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A Review of Surface Haptics:Enabling Tactile Effects on Touch Surfaces

Cagatay Basdogan, Frederic Giraud, Vincent Levesque, Seungmoon Choi

arXiv:2004.13864v1cs.HCcs.RO

TL;DR

Touch devices largely lack tactile feedback despite its relevance to task performance, realism, and product-surface preferences. This review synthesizes surface-haptics technologies, tactile perception, human-machine interaction, applications, and commercialization challenges, primarily for vibrotactile, electrostatic, and ultrasonic methods. It surveys mechanisms and applications while identifying limitations such as difficult shape rendering and high energy or integration demands.

  • Problem

    Commercial touch devices provide visual and auditory feedback but almost no tactile feedback, motivating research into techniques that render tactile information on touch-enabled devices.

  • Method

    The review synthesizes machine haptics, human haptics, and human-machine haptics, focusing on vibrotactile, electrostatic, and ultrasonic surface-haptics methods.

  • Results

    Across reviewed interactions, friction modulation can improve single-target acquisition, with electrovibration yielding a 7.5% improvement when the entire target has tactile texture.

  • Takeaways & Limitations

    Surface haptics can render virtual shapes, textures, and controllers and support applications including interfaces, shopping, education, entertainment, arts, and accessibility.

  • Takeaways & Limitations

    Electrovibration produced difficult-to-read Braille and only a 56% success rate for identifying simple geometric shapes, while high energy and integration demands hinder commercialization.

Abstract

from arXiv · show

We review the current technology underlying surface haptics that converts passive touch surfaces to active ones (machine haptics), our perception of tactile stimuli displayed through active touch surfaces (human haptics), their potential applications (human-machine interaction), and finally the challenges ahead of us in making them available through commercial systems. This review primarily covers the tactile interactions of human fingers or hands with surface-haptics displays by focusing on the three most popular actuation methods: vibrotactile, electrostatic, and ultrasonic.

1 INTRODUCTION

Surface haptics aims to add tactile effects to touch surfaces and support applications across interfaces, shopping, education, entertainment, arts, and accessibility. This review covers machine haptics, human tactile perception, and human-machine interaction, focusing on vibrotactile, electrostatic, and ultrasonic methods.

  • Surface haptics generates tactile effects on touch surfaces such as smartphones, tablets, kiosks, displays, appliances, and car panels.
  • Adding haptics to touch surfaces supports applications including online shopping, education, gaming, entertainment, arts, tactile interfaces, and assistance for visually impaired users.
  • Its primary scope is tactile interaction by human fingers or hands using vibrotactile, electrostatic, and ultrasonic actuation.
  • The review excludes less-common electromagnetic and fluidic methods, kinesthetic interactions, shape-changing surfaces, mid-air haptics, and pen- or stylus-mediated interactions.
  • The review covers machine haptics, human haptics, and human-machine haptics for rendering virtual shapes, textures, and controllers.

2 MACHINE HAPTICS

The machine-haptics discussion introduces the actuation technologies that create tactile feedback on touch surfaces, organizing them by stimulation direction before explaining their operation.

  • The review groups actuation technologies by stimulation direction and briefly explains how each technology works.

2.1 Classification

Surface-haptics technologies are classified by the direction of forces or stimulation applied to the finger, then by the methods used to generate those forces. Methods include normal vibration, tangential vibration, friction modulation, and net tangential force generation.

  • 2.1 Classification: Surface-haptics stimulation is classified as normal to the surface or tangential to it, using force components Fn, Ft, and Fo.
  • Normal stimulation: Normal vibration propagates from peripheral actuators through the surface and is directly detectable below 1 kHz.
  • Normal stimulation: Multiple actuators can create static or moving phantom sensations through amplitude or phase modulation, while inverse filtering and modal composition localize vibrations.
  • Normal stimulation: Short normal-vibration pulses require synchronized actuators to cancel surface echoes and produce localized bursts.
  • Tangential stimulation: Tangential contact-force modulation can render virtual textures when relative finger-surface displacement induces lateral forces inside the finger pulp.
  • Friction modulation: Ultrasonic actuation reduces friction through active lubrication, whereas electrostatic actuation increases friction by attracting a sliding finger toward the conductive touchscreen layer.
  • Net tangential force: Net tangential force can be generated by physically displacing the surface along the finger’s movement direction, asymmetric friction, or elliptical particle motion from high-frequency bending modes.
  • 2.1 Classification: Figure 3 classifies proposed surface-haptics display methods, followed by discussion of their actuators and stimulation mechanisms.

