Piezoelectric film, laminated piezoelectric element, and electroacoustic transducer
An object is to provide a piezoelectric film that has excellent flexibility in a high temperature environment at higher than 50° C. and exhibits good flexibility even at room temperature, a laminated piezoelectric element in which the piezoelectric films are laminated, and an electroacoustic transducer using the piezoelectric film or the laminated piezoelectric element. The object is solved by the piezoelectric film including: a polymer-based piezoelectric composite material in which piezoelectric particles are dispersed in a matrix including a polymer material; and electrode layers provided on both surfaces of the polymer-based piezoelectric composite material, in which a loss tangent at a frequency of 1 Hz according to dynamic viscoelasticity measurement has a maximal value of greater than or equal to 0.1 existing in a temperature range of higher than 50° C. and lower than or equal to 150° C., and has a value of greater than or equal to 0.08 at 50° C.
1. A piezoelectric film comprising:
a polymer-based piezoelectric composite material in which piezoelectric particles are dispersed in a matrix including a polymer material; and
electrode layers formed on both surfaces of the polymer-based piezoelectric composite material,
wherein a loss tangent at a frequency of 1 Hz according to dynamic viscoelasticity measurement has a maximal value of greater than or equal to 0.1 existing in a temperature range of higher than 50° C. and lower than or equal to 150° C., and has a value of greater than or equal to 0.08 at 50° C.
2. The piezoelectric film according to claim 1 , further comprising:
a protective layer provided on a surface of the electrode layer.
3. The piezoelectric film according to claim 1 ,
wherein the piezoelectric film is polarized in a thickness direction.
4. The piezoelectric film according to claim 1 ,
wherein the piezoelectric film has no in-plane anisotropy in piezoelectric properties.
5. The piezoelectric film according to claim 1 , further comprising:
a lead wire for connecting the electrode layer to an external power source.
6. A laminated piezoelectric element formed by laminating a plurality of layers of the piezoelectric films according to claim 1 .
7. The laminated piezoelectric element according to claim 6 ,
wherein the piezoelectric films are polarized in a thickness direction, and
polarization directions of the piezoelectric films adjacent to each other are opposite to each other.
8. The laminated piezoelectric element according to claim 6 ,
wherein the laminated piezoelectric element is formed by laminating a plurality of layers of the piezoelectric film by folding back the piezoelectric film one or more times.
9. The laminated piezoelectric element according to claim 6 , comprising:
a bonding layer which bonds the piezoelectric films adjacent to each other.
10. An electroacoustic transducer comprising:
a vibration plate; and
the laminated piezoelectric element according to claim 6 .
11. The electroacoustic transducer according to claim 10 ,
wherein a product of a thickness of the laminated piezoelectric element and a storage elastic modulus at a frequency of 1 Hz and 25° C. according to dynamic viscoelasticity measurement is 0.1 to 3 times a product of a thickness of the vibration plate and a Young's modulus.
12. The electroacoustic transducer according to claim 10 ,
wherein a product of a thickness of the laminated piezoelectric element and a storage elastic modulus at a frequency of 1 kHz and 25° C. in a master curve obtained from dynamic viscoelasticity measurement is 0.3 to 10 times a product of a thickness of the vibration plate and a Young's modulus.
13. The electroacoustic transducer according to claim 10 , further comprising:
a bonding layer which bonds the vibration plate to the laminated piezoelectric element.
14. An electroacoustic transducer comprising:
a vibration plate; and
the piezoelectric film according to claim 1 .
15. The electroacoustic transducer according to claim 14 ,
wherein a product of a thickness of the piezoelectric film and a storage elastic modulus at a frequency of 1 Hz and 25° C. according to dynamic viscoelasticity measurement is 0.1 to 3 times a product of a thickness of the vibration plate and a Young's modulus.
16. The electroacoustic transducer according to claim 14 ,
wherein a product of a thickness of the piezoelectric film and a storage elastic modulus at a frequency of 1 kHz and 25° C. in a master curve obtained from dynamic viscoelasticity measurement is 0.3 to 10 times a product of a thickness of the vibration plate and a Young's modulus.
17. The electroacoustic transducer according to claim 14 , further comprising:
a bonding layer which bonds the vibration plate to the piezoelectric film.