A transducer comprising an acoustic energy generating means and a resonator. The acoustic energy generating means generates acoustic energy and is adapted for delivering an approximately uniform amount of acoustic energy to each unit of surface area on a substrate in a given time period when the substrate is rotating. The acoustic energy generating means has a surface area that is less than the surface area of the substrate, and may comprise two or more piezoelectric crystal segments that are separately controllable with respect to power and/or time. When assembled, the two more piezoelectric crystal segments give the acoustic energy generating means a rectangular shape, a wedge shape or a triangle shape. The resonator is attached to the acoustic energy generating means for transmitting the acoustic energy to the substrate.