Multiple-element transducers.

Multiple-element transducers, commonly called arrays, contain groups of transducer elements. The complete name of an array, such as the linear sequenced array, describes both how the array is constructed (linear) and how it is operated (sequenced); however, the names most often used are incomplete descriptions, such as the commonly used linear array. The arrays are arranged as a straight or a curved line of rectangular elements (linear or convex array) or concentric rings (annular array). Except for the annular array, which focuses the beam two-dimensionally but cannot steer it, the arrays electronically scan the ultrasound beam without mechanical movement. The image formats produced are a rectangle, parallelogram, and sector. To improve image quality, arrays can electronically focus the transmitted beam at a desired depth or at multiple depths to, in effect, achieve a long focal region. Focusing of received echoes is also accomplished electronically. Dynamic aperture and apodization also improve image quality with arrays.