Reliability
Majority of failure mode of multilayer piezoelectric actuators is the short circuit due to degraded insulation.
Though the cause of degradation of insulation has not been clarified perfectly, it has been found that the
failure rate varies greatly between statistic uses（DC voltage application）and dynamic uses（pulse voltage
application）. Like other electrical components, piezo actuators can be influenced by humidity as well as
applied voltage and ambient temperature. NEC TOKIN has added the metal sealed type piezo actuators
featuring high reliability by eliminating influence of the ambient atmosphere.
This section describes reliability guidelines for static and dynamic usages of the resin-coated and metal
sealed types actuators.
Reliability of our multilayer piezoelectric actuators is represented by MTTF（mean time to failure）in case of
static usage. Though the number of repetitions is considered to be used to represent the reliability in the
case of dynamic usage, the accurate relationship between the indicator and cause has not been determined
because of various influential causes and the mutual action between them. For the present, therefore, only
the obtained data and our concept are described.
（1）Resin-coated Type（AE Series）
a. DC voltage application
The acceleration factors have been obtained empirically for each of the drive voltage, ambient
temperature and relative humidity based on many experimental result. The MTTFr in actual
applications is estimated using equation（1）below with MTTFs observed under accelerated condition
as the reference value.
MTTF
r
=MTTF
s
×A
: Estimated value
: Reference value (=500h)
v
×A
h
×A
t
• • • (1)
MTTF
MTTF
r
s
3.2
150
A
A
A
v
h
t
: Acceleration factor for drive voltage=
V
r
: Actual voltage (V)
V
r
4.9
90
: Acceleration factor for relative humidity=
H
r
: Actual relative humidity (RH%)
H
r
40–Tr
10
: Acceleration factor for ambient temperature=1.5
Tr : Actual ambient temperature(℃)
[Example] The following calculation is made for the case of use at 25℃, 60% RH and 100 V:
3.2
4.9
40–25
10
150
100
90
60
MTTF
r
=500×
×
×1.5
=500×3.66×7.29×1.84
24,500h (2.8years)
b. Pulse voltage application
When this element is driven by a pulse voltage, temperature rises as a result of heating due to
dielectric loss of ceramics. Therefore, the element is not likely to be influenced by the humidity, thus
extending the service life greatly. Since this effect is affected by the element shape, pulse waveform
and frequency, it cannot be calculated by an equation as in the case of DC voltage application.
In NEC TOKINʼs testing on the AE0203D08, there was no failure confirmed after 0-150 V rectangular
pulse wave was applied with 500 Hz for 500 hours（equivalent to 900 million pulses were applied）.
Please pay attention to the physical damage due to ringing phenomenon caused by the fixed method
of the element and the speed of the voltage rise.
Please refer to the separately printed literature, “ NEC TOKIN Multilayer Piezoelectric Actuators Userʼs
Manual” for more detail.
Multilayer Piezoelectric Actuators Vol.06 19
●All specifications in this catalog and production status of products are subject to change without notice. Prior to the purchase, please contact NEC TOKIN for updated product data.
●Please request for a specification sheet for detailed product data prior to the purchase.
●Before using the product in this catalog, please read "Precautions" and other safety precautions listed in the printed version catalog.
2011.06.22 9307MPAVOL06E1106H2
NEC [ NEC ]
