The ultrasonic transducer.
D001826:Body Fluids; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004735:Energy Transfer; D005123:Eye / Q000033:anatomy & histology; D007909:Lenses / Q000295:instrumentation; D008433:Mathematics; D013499:Surface Properties; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation*; D014463:Ultrasonography