Strongly convex curvilinear-array transducers
Curvilinear arrays can be made with such tight curvature that their fi eld of view becomes sector-shaped . Th e advantages of a sector format include a small ‘acoustic window’ at the body surface, and an increasingly wide fi eld of view at depth. Phased-array scanning systems (discussed next) are particularly well suited to sector scanning, but strongly convex curvilinear arrays allow manufacturers of linear-array systems to off er sector scanning transducers, without having to build in the specialized electronics that phased-array transducers require. However, the convexity of the curvilinear transducer face means that it is less suitable in situations where the flat face of a phased-array transducer is needed.
The maximum useful size of the active element group of a curvilinear array is more limited than in a linear array employing the same-sized elements. Consequently, beam width in the focal zone is greater, and lateral resolution is poorer, than in a comparable linear array. Th is is primarily due to the fact that, as the number of active elements is increased, the outermost elements point more and more away from the centre line of the group (scan line), until eventually they cannot transmit or receive in that direction at all. Also, the longer paths between the outer elements and a receive focus mean that the problems of providing compensating delays are more challenging.