Ultrasonic transducers patterns

Typically, ultrasonic images are produced by mechanically scanning an ultrasonic transducer in a raster pattern over an area of a structure and... 

Local existence of the cavitation phenomena just near the irradiating surface in the case of ultrasonic transducers and wide distribution of the energy dissipation patterns in the reactor due to uneven energy dissipation. 

Campbell CK (1984) Simplified computer-aided fabrication of SAW transducer pattern masks. IEEE Trans Sonic Ultrason 31(3) 185-186... 

Flow measurement can also be deducted by correlating thermal noise in the flow channel. The basis for this technique is the measurement of transport time of the noise pattern (caused by local turbulence and bubble collapse) between two thermocouples located a few pipe diameters apart in the fluid. In this case accuracies in the range of 3 to 5% are possible. The use of ultrasonic transducers allows another possible correlation, and in this case no penetration in the pipe is necessary, and, over a limited range of flow, we can have accuracies in the order of 5%. Another possible correlation is the measurement of activity between two distinct points in the coolant system piping. This technique is actually under study, and can be used to attend the requirement of functional diversity for flow measurement. 

A resonance in the layered stracture occurs when echoes between two boundaries travel back and forth due to differences in acoustic impedances at the boundaries. For multi-layer structures a number of resonances can be observed depending on their geometry and condition. For each particular defect-free structure and given transducer we obtain a characteristic resonance pattern, an ultrasonic signature, which can be used as a reference. 

The most commonly employed US transducers are thin platelets of piezoelectric (mainly ceramic) materials with metallic electrodes on both surfaces (see Section 1.4). Such transducers have resonance frequencies determined by the interference of the ultrasonic signals created at both surfaces and internal reflections. The interferences cause distortions (broadening) in the echo pattern in pulse-echo measurements. The resonances also introduce phase shifts in the signals and lead to restrictions in the bandwidth. The frequency range can be expanded by using concave, cylindrical or spherical piezotransducers. 

At lower ultrasonic frequencies (0.5-10 MHz), Raman-Nath diffraction of laser light by plane acoustic waves was used to measure the decay of acoustic energy inside an aerogel specimen [57], This method relies on the density variations produced by the sound wave that create a phase pattern inside the specimen. The intensity of the first order of the diffracted light beams is proportional to the sound intensity at the intercept of light and sound beam. In a log plot of sound intensity versus distance from the transducer, the slope is a measure of the attenuation. 

C-scan ultrasonics, or ultrasonic microscopy, is essentially a three-dimensional technique. The transducer is rastered across the sample surface in the same pattern as the electron beam in a television. Information on the depth of flaws beneath each position on the sample surface is recorded and stored in a computer. The computer then allows projection of the three-dimensional network of flaws onto the screen. The image is usually rotatable to take advantage of the dimensionality of the data. C-scan may be used to characterize and display the complete flaw distribution in a sample. 

SLAM. A transducer beneath the sample produces a collimated ultrasonic beam which is altered by voids, cracks or inclusions in its path. The resultant upper surface displacement pattern of ripples is scanned by a laser beam and converted into a magnified visual image. SCARE. See cares. 

Figure 47. Interdigilal metal pattern of a uniform transducer the IDT behaves like a sequence of ultrasonic sources or receivers [247]...

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