Preferential Contamination in Electroadhesive Touchscreens: Mechanisms, Multiphysics Model, and Solutions

Electroadhesive surface haptic touchscreens can help augment user experiences by providing tactile effects. The electrode layout in current commercialized designs has separated electrodes for the sensing and actuating functions. During regular use, it is observed that fingerprint residue preferentially deposits on the actuating electrodes far more than the sensing electrodes, which makes the underlying electrode pattern apparent and is highly undesirable for touchscreen users. To address this issue, various physical phenomena (electrohydrodynamic deformation, capillary bridge stabilization, electrowetting, and electrophoretic deposition) are investigated to understand the mechanism. Through experimentation, multiphysics modeling, and surface characterization, it is found that the root cause can be attributed to two mechanisms occurring in the actuating regions: 1) electrohydrodynamic deformation of sebum droplets attached to the finger valleys leading to the formation of additional capillary bridges and residual droplets on the screen surface after their rupture, and 2) electric field-induced stabilization of sebum capillary bridges existing between the finger ridges and the screen, leading to the coalescence and formation of larger-sized droplets. The developed model can then be used to address the issue during the screen design process. An example of using the model to explore the impact of changes in screen oleophobicity is shown.