Gesture sensing with flexural ultrasonic transducers

Abstract

As everyday devices become increasingly interactive, there is a need for improved interface sensors between humans and machines, as well as for expansion of the form factors and materials through which such sensors can operate. This thesis explores sensing technologies to enable user input on a consumer electronics device, specifically technologies that are capable of sensing touch and hover gestures through a metal substrate. Electromagnetic, optical, and acoustic technologies are explored. Capacitive and pinhole camera approaches for sensing through a mostly metal substrate are presented briefly. The bulk of the thesis focuses on the development of an array of flexural ultrasonic transducers to allow sensing through a fully metal substrate. An analytical model, finite element simulations, and experiments are presented to characterize and optimize the transducers, and a prototype is developed as a proof of concept of the combined touch and hover sensor system. The prototype successfully demonstrates the capability of a mesoscale piezo unimorph array to detect and distinguish between tap, touch, and swipe contact gestures and to detect a hovering object, albeit in a limited range, above a metal substrate. There are opportunities for improvements in circuitry, sensor design, and fabrication that could lead to finer resolution, decreased sensor size, and a larger range for hover detection.