Which outcome describes the near-field region when a transducer is moved laterally in testing?

• A. Fluctuating amplitude due to lateral movement
• B. Stable amplitude
• C. No reflections
• D. Continuous-wave only

Answer: (A)

In the near-field, the beam is in a Fresnel-like zone where the energy distribution is highly sensitive to position. Moving the transducer laterally changes how the wavelets from the transducer face overlap at a given point in the material, so constructive and destructive interference varies. That causes the received amplitude to rise and fall as you shift sideways. This lateral sensitivity is a hallmark of the near-field. In the far-field, the beam tends to spread and stabilize, so amplitude fluctuations from small lateral moves are less pronounced. The ideas of no reflections or being limited to a continuous wave don’t describe this positional variability seen in the near-field.