This paper presents a review of the art of small cryogenic refrigerator and considers problems for future demand. In this paper, I would limit my discussion to only five cycles; Stirling, Gifford-McMahon, Solvay, Vuilleumier and Taconis. Because the majority of successful small refrigerators use thermal regenerators, and these cycles are the typical cycles using thermal regenerators.
Among many cryogenic applications, the Parametric amplifier for telecommunications is already in industrial use. Now, Infrared detector and superconducting applications are in progress and look promising.
When we think about future demand for small cryogenic refrigerators, high reliability and low cost of refrigeration will be the decisive factors.