UC Santa Barbara

A longstanding goal in haptics is to engineer high-fidelity displays for spatially distributed haptic feedback, specified as digital media. Such haptic displays would make it possible to touch, feel, and interact with dynamic scenes, objects, or information presented anywhere in a continuous display medium, such as an interactive surface or three-dimensional environment. They would thus represent the haptic analogs of two- or three-dimensional video displays. This dissertation advances knowledge in the design and operational principles of such haptic displays, focusing on emerging technologies that harness and control propagating mechanical waves to deliver spatially distributed haptic feedback. Central to the innovation of wave-mediated haptic display is that the spatial resolution of haptic feedback is governed by the control of wave transmission rather than by the number and density of actuators, as would be the case in conventional approaches. This wave-mediated strategy reduces complexity, enabling practical and scalable displays capable of reproducing dynamic haptic media. This Ph.D. dissertation contributes new display designs exploiting wave transmission, algorithms and methods for wave-mediated haptic display, experimental findings that mechanically and perceptually characterize the proposed display methods, and investigations of the influence of skin biomechanics on display fidelity.

The first part of this dissertation details two wave-mediated surface haptic displays composed of soft elastomers, which reproduce software-specified haptic media via viscoelastic wave field control. These displays can generate haptic feedback at multiple, arbitrary display locations with sub-centimeter resolution and accuracy using only a limited number of remotely positioned actuators. Using high-resolution measurements of wave field surface oscillations and behavioral studies, I also evaluate several proposed rendering algorithms that generate expressive, dynamic haptic content for several emerging interaction paradigms, such as multi-touch settings or when an entire hand rests on the display surface.

In the second part of this dissertation, the computational control methods developed in the first part are extended to rigid touch surfaces. Rigid display media at low frequencies (< 1000 Hz) typically exhibit wavelengths of mechanical energy of tens of centimeters or more, making it difficult to control propagating waves. To address these challenges, I design a locally resonant metamaterial plate consisting of a periodic array of local resonators attached to a rigid base, which exhibits subwavelength dispersion across a wide bandwidth. Leveraging the wave transmission properties of this medium, I realize spatially distributed haptic feedback on rigid touch surfaces via flexural wave control.

The final part of this dissertation investigates the role of skin biomechanics in rendering dynamic haptic content. In this section, I leverage another class of wave-mediated haptic displays—holographic haptic displays—which focus airborne ultrasound waves directly on the skin to allow users to interact with and manipulate three-dimensional virtual objects without contact with a physical device. I demonstrate that the spatial resolution and dynamic range of these devices are dominated by effects of viscoelastic wave transport in the skin and the presence of ancillary shock wave artifacts generated during the dynamic motion of focused ultrasound sources across the skin. Motivated by these findings that skin biomechanics modifies the perception of holographic haptic displays, I created an open-source, data-driven software package that predicts surface wave fields on the human upper limb in response to applied forces. The software package incorporates a dataset of 3-axis impulse response measurements gathered from the upper limbs of four participants and can be used to integrate knowledge about wave transmission in the upper limb in haptic research and design applications.