Which type of ultrasound transducer provides adjustable multi-focus due to its design?

• A. Single-element
• B. Mechanical sector
• C. Linear non-phased
• D. Phased array

Answer: (D)

Phased array transducers enable adjustable multi-focus through electronic beam shaping. They contain many small elements, and by applying precise time delays to the signals sent from each element, the emitted waves constructively interfere at a chosen depth. Changing those delays reshapes the focus and can create multiple focal zones, all without moving the transducer. This electronic focus and steering—made possible by phasing across the array—is what allows rapid, adjustable multi-focus.

Other designs lack this capability. A single-element transducer has just one source, so it can’t electronically focus at multiple depths or steer the beam. A mechanical sector uses a moving aperture to sweep the beam, with focusing determined by fixed geometry rather than programmable delays. A linear non-phased transducer can’t adjust focus or steer electronically because it lacks the timing control that phasing provides, so it can’t produce dynamic multi-focus like a phased array.