Half-day workshop on “Contact Mechanics for Electrovibration

with Dr. Bo Persson appearing as special guest speaker, a well-known expert on sliding friction.



When an alternating voltage is applied to the conductive layer of a capacitive touch screen, a uniform and attractive electrostatic force field is generated between finger pad and the touch screen in the direction normal to the its surface. Although the magnitude of this electrostatic force is small relative to the normal force applied by the finger, it results in a perceivable frictional force in tangential direction when the finger pad slides on the touch screen. This frictional force can be modulated by altering the magnitude, frequency, and phase of the voltage signal applied to the conductive layer of the touch screen. This technology has exciting potential applications in mobile computing in the areas such as online shopping, gaming, interfaces for blind, education, and data visualization. 


Problem Statement:

While the technology for generating tactile feedback on a touch screen via electrovibration (i.e. electroadhesion under an oscillating electric field) is already in place and straightforward to implement, our knowledge on contact mechanics for electrovibration is highly limited. In particular, we still do not know the exact mechanism leading to an increase in tangential frictional forces under electrovibration. Analytical models for estimating the electrostatic forces in normal direction and the friction forces acting on the finger in tangential direction are insufficient and the simulations produced by those models do not match well with the experimental data. This workshop aims to bring the experts working in the areas of contact mechanics, sliding friction, mechanical and electrical modeling of human finger, and electrovibration to discuss in depth the reasons behind this mismatch.



The workshop is open to any student, researcher as well as developer and end user interested in the design, development, and use of electrovibration for various applications in mobile computing. Although the focus of the workshop will be on contact mechanics and friction between finger and a touch surface, the basic concepts of contact mechanics and electrovibration will be covered for the beginners. We also plan to have a Q&A session where the participants can ask questions to the speakers and the audiance can discuss the next greatest challenges in electrovibration.


Tentative program:

8.30 – 8.45 Welcome by the organizer

8.45 – 9.30 Guest Speaker: Dr. Bo N.J. Persson, “Electroadhesion and Contact Mechanics for the Human Skin”

9.30 – 10.00 Dr. Vincent Hayward, “Tactual Curiosities”

10.00 – 10.30 Coffee Break

10.30 – 11.00 Dr. Ed Colgate, “The Mechanics of Electroadhesion

11.00 – 11.30 Dr. Cagatay Basdogan, “Experimental Investigation of Contact Mechanics for Electrovibration

11.30 – 12.00 Panel discussion



Cagatay Basdogan (http://portal.ku.edu.tr/~cbasdogan)

Robotics and Mechatronics Laboratory (http://rml.ku.edu.tr/)

College of Engineering, Room: ENG-247

Koc University (http://www.ku.edu.tr)

Sariyer, Istanbul, TURKEY 34450



Special Guest Speaker:  

Bo N.J. Persson

Research Center Juelich, Germany.

(Google Scholar)

Dr. Persson is a research scientist at Research Center Juelich. He is also the founder and CEO of MultiscaleConsulting, which is helping companies (e.g., tire and medical companies) to understand and solve contact mechanics problems involving friction, adhesion, leakage of seals, the electric and thermal contact resistance, and related problems. During 1983-1984 Persson worked at IBM research lab in Yorktown Height, New York, and 1986-1987 at the IBM Zurich research lab. His early interest was in ultra high vacuum surface science (e.g. theories for surface spectroscopy's, and studies of dynamical processes at surfaces) but starting ~ 1995 his main research activity is in tribology (adhesion, friction, contact mechanics). He is author of~ 400 articles published in internationals Journals, and of two books on tribology, and a book on the electromagnetic fluctuations at the nanoscale.

Title: Electroadhesion and contact mechanics for the human skin


All solids have surface roughness. When two elastic solids are squeezed into contact, the area of real contact is usually only a small fraction of the nominal contact area. This is true even for elastically soft solids such as rubber or the human skin. Thus, for example, the contact area between a tire on a passenger car and an asphalt road surface may be only 1cm x 1cm (or less). I have developed a contact mechanics theory which is valid under very general conditions, e.g., for layered and viscoelastic materials and including plastic deformations. In this presentation, I will briefly describe this theory and present applications to the contact between the human skin and a smooth glass surface. I will discuss how  adhesion, in particular due to capillary bridges or an applied electric voltage (electroadhesion), affect the skin-glass contact area and the sliding friction.



