22 Lecture ] 
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oO 
a 
SS 
wn 
— 
=) 
fo} 
> 
+20 
T T T r u r u u Fig. 1.14. Sensitivity at 200 
Loe> Gee Se < == = cps vs hydrostatic pressure. 
18 5 
2ND cycLe 
16 |= i —————— {a 
° | 2 3 4 5 6 7 8 
PRESSURE (10° PS1) 
Figures 1.14 and 1.15 show the effect of pressure on the sensitivities of a 
barium titanate and a PZT-4 spherical hydrophone at 200 cps for the first and 
second cycles of pressure; there is little change in the barium titanate but the 
sensitivity of the PZT-4 unit is reduced from approximately 24uvolts/ubar to 
20pvolts /ubar. 
Very little work has been published onthe effect of pressure on the important 
parameters of transducer materials. However, some work has been published on 
the effect of stress on the dielectric properties of ceramic ferroelectrics [18] 
and it has been shown that large changes in dielectric constant can occur. The 
effect of stress is complicated; and the results depend on a number of variables 
in addition to the stress; the state of polarization of the samples, their history, 
time of measurement after the application of stress, and whether the stress is 
unidimensional, planar, or hydrostatic. These facts probably account for some of 
the disagreement among the papers. 
26 
22 ST CYCLE 
| 
n 
n 
}# VOLTS / & BAR 
n 
> 
Fig. 1.15. Sensitivity at 200 
cps vs hydrostatic pressure call 
of PZT-4 sphere. 
2ND cycLe 
PRESSURE (10> PS!) 
