Shear shock waves mediate haptic holography via focused ultrasound

Inflatable acoustic metasurfaces for tunable wave focusinga)

Acoustic metasurfaces are two-dimensional architected materials designed to enable non-trivial control of waves, with a thickness that is either thinner than or comparable to the wavelength. However, most metasurfaces today have a fixed geometry and lack the ability to tune acoustic waves on command. This limits their ability to perform multiple functions, such as beam steering and dynamic focusing. This study introduces inflatable acoustic metasurface (IAM) lenses that enable tunable focusing. The IAMs feature two-dimensional diffractive focusing patterns embedded in a membrane that can be inflated nonplanarly through hydraulic control. It is experimentally demonstrated that inflation allows continuous focal length adjustment from -2.49λ to +3.17λ. To characterize the lens performance, changes in focal characteristics, including peak pressure, full width at half-maximum, and full length at half-maximum, are tracked at different levels of inflation. Furthermore, it is shown that IAMs can correct aberrations that occur as the angle of incidence increases in conventional planar lenses. To validate this, IAMs were tested in a concave configuration at a 20° oblique incidence angle. The results of this study may be applicable to fields requiring continuous and real-time response in tunable focusing, including acoustic imaging and communication, ultrasound surgery, and neuromodulation.

Enhancing haptic continuity in virtual reality using a continuity reinforcement skeleton

Haptic displays are crucial for facilitating an immersive experience within virtual reality. However, when displaying continuous movements of contact, such as stroking and exploration, pixel-based haptic devices suffer from losing haptic information between pixels, leading to discontinuity. The trade-off between the travel distance of haptic elements and their pixel size in thin wearable devices hinders solutions that solely rely on increasing pixel density. Here we introduce a continuity reinforcement skeleton, which employs physically driven interpolation to enhance haptic information. This design enables the off-plane displacement to move conformally and display haptic information between pixel gaps. Efforts are made to quantify haptic display quality using geometric, mechanical, and psychological criteria. The development and integration of one-dimensional, two-dimensional, and curved haptic devices with virtual reality systems highlight the impact of the continuity reinforcement skeleton on haptic display, showcasing its potential for improving haptic experience.

Enhanced Dye-Sensitized Mechanosensation Utilizing Pulsed and Digitally Modulated Light

The generation of pressure perturbations in matter stimulated by pulsed light is a method widely recognized as the photoacoustic or light-induced thermoelastic effect. In a series of psychophysical experiments, the robustness of the tactile perception generated with a variety of light sources is examined: a diverging pulsed laser used for photoacoustic tomography optical parameter oscillation (OPO), a miniature diode laser (MDL), and a commercial digital light processing (DLP) projector. It is demonstrated that participants can accurately detect, categorically describe the sensations, and discern the direction of pulsed light travel. High detection accuracy is reported as follows: (d' = 4.95 (OPO); d' = 2.78 (modulated MDL); d' = 2.99 (DLP)) of the stimulus on glabrous skin coated with a thin layer of dye absorber. For all light sources, the predominant sensation is felt as vibration at the distal phalanx (i.e., fingertip, 55.21-57.29%) and the proximal phalanx (41.67-44.79%). At the fingertip, thermal sensations are perceived less frequently than mechanical ones. Moreover, these haptic effects are preserved under a wide range of pulse widths, spot sizes, optical energies, and wavelengths of the light sources. This form of sensory stimulation demonstrates a generalizable non-contact, non-optogenetic, in situ activation of the mechanosensory system.

Haptic Sensing and Feedback Techniques toward Virtual Reality

Haptic interactions between human and machines are essential for information acquisition and object manipulation. In virtual reality (VR) system, the haptic sensing device can gather information to construct virtual elements, while the haptic feedback part can transfer feedbacks to human with virtual tactile sensation. Therefore, exploring high-performance haptic sensing and feedback interface imparts closed-loop haptic interaction to VR system. This review summarizes state-of-the-art VR-related haptic sensing and feedback techniques based on the hardware parts. For the haptic sensor, we focus on mechanism scope (piezoresistive, capacitive, piezoelectric, and triboelectric) and introduce force sensor, gesture translation, and touch identification in the functional view. In terms of the haptic feedbacks, methodologies including mechanical, electrical, and elastic actuators are surveyed. In addition, the interactive application of virtual control, immersive entertainment, and medical rehabilitation is also summarized. The challenges of virtual haptic interactions are given including the accuracy, durability, and technical conflicts of the sensing devices, bottlenecks of various feedbacks, as well as the closed-loop interaction system. Besides, the prospects are outlined in artificial intelligence of things, wise information technology of medicine, and multimedia VR areas.

Rendering Dynamic Source Motion in Surface Haptics via Wave Focusing

Emerging surface haptic technologies can display localized haptic feedback anywhere on a touch surface by focusing mechanical waves generated via sparse arrays of actuators. However, rendering complex haptic scenes with such displays is challenging due to the infinite number of physical degrees of freedom intrinsic to such continuum mechanical systems. Here, we present computational focusing methods for rendering dynamic tactile sources. They can be applied to a variety of surface haptic devices and media, including those that exploit flexural waves in thin plates and solid waves in elastic media. We describe an efficient rendering technique based on time-reversal of waves emitted from a moving source and motion path discretization. We combine these with intensity regularization methods that reduce focusing artifacts, improve power output, and increase dynamic range. We demonstrate the utility of this approach in experiments with a surface display that uses elastic wave focusing to render dynamic sources, achieving millimeter-scale resolution in experiments. Results of a behavioral experiment show that participants could readily feel and interpret rendered source motion, attaining 99% accuracy across a wide range of motion speeds.