the body portion 12 or attached to the body portion by suitable securing methods as shown there are two elevated regions 14 each elevated region 14 is coextensive with one of the opposite ends 20 of the cylindrical body portion 12 so as to extend therefrom and terminates in an outer edge 24 of the elevated region 14 the positioning of the elevated region 14 at opposite ends 20 of the cylindrical body portion 12 has been found to be optimal for the ultrasonic transmitter of the present invention however this arrangement should not be construed to eliminate the possibility of the elevated region 14 being set in from one or more opposite ends 20 of the cylindrical body portion 12 of the spool 10 further the outer peripheral edge 24 of the elevated region 14 is shown to be at least 0 1 mm from the outer peripheral surface 16 of the body portion 12 the determination of that optimum distance and its effect will be described in the following referring now in further detail to fig2 there is shown a film 26 wrapped around the spool 10 in particular the film 26 is a pvdf film similar to the type used in the conventional art but applied to a cylinder in a different manner than known in the art as shown here the film 26 is of a sheet type having opposite longitudinal edges and opposite lateral edges the longitudinal edges are positioned to surround the outer peripheral edge 24.