7© KEMET Electronics Corporation • P.O. Box 5928 • Greenville, SC 29606 (864) 963-6300 • www.kemet.com P0101_AE • 4/6/2016
Multilayer Piezoelectric Actuators – AE Series Resin Coated
Reliability
The majority of failure modes on multilayer piezoelectric actuators are short-circuits due to degraded insulation. Although the cause of
degradation of insulation has not been claried, it has been found that the failure rate varies greatly between static uses (DC voltage
application) and dynamic uses (pulse voltage application). Like other electrical components, piezoelectric actuators can be affected by
humidity as well as applied voltage and ambient temperature. KEMET has added the metal sealed piezoelectric actuators featuring high
reliability by eliminating the effects of the ambient atmosphere.
This section describes reliability guidelines for static and dynamic usage of the resin coated type actuators. Reliability of our multilayer
piezoelectric actuators is represented by MTTF (mean time to failure) in case of static usage.
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 results. The MTTFr in actual applications is estimated using equation (1) below with MTTFs observed under
accelerated conditions as the reference value.
(1) MTTFr = MTTFs × A
v
× A
h
× A
t
MTTFr : Estimated value
MTTFs : Reference value (= 500 hours)
A
v
: Acceleration factor for drive voltage = (150/V
R
)
3.2
V
R
: Actual voltage (V)
A
h
: Acceleration factor for relative humidity = (90/H
R
)
4.9
H
R
: Actual relative humidity (RH%)
A
t
: Acceleration factor for ambient temperature = 1.5
(40 -Tr)/10
T
R
Actual ambient temperature (ºC)
The following calculation is made for the case of use at 25°C, 60% RH and 100 V.
MTTFr = 500 X (150/100)
3.2
X (90/60)
4.9
X 1.5
(40-25)/10
= 500 X 3.66 X 7.29 X 1.84
≈ 24,500 hours (2.8 years)
Pulse Voltage Application
In driving dynamic applications, temperature rises as a result of self-heating allowing the component not to be affected by the humidity,
thus extending the operational lifetime. This phenomenon is explained as a result of the humidity factor elimination caused by the self-
heating.
Since the self-heating value is affected by multiple factors such as the element’s shape, pulse waveform and frequency, it is difcult to
estimate the actual rising value. Therefore, the life of the actuator cannot be determined by using an equation, unlike the case of DC
voltage applications.
When testing the AE0203D08DF part, there was no failure conrmed after 500 hours end of the pulse driving test. (500 Hz, 0 – 150 V
rectangular pulse).
Users should be careful about the inuence of physical damage which can be caused by the xing method of the element and/or the
driving conditions.
