To focus the beam at greater depths, which design change to the transducer element is recommended?

• A. Increase element thickness
• B. Increase curvature
• C. Decrease element width
• D. Increase element diameter

Answer: (D)

Focusing depth is largely governed by the transducer’s aperture. The active diameter acts like a lens: a larger aperture lets the wavefront converge more effectively to a focus that lies farther from the element. For a given center frequency, widening the aperture lowers the f-number (focal length divided by diameter), which tightens the beam and allows accurate focusing at greater depths.

Increasing curvature would pull the focus closer (shallower), not deeper. Decreasing the element width shrinks the aperture, reducing the ability to focus far away. Increasing the element thickness would change the resonance frequency rather than where the beam can be focused in depth. So increasing the element diameter is the design change that best enables focusing the beam at greater depths.