Vincent Hayward

Professor of Tactile Perception and Technologies, Leverhulme Fellow 

School of Advanced Study, University of London 


Chief Scientific Officer, Actronika SAS, Paris 


Professeur des Universités (on leave) 


(Google Scholar)

Vincent Hayward is a Professor at the Sorbonne Université in Paris, presently on leave. Before, he was with the Department of Electrical and Computer Engineering at McGill University, Montréal, Canada, where he became a full Professor in 2006 and was the Director of the McGill Centre for Intelligent Machines from 2001 to 2004. Vincent Hayward is an elected a Fellow of the IEEE. Since January 2017, he is Professor of Tactile Perception and Technology at the School of Advanced Studies of the University of London, supported by a Leverhulme Trust Fellowship. Over the past decade Vincent developed a computational theory of tactile perception that is grounded in the physics of mechanical interactions. During his tenure at the University of London’s School of Advanced Study, Vincent relates this theory to the cognitive and metacognitive functions of the brain: i.e. how judgments about objects are made through touch. He spends part of his time contributing to the development of a start-up company in Paris, Actronika SAS, dedicated to lowering the accessibility barrier of haptic technology and also helps develop a tactile communication technology for use by the Deafblind.

Title: Tactual Curiosities


The astonishing variety of phenomena resulting from the contact between fingers and objects can be regarded as a formidable trove of information that can be extracted by organisms and robots to learn about the nature and the properties of objects. This richness is likely to have fashioned our somatosensory system at all levels of its organisation, from early mechanics to cognition. The talk will illustrate this idea through examples that show how the physics of mechanical interactions shape the messages that are sent to the brain, providing new opportunities for applications to robotics and human machines interfaces.



J. Edward Colgate

Breed University Professor of Design

Department of Mechanical Engineering

Northwestern University

Evanston, Illinois, USA


(Google Scholar)

J. Edward Colgate is the Breed University Design Professor and a member of the Department of Mechanical Engineering at Northwestern University. Dr. Colgate’s principal research interest is haptic interface.  He is the co-inventor of a class of collaborative robots known as “cobots” and a suite of technologies for bringing programmable haptic feedback to touch surfaces. He served as the founding Editor-in-Chief of the IEEE Transactions on Haptics and is a Fellow of the IEEE and the National Academy of Inventors.  Dr. Colgate has founded three startup companies the most recent of which, Tanvas Inc., is commercializing haptic technologies.

Title: The Mechanics of Electroadhesion


Electroadhesion is a promising approach to surface haptics:  it is solid state, requires modest power, exhibits high bandwidth, and is compatible with modern touchscreen manufacture.  Yet, the underlying mechanics of electroadhesion are poorly understood, leaving engineers little basis for selecting parameters such as surface layer thickness, dielectric constant, roughness, and so on.  In this talk, I’ll present a picture of electroadhesion which is emerging as the result of extensive experimentation and modeling in our laboratory.  Certain factors that were once routinely ignored are now known to be critical.  These include the nanoscale roughness of skin, the high elastic modulus of the outermost layers of stratum corneum, and the crucial role of the air gap, especially during motion.



Cagatay Basdogan

Robotics and Mechatronics Laboratory (http://rml.ku.edu.tr/)

College of Engineering, Room: ENG-247

Koc University


Sariyer, Istanbul, TURKEY 34450

Phone: +90 212 338 1721

Fax:     +90 212 338 1548

e-mail: cbasdogan@ku.edu.tr


(Google Scholar)

Prof. Basdogan is a member of faculty in College of Engineering at Koc University since 2002. Before joining to Koc University, he was a senior member of technical staff at Information and Computer Science Division of NASA-Jet Propulsion Laboratory of California Institute of Technology (Caltech) from 1999 to 2002. At JPL, he worked on 3D reconstruction of Martian models from stereo images captured by a rover and their haptic visualization on Earth. He moved to JPL from Massachusetts Institute of Technology (MIT) where he was a research scientist and principal investigator at MIT Research Laboratory of Electronics and a member of the MIT Touch Lab from 1996 to 1999. At MIT, he was involved in the development of algorithms that enable a user to touch and feel virtual objects through a haptic device. He received his Ph.D. degree from Southern Methodist University in 1994 and worked on medical simulation and robotics for Musculographics Inc. at Northwestern University Research Park for two years before moving to MIT. Prof.Basdogan is currently the associate editor in chief (AEiC) of the IEEE Transactions on Haptics and serves in the editorial boards of IEEE Transactions on Mechatronics, Presence: Teleoperators and Virtual Worlds (MIT Press), and Computer Animation and Virtual Worlds (Wiley) journals. In addition to serving in the program and organizational committees of several conferences, he also chaired the IEEE World Haptics Conference in 2011.

Title: Experimental Investigation of Contact Mechanics for Electrovibration


Allthough the technology for generating tactile feedback on a touch screen via electrovibration is already in place and straightforward to implement, our knowledge on contact mechanics for electrovibration is highly limited. In particular, we still do not know the exact mechanism leading to an increase in tangential frictional forces under electrovibration. Based on the results of our experimental studies, we speculate that the main cause in increase in tangential frictional force under electrovibration during full slip is due to an increase in real contact area. We argue that the increase in frictional forces under electrovibration causes a further reduction in apparent contact area due to nonlinear stiffening of finger in tangential direction, which results in an increase in real contact area due to the rounded geometry of fingerpad and existence of its asperities.