Yes there is one supposedly Gavreau US# 2757247 July 1956. I believe you
guys can see the patent synopsis at some of the local libraries, since this
one is a bit too old for the IBM server it may be best to look in the
library.
I agree its not patented as a infrasound canon. I worked in the arms
industry for many years and all I heard was rumours about this thing. And of
course the story that it was rather indiscriminate. I am however interested
in the possible OU effects of the device, it appears to cause damage that
may be a little out of proportion with its input.
Regards
Martin
http://www.geocities.com/CapeCanaveral/Lab/7919/