Chapter 14 Low Temperature Materials and Mechanisms: Applications and Challenges

Mechanisms ........................................................................................................................ 187 7.3 Figure of Merit of Piezoelectric Materials ...................................................................... 189 7.4 Materials Properties versus Temperature ...................................................................... 1927.4.1 Cryogenic PZT Ceramics ...................................................................................... 192 7.4.2 Cryogenic Relaxor-PT Crystals ............................................................................ 1967.5 Recent Development of Cryogenic Actuators and Sensors .........................................200 7.5.1 Multilayer Stack Actuators ...................................................................................200 7.5.2 Piezoelectric Motors .............................................................................................. 201 7.5.3 Active Tuning in Cryogenic Superconducting Radio Frequency (SRF)Cavities .................................................................................................................... 204 7.5.4 Structural Health Monitoring .............................................................................. 204 7.5.5 Cryogenic Liquid Sensing .................................................................................... 205 7.5.6 MEMS and NEMS Devices at Cryogenic Temperature .................................... 2067.6 Summary ............................................................................................................................. 207 Acknowledgments ...................................................................................................................... 208 References ..................................................................................................................................... 208material processing, hardening [Kalia, 2010; Zurecki, 2005], and quenching [Barron, 1982; Zurecki, 2005]. Many of these systems require actuators to control structure shapes, to operate local valves to control cryo¤uid ¤ows, or to position structures during operation. In the aerospace area, there are a variety of potential mission targets identi†ed in theDecadal Survey that have cryogenic environments [Squyres, 2011]. For example, unlike Earth, other bodies in the solar system do reach the cryogenic temperature range, as shown in Figure 7.1. The outer planets including the dwarf planet Pluto and the moons of Saturn and Neptune all reach temperatures below –150°C. Even though the average temperatures on the Moon and Mars are within the range of Earth temperatures, the lack of substantial atmosphere on these bodies produces extreme temperature ranges with the poles of Mars reaching –140°C and the nighttime temperature of the Moon reaching –170°C. Although Mercury is the closest planet to the Sun, it has temperature extremes that reach –173°C. The need for reliable surface sampling and handling technology has been identi†ed as a challenge that must be met if sampling missions to these destinations are to move past the planning stage. As well as the standard actuators required for exploration systems [Sherrit, 2005], novel actuators and sensors are required for valves [Sherrit et al., 2014], vibrators [Sherrit et al., 2009], drills [Bar-Cohen and Zacny, 2009], penetrators [Bao et al., 2006], sonar [Towner et al., 2006], microphones [Fulchignoni and Ferri, 2006], and other transduction applications. Another space application for cryogenic actuators is in infrared telescopes that may beground-based, airborne, or space telescopes. The common component of each of these telescopes is the infrared solid-state detector that must be cooled to cryogenic temperatures. In addition, infrared space telescopes require cryo-cooling systems to maintain sensitivity, which requires the use of valves. A variety of missions have been proposedusing infrared cameras or detectors including SIRTF/SAFIR, the mid infrared instrument (MIRI) of the James Webb Space Telescope (JWST) [Stockman, 1997]. JWST, previously known as Next Generation Space Telescope (NGST), was designed as a large space infrared telescope to achieve a 1000 times greater sensitivity than any currently existing or planned facilities [Stockman, 1997]. The design requirements include a large primary mirror (6-8 m diameter), orbit at the second Lagrange point (L2), and an operation temperature between 35 and 65 K. Due to the long distance (1.5 million kilometers) between the telescope and the space shuttle, JWST's orbit will be unserviceable, rendering the active optics a necessity. Cryogenic actuators are used to position the mirror segments by image plane wavefront sensing. Occasional refocus is needed every few days after the initial con†guration. Based on the three-mirror anastigmatic design, the telescope has secondary and tertiary mirrors to deliver images that are free of optical aberrations, which could be achieved using adaptive optics consisting of cryogenic deformable mirrors. Cryogenic actuator arrays with large stroke, high force, high resolution and low power consumption become very critical for the development of the deformable mirrors. On the other side, for infrared detection, a cryogenic environment could greatly diminish the noise caused by the Stefan-Boltzmann law, which provides a huge advantage in the sensitivity over those detectors that are not cooled. Cryogenic sensors, actuators, and motors are hence essential for proper operation of these space instruments. The Spitzer Space Telescope [Finley et al., 2004], shown in Figure 7.2, has detectors thatmust be cooled to only about 5° above absolute zero to ensure that the telescopes internal heating does not interfere with its observations of cold cosmic objects. To accomplish this, the telescope has a cryostat of liquid helium that requires low-power cryogenic actuators to open venting valves. Some scienti†c instruments in which cryogenic devices are becoming more commoninclude probes, stages, and scanners of the scanning tunneling microscope (STM) and the atomic force microscope (AFM) for surface science study [Saitoh et al., 2009], shown in Figure 7.3. The precise tip-surface positioning in a cryogenic environment is possible because of very low thermal drift. On the other hand, some special phenomena, for example, charge density wave (CDW), superconductivity, and structural phase transition, are only observable at a cryogenic state. Other commercial and space applications of cryogenic transducers include the transferand transportation of lique†ed gases [Park et al., 2008]. The processes of separating air into its components and the resulting production of liquid oxygen, liquid nitrogen, liquid helium, and liquid argon are some of the primary commercial cryogenic applications. Cryogenic ¤uid devices including valves are needed to control the ¤ow of these liquid gases in various scenarios, for example, liquid oxygen and liquid hydrogen for space shuttle propulsion, liquid nitrogen for food freezing, cooling of chamber systems for high-vacuum state, cooling of infrared detector and medical applications, liquid argon for plasma technologies, etc. In addition to these cryogenic actuator applications, transducer materials have manysensing applications at low temperatures. One typical application is the monitoring of the integrity of structures working in cryogenic surroundings. For instance, pressure vessels in liquid rocket engines can fail due to many causes including corrosion, pitting, stress corrosion cracks, seam weld cracks, and dents due to internal or external impacts [Qing et al., 2008]. The detection of defects and monitoring of their growth are important for ensuring the safety and reliability of advanced space exploration vehicles/ propulsion systems. Also, the sensing of cryogenic liquid level, ¤ow pressure, and velocity is important for many cryogenic ¤uid handling applications [Fisher and Malocha, 2007].