Haptic feedback device provided with stiffeners

A haptic-feedback device comprising a vibratable plate a first face of which is coated with at least one layer incorporating a means for detecting the position of a finger of a user, said device comprising electromechanical actuators that are aligned on an edge of the plate or of the layer and that are capable of making said plate and said layer vibrate at an ultrasonic resonant frequency, wherein said plate comprises, on its second face, a set of stiffeners parallel to each other and distributed over the whole of said second face, said stiffeners protruding over said second face and being placed to make it more difficult to bend the plate about an axis perpendicular to the stiffeners in order to achieve an axial and uniform mode of vibration of the plate, said stiffeners having a thickness in relief with respect to said plate, a width, and a distance by which the stiffeners are spaced apart selected such that a flexural wave that propagates along an axis perpendicular to the stiffeners propagates more slowly than a flexural wave that propagates along an axis parallel to the stiffeners, and such that localized confinement of the flexural waves is avoided.