SCANNING ACOUSTIC MICROSCOPY MODELING FOR MICROMECHANICAL MEASUREMENTS OF COMPLEX SUBSTRATES

Abstract

The Scanning Acoustic Microscope (SAM) is a powerful tool for understanding the mechanical characteristics of substrates with micro-scale near-surface graded layers. To interpret the SAM results from such substrates, a theoretical model was developed that incorporated the interaction of focused ultrasonic field, with a substrate having a near-surface graded layer. The focused ultrasonic field model was formulated in terms of spherical wave expansions. The substrate wave propagation was computed with a multilayered stiffness method. The bridging between the two models was accomplished by utilizing the angular spectrum. A commercial SAM was used to characterize a dentin substrate subjected to acid-etching. Calibration and a homotopic measurement protocol were developed for data accuracy and meaningful data comparison from pre and post etching states. The reflection coefficients from the SAM measurement for the etched dentin exhibited frequency dependent attenuation. The developed theoretical model was successfully applied to explain the observed frequency dependent phenomenon.