Lamb wave ultrasonic touchscreen [electronic resource]

Touchscreen sensors are widely used in many devices such as smart phones, tablets, laptops, etc., with diverse applications. This dissertation presents the design, analysis, and implementation of an ultrasonic touchscreen system that utilizes interaction of transient Lamb waves with objects in contact with the screen. It attempts to achieve an order of magnitude improvement on the existing ultrasound technologies, with the potential of addressing some of the weaknesses of the dominant technologies, such as the capacitive or resistive ones. Compared to the existing ultrasonic and acoustic modalities, among other advantages, it uniquely provides the capability of detecting several simultaneous touch points, and also a more robust performance. The localization algorithm, given the hardware design, can detect several touch points with a very limited number of measurements (one or two). This in turn significantly reduces the manufacturing cost. The basic governing principle revolves around the propagation of guided elastic waves in a bounded space. Wave propagation in enclosures can lead to mixing of the wave energy, ultimately leading to an incoherent spreading of information. This is the manifestation of a reverberant field, which makes the localization problem very challenging. Reverberant fields in enclosures can potentially carry useful information, however, in an incoherent way. Incoherency comes from consecutive reflections of the wave energy several times in the domain. This along with diffraction and dispersion effects can ultimately lead to mixing of the wave energy in a seemingly random way. However, spreading of the wave energy can lead to multiple interrogations of each point in the enclosure. Hence, any substructural changes in the enclosure can be sensed with sufficient information carried by the wave energy flow. Furthermore, the temporal information buried in the data makes it feasible to conduct only a few spatial measurements. I present localization schemes that benefit from the reverberant field and can reduce the required number of spatial measurements. I investigate two different approaches to address the localization problem in reverberant fields: (1) learning method and (2) the Waveform inversion (WI) approach. I show the application of the learning method to the experimental data and motivate the application of WI. Finally, I propose Lamb wave stylus designs based on three different physical mechanisms. Stylus as an input tool is used with touchscreen-enabled devices, such as Tablet PCs, to accurately navigate interface elements, send messages, etc. The main and desired features of a stylus are quiet different from a smooth touch contact such as human finger. Thus, almost all mainstream touch technologies have an accompanying stylus design with possibly a different interfacing mechanism. I propose stylus designs based on the Hertzian contact mechanics, photoacoustic, and thermoacoustic effects. The designs are conceptually motivated and demonstrated through a set of supporting measurements as the proof of concept.

Keywords: Mechanical Engineering.
Advisor: Kenny Thomas William primary advisor. Thesis advisor
Khuri-Yakub Butrus T.
Pinsky Peter M. (Peter Michael)