Review of Cryogenic Piezoelectric Ultrasonic Motors for Aerospace Applications

One challenge for NASA's Artemis missions is ensuring the development of efficient actuation systems that can function within the harsh temperature range of -230°C to 125°C found on the lunar surface. The performance, efficiency, and torque output of conventional electromagnetic motors depend on the interplay between electric currents and magnetic fields, is significantly reduced below -80°C or over 80°C. For a solution to this restriction, NASA is investigating the possibilities of superconducting motors, which function at cryogenic temperatures, having no electrical resistance when cooled below a threshold temperature. However, the efficiency of metal based superconduct material will be significantly reduced even temperature raise to -263 C (10 K) and ceramic based super conductive material is not in commercial stage yet. In the last two decades, the piezoelectric device community develop piezoelectric ceramic PZT based ultrasonic motors (USMs) exhibits some promises. In addition, recently developed relaxer piezoelectric Pb(Mg1/3Nb2/3)1-xTixO3 (PMN-PT) single crystal, and (1−x)Pb(In1/2Nb1/2)O3–0.33Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PIN–PZN–PT) exhibit excellent cryogenic properties with energy conversion efficiency at 80%. This paper provides a comprehensive review on related technologies. First, the major material properties, such as elastic properties, dielectric properties, piezoelectric properties, electromechanical coupling factors, mechanical quality factor of relaxer piezoelectric materials from room temperature down to -263 C (10 K) are summarized. Example of cryogenic actuators performance is also presented. Ultra-high electromechanical coupling factor and mechanical quality factor of relaxer piezoelectric materials at cryogenic temperature are excellent properties for USM application. Secondly, the working principles of USMs and the classifications of USMs are discussed. Examples of recently developed cryogenic USMs are provided and summarized. Third, the potential aerospace applications of cryogenic USMs are discussed. Finally, the future perspectives and challenges of cryogenic USM predicted. The cryogenic USMs technologies provide NASA Space missions an alternative technology for various power and dynamic control solutions.