Acoustic Micro-Metrology

Abstmct-The ability to measure elastic properties of materials and layered structures nondestructively on a microscopic scale gives rise to a new field of metrology via the reflection acoustic microscope. Acoustic micro-metrology accomplishes this task via the acoustic material signature (AMS), which is obtained from planar and curved surface specimens alike. The AMS constitutes a unique function that arises from interference of elastic propagating modes. These are simultaneously and coherently excited in the wide-angle lens ensembles that distinguish the acoustic microscope from other forms of ultrasonic pulse-echo systems. Several potential applications taken from diverse fields are described with experimental case studies. Examples of both materials and layered structures are described. Distinguishing features of different crystal orientations of single crystals may be readily detected. It is shown that the film thickness measurement of a wide variety of opaque materials is readily accomplished nondestructively and without a step. Machining damage in a Be surface may also be determined nondestructively. The AMS limitations imposed by frequency and material combinations, as presently viewed, are treated in the concluding section.