Developments in Ceramic Materials Research

228
R. Ramesh, H. Kara, Ron Stevens and C. R. Bowen
of a foam- reticulated piezocomposite sample shown in the figure. The complete 3-D model
along with the surrounding fluid medium is shown in Figure 5. One fourth of the geometry is
modelled due to symmetry and the plane of symmetry boundary conditions are applied on the
xz and yz planes. Although 1/8 th model could save considerable computing time, the nonsymmetry
of the electric potential along the z-axis does not allow such a possibility in the
present model. The ceramic volume fraction of the piezocomposite disc is taken as 22%. The
receiving sensitivity and electrical impedance are evaluated in two successive analyses
imposing appropriate boundary conditions. The boundary conditions are same as those of the
dense PZT hydrophone explained in the previous section. The material parameters used in the
model analysis are given in Table 1.
Table 1. Material parameters used in the model calculations. Data for PZT5H are taken
from Ref. [42] and typical values are taken for other materials
Parameter Value
I. PZT5H
Elastic coefficients (10 10 Nm -2 )
D
c11 D
c12 D
c13 D
c33 D
c44 D
c66 Piezoelectric coefficients (10 9 Vm -1 )
h 31
h 33
h
15
13.03
8.33
7.33
15.89
4.22
2.4
-0.5
1.8
1.13
Density (kgm -3 ) 7500
Dielectric constant 1470
II. Electrode
Density (kgm -3 ) 8250
Young’s modulus (GPa) 110
Poisson’s ratio 3.4
III. Encapsulation
Density (kgm -3 ) 940
Young’s modulus (MPa) 2.0
Poisson’s ratio 0.45
IV. Water
Density (kgm -3 ) 1000
Velocity of sound (ms -1 ) 1460