Ultrasonic reflection

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. 

Under ideal conditions (e.g., point sources producing spherical waves and no multiple reflections) a rectified backscattered signal represents line integrals of the ultrasonic reflectivity over concentric arcs centered at the transducer position. To reconstruct the reflection tomo-... 

Fig. 5. shows six ultrasonic reflection tomograms. Three of these are from the Plexiglas specimen (shown left) and three are from the AlSi-alloy (shown right). The tomograms are reconstructed from reflection data measured across the plane (b), (c) and (e), respectively. The dark regions indicate high reflectivity and represent specimen interfaces and discontinuities. 

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. 

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). 

Ultrasonic reflections out of the weld volume are documented in a top and side view together with the area of weld volume scanned. A new coupling monitoring system ensures 100% coupling reliability. Furthermore the systems does not require any mechanics to monitor the probe position as the position data is monitored by airborne sound sensors. 

An application of ultrasound that is becoming increasingly popular in the food industry is the determination of creaming and sedimentation profiles in emulsions and suspensions (Basaran et al., 1998). Acoustic techniques can also assess nondestructively the texture of aerated food products such as crackers and wafers. Air cells, which are critical to consumer appreciation of baked product quality, are readily probed due to their inherent compressibility (Elmehdi et al., 2003). Kulmyrzaev et al. (2000) developed an ultrasonic reflectance spectrometer to relate ultrasonic reflectance spectra to bubble characteristics of aerated foods. Experiments were carried out using foams with different bubble concentration and the results showed that ultrasonic reflectance spectrometry is sensitive to changes in bubble size and concentration of aerated foods. 

Kulmyrzaev, A., Cancelliere, C., and McClements, D.J. 2000. Characterization of aerated food using ultrasonic reflectance spectroscopy. J. Food Eng. 46, 235-241. 

Fig. 3. Ultrasonic reflectance amplitude from the interface between a piece of Plexiglas and sample of confectionary coating fat during cooling. As the sample crystallized, it became more acoustically similar to the Plexiglas and less sound was reflected.

Fig. 34a. Schematic views of ultrasonic reflections at three different points of CFRP specimen b Corresponding time-domain waveforms of reflections...

Telemetry. In order to optimise known means, a study and a series of in-water tests have been performed. A measurement accuracy of 2 mm at a distance of 5 m was achieved. This accuracy will have to be confirmed by in-sodium tests on some particular points and by an overall qualification at full-scale 1 probe. New woric is in progress in the CEA in order to develop a technique using ultrasonic reflection ... 

Cawley, R, Pialucha, T.P. and Zeller, B.D., The characterisation of oxide layers in adhesive joints using ultrasonic reflection measurements. Proc. R. Soc. London, Ser. A, 452, 1903-1926(1996). 

The ultrasonic velocimetric technique is based on ultrasonic reflections on bubbles to depict the velocity profile across the pipe. This gives information about the bubble distribution and their mean velocity. However, this is a new technique that requires further studies and some tuning before it can be used outside of the laboratory. 

Several methods of displaying ultrasonic reflections are available, the most common being A and C-Scans. The simplest presentation is an A-Scan which shows the amplitude of the signal as a function of time (or distance, if a value for the velocity of sound in the medium is known), as shown in O Figs. 42.14 and O 42.15. In manual testing, an A-scan is obtained at each test point and is interpreted by the operator. 

A spring model was used to determine maps of contact stiffiiess from interference fit ultrasonic reflection data. A calibration procedure was then used to determine the pressure. 

Dwyer-Joyce, R.S., Drinkwater, B.W., "Analysis of Contact Pressure Using Ultrasonic Reflection", Experimental Mechanics, Proceedings of the 11th International Conference on Experimental Mechanics, Balkema, Rotterdam, pp747-754. 

Journal Bearing Oil Film Measurement Using Ultrasonic Reflection... 

Paper XIII (ii) Journal Bearing Oil Film Measurement Using Ultrasonic Reflection by Mr B Harper , Mr B Hollingsworth Dr R S Dwyer-Joyce and Dr B W Drlnkwater ((a) Department of Mechanical Engineering, University of Sheffield. UK (b) Department of Mechanical Engineering, Brown University, Providence, Rhode Island, USA (c) Department of Mechanical Engineering, University of Bristol, UK). 

Calibration was performed using two glass plates separated by a known thickness shim at one end and a known, but different, shim thickness at the other end. The change in the thickness of the separation with distance was then measured using ultrasonic reflection. The results were compared to the expected geometrical change in thickness with distance. 

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