STACKED PIEZOELECTRIC ELEMENT AND MULTIFEED DETECTION SENSOR

摘要

The objective of the invention is to provide a stacked piezoelectric element, wherein neither degradation of electric characteristic nor increase of acoustic wave frequency occur even through the element size is reduced, and a multifeed detection sensor. A stacked piezoelectric element (11) comprises a piezoelectric element layer (11B) and a matching layer (11A). The piezoelectric element layer (11B) has a structure in which a piezoelectric substance layer (11B2) and an electrode layer (11B1) are stacked on top of each other in multiple layers. The matching layer (11A) is stacked on the piezoelectric element layer (11B) and has an acoustic impedance different from that of the piezoelectric element layer (11B). If the acoustic velocity in the piezoelectric element layer (11B) is Vp, the acoustic velocity in the matching layer (11A) is Vm, the thickness dimension of the piezoelectric element layer (11B) is Tp, and if the thickness dimension of the matching layer (11A) is Tm, then Vp/Vm = Tp/Tm. Further, if the dimension in the width direction is W, then Tp + Tm > W.