Ultrasonic tomography

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]. 

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LASAYGUES (P.) and LEFEBRE (J.P.), Applications of wavelets analysis in ultrasonic tomography, Traitement du signal, 1995, 12, 373. 

Hildebrand B.P., Harrington TP. Mapping of materials stress with ultrasonic tomography //Proc. Symp. Microstmctural Characterization and Reliability Strategies - Pittsburgh, 1980. -P. 349-365. 

In this paper, we have exposed a solution to improve the resolution in Low Frequency Ultrasonic Tomography. Since the basic principle of ultrasonic reflection tomography prohibits the inspection of objects with strong contrast and large extension, we turn down the frequency of the transducer, in order to increase the penetration length of the wave and the validity of the method. But this is done at the expense of resolution. 

Reilly D., Brown G.J. and Mills D., Development of an ultrasonic tomography system for application in pneumatic conveying, Meas. Sci. Technol., 7,396-405,1996. 

Three-Dimensional Ultrasonic Reflection Tomography of Cylindrical Shaped Specimens. 

There have been numerous efforts to inspect specimens by ultrasonic reflectivity (or pulse-echo) measurements. In these inspections ultrasonic reflectivity is often used to observe changes in the acoustical impedance, and from this observation to localize defects in the specimen. However, the term defect is related to any discontinuity within the specimen and, consequently, more information is needed than only ultrasonic reflectivity to define the discontinuity as a defect. This information may be provided by three-dimensional ultrasonic reflection tomography and a priori knowledge about the specimen (e.g., the specimen fabrication process, its design, the intended purpose and the material). A more comprehensive review of defect characterization and related nondestructive evaluation (NDE) methods is provided elsewhere [1]. 

In this paper, discontinuities in cylindrical specimens were studied by ultrasonic reflection tomography. The aim was threefold. First, to localize discontinuities from circular C-scan images. Second, to reconstruct quantitative cross-sectional images from circular B-scan profiles (i.e., reflection tomograms). Finally, to obtain three-dimensional information (i.e., discontinuity location, dimension and type) by stacking these reflection tomograms in multiple planes, in the third dimension. 

Although the discontinuities may be seen clearly in the circular C-scan image, the image represents only a projection of discontinuities in a specific direction (i.e., a shadow of overlapping discontinuities). More information of the discontinuities according to location, dimension and type may be achieved by ultrasonic computed tomography (UCT) imaging. 

Nielsen, S.A. Borum, K.K. and Gundtoft, H.E (1995). Verifying an ultrasonic reconstruction algorithm for non-destructive tomography. Proc. of 1st World Congress on Ultrasonics, Berlin, Vol. 1, 446-450. 

Article is denoted to the investigation and the creation of the new ultrasonic and information technologies (IT) and the technical methods of non-destructive evaluation (NDE) of material state in the product, which are based on principles of ultrasonic computing tomography (USCT). These results concern two important questions ... 

Hiller, D., and Ermert, H., System Analysis of Ultrasound Reflection Mode Computerized Tomography, IEEE Trans. Sonic Ultrasonic SU-31, pp 240-250, (1984). 

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). 

Lasaygues, P.,. Lefebvre, J.P., and Mensah S., Deconvolution and Wavelet Analysis on Ultrasonic Reflection Tomography, III International Workshop, Advances in Signal Processing for Non Destructive Evaluation of Materials, Quebec, Canada, (1997). 

Schlaberg, H.I., Yang, M., and Hoyle, B.S. (1997) Ultrasound reflection tomography for industrial processes. 17th Ultrasonics International Conference (U1 97), 1997, Delft. 

Yang, M. et al. (1999) Real-time ultrasound process tomography for two-phase flow imaging using a reduced number of transducers. IEEE Trans. Ultrason. Ferroelectr. Freq. 

As in the established imaging modalities, such as X-ray, computed tomography (CT), magnetic resonance imaging (MRI) and ultrasonic imaging (US), the... 

Ultrasound tomography (UST), 205 Ultrasound transducer arrangement, 14 Urea-formaldehyde microcapsules, 67 UVP-DUO systems, 2, 7, 12-13 UVP measurements. See Ultrasonic velocity profiler (UVP) measurements... 

Planar tomography could be complementarily adopted to indicate cracks and determine their depth propagation with high resolution, while time of flight diffraction (TOFD) has been considered not suitable as a surface crack inspection. Ultrasonic equipment such as phased array technique, on the other hand, allows complete weld inspections, improving, for instance, the separation between back wall and defect indication [10]. 

Malyarenko EV, Hinders MK. Ultrasonic Lamb wave diffraction tomography. Ultrasonics 2001 39(4) 269—81. http //dx.doi.org/10.1016/s0041-624x(01)00055-5. 

Utomo, M.B., Warsito, W., Sakai, T, and Uchida, S. (2001), Analysis of distributions of gas and Ti02 particles in slurry bubble column using ultrasonic computed tomography, Chemical Engineering Science, 56 6073-6079. 

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