Which statement accurately describes the near field and far field of a transducer beam?

• A. The near field is the converging region close to the transducer; the far field is where the beam forms a stable main lobe.
• B. The near field is the far-away region where the beam is stable.
• C. Far field is where the beam converges.
• D. Near field and far field are the same.

Answer: (A)

Think of the beam as evolving as it travels: near the transducer you’re in the developing, Fresnel region where the wavefronts are still curving and the pattern is changing with distance. As you move farther away, diffraction shapes the energy into a more predictable pattern, and the beam settles into its main lobe with a relatively stable angular spread—this is the far field (Fraunhofer region). Saying the near field is the converging region close to the transducer and the far field is where the beam forms a stable main lobe matches how these zones behave in practice, including how the beam narrows toward a focus before diverging beyond it. The other statements mischaracterize the distance and behavior of the regions.