Non-Destructive Testing (NDT) Practice Test

What happens when the impedance mismatch between two materials increases?

1. The sound transmission improves

2. More energy is transmitted into the second material

3. A greater percentage of energy is reflected at the interface

4. The materials bond stronger together

The correct answer is: A greater percentage of energy is reflected at the interface

When the impedance mismatch between two materials increases, a greater percentage of energy is reflected at the interface between them. Impedance is a measure of how much resistance a medium provides to the propagation of sound waves, and it is determined by the density and the speed of sound in the material. When two materials with significantly different acoustic impedances are in contact, the incident sound wave encounters a barrier to its propagation when it tries to move from one material to the other. Since the two materials have different properties, the mismatch means that less energy can effectively cross the boundary. As a result, a larger portion of the sound wave's energy is reflected back into the first material instead of being transmitted into the second material. This phenomenon is critical in various fields, including ultrasonics and materials testing, as it can influence the efficiency of techniques used to assess the integrity of materials and detect flaws. Understanding that increased impedance mismatch leads to greater reflection can help professionals make informed decisions in applications such as non-destructive testing.