ANOMALOUS ATTENUATION EFFECT ON REFLECTIVITY OF AN ULTRASONIC WAVE FROM A THIN-LAYER BETWEEN DISSIMILAR MATERIALS

Distinctive features of ultrasonic spectroscopy of adhesive joints of dissimilar materials (including anisotropic) are addressed both in the ory and experiment. It is found that for dissimilar joining materials the depth of the reflection spectrum minimum depends nonmonotonically on attenuation in the layer and differs for measurements from opposite sides of the joint. It depends on both the attenuation in the adhesiv e and on adhesive/substrate impedance mismatches, resulting sometimes in zero reflectivity at nonzero attenuation in the adhesive. The effec t is observed at normal and oblique incidence. A technique for measure ment of the layer attenuation from amplitude and phase spectra is prop osed. Experimental results show good agreement with theoretical predic tions. (C) 1997 Acoustical Society of America.