According to Paschen's Law, the breakdown voltage of a gas depends on the product of the pressure p and the electrode gap s. Air has very good insulation values at atmospheric pressure and at very low pressures. The minimum breakdown voltage of 300 V corresponds to a ps product of 1000 Pa mm.
PICMA® stack actuators of nominal voltages of considerably less than 300 V can therefore be operated at any intermediate pressure. In order to prevent breakdowns, PICA piezo actuators with nominal voltages of more than 300 V, however, should not be operated or only be driven at strongly reduced voltages when air is in the pressure range of 100 to 50,000 Pa.
The outgassing behavior depends on the design and construction of the piezo actuators. PICMA® actuators are excellently suited for use in ultrahigh vacuums, since they can be manufactured without polymer components and can be baked out at up to 150 °C. UHV options with minimum outgassing rates are also offered for different PICA actuators.
Piezo actuators are suitable for use in inert gases such as helium, argon, or neon. However, the pressure-dependent flashover resistances of the Paschen curves must be observed here as well.
For this use, the ceramic-insulated PICMA® actuators are recommended, since their nominal voltage is below the minimum breakdown voltages of all inert gases. For PICA actuators of higher nominal voltages, the operating voltage should be decreased in particular pressure ranges to reduce the flashover risk.
Piezo actuators are excellently suited to be used in very high magnetic fields, e.g., even at cryogenic temperatures. PICMA® are manufactured completely without ferromagnetic materials.
PICA stack actuators are optionally available without ferromagnetic components. Residual magnetisms in the range of a few nanotesla have been measured in these products.
Environments with High Humidity
When piezo actuators are operated in dry environments, their lifetime is always higher than in high humidity. When the actuators are operated with high-frequency alternating voltages, they self-heat, thus keeping the local moisture very low.
Continuous operation at high DC voltages in a humid environment can damage piezo actuators. This especially holds true for the actuators of the PICA series, since their active electrodes are only protected by a polymer coating that can be penetrated by humidity.
The actuators of the PICMA® series have an all-ceramic insulation, which considerably improves their >> Lifetime in Humid Ambient Conditions compared with polymer-coated actuators.
Temperature Operating Range
The standard temperature operating range of glued actuators is -20 to 85 °C. Selecting piezo ceramics with high Curie temperatures and suitable adhesives can increase this range. Most PICMA® multilayer products are specified for the extended range of -40 to 150 °C.
With special solders, the temperature range can be increased so that special models of PICMA® actuators can be used between -271 °C and 200 °C, i.e., over a range of almost 500 K.
For use in liquids, encapsulated PICMA® or specially encased PICA actuators are available. With all other actuator types, direct contact with liquids should be avoided. Highly insulating liquids can be exceptions to this rule. Normally, however, the compatibility of the actuators with these liquids must be checked in lifetime tests.