User Manual

Page 25
Figure 23. Thermal stability of d33 constant - 70b
bb
bC annealed PVDF
Figure 24. Temperature coefficient for d33 and g31
constants - PVDF
Figure 25a. Dielectric loss tangent vs. temperature
COPOLYMER
Figure 25b. Dielectric constant vs. temperature
COPOLYMER
TEMPERATURE EFFECTS
Many of the properties of piezo film
change with excitation frequency and
temperature. These properties are
reversible and repeatable with either
frequency or temperature cycling.
In addition, Figure 23 shows the
permanent decay of the piezoelectric
strain constant d
33
for PVDF,
annealed at 70
o
C, after long term
exposure to elevated temperatures.
Having reached a stabilizing temperature, the material properties then remain constant with time. Piezo film
can be annealed to specific operating (or maximum storage) temperatures to achieve long-term stability for
high temperature applications. Figure 24 shows
the reversible temperature effects on d
33
and g
31
coefficients for PVDF.
In Figures 25a and 25b, the effect of temperature
on the dielectric constant (ε/ε
O
) and dissipation
factor (tan δ
e)
are shown for copolymer films.
Piezo films have been shown to offer excellent
transducer properties at very low (cryogenic)
temperatures.