Nonlinear acoustic/ultrasound methods for civil applications

This chapter presents an overview of nonlinear acoustic and ultrasound methods and their application to civil structures. The major nonlinear ultrasonic methods are thoroughly reviewed, and the underlying physics and laboratory studies are reported. In particular, phenomena such as higher-harmonic generation, subharmonic generation, nonlinear resonance, or mixed frequency response were discussed, and the basic physical mechanism of each phenomenon is introduced with applications for evaluation of damage in civil structures. Research results to date showed higher sensitivity of these techniques than the conventional linear ultrasonic methods in detecting microdamage in commonly used materials for civil structures, such as concrete and mortar. Finally, current and future challenges are discussed for the successful future implementations of these methods in a maintenance program.