In immersion testing, near-field effects may be eliminated by using a transducer with a larger diameter. Which choice best describes this effect?

• A. Shortens near-field
• B. Lengthens near-field
• C. Eliminates near-field effects
• D. No effect

Answer: (C)

In immersion testing, near-field effects come from the irregular, interference-filled beam that starts right at the transducer face. A transducer with a larger diameter emits a beam that is more collimated and dominated by a Strong central lobe, giving a more uniform field as it travels through the water toward the test piece. That more uniform, plane-like wavefront reduces the unpredictable variations that characterize the near-field, so the region where those near-field distortions occur becomes negligible in the area where you’re inspecting. In practice, using a larger diameter transducer tends to eliminate the visible near-field effects in the measurement zone by producing a steadier beam.