Annular array transducers (not testable)

Annular array transducers

These are now historical. They were used in the 80's and early 90's but have now been replaced by phased and linear array transducers. You will not be tested on annular arrays, but if you want

Annular array transducers were constructed using a concentric ring of crystals. (The word annular means ring) Typically an annular array consisted of a ring of 5 to 9 elements, each of which was individually wired and isolated from its neighbour. The overall diameter of the array was typically 1 to 2 cm. In a fashion similar to a phased array, annular arrays fired all the elements together to produce each scan line. However, unlike a phased array, an annular array was unable to electronically steer the beam because of its ringed construction.

In order to sweep the beam through a region of interest the annular array had to be mechanically scanned. The most common method of doing this was to oscillate (wobble) the array elements in the same way as a mechanical single element transducer was scanned. This produced a pie-shaped or sector scan FOV. Thus, an annular array was often thought of as a hybrid type of transducer because it was mechanically scanned but its multiple elements had the capability of being electronically focused like all array transducers.

Annular array transducers were popular in the 80's and early 90's due to their small footprint and their ability to electronically focus the beam. However, in recent years, the annular array has almost been entirely replaced by the phased array for cardiac work and by the convex array for abdominal and obstetrical work