2.2 Actuator Technologies

Surface-haptics displays use actuators that convert electrical power into mechanical power and control finger-surface contact forces. Actuator choices trade off bandwidth, displacement, force, voltage, compactness, and robustness.

  • Actuators convert electrical power into mechanical power and are positioned to control contact forces through the touch surface.
  • Electromagnetic actuators include vibration motors, voice coils, and LRAs, offering different waveform control, response, bandwidth, voltage, displacement, and force characteristics.
  • Vibration motors provide relatively large vibrations in diverse sizes and shapes, but fixed displacement amplitudes and actuation lags restrict rendered waveforms.
  • Piezoelectric actuators support high-frequency, high-force, low-displacement actuation and compact mounting, but require very high voltage and are brittle under external shock.
  • Electroactive polymers can cover large surfaces in varied forms because of their softness, although their voltage requirements are often very high.
  • Table 1 gives examples of actuator technologies for each method classified in Figure 3, with subsequent sections describing their operating principles.

2.3 Force Modulation in the Normal Direction

Normal-direction force modulation delivers tactile feedback through vibrations propagating from actuators into the contacted surface and finger. The section covers phantom sensations and localized vibration strategies for producing spatially targeted effects.

  • Multiple actuators can create illusory tactile sensations between excitation positions or localize vibration to a small surface area.
  • 2.3.1 Tactile Phantom Sensations on Touch Surfaces: Phantom sensation produces an illusory stimulus midway between distant tactile inputs, improving spatial resolution with few actuators.At the fingertip, tactile spatial resolution is 1–2 mm, while dense distributed displays remain beyond current technology.
  • 2.3.1 Tactile Phantom Sensations on Touch Surfaces: On rigid touch surfaces, phantom effects can be elicited along a line between two points or within a polygon surrounded by multiple points.
  • 2.3.1 Tactile Phantom Sensations on Touch Surfaces: Stationary phantom sensations require vibration damping; without dampers, overlapping actuator vibrations generally produce only moving phantom sensations.A mobile-phone surface study measured identification accuracy and estimated perceived-position distributions for stationary sensations.
  • 2.3.2 Localized Stimulation on Touch Surfaces: Localized vibrotactile feedback can be produced by narrowing the plate, using transparent active films, vibration maps, or superimposed vibration modes.One transparent relaxor ferroelectric polymer surface produced localized 500 Hz vibrations with 1 µm amplitude at 200 V.

2.4 Force Modulation in the Tangential Plane

Tangential-plane force modulation uses lateral vibration or friction modulation to stimulate the finger during relative motion. The review emphasizes vibrotactile, electrostatic, and ultrasonic approaches, along with their contact-mechanics and uniformity limitations.

  • Lateral Vibration: Lateral movement of a touch surface can induce tangential forces and render virtual textures, while peripherally placed actuators avoid obstructing the display.
  • Friction Modulation: Voltage-controlled electrovibration can feel nonuniform because human and environmental impedances vary, whereas current feedback produced significantly more uniform perceived intensity.
  • Friction Modulation: Electrovibration’s implementation is straightforward, but the underlying contact mechanics and tactile perception remain highly limited because skin–surface interactions are complex.
  • Friction Modulation: Electrostatic attraction can increase the finger–screen real contact area and thereby increase sliding friction, although real contact area is difficult to measure experimentally.
  • Friction Modulation: Electrovibration increases friction during full slip, while apparent contact area becomes significantly smaller than without electrovibration.The reported interpretation attributes increased friction to real-area growth and reduced apparent area to tangential stiffening of finger skin.
  • Ultrasonic Actuation: Ultrasonic displays typically use piezoelectric films driven by sinusoidal signals above 20 kHz, with design choices affecting power efficiency and voltage requirements.A reported silicon substrate achieved 1.1 µm vibration amplitude at 8 Vpp.
  • Ultrasonic Actuation: Combining two ultrasonic vibration modes with controlled amplitude and phase can differentiate tactile stimulation at two plate locations.

2.5 Net Tangential Force

Net tangential-force methods create directional shear on the finger rather than only modulating friction during sliding. Approaches combine asymmetric friction, low-frequency motion, or coordinated ultrasonic and electrostatic actuation.

