In ultrasound beam zones, which zone describes the far-field region after the focal point where the beam diverges?

• A. Near field
• B. Focal point
• C. Fraunhofer zone
• D. Fresnel zone

Answer: (C)

In ultrasound beam geometry, the beam goes from the transducer through a near field where it’s still converging, reaches a focal point where the beam is narrowest, and then enters the far field where the beam begins to diverge. The far-field region after the focus is called the Fraunhofer zone. This term captures the idea that, at a distance, the wavefronts are effectively spreading out and the beam pattern becomes dominated by diffraction from the aperture, rather than by convergence. The near-field or Fresnel zone refers to the region before the focus where the beam is still moving toward convergence, and a focal point is simply the location of the tightest focus, not a zone. So the description of the far-field divergence after the focal point matches the Fraunhofer zone.