Abstract: A device for generating .[.ultrasonic.]. waves in a fluid preferably used in emulsifying water and fuel oil and the like constructed of two side plates (each having at least one recess, occurring in adjacent pairs) and a thin steel membrane disk having a liquid access groove (discontinuities) cut out of said disk and extending into said recess such that the remaining portion of the membrane disk extending across each recess pair vibrates (preferably resonates) in the liquid flowing through said groove and into one of said recesses to pass out a discharge conduit extending from the base of such recess.