Multitouch Vibrotactile Feedback on a Tactile Screen by the Inverse Filter Technique: Vibration Amplitude and Spatial Resolution.

Nowadays, tactile surfaces, such as smartphones, provide haptic feedback to signify that a task has been performed correctly or more generally to enrich the interaction. However, this haptic feedback induces vibrations in the surface that propagate to the whole surface, reverberate and attenuate, thus making multi-finger interaction, with different feedbacks, difficult. Recently, the Inverse Filter Method has been proposed to control the propagation of these vibrations, and thus enable to product localized multitouch on a glass surface. This way, a user can put several fingers on a tactile surface and yet feel stimuli independently on his/her different fingers. This article continues this work and demonstrates that a localized multitouch haptic feedback can be delivered in real time using a capacitive screen. To achieve this, this article presents the two necessary steps: a calibration step and an interpolation calculation in order to save calculation and learning time. Furthermore, the paper describes the performance of the device through a study on the behaviour of the screen subjected to the Inverse Filter Method, indicating the movement of the whole screen and the voltage requirement for any haptic feedback.