Most of the modern commercially available tactical split Stirling linear cryocoolers rely on a dual-piston, internally counterbalanced compressor, and a single-piston resonant pneumatic expander interconnected by a flexible transfer line.
The industry adopted this concept in the late 90s when cryogenic technology reached the maturity level sufficient for integration with inherently vibration-sensitive cryogenically cooled infrared detectors.
In the dual-piston compressor, the vibration export is, to a specific extent, counterbalanced by the opposite motion of the ‘should be similar’ moving sub-assemblies.
In the expander, the imbalanced motion of the displacer assembly generates vibration export, which is inherently small because of the relatively low weight of the moving assembly. It is interesting to note, nevertheless, that the vibration export produced by such an expander may be higher in comparison to the dual-piston compressor and, therefore, cannot be disregarded.
In the most general case, the vibration export produced by such a cryocooler comprises force and moment components. The resulting cryocooler-induced vibration, therefore, comprises translation and tilt eventuating, in some cases, in the excessive line of sight jitter. It is worth noting that vibration export produced by the expander may be a major contributor to the tilting components of cooler-induced vibration resulting in smeared imagery.
Read how CryoTech’s ARNE tackles this problem in our TechNote.