TRANSDUCER MISALIGNMENT EFFECTS IN-BEAM REFLECTION FROM ELASTIC STRUCTURES

In two-transducer, fluid-coupled ultrasonic reflection measurements ph ase matched to guided modes of elastic solid structures, the effects o f misalignment (i.e., differences) between the receiver angle and the incident beam angle on the receiver voltage have been studied. The rec eived voltage is typically due to contributions from the specular refl ection and any of the several possible guided wave modes excited by th e incident wave field. It is found that misalignment leads to changes in the relative amplitudes of the various contributions. Further, the more highly collimated the beam (or the contributor), the more pronoun ced are the effects. It is shown that the signal maximum is not a reli able indicator of receiver alignment. These conclusions are based on m easurements and on calculations that have been performed at incident a ngles selected both close to, or far from, phase-matching angles to gu ided wave modes on plates, curved surfaces, and cylindrical shells. Re ceiver voltage coordinate scans have been performed with receiver angl es misaligned from the incident beam axis by 1 to 4 degrees. The recei ver voltage versus scan parameter in planar and curved structures is c alculated by employing complex transducer points to synthesize two-dim ensional, sheet-beam transducer fields with Gaussian apertures, spectr al analysis to formulate the beam-structure interaction problem, and a symptotic methods to evaluate the resulting spectral integrals. The mo del predictions are generally in good agreement with the experiments. (C) 1998 Acoustical Society of America. [S0001-4966(98)06709-5]