Electronic focusing in the transmit mode is accomplished using:

• A. Curved crystal elements
• B. Changeable lens
• C. Time delays to excite transducer elements
• D. High pulse repetition frequency

Answer: (C)

Electronic focusing in transmit mode is achieved by applying time delays to excite the individual elements of the transducer array. By delaying the drive signals across the elements, the emitted waves arrive in phase at a chosen focal point, creating a curved wavefront that concentrates energy at a specific depth. This electronic control allows dynamic focusing and beam steering without moving parts, improving lateral resolution at the focal depth. Fixed focusing from a curved crystal would be limited to a single focal length, a changeable lens isn’t how transmit focusing is typically implemented, and a high pulse repetition frequency affects imaging speed rather than shaping the focus.