Some discontinuities may be identified by a conventional two-dimensional ultrasonic technique, from which the well-known C-scan image is the most popular. The C-scan technique is relatively easy to implement and the results from several NDE studies have been very encouraging [1]. In the case of cylindrical specimens, a circular C-scan image is convenient to show discontinuity information. The circular C-scan image shows the peak amplitude of a back-scattered pulse received in the circular array. The axial scan direction is shown as a function of transducer position in the circular array. The circular C-scan image serves also as an initial step for choosing circular B-scan profiles. The latter provides a mapping between distance to the discontinuity and transducer position in the circular array. 

Lefebvre, J.P., Progress in linear inverse scattering imaging NDE application of Ultrasonic Reflection Tomography, in Inverse Problem in Engineering Mechanies, pp 371-375, (A.A.Balkema/ Rotterdam rookfleld, 1994). 

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

The Doppler meter may be used wherever small particulate solids, bubbles or droplets are dispersed in the fluid and are moving at essentially the same velocity as the fluid stream which is to be metered. A continuous ultrasonic wave is transmitted, again at an acute angle to the wall of the duct, and the shift in frequency between the transmitted and scattered waves is measured. This method of measurement of flowrate is frequently used for slurries and dispersions which present considerable difficulties when other methods are used. 

Ultrasonic methods can also be applied to velocity measurements based on measurement of the Doppler shift in the frequency of an ultrasonic wave scattered from a moving particle. The angle between the velocity vector and the direction of ultrasound propagation must be known, which practically limits the appHcation of the technique to the measurement of unidirectional flows. However, this Hmitation may be overcome again by the use of an array of transducers [11]. 

In order to check these results, Lutz et al. degraded polymer samples which had been isolated shortly before macrogelation, by ultrasonic waves [213]. Figure 38A shows the decrease of Mw and of the hydrodynamic diameter dz, measured by static and dynamic light scattering respectively, on ultrasonic treatment of a polymer of Mw = 2.2 X10. Both Mw and dz decrease first abruptly but then... 

Ultra-small-angle neutron scattering spectrometer (usans), 20 339 Ultrasonic... 

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