• How does it all work?
• Other Cooling Technologies
• Competitive Comparison

Helium gas in the thermal buffer tube, hot heat exchanger, inertance tube, and reservoir does some, but only minor, heat pumping. Mainly, this acoustic tuning section acts like a mechanical piston, expanding the precooled gas parcel in the cold heat exchanger. This is one of the major benefits of acoustic Stirling technology, there are no mechanical parts operating in the cold region of the system (such as in traditional Stirling machines), only an acoustic network of compressed helium that acts like a piston.

Liquid nitrogen (LN2) has long been the standard cryogenic cooling method.  It is inexpensive and provides reliable unlimited cooling capacity.  However, LN2 can only cool to its liquefaction temperature 77K, and the need to constantly replace the expendable cryogen leads to logistical inconvenience, cost, and delivery risk.

Because of its limited cooling temperature and the inconvenience — and in some applications the impossibility — of using LN2, users have frequently sought alternate ways to produce cryogenic cooling capacity. This has led to the development of many types of mechanical coolers including: displacer Stirling, Joule-Thomson, Gifford-McMahon, and acoustic Stirling type coolers. All cooler types have inherent strengths and weaknesses that make them better or worse for any particular applications.

Displacer Stirling cryocoolers use a mechanical displacer in the cold region of the cryocooler to expand compressed helium gas and create cooling. Typically these systems provide good efficiency and are fairly reliable and provide a range of cooling capacities at 77K. A major disadvantage of these systems is that the mechanical displacer motion creates vibration that is often at an unacceptable level for some sensitive applications.

Joule-Thomson (JT) systems use high-ratio oiled compressors that compress a specific mixture of refrigerant gas. The gas is expanded through a small orifice and cooling is produced. JT systems provide cryogenic cooling with a minimum of vibration because there are no moving parts in the cold region. The gas mixture that is expanded is specific to the desired cooling temperature, and JT systems often have poor cooling efficiencies across the cooling envelope. Also, they are unreliable as the small expansion orifice can easily become clogged with oil/particles and regular service, maintenance, and even unit replacement is common with these types of systems.

Gifford-McMahon (GM) systems use a conventional oiled gas compressor to supply a steady compressed stream of compressed helium to a coldhead through which the helium is expanded with mechanically driven valves. GM systems are preferred for temperatures that require temperatures well below 77K, but because of the coldhead valve wear and oil in the compressors they require regular maintenance and service.  Also, the compressors can only be used when resting still on a level surface, making them unsuitable for some military and aerospace applications. GM coolers also produce a significant noise and vibration in the coldheads, making them unusable in laboratory situations.