The Fraunhofer region in ultrasound corresponds to which zone?

• A. focus
• B. near zone
• C. far zone
• D. penetration depth

Answer: (C)

In ultrasound diffraction, the Fraunhofer region is the far field. Right in front of the transducer the beam is in the near (Fresnel) zone, where the pattern is complex and changes with depth due to interference and imaging geometry. Once you move into the far field, the wavefronts have spread enough that the beam pattern is governed mainly by diffraction from the transducer aperture, becoming more stable with distance and predictable by its angular distribution. The boundary between these zones depends on aperture size and wavelength. So, the Fraunhofer region corresponds to the far zone, not the focus or penetration depth.