  • Asymmetric-friction systems can create shear forces independently of finger speed and direction, reaching up to 100 mN ultrasonically and 0.45 N with electrovibration.
  • A combined system using electrostatic friction modulation and 30 kHz in-plane ultrasonic oscillation generated active lateral forces up to 0.4 N.The force direction and magnitude were adjusted by varying the phase between the oscillation and electroadhesion signals.
  • A touch surface can generate direct driving force by simultaneously exciting out-of-plane and in-plane modes with the same 22.3 kHz resonant frequency.

3 HUMAN HAPTICS

Human haptics research examines how fingers perceive tactile stimuli on surface-haptics displays, including vibrotactile and frictional cues. Perception depends on stimulus and contact conditions, with studies showing distinct effects for masking, friction changes, and spatial gratings.

  • Perceptual foundations: Surface-haptics perception involves mechanoreceptor encoding followed by neural processing, while active touch adds movement-related complexity beyond passive vibrotactile perception.Passive touch involves maintained contact without motor commands; sliding for friction perception engages more complex mechanisms.
  • Vibrotactile stimuli: Vibrotactile perception varies with frequency, amplitude, waveform, body site, duration, contact area, and age.Pacinian and Meissner-mediated channels differ in frequency sensitivity, spatial resolution, and summation properties.
  • Frictional stimuli: Masking raises electrovibration detection thresholds, with stronger effects when target and masking frequencies match and remote masking also producing a central neural effect.Remote masking increased the electrovibration threshold by approximately 0.19 dB per dB of masking intensity.
  • Frictional stimuli: Rising friction is perceived more strongly than falling friction, while normal force and sliding velocity significantly influence friction perception.These perceptual findings were supported by tribological measurements of finger-surface contact.
  • Frictional stimuli: Electrovibration texture perception is structured along three perceptual dimensions, while roughness depends on waveform, spatial period, and tangential-force change.Square waveforms were perceived as roughest, and roughness generally decreased as spatial period increased.
  • Frictional stimuli: Ultrasonic periodic-grating discrimination worsens as spatial period increases, with JNDs of 0.2, 0.32, 0.47, and 0.8 mm for periods of 2.5, 3.5, 5, and 10 mm.The Weber fraction remained almost constant at 8–10%.

4 HUMAN-MACHINE HAPTICS

Human-machine haptics connects tactile rendering on ubiquitous touch devices with interfaces and applications that add tactile information to digital content. The section focuses on rendering virtual textures and shapes, interface design, and current applications.

  • Motivation: Commercial smartphones and tablets provide mostly visual and auditory feedback, despite tactile feedback improving task performance and realism during digital interaction.Tactile sensation also contributes to preferences and positive attitudes toward consumer products through surface texture.
  • Scope: The review covers tactile algorithms for virtual textures and shapes, surface-haptics interface and experience design, and current applications.It summarizes how surface-haptics technologies implement these techniques in Figure 3 and Table 3.

4.1 Tactile Rendering

Tactile rendering uses friction modulation and related algorithms to synthesize textures, shapes, and surface features on flat touch surfaces. Current methods can evoke material sensations and 3D features, but realism and precise shape identification remain constrained by spatial and actuation limitations.

  • Rendering goals: Virtual textures and shapes provide material simulation, informative feedback, and spatial cues for buttons or graphical content.Tactile features can indicate location, function, state, or other properties.
  • Virtual textures: Friction modulation supports realistic texture rendering because textures are felt during finger brushing and remain inherently passive.This passivity is independent of display-actuation responsiveness.
  • Virtual textures: Time-varying periodic signals can evoke material and surface sensations, but spatially registered or velocity-modulated signals improve realism by preserving spatial consistency.Spatial corrections matter more for large tactile patterns than for fine patterns.
  • Virtual textures: Data-driven and image-based algorithms model friction profiles or local image gradients to control rendering signals, with frequency modulation further improving tactile realism.Physical texture data can be acquired from instrumented probes or tribometers.
  • Limitations: Current tactile rendering has not reached sufficient realism for simulating a wide range of textures because of actuation and tactile-perception limitations.The limitation concerns both the technology and the understanding of perception.
  • Virtual shapes and surface features: Electrovibration produced difficult-to-read Braille and only 56% success identifying simple geometric shapes, likely because it cannot create distributed moving-edge cues.The same friction sensation across the surface limits precise shape simulation.
  • Virtual shapes and surface features: Gradient-based electrovibration algorithms can make 3D bumps perceptible, but identifying bumps and holes required contextual information for moderate success.The approach maps depth-map gradients to friction and normalizes output amplitude linearly.
  • Virtual shapes and surface features: Localized tactile edges and net tangential forces can reduce spatial integration demands and facilitate contour following.Forces orthogonal to finger motion support following surface contours.

