Advanced audio applications are more and more demanding with respect to the visual impact of loudspeakers while still requiring more channels for high quality spatial sound rendering. The use of arbitrary plate-like structures driven by electromagnetic actuators or by piezoelectric elements appears as a promising solution to tackle both issues. However, to meet spatial rendering audio constraints (omnidirectional piston-like sources), the generated bending waves must be focused to a certain extent within the host plate. Theoretically, this means being able to invert the spatio-temporal wave propagation operator for the generated bending waves to fit a given target shape. Several methods are here investigated to perform this task depending on the available knowledge of wave propagation in the plate (theoretical, partial spatial and full spatial knowledge). The various methods are presented in a unified theoretical framework and their performances are compared in terms of sound radiation by means of two key performance indexes.