A search unit with three or more individual elements is known as what?

The term for a search unit with three or more individual elements is known as an array transducer. An array transducer consists of multiple elements that can be individually controlled and used simultaneously or in various combinations, which allows for more complex operation and better image resolution in ultrasonic testing. This design enables the production of focused ultrasound beams, dynamic control of beam angles, and the ability to perform applications such as phased array ultrasonic testing.

While a mosaic transducer may sound like it pertains to the arrangement of individual elements, in the context of ultrasonic testing and NDT, array transducer is the more accurate and widely accepted term to describe such devices. The other types of transducers listed either refer to different configurations or simply do not meet the criteria of having three or more individual elements working together.