Who invented the first single piston hot air engine?

[kenway]

I like stirling engines but there's an engine with just one piston called a Lag engine or thermo acoustic engine. Sometimes these engines are referred to as Lamina flow engines. I was wondering if anyone knew when this was invented? I don't understand patents too well but I found this patent that was issued in the 1990s :

http://www.google.com/patents?id=wngjAAAAEBAJ&pg=PA2&dq=lag+engine&source=gbs_selected_pages&cad=4#v=onepage&q=lag%20engine&f=false

I have recently read E. T. Warbrooke's book Building Stirling 1 that suggested that single piston hot air engines have been around for decades. Can anyone shed some light on this or point me in a direction I could find more info?