Ultrasonic waves are sound waves with frequencies higher than the upper audible limit of human hearing (20 kHz). They are commonly used in medical imaging, industrial testing and cleaning, and various other applications. Ultrasonic waves can penetrate solid objects and liquids, allowing for non-destructive testing and imaging techniques. The field of ultrasonics involves the study of the behavior and properties of ultrasonic waves, as well as the development of new technologies and applications for their use.