What type of transducer is characterized by utilizing concentric rings?

The correct answer is the annular array transducer. This type of transducer is designed with multiple concentric rings, which allows it to focus ultrasound beams at various depths effectively. The arrangement of these rings enables better lateral resolution and provides the ability to steer the beam electronically, resulting in enhanced image quality.

Annular array transducers are particularly advantageous for imaging deeper structures as they can generate a focused beam at different depths without needing to change the physical configuration of the transducer. By activating the specific rings, sonographers can control the focal zone and improve the detail in the region of interest.

Other transducer types like the linear array, curvilinear, and phased array use different methods of beam formation. Linear arrays utilize a straight row of elements and generate rectangular images. Curvilinear arrays use a curved arrangement to produce a wider field of view but do not employ concentric rings. Phased arrays rely on time delays between individual elements to steer beams and focus at differing depths, but these elements are typically in a straight or slightly curved arrangement rather than concentric rings.

Thus, the unique structure of the annular array makes it distinct and particularly useful in certain imaging applications, establishing it as the correct response.