The widening of the sound beam in the far field is called what?

• A. Angle of Divergence
• B. Angle of Incidence
• C. Focal Length
• D. Beamwidth

Answer: (A)

Understanding how an ultrasound beam spreads as it travels is being tested here. In the far field, the beam expands due to diffraction, and the rate of that expansion is described by the angle of divergence. This angle captures how quickly the beam widens with distance, essentially the cone of spread from the transducer. The other terms refer to different ideas: angle of incidence is how the beam meets a boundary, focal length is the distance to the focal point, and beamwidth is the actual width of the beam at a particular depth, not the rate of angular spread. So the widening in the far field is described by the angle of divergence.