The internal electrodes and the piezo ceramic are sintered together (cofiring technology) resulting in a monolithic piezoceramic block. The inorganic, ceramic insulation layer prevents the penetration of water molecules and thus extends the lifetime by several orders of magnitude when compared with merely polymer-coated multilayer actuators (Fig. 2). At the same time the sensitive internal electrodes are protected reliably against mechanical damage and soiling.
Reducing Mechanical Tension
Slots on the side of the PICMA® actuators effectively prevent excessive mechanical tensile stress in the passive regions of the stack and the formation of uncontrolled expansion cracks, that may lead to electrical breakdowns causing damage to the actuator (Fig. 3).
The meander-shaped design of the external contact strips ensures stable electrical contact with all inner electrodes, even under extreme dynamic loads (Fig. 4).
Accelerated Lifetime Test under Quasi-Static Conditions
Their high reliability makes it practically impossible to experimentally determine the lifetime of PICMA® actuators under real application conditions.
Therefore, tests under extreme load conditions are used to estimate the lifetime: Elevated atmospheric humidity and simultaneously high ambient temperatures and control voltages (Fig. 6).
Leakage current measurements impressively demonstrate how effective the monolithic design of the PICMA® actuators prevents the penetration of moisture (Fig. 7).
The high insulation resistance of the PICMA® actuators remains stable over several time decades, whereas conventional polymer-coated actuators already exhibit a significantly increased leakage current after only a few hours.