Proximity sensing through air-film damping effect caused by length-extensional-mode piezoelectric vibrator

Proximity sensing through the air-film damping effect caused by a length-extensional-mode vibrator is studied. Lateral flow of viscous fluid sandwiched between a test object and a vibrating (sensing) plate is subjected to resistive force. Therefore, it acts as a damper for the motion of vibration. Because the sensing plate is vibrated in its normal direction by a longitudinal-mode piezoelectric vibrator, electric properties of the vibrator vary depending on the vibrator-to-object distance. It is shown that the Q-value of the vibrator decreases from 8,000 to 1,000 in the range where the plate-to-objective distance is less than 0.5 mm.