On the electrical characterization of electroadhesive displays and the prominent interfacial gap impedance associated with sliding fingertips

We report on the characterization of two variable friction electroadhesive displays using careful electrical and electrochemical impedance measurements. We qualitatively and quantitatively examine the properties of the skin, body, surface coating, and various electrode interface impedances in isolation using different contact interface conditions and measurement types. A lumped series impedance model explains how all impedances are related during normal usage, and the linearity of this model is shown to be valid under certain assumptions, such as high applied frequencies or small applied currents. Speculation as to the physical mechanisms underