plate shaped vibration element se2 with a superpositional subdivision g3 at both surfaces these subdivisions in their cross sectional profile are in accordance withthe superpositional edge subdivision g of fig1 as already explained the regions of enhanced or reduced bending rigidity resp are forming here a system of juxtaposed longitudinally extending ridges or grooves resp which transversely to their longitudinal direction are forming superpositional subdivisions of the kind explained already fig3 represents in a schematical manner the possibility of further refining a superpositional surface subdivision i e in the form of two systems of ridge shaped regions a1 a2 a3 of enhanced bending rigidity these systems crossing each other on one surface of a plate shaped vibration element se3 and forming two superpositional subdivisions g3 and g4 in the kind of fig2 between the ridge shaped regions there are formed groove shaped surface regions of reduced bending rigidity not being provided with reference symbols for the sake of clearness subdivisions of this kind are allowing for a well defined influence on two dimensional standing wave patterns and should be taken into consideration for enhanced efficiency particularly with more ample resonant assemblies in cases where portions of plate resonators with an extraordinarily diminished remaining cross sectional thickness are to be avoided a crossing arrangement of a ridge groove subdivision on each of both plate surfaces is recommended similar subdivisional effects in principal can be obtained with the aid of a non uniform mass distribution also in particular with plate resonators presuming a uniform distribution of the deformation.