Tactile process based on the ultrasonic diffraction
This thesis is a contribution to the development of an acoustic tactile process based on the disturbance of Lamb waves making it possible to detect a simple or multitouch interaction on thin objects of various shapes. After studying the propagation of Lamb modes in thin objects such as a copper plate 450 µm thick, we show that the energy of antisymmetric Lamb modes is essentially related to the normal component of displacement and that it is easy to disturb bending waves either with a stylus based punctual touch or finger based surfacic touch, whereas in the case of a symmetric Lamb mode, energy is essentially due to the tangential mechanical component of displacement, therefore more difficult to disturb with a touch of the finger. Consequently, we have exploited the touch disturbed radiation of an acoustic bending wave and measured the disturbance of diffracted Lamb waves at one or two receiving points of the plate. Thus, a method based on the diffraction of Lamb waves has been proposed for the development of a compact, efficient and low cost tactile interface. This method named Amplitude Disturbed Diffraction Pattern (ADDP) method can be used to produce a tactile surface that can achieve a spatial resolution of the order of one millimeter and a response time of 10 ms. Two optimization methods are proposed to obtain near 100% correct localization. The proposed process and optimization methods have been tested on several kinds of objects made with different materials and forms. These realizations have shown satisfying performances in terms of form factor, consumption and reliability of localization of simple or plural contact points.