User Manual
Page 4
Table 2. Comparison of piezoelectric materials
Property Units PVDF Film PZT BaTi0
3
Density 10
3
kg/m3 1.78 7.5 5.7
Relative Permittivity ε/ε
0
12 1,200 1,700
d
31
Constant (10
-12
)C/N 23 110 78
g
31
Constant (10
-3
)Vm/N 216 10 5
k
31
Constant % at 1 KHz 12 30 21
Acoustic Impedance (10
6
)kg/m
2
-sec. 2.7 30 30
OPERATING PROPERTIES FOR A TYPICAL PIEZO FILM ELEMENT
The DT1 element is a standard piezo film configuration consisting of a 12x30 mm active area
printed with silver ink electrodes on both surfaces of a 15x40 mm die-cut piezo polymer substrate.
1. Electro-Mechanical Conversion
(1 direction) 23 x 10
-12
m/V, 700 x 10
-6
N/V
(3 direction) -33 x 10
-12
m/V
2. Mechano-Electrical Conversion
(1 direction) 12 x 10
-3
V per microstrain, 400 x 10
-3
V/µm, 14.4V/N
(3 direction) 13 x 10
-3
V/N
3. Pyro-Electrical Conversion
8V/
o
K (@ 25
o
C)
4. Capacitance
1.36 x 10
-9
F; Dissipation Factor of 0.018 @ 10 KHz; Impedance of 12 KΩ @ 10 KHz
5. Maximum Operating Voltage
DC: 280 V (yields 7 µm displacement in 1 direction)
AC: 840 V (yields 21 µm displacement in 1 direction)
6. Maximum Applied Force (at break, 1 direction)
6-9 kgF (yields voltage output of 830 to 1275 V)
Electrical to Mechanical Conversion
Large displacements of forces are not generally available from piezo film. This becomes apparent
when designing loudspeaker elements for instance, as low frequency performance (below 500Hz)
tends to be limited. Even a large sheet of film is unable to create high amplitude pressure pulses as
low audio frequencies. This does not apply, however, to low to high frequency ultrasonic
frequencies, as seen in current designs for ultrasound air ranging transducers (40-50 KHz) and in
medical ultrasonic imaging applications. In enclosed air cavities (headset speakers, hearing aids), the
low frequency response of piezo film is excellent. For air ranging ultrasound, the piezo film element
height controls vertical beam angle and the curvature and width of the transducer controls
horizontal beam pattern. Piezo film air ranging transducers can provide up to 360
o
field of view,
ranging object from a few centimeters to several meters with high resolution.