Ultrasonic multiple transducer

Through-transmission techniques use two aligned transducers located in opposite sides of the part. One transducer acts as transmitter and the other as receiver. The transducers can be in contact or immersed. 

Time of flight diffraction technique is a hybrid of the direct and indirect pitch and catch tests. Ultrasonic waves from a transmitter probe are diffracted from the tips of a crack as well as transmitted along the scanning surface and reflected from the back wall. 

The diffraction patterns are separated in space so their reception by the receiving transducer is separated by time. This difference in time can be used to locate and size the crack. 

Dual element transducer is an extended example of multiple probe technique in which one element acts as emitter and the other as receiver. These transducers are designed for measuring very thin materials or when detecting near surface discontinuities. Using this concept, it is possible to focus the ultrasonic beam. One of the major uses of focused probes is defect sizing by means of diffraction techniques. 

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An ultrasonic horn transducer consists of a transducer unit attached to a horn (rod) usually made from titanium alloy and which has a length a multiple of half-wavelengths of the sound wave. For the commonly encountered 20-kHz horn this corresponds to 12.5 cm. The horn is then partially inserted into the fluid medium of interest and intense ultrasound is generated at its tip so that, for adequately large intensities, a cloud of cavitation bubbles is visible. This arrangement permits significantly higher ultrasonic intensities (10-1000 W cm ) to be applied than are achievable with a bath. 

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-... 

In the most common bath design, the ultrasonic transducer is attached to the underside of the metallic base of the bath and the strongest power level occurs directly above the transducer. However, the ultrasonic power profile in the bath liquid varies in a non-uniform manner with the distance from the base. This has been ascribed to the fact that US is driven through the liquid as waves, so there are points where the irradiation amplitude is maximal and others where it is zero. Maxima are always desirable and can be calculated as multiples of the half-wavelength of sound X) in the medium. Such distances can be calculated from the equation ... 

An improvement over the individual transducers is thephased-array transducer systems that may have many elements (e.g., from 16 to over 128 elements) in a linear arrangement [23,27]. The phased-array electronic systems will pulse multiple small (e.g., 1 mm wide) elements in a timed sequence to create an ultrasonic beam with directional or focused properties based on the time phasing of the transducer pulses... 

Another limitation is posed by the shadowing effect in PMC. The delamination closest to the transducer will reflect the ultrasonic pulse to such an extent that delaminations below will be masked, unless their lateral size is larger. Even C-scans taken on both sides do not necessarily guarantee detection of delaminations in all layers. In the reflection mode, repeat echoes from multiple reflections have to be distinguished from real indications, especially in relatively thin PMC shells. 

Multiple stages of spray or immersion rinse where immersion rinse is enhanced by agitation generated by ultrasonic transducers. 

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