Feasibility study of proximity sensing by using a conventional airborne transducer

Ultrasonic proximity sensors utilizing non-radiant (evanescent) acoustic fields created in the vicinity of piezoelectric vibrators were proposed. When an object is brought into the evanescent field, electric admittance of the vibrator varies depending on the vibrator-to-object distance. In former reports, the air-film damping effect occurred between the sensing plate attached to the length-extensional mode vibrator and the test-object plate was studied. In this study, the sensing system is constructed by using a commercially-available airborne transducer. Distance dependent variation in the electric admittance level such as that observed in the former study has been confirmed.