An immersible plate for large-scale cleaning systems, available from Granbo .
HC-SR04 Ultrasonic Sonar Distance Sensor + 2 x 10K resistors Adafruit Industries Go to product viewer dialog for this item. buy ultrasonic transducer
A linear array probe used for vascular and musculoskeletal exams, also found at reLink Medical . Ultrasound buy ultrasonic transducer