Differential Sensing of Lamb Wave Using Piezoelectric Transducer for Baseline-Free Tactile Sensing on a Glass Plate

This paper utilizes only the anti-symmetric fundamental (A0) mode of Lamb waves for tactile sensing to realize a baseline-free ultrasound-based touchscreen. Disk-shaped piezoelectric transducers are mounted in pair on a glass plate to excite and detect pure A0 mode Lamb waves. When there is no finger touch, the symmetric nature of the boundary conditions ensures that the combined output wave signals from paired transducers are basically zero, which eliminates the need for reference or baseline signals. When there is a finger touch, the output wave signals can directly couple with a trained artificial intelligence (AI) model based on a convolutional neural network (CNN) to identify the touch and its touch position. Field tests show the accuracy for tactile position sensing is 96% and is not affected by environmental temperature variation. This demonstrates the effectiveness and robustness of the proposed baseline-free Lamb wave touchscreen as a human–machine interface.