An array transducer where the elements are arranged as circular rings with a common center.

An array transducer where the elements are arranged as circular rings with a common center.

• A. Linear array
• B. Curvilinear array
• C. Phased array
• D. Annular array

Answer: (D)

An annular array is defined by concentric circular rings sharing a common center. That ringed, circular geometry is the hallmark of annular arrays, which creates a circular aperture that can be focused by applying appropriate timing delays to each ring during transmit and receive. This arrangement gives precise focal control and strong lateral resolution at the focal depth, but steering the beam is more limited than with a phased array. This differs from a linear array (elements in a straight line), a curvilinear array (arc-shaped surface), and a phased array (phase delays across a 2D aperture to steer the beam).

An annular array is defined by concentric circular rings sharing a common center. That ringed, circular geometry is the hallmark of annular arrays, which creates a circular aperture that can be focused by applying appropriate timing delays to each ring during transmit and receive. This arrangement gives precise focal control and strong lateral resolution at the focal depth, but steering the beam is more limited than with a phased array. This differs from a linear array (elements in a straight line), a curvilinear array (arc-shaped surface), and a phased array (phase delays across a 2D aperture to steer the beam).