Consequences of resonant surface-wave excitation on contrast in reflection scanning acoustic microscope

The scanning acoustic microscope (SAM) is a confocal imaging system that is very similar in structure to the scanning optical microscope. The purpose of the paper is to show that when surface-wave excitation is the predominant contrast mechanism, the imaging performance cannot be described within the same framework that is used to explain image formation in the scanning optical microscope. The paper explains that concepts such as the optical transfer function and the point spread function, which rely for their usefulness on the linear superposition of object features, are not applicable because surface-wave excitation is a resonant phenomenon. The paper shows how the images expected in acoustic micro-graphs can be severely perturbed by resonance in the specimen. It is therefore important that these effects are understood so that acoustic images are correctly interpreted. The specimen is modelled in the simplest possible manner to account for surface-wave excitation so that the features unique to imaging in the reflection acoustic microscope can be demonstrated