Normal beam ultrasonics

Another variation of the normal beam ultrasonic technique is illustrated in Fig. 6 for a so-called resonance method. In this case, continuous wave ultrasonic energy travels from the ultrasonic transducer through the entire adhesive bond structure. When encountering a delamination, notice that the wave resonance set up is of a different wavelength than one where ultrasonic energy can nicely traverse the entire adhesive bond structure. There are many resonance techniques and instrumentation possibilities on the market that work very well for cohesive bonding problems and in some cases are even acceptable for adhesive defect situations. Standing waves are established and the frequency observed is equal to the wave velocity over twice the thickness, in this case either twice d or twice D. 

Figure 39. Normalized beam patterns obtained from a single ultrasonic source (980 kHz) using three different probes.

Oblique incidence ultrasonic test techniques like those illustrated in Fig. 7 are also quite useful. In fact, it has been found in earlier studies that the normal beam shear wave incidence technique is often more sensitive to subtle interfacial weakness problems than a normal beam longitudinal incident wave. It is difficult, however, to produce shear wave incidence in a normal beam mode because of the somewhat permanent adherence to the substrate that is required. As a result, it was... 

In order to move the samples under the laser beam, the stainless steel (SS) disks were mounted on a precise, computer-controlled ZABERT-LS80 X-Y translation stage. The power of the incident laser beam was adjusted in the range of 5 to 1700 mW and the scanning speed varied from 250 to 1850pm/s. The samples were irradiated at normal incidence in air and then subjected to an ultrasonic bath for 2 min in acetone to remove all the debris off the patterned surface. 

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