What is the term for the phenomenon where an ultrasonic wave changes direction upon crossing a boundary between different materials?

The phenomenon where an ultrasonic wave changes direction upon crossing a boundary between different materials is known as refraction. When an ultrasonic wave travels from one medium to another—such as from air to water or from steel to aluminum—the change in density and elasticity of the materials alters the speed of the wave. As a result, the wave not only changes speed but also bends at the interface. This bending effect follows Snell's Law, which relates the angles and velocities of the wave in the two different media.

Understanding refraction is essential in ultrasonic testing because it affects how sound waves are propagated and detected in various materials. It plays a significant role in the design and interpretation of ultrasonic inspection setups, ensuring that the ultrasonic waves effectively reach and evaluate the material under inspection.

Reflection, on the other hand, refers to the bouncing back of waves when they hit a boundary, which is not the same as changing direction as in refraction. Diffraction involves the bending of waves around obstacles or the spreading of waves when they pass through narrow openings, while transmission refers to the wave passing through a boundary into a new medium without any change in direction.