ABSTRACT
Nondestructive evaluation (NDE) is a huge and diverse field. Regarding experimental methodology, it includes not only ultrasonics but also a wide range of complementary techniques such as x-rays, optical, thermal, electrical, and magnetic measurements. Material surface coatings, layers, or surface modifications are an important part of modern technology. Clearly, NDE of such structures to determine their quality is important. Surface acoustic wave is also ideally suited to Type II NDE of surface structure, the determination of elastic constants, for example, in the reconstruction of the gradient of near-surface elastic properties. Critical angle reflectivity (CAR) is a very useful laboratory tool for Type II NDE. The physics of CAR is at the basis of much of modern NDE of surface regions by ultrasonics and is an essential component of acoustic microscopy. Formal NDE classification procedures make a clear distinction between forward (inductive and predictive) and inverse (deductive) approaches.
