An immersible plate for large-scale cleaning systems, available from Granbo .

A reliable industrial transducer for precision cleaning available at Asonic .

A high-power converter for plastic welding applications, found on eBay.

A linear array probe used for vascular and musculoskeletal exams, also found at reLink Medical . Ultrasound

. These are low-cost, easy to interface with microcontrollers like Arduino, and typically include both a transmitter and receiver.