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.

Vascular contributions to cognitive impairment and dementia (VCID) are the second leading cause of dementia and increasing in prevalence as lifespans increase. Clinical MRI traditionally relies on structural abnormalities to identify this vascular dysfunction but lacks microstructure and functional information that could be critical for early identification and assessment of disease. Cerebrovascular dysfunction is one of the only contributors to dementia that can currently be treated, and therefore, earlier identification and subsequent intervention could prevent irreversible structural changes that lead to cognitive decline.Magnetic resonance fingerprinting (MRF) is a novel approach to MRI acquisition and reconstruction using biophysical modeling in parallel to image acquisition for the simultaneous collection of quantitative, multiparametric brain maps. MRF can be adapted to specifically measure cerebrovascular parameters via MR vascular fingerprinting (MRvF), which produces quantitative cerebral blood volume (CBV), microvascular vessel radius (R), and tissue oxygen saturation (SO2) maps of the whole brain. This dissertation aims to advance MRvF for contrast-free, dynamic mapping of cerebrovascular function. First, we compare MRvF to another quantitative MRI method, quantitative blood oxygen level dependent (BOLD) imaging, and show consistency between the techniques, reliable oxygen extraction fraction (OEF) measurements, and expected changes in OEF in response to hypoxia and hyperoxia. Next, we describe a new MRvF pattern-matching algorithm developed for improved mapping without contrast agents, investigate the tradeoffs between SNR, sensitivity, and temporal resolution, and optimize an accelerated spin- and gradient-echo (SAGE) sequence for dynamic MRvF. We show adequate SNR with the SAGE sequence from just one repetition for robust whole-brain vascular parameter mapping every 4.5 seconds. Following this, we demonstrate a novel protocol in which this optimized SAGE sequence allows for dynamic and simultaneous acquisition of MRvF and BOLD measures. By combining this with a tailored hypercapnic (5% CO2) breathing paradigm, we show parameter consistency over time and regional changes in BOLD, CBV, R, and SO2 in response to this stimulus, enabling the calculation of cerebrovascular reactivity (CVR). Finally, we use this newly developed imaging paradigm to compare differences in MRvF-derived CVR measurements in healthy young and healthy old adults. We juxtapose these CVR results against more commonly utilized techniques of measuring CVR to compare and validate our MRvF metrics. Collectively, we demonstrate the development of dynamic MRvF in an ongoing effort toward new quantitative functional imaging biomarkers of cerebrovascular dysfunction with the potential to enable better understanding and earlier diagnoses of diseases like VCID.

The production of a W boson in association with a single charm quark is studied using140 fb−1 of √s = 13 TeV proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider. The charm quark is tagged by the presence of a charmed hadron, reconstructed with a secondary-vertex fit. The W boson is reconstructed from the decay to either an electron or a muon and the missing transverse momentum present in the event. The W + D(∗) process is sensitive to the strange quark PDF, and can be combined with other measurements to improve uncertainties and central values of global PDF fits. Charmed mesons are reconstructed in the decay channels D+ → K−π+π+, D∗+ → D0π+ → (K−π+)π+, D+ → φπ → (KK)π, and Ds → φπ → (KK)π and the charge conjugate decays in the fiducial regions where pT(e, μ) > 30 GeV , |η(e, μ)| < 2.5, pT(D(∗)) > 8 GeV , and |η(D(∗))| < 2.2. The integrated and normalized differential cross-sections as a function of the pseudorapidity of the lepton from the W boson decay, and of the transverse momentum of the charmed hadron, are extracted for the D+ → Kππ and D∗ → D0π → Kππ decay modes. The total fiducial cross section is measured for the Ds → φπ → (KK)π and D+ → φπ → (KK)π decay modes. All observables are extracted from the data using a profile likelihood fit. The measured total fiducial cross-sections for the D+ → Kππ and D∗ → D0π → Kππ modes are σ(OS−SS, fid) (W −+D+) = 50.2 ± 0.2 (stat.) +2.4−2.3 (syst.) pb, σ (OS−SS, fid) (W ++D−) = 48.5 ± 0.2 (stat.) +2.3−2.2 (syst.) pb, σ(OS−SS, fid) (W −+D∗+) = 51.1 ± 0.4 (stat.) +1.9−1.8 (syst.) pb, and σ(OS−SS, fid) (W ++D∗−) = 50.0 ± 0.4 (stat.) +1.9−1.8 (syst.) pb. These differential and total cross section results are compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the-art parton distribution functions. Additionally, the ratio of charm to anti-charm production cross-sections is studied to probe the s- ̄s quark asymmetry. The ratio is found to be Rc = 0.971 ± 0.006 (stat.) ± 0.011 (syst.). The ratio and cross-section measurements are consistent with the predictions obtained with parton distribution function sets that have a symmetric s- ̄s sea, indicating that any s- ̄s asymmetry in the Bjorken-x region relevant for this measurement is small. For the Ds → φπ → (KK)π and D+ → φπ → (KK)π analysis, the observables that are measured are the inclusive cross section in both charges for the W +Ds process, the ratio of the cross sections with respect to the charge, and the ratio of the Ds to the D+ process. The measured values are σ(OS−SS, fid) (W −+D+s ) =17.8±0.4 (stat.) +1.8−1.6 (syst.) pb, σ(OS−SS, fid) (W ++D−s ) = 15.8±0.4 (stat.) +1.5−1.4 (syst.) pb, Rc (Ds) =0.885 ± 0.029 (stat.)+0.059−0.057 (syst.), and R(D+/Ds) = 2.93 ± 0.06(stat.) ± 0.24 (sys.). These result are consistent with the differential W + D+ analysis within 1.5 standard deviations, and are at a lower precision due to lower data and MC simulation statistics and increased systematic uncertainties related to background modeling.