User Manual

Page 35
V 
(30x10
6
C/m
2
bK)(9x10
6
m)(1bK)
(106x10
12
C/Vm)
V  2.55 volts
The charge and voltage produced in a given film of area A permittivity ε, and thickness t is given
by :
Q  p∆ TA
V  pt∆ T/ε
EXAMPLE 5:
A piezo film pyroelectric detector having a film thickness (t) of 9µm, a permittivity (ε) of 106x10
-
12
C/Vm and a pyroelectric coefficient (p) of 30x10
-6
C/(m
2o
K), undergoes a temperature increase
(∆T) of 1
o
K due to incident IR radiation. The output voltage is given by:
The pyroelectric voltage coefficient of piezo film is about an order of magnitude larger than those of Lead
Zirconate Titanate (PZT) and Barium Titanate (BaTiO
3
). Table 5 compares the pyroelectric properties of
these materials, but a far lower figure of merit due to the low capacitance of PVDF.
Table 5. Comparison of pyroelectric materials
Material TGS LiTaO
3
BaTiO
3
PZT PbTiO
3
PVDF VF
2
VF
3
ρ
Q
350 200 400 420 230 30 50
ε / ε
O
30 45 1000 1600 200 10.7 8.0
α .16 1.31 1.00 .44 .67 .06 .06
L 225 646 564 374 461 138 138
P
v
1.32 .50 .05 .03 .10 .47 .71
M
l
.53 .16 .02 .01 .03 .20 .31
Pyroelectric Charge Coefficient
(
ρ
Q
)µCoul/[m
2
•bK]
Dielectric Constant
(
ε/ε
o
),where ε
o
8.85pF/m
Thermal Diffusivity (α)m
2
/sec •10
-6
Thermal Diffusion Depth @ 1Hz (L)µm
Pyroelectric Voltage Coefficient
(P
V
)ρ
Q
/ε, V/[µm•bK]
Figure of Merit
(M
l
)ρ
Q
/[C
V
•ε], V •mm
2
/J