Design aspects of linear motor for a two-stage stirling cryocooler

Two-stage cryocoolers are used to maintain a lower temperature than that can be achieved in one stage. These are also used to have more than one temperature in electronic instruments. A two-stage expander has a large dead volume compared with that in a single stage; therefore two compressors are used to provide the alternating pressure. A dynamically balanced opposed piston compressor not only makes the system quiet in operation but also eliminates vibration. The reciprocating motion of the piston is obtained from a moving magnet type linear motor. The design of the linear motor to power the piston is a critical one for the efficient and reliable operation of the cooler. In this paper, various configurations of linear motor have been identified and electromagnetic analysis has been performed. The design of the motor involves the size estimation followed by the optimisation of different geometrical and electromagnetic parameters. Based on the analysis of existing structures of linear motors, a novel structure has been identified which would meet the characteristics such as high air-gap flux density, small volume, light weight and simple installation.