Touchscreen Surface Based on Interaction of Ultrasonic Guided Waves With a Contact Impedance

In this paper, a touchscreen device is proposed, based on guided-wave reflection and transmission induced by the presence of an object. The principle uses the advantages of other acoustic wave devices in terms of simplicity and applicability to any thin surface but is not subject to classical drawbacks (single touch, sensitivity to scratches or contaminant, and impossibility to follow motion of contact point). The theoretical interaction of guided waves with contact impedance is first derived in order to define the requirements of the sensor in terms of frequency range, mode, sensor type and location, and embedded electronics. Design criteria and experimental validation on a small prototype (
$200 \times 250$
mm) are proposed to demonstrate the potential of the approach for simple, robust, and reliable contact detection of pointlike or extended objects for consumer electronics or biomedical applications.