Ultrasonic NDE is one of the most widely used NDE methods today. This chapter discusses ultrasonic theory, transducers, inspection principles, applications, and advanced topics.

Although ultrasonic techniques and theory can be quite complex, the basic concepts behind ultrasonic NDE are simple. Ultrasonic waves (sound waves vibrating at a frequency too high to hear) can propagate in solids-that is, travel through them. (Of course, such waves can also travel through liquids or air.) As the waves travel, they interact with solids in ways that we can predict and represent mathematically. Armed with this kind of understanding, we can create our own ultrasonic waves with a transducer, and thereby use ultrasonics as a way of finding out the nature of a solid material-its thickness, its flaws, its elasticity, and more. As you can imagine, this knowledge has many applications in the aircraft, piping, semiconductor, fabrication, railroad, power, and other industries.