To date, several focusing techniques have been proposed to realize localized stimulation on haptic interfaces. The localized stimulation can be achieved using arrays of actuators with delayed excitation, or by time reversal techniques which require a preliminary learning phase. The stimulation is thus limited to prerecorded cases. Additionally, these techniques are sensitive to parameters variation and disturbances. On the other hand, modal decomposition is another technique which allows to realize arbitrary vibration fields congruent with the boundary conditions without any preliminary learning phase. In this paper, we propose to use modal decomposition to realize a desired vibration velocity field in order to have differentiated stimuli. The experimental results validate the ability of the method to approximate satisfactorily a desired reference form. The psychophysic evaluations show that users can differentiate and localize the stimulation while exploring a surface with two fingers.

In the field of tactile feedback, researchers try to generate localized stimulations on screens. Some solutions such as time reversal or phased array use vibration induced in the screen equipped with piezoelectric ceramics. We propose to use the modal basis to reproduce a specified velocity field on such devices. We explain the theory and propose a methodology to practically synthesize the voltages to achieved a controlled focusing in a given time. Experiments on a simple demonstrator are in good agreement with the theory for various velocity fields and a reduced number of modes.