Large-Panel Multi-Touch Ultrasonic Touchscreen Using Lamb Wave

Touchscreen sensors are used in various devices, including smartphones, tablets, and large panels. Many existing touch-sensing technologies have disadvantages for application to large-size panels. Ultrasonic technology is one of the several methods developed to address this problem; however, it has only been implemented in small panels less than 23 inches in size. In this study, ultrasonic touch sensing technology capable of multi-touch on a 55-inch glass panel using the Ao mode of a Lamb wave was developed. A pair of lead magnesium niobite-lead titanate (PMN-PT) sensors with a size of 3mm×3mm×1 mm was used as a set; one for transmitting and one for receiving. Four pairs of sensors (4-TX, 4-RX) were installed on 3-mm-thick glass, and the measured center frequency was 220 kHz. Traditional synthetic aperture imaging was used to detect the location of a finger touch. Signal difference data according to the presence or absence of the finger was used. Finally, a fingertip image was reconstructed by the delay-and-sum method, which proved successful detection of the finger.