Breakthrough Thermoacoustic Stirling Generator Converts Energy No Moving Parts
nextbigfuture.com
nextbigfuture.com
Surprisingly it is still plausible. It is a niche application for a very specific form factor and purpose.
As stated there is also a military application. Since they run so quietly they are suitable to make power (to run systems, not thrust) on submarines, especially nuclear subs, which want to be as quiet as possible. I think subs already actually use stirling generators but this design is potentially quieter and more reliable.