Abstract: A base of piezoelectrically active material having a plurality of spaced apart reflectors formed thereon and transducers positioned between at least some of said adjacent reflectors to produce standing waves at a predetermined frequency, the reflectors between transducers being formed with less than one hundred percent reflectivity so that energy from a standing wave between a pair of adjacent reflectors is coupled through the system to other pairs of reflectors for producing standing waves therebetween. The transducers may operate as electrical energy inputs or as taps to remove energy from the system.