What is the narrowest portion of the beam, where the width at the focal point is about half the transducer width and maximum intensity occurs?

• A. Focal Point
• B. Near Zone
• C. Focal Zone
• D. Far Field

Answer: (A)

The narrowest part of the beam occurs at the focus, where the wavefronts converge to its smallest lateral size and energy is most concentrated. At the focal point the beam width is about half the transducer width, and this tight convergence produces the maximum intensity. Before this point, in the near field, the beam is still tightening as it approaches the focus; after it, in the far field, the beam begins to diverge and the width increases while the intensity falls. While the surrounding area around the focus is often referred to as the focal zone, the specific location where the beam is narrowest and intensity is greatest is the focal point.