Answer :
Final answer:
The area from the face of the unfocused transducer to the point of beam divergence is the near zone, where the beam remains parallel and constant in width, crucial for clear ultrasound imaging. The correct answer is option a).
Explanation:
The area from the face of an unfocused transducer to where the beam starts to diverge is known as the near zone or the Fresnel zone. In this region, the sound waves emitted by the transducer are relatively parallel and the beam width remains constant. As the waves travel further from the transducer, they enter the far zone or Fraunhofer zone, where the beam begins to expand or diverge.
The point at which the beam width begins to expand and the near zone ends is often termed as the end of the near zone or the near zone length. The near zone is significant in medical ultrasound as it denotes the region of the most uniform intensity and least divergence, allowing for the clearest images.
Decisions regarding the focal depth of an ultrasound transducer rely heavily on understanding the properties of the near zone. As we transition from the near to the far zones, diagnostic capabilities can be affected, making these concepts crucial for medical imaging and other applications using ultrasonic transducers.