4.2 User Interface Design

Surface-haptics interfaces use design tools, friction modulation, and vibrotactile or ultrasonic feedback to support virtual controls and target acquisition. Their benefits depend on interaction type because friction feedback requires sliding and is spatially uniform.

  • Design Tools: Few design tools currently support the sketching, prototyping, and production stages for surface-haptics interfaces.
  • Design Tools: Chemically etched glass can mislead because etched patterns do not reproduce the distributed tactile stimuli produced under the fingerpad.
  • Designing for Friction Modulation: Friction modulation is felt only while the finger slides and is identical across the entire surface.
  • Designing for Friction Modulation: Friction modulation typically cannot support touch-and-hold feedback, so interfaces may combine vibrotactile actuation or redesign controls around sliding interactions.Combining actuators increases cost and complexity; sliding toggles are one alternative.
  • Designing for Friction Modulation: Friction modulation constrains spatial resolution and multi-touch because multiple sliding fingers receive the same feedback.Anchored gestures and two-handed asynchronous manipulation can work around this limitation.
  • Target Acquisition: 7.5% improvement in targeting performance was found with electrovibration when the entire target contained a tactile texture.
  • Target Acquisition: Close to 9% improvement in targeting performance was observed with ultrasonic friction modulation without distractors, while performance was similar with distractors.
  • Virtual Controls and Widgets: Virtual controls lack the haptic feedback of physical controls, which can reduce performance and task precision and increase reliance on visual attention.

4.3 Applications

Surface haptics has been explored for tactile effects in interfaces, communication, accessibility, augmented reality, and tangible objects. Demonstrations include friction-based textures, detents, impacts, tactile overlays, and remote touch traces.

  • Applications: Researchers have explored surface-haptics applications, particularly novel possibilities enabled by friction modulation.
  • Applications: Proposed applications include realistic tactile effects, non-visual information layers, and augmented graphical-interface widgets.
  • Applications: Ultrasonic friction modulation supported applications including alarm-clock detents, file-dragging resistance, game impacts, and pop-through sensations in text editing.
  • Applications: Scrolling studies examined detent identification and density perception across webpage scrolling and numerical-slider scenarios.
  • Applications: Ultrasonic friction modulation was evaluated for affective communication through friction-pattern messaging, annotated images, and remote partners’ touch traces.
  • Accessibility: Electrovibration-based Braille and tactile graphics were difficult to read, partly because the method cannot produce patterns smaller than the fingertip.
  • Tactile Augmented Reality: Tactile augmented-reality concepts extend feedback to projected surfaces, real-world objects, physical prints, public displays, and assistive guidance.

5 DISCUSSION AND CHALLENGES AHEAD

Surface-haptics displays face challenges in localization, scale, transparency, directional and receptor coverage, power, integration, and realistic rendering. These constraints arise from actuator behavior, material properties, manufacturing, and energy requirements.

  • Challenges: Large tactile areas remain difficult because ultrasonic resonance creates limited friction-modulation zones and large capacitive screens can develop nonuniform charge distributions.
  • Directional and Receptor Coverage: A single actuation technique cannot always provide tactile effects simultaneously in both normal and tangential directions.
  • Directional and Receptor Coverage: Current actuation technologies mostly stimulate rapidly adapting mechanoreceptors, limiting sensations such as stationary bumps or edges and leaving other receptor types less studied.
  • Low Power Consumption: High voltage requirements for ultrasonic and electrostatic actuation hinder mass-market deployment, while amplitude modulation improves complex rendering but increases energy cost.
  • Easy Integration and Compact Design: Integration depends on surface geometry, materials, actuator placement, housing, resonance behavior, insulating-layer thickness, and breakdown voltage.
  • Realistic Tactile Effects: Realistic texture rendering remains difficult because ultrasonic and electrostatic friction modulation cannot directly display texture topography.
  • Localized, Distributed, and Multi-Finger Interactions: Localized multi-finger stimulation is difficult, and projected-capacitive electrode structures complicate electrovibration compared with single-touch screens.
  • Localized, Distributed, and Multi-Finger Interactions: Distributed surface haptics is currently unavailable, so an edge smaller than a fingertip cannot be displayed to one touching finger.
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