Variation of Bending-Vibrator Characteristics when an Object is Brought into Close Proximity with the Vibrator End

Evanescent acoustic fields which decay exponentially from the plate surface can be created in the vicinity of a piezoelectric bending vibrator. When an object is brought into this evanescent field, the electric admittance of the vibrator undergoes some change depending on the vibrator-to-object distance d. The authors' group has found so far that as an object comes into close proximity with the plate end, an unexpected phenomenon occurs such that the Q-factor which once decreased starts to increase in the range where d becomes small. In this study, this unique phenomenon is examined in detail by experiments and some new findings are shown on the variation of bending-vibrator characteristics. Also, theoretical explanations are given to conjecture the mechanism of this phenomenon by using a simple model.