Ultrasound haptics is a contactless haptic technology that enables novel mid-air interactions with rich multisensory feedback. This article surveys recent advances in ultrasound haptic technology. We discuss the fundamentals of this haptic technology, how a variety of perceptible sensations are rendered, and how it is currently being used to enable novel interaction techniques. We summarize its strengths, weaknesses, and potential applications across various domains. We conclude with our perspective on key directions for this promising haptic technology.

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A Survey of Mid-Air Ultrasound Haptics and Its Applications

Interactive digital signage is increasingly deployed in urban environments, from airports and train stations, to cinemas and shopping malls, whilst their integration into public spaces introduces new possibilities in multimedia presentation. In this paper, we explore the impact of mid-air haptic feedback on user engagement during gesture-based interactions with digital posters. To that end, a user study with seventeen participants was undertaken with two independent variables: interactivity (high/low), and mid-air haptic cues (on/off), whilst user engagement and emotional affect was measured with respect to various metrics. In this first attempt to understand the significance of mid-air haptic interactions for digital signage, we found increased user engagement levels, comparable to, if not greater than those achieved by content gamification. In particular, our analysis suggests that mid-air haptic feedback significantly improved usability and aesthetic appeal in comparison to digital signage without haptic feedback. Similarly, a higher level of gamification was also found to boost user engagement and helped to offer more compelling experiences with digital signage.

User engagement for mid-air haptic interactions with digital signage

Holographic methods from optics can be adapted to acoustics for enabling novel applications in particle manipulation or patterning by generating dynamic custom-tailored acoustic fields. Here, we present three contributions towards making the field of acoustic holography more widespread. Firstly, we introduce an iterative algorithm that accurately calculates the amplitudes and phases of an array of ultrasound emitters in order to create a target amplitude field in mid-air. Secondly, we use the algorithm to analyse the impact of spatial, amplitude and phase emission resolution on the resulting acoustic field, thus providing engineering insights towards array design. For example, we show an onset of diminishing returns for smaller than a quarter-wavelength sized emitters and a phase and amplitude resolution of eight and four divisions per period, respectively. Lastly, we present a hardware platform for the generation of acoustic holograms. The array is integrated in a single board composed of 256 emitters operating at 40 kHz. We hope that the results and procedures described within this paper enable researchers to build their own ultrasonic arrays and explore novel applications of ultrasonic holograms.

Generating Airborne Ultrasonic Amplitude Patterns Using an Open Hardware Phased Array

We present advancements in the design and development of in-vehicle infotainment systems that utilize gesture input and ultrasonic mid-air haptic feedback. Such systems employ state-of-the-art hand tracking technology and novel haptic feedback technology and promise to reduce driver distraction while performing a secondary task therefore cutting the risk of road accidents. In this paper, we document design process considerations during the development of a mid-air haptic gesture-enabled user interface for human-vehicle-interactions. This includes an online survey, business development insights, background research, and an agile framework component with three prototype iterations and user-testing on a simplified driving simulator. We report on the reasoning that led to the convergence of the chosen gesture-input and haptic-feedback sets used in the final prototype, discuss the lessons learned, and give hints and tips that act as design guidelines for future research and development of this technology in cars.

Designing Mid-Air Haptic Gesture Controlled User Interfaces for Cars

Ultrasonic phased arrays are used to deliver midair haptic feedback in both research and commercial applications and strongly rely on the Acoustic Radiation Pressure (ARP) that arises at the air-skin interface. The ARP generated by ultrasonic mid-air haptic feedback technology today is orders of magnitude lower than most forces involved in traditional contact haptic devices, however can be leveraged to produce a rich plethora of perceptible tactile sensations. Therefore, how a viscoelastic structure such as the human skin responds to the ARP is an important research topic that merits further investigation. To that end, we detail herein a methodology to investigate the mechanical response of viscoelastic materials to this type of stimulation. Our research is divided into a laser doppler vibrometry experimental study and a Finite Element Model (FEM) computer simulation of a skin-mimicking phantom slab. Through comparison of experimental and simulation results under different ultrasound stimulation schemes we observe good qualitative and quantitative agreement, thus successfully advancing towards the development of a numerical tool for optimising ultrasonic mid-air haptic stimuli.

Laser Doppler Vibrometry and FEM Simulations of Ultrasonic Mid-Air Haptics

This demo presents the concept of Interactive Digital Signage with Haptics, where users can interact with public digital screens with their bare hands, utilizing tracking technology and ultrasonic mid-air haptic feedback. Using these three main components: a digital screen, a tracking device, and Ultrahaptics technology for tactile feedback in mid-air, users are offered a multi-sensory experience that can potentially dramatically improve the advertising experience, increasing brand engagement, dwell time and brand recall. To this end, we present an example of a movie poster that transforms into an interactive mini game.

Touchless Tactile Displays for Digital Signage: Mid-air Haptics meets Large Screens

Augmented Reality mid-air environments are currently re-evaluating the interaction principles of the objects rendered in space. The surface, texture complexity, compliances and dynamics can be represented through volumetric rendering, comprised of shape, size and/or volume. Haptic representation of the graphical content and the dynamics of the interface can be tailored to the application requirements. The solution, however, is highly dependent on the tasks and the need for tactile feedback. The ideal system must blend the right level of factors and attributes to maximize user performance and satisfaction. The mechanics and perceptual correlation of mid-air haptics are still unresolved. Based on human tactile limitations, the prime classification of the tactile interactions was proposed, based on spatial and temporal requirements and limitations. Proposed classes are intuitive and proved to be easily adapted to many interactions, as well as compatible with gesture recognition. This paper discusses the haptic design criteria for mid-air, tactile-enhanced interactions suitable for interface AR applications. Design evaluation involved a sequence of six scenes, directed to engage user attention and strengthen performance. Proposed solution and its influence on ergonomics and efficiency, were subjected to user cognitive evaluation. A non-contact, interactive demo, blending cross modal stimulations, combining vision, auditory and tactile sensations was produced, and user studies were discussed.

Richard Hayden

Papers

User engagement for mid-air haptic interactions with digital signage

Touchless Tactile Displays for Digital Signage: Mid-air Haptics meets Large Screens

Design and Evaluation of Mid-Air Haptic Interactions in an Augmented Reality Environment