What type of transducer could you choose to produce a beam that is symmetrical about the beam axis?

• A. Annular array
• B. Linear sequenced array
• C. Phased array
• D. Curved array

Answer: (A)

An annular array is designed with concentric circular rings, giving the aperture circular symmetry. When the rings are driven with the right delays and amplitudes, their waves combine to form a wavefront that is essentially the same in all azimuth directions around the central axis. That rotational symmetry means the beam’s lateral shape is uniform about the beam axis, so the beam is symmetrical as you look around the axis. Other transducer geometries have rectangular or arc-shaped apertures that create directional patterns that vary with angle, so they don’t produce a truly circularly symmetric beam.