In which zone does beam divergence occur?

• A. At the face of the transducer
• B. Focal zone
• C. Fraunhofer zone
• D. Fresnel zone

Answer: (C)

Beam divergence occurs primarily in the Fraunhofer zone. This is the region where the wavefronts begin to spread out after passing through the focal point. In this zone, the ultrasonic beam expands, causing the energy to become less concentrated as the distance from the transducer increases. This divergence is important for understanding how ultrasound beams behave in medical imaging and other applications, as it impacts resolution and the ability to visualize structures at various depths.

In contrast, at the face of the transducer, the beam is generally collimated (tight and focused), with little divergence occurring directly at that point. The focal zone is where the beam is tightly focused, maximizing resolution before it begins to diverge in the following zones. The Fresnel zone refers to the near field, where the beam is still relatively focused but has not yet reached the point of significant divergence that characterizes the Fraunhofer zone.