MudPad is a prototype system to explore the possibilities for localized active haptic feedback on touch surfaces. Since the introduction of the iPhone, touchscreens became very common and most people probably have used one by now. While using a touchscreen is often described as enjoyable due to more direct interaction techniques, such screens also lack tactile feedback. Over the last years mobile phones with tactile feedback were released. But as of yet they only provide feedback in a global manner applied to the whole screen, usually depending on vibrotactile feedback. Recently, first prototypes with localized tactile texture displays were presented such as TeslaTouch by Olivier Bau et al. and also by companies such as Toshiba and Nokia. Still, these devices are not capable of producing different tactile feedback for each finger touching the screen. MudPad takes a different approach: it is capable of producing localized active haptic feedback using magnetorheological (MR) fluid and an array of electromagnets to actuate the fluid. This fluid is called a “smart fluid” because one of its properties – its viscosity – can be controlled by a magnetic field. It consists of carbonyl iron powder dissolved in glycerin. The viscosity of this fluid, when in off state, depends on the percentage of iron powder but is generally rather low (comparable to oil). When it is exposed to a magnetic field it immediately turns stiff. The reaction time of the fluid is within 2ms thereby making it suitable for real-time interactions.
Yvonne Jansen, Thorsten Karrer, Jan Borchers. MudPad: tactile feedback and haptic texture overlay for touch surfaces. ACM International Conference on Interactive Tabletops and Surfaces (ITS ’10), ACM, Nov 2010, Saarebruck, Germany. pp.11-14, ff10.1145/1936652.1936655. [pdf]