Non-Destructive Testing (NDT) Practice Test

Where do sound waves become most uniform during ultrasonic testing?

1. Near Field

2. Far Field

3. Surface interface

4. Mid Field

The correct answer is: Far Field

In ultrasonic testing, sound waves begin to exhibit more uniform characteristics in the far field region. This area is located beyond the near field and allows for effective wave propagation that is less influenced by the initial beam characteristics produced by the transducer. As sound waves travel through a medium, they undergo diffraction and attenuation; in the far field, the interference effects become minimized, and the sound waves tend to spread out evenly. In contrast, in the near field, sound waves are still tightly focused and exhibit variations in intensity, leading to non-uniformity. The mid field zone still contains some of these variations before the waves fully transition into the far field. Surface interfaces refer to the areas at the start of wave propagation where reflections can lead to dispersion and non-uniformity as well. This makes the far field the optimal region for accurate measurements and uniform wave characteristics in ultrasonic testing.