At the beginning of the far zone the beam is how wide compared to the transducer?

At the beginning of the far zone the beam is how wide compared to the transducer?

• A. Only one half as wide as it is at the transducer
• B. The same width
• C. Twice as wide
• D. Three times wider

Answer: (A)

Understanding how ultrasound beams diffract helps here. The transducer acts like a circular aperture, and as the waves move away, diffraction causes the beam to diverge. The boundary between the near and far field is roughly where the main beam starts to spread significantly. At that starting point, the diffraction pattern predicts the beam’s width to be about 0.6 times the transducer diameter—roughly half as wide as the transducer itself. So, at the beginning of the far zone the beam is about half as wide as the transducer. Beyond that point the beam continues to widen with distance.

Understanding how ultrasound beams diffract helps here. The transducer acts like a circular aperture, and as the waves move away, diffraction causes the beam to diverge. The boundary between the near and far field is roughly where the main beam starts to spread significantly. At that starting point, the diffraction pattern predicts the beam’s width to be about 0.6 times the transducer diameter—roughly half as wide as the transducer itself. So, at the beginning of the far zone the beam is about half as wide as the transducer. Beyond that point the beam continues to widen with distance.