Laminated piezoelectric element and multi-feed detection sensor
A laminated piezoelectric element that includes a piezoelectric element layer and a matching layer. The piezoelectric element layer is configured to have a plurality of piezoelectric layers and a plurality of electrode layers laminated together. The matching layer is laminated on the piezoelectric element layer, and is different in acoustic impedance from the piezoelectric element layer. When Vp represents the acoustic velocity in the piezoelectric element layer, Vm represents the acoustic velocity in the matching layer, Tp represents the thickness dimension of the piezoelectric element layer, and Tm represents the thickness dimension of the matching layer, Vp/Vm=Tp/Tm holds. Further, when W represents the dimension of the laminated piezoelectric element in the width direction, Tp+Tm>W holds.
1. A laminated piezoelectric element comprising:
a piezoelectric element layer having a plurality of piezoelectric layers and a plurality of electrode layers laminated in a thickness direction; and
a matching layer laminated on the piezoelectric element layer in the thickness direction, the matching layer being different in acoustic impedance from the piezoelectric element layer,
wherein, when Vp represents the acoustic velocity in the piezoelectric element layer, Vm represents the acoustic velocity in the matching layer, Tp represents the dimension of the piezoelectric element layer in the thickness direction, and Tm represents the dimension of the matching layer in the thickness direction, Vp/Vm=Tp/Tm, and
wherein, when W represents the dimension of the laminated piezoelectric element in a width direction perpendicular to the thickness direction, Tp+Tm>W.
2. The laminated piezoelectric element according to claim 1 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or less than 1/1.39.
3. The laminated piezoelectric element according to claim 1 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or less than 1/1.88.
4. The laminated piezoelectric element according to claim 1 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or greater than 1/2.27.
5. The laminated piezoelectric element according to claim 1 , wherein the acoustic impedance of the matching layer matches an acoustic impedance between the piezoelectric element layer and air.
6. A multi-feed detection sensor comprising:
a wave transmission ultrasonic transducer; and
a wave reception ultrasonic transducer spaced from the wave transmission ultrasonic transducer with a detection position interposed therebetween,
wherein at least one of the wave transmission ultrasonic transducer and the wave reception ultrasonic transducer is the laminated piezoelectric element according to claim 1 .
7. The multi-feed detection sensor according to claim 6 , wherein both the wave transmission ultrasonic transducer and the wave reception ultrasonic transducer are the laminated piezoelectric element.
8. The multi-feed detection sensor according to claim 7 , wherein a number of laminations of the piezoelectric layers and the electrode layers in the laminated piezoelectric element of the wave transmission ultrasonic transducer is larger than a number of laminations of the piezoelectric layers and the electrode layers in the laminated piezoelectric element of the wave reception ultrasonic transducer.
9. The multi-feed detection sensor according to claim 6 , wherein a frequency f of acoustic waves is equal to or higher than 100 kHz.
10. The multi-feed detection sensor according to claim 6 , further comprising:
an oscillator connected to the wave transmission ultrasonic transducer;
an oscilloscope connected to the wave reception ultrasonic transducer; and
an amplifier connected between the oscilloscope and the wave reception ultrasonic transducer.
11. The multi-feed detection sensor according to claim 6 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or less than 1/1.39.
12. The multi-feed detection sensor according to claim 6 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or less than 1/1.88.
13. The multi-feed detection sensor according to claim 6 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or greater than 1/2.27.
14. An ultrasonic transducer comprising:
the laminated piezoelectric element according to claim 1 ;
a resin case surrounding the laminated piezoelectric element and having first and second opposed open ends, the resin case holding the laminated piezoelectric element such that an end portion of the laminated piezoelectric element projects from the first open end; and
a pair of metal terminals extending into the resin case from the second open end and contacting the laminated piezoelectric element.
15. The ultrasonic transducer according to claim 11 , further comprising a metal cover surrounding the resin case.
16. The ultrasonic transducer according to claim 11 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or less than 1/1.39.
17. The ultrasonic transducer according to claim 11 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or less than 1/1.88.
18. The ultrasonic transducer according to claim 11 , wherein W=k1×(Tp+Tm), and the coefficient k1 is greater than 0 and is equal to or greater than 1/2.27.