Actuator materials for extreme environments

There is a growing need for actuator materials that can operate efficiently at extreme temperatures. For example: the James Webb Space Telescope (JWST) requires shape and position control actuators that operate near 30 K (-243°C); while NASA´s planned Venus mission requires actuators that operate at 460°C (733 K). This paper discusses novel piezoelectric single crystal actuators and ultrasonic motors have been developed for use in cryogenic environments as low as 20 K (-253°C) and new ceramic piezoelectrics that operate at temperatures as high as 500°C (773 K). Various single crystal piezoelectric actuators have been developed including stack actuators and flextensional actuators with strokes up to 250 μm and resolutions of >1 nm at temperatures between 20 K and 300 K. A wobbling mode cryomotor has also developed with a stroke of 1 to 10 mm and a resolution of 20 nm in the temperature range of 77 K to 300 K. The cryogenic actuators presented in this paper feature high precision displacement control, high force output, quick response, low power consumption, and are free of magnetic field interference. These cryogenic actuators are very promising for shape control, precision positioning and force control in various NASA, military and civilian applications such as cryogenic adaptive optics for space telescopes, interferometers in terrestrial planet finder missions, and spectrometers for remote sensing applications. New actuator materials have also been developed specifically for high-temperature applications. This paper addresses development of this material for an ultrasonic rock drilling-coring-abrading tool to quickly sample Venus surface material for chemical analysis. The key innovation behind this device is a BiScO₃-PbTiO₃ based piezoelectric ceramic that has been modified to have high resistivity up to 500°C. This material was found to have very good piezoelectric properties to the depoling temperature of 420°C, and at 450°C it functioned as an electrostrictor with an induced piezoelectric coefficient of ∼450 pC/N under a 7 kV/cm DC bias.