What is a phased-array transducer and how does it steer the beam?

• A. Doppler ultrasound probe
• B. A multi-element array with electronic delays to steer and focus the beam
• C. A single-element fixed beam
• D. Mechanically scanned lens

Answer: (B)

A phased-array transducer steers and focuses the ultrasound beam by using multiple small elements whose electronics apply precise time delays to each element. By introducing these delays, the emitted waves interfere constructively in a chosen direction, tilting the wavefront so the beam points at an angle without moving the probe. Those same delays can also be varied to shape the wavefront so it converges at a focal point, giving electronic focusing at different depths. This combination of steering and focusing through electronic delays is what characterizes a phased-array and sets it apart from a single-element fixed beam or a mechanically scanned lens that requires moving parts. The Doppler capability is a separate measurement mode and does not define the transducer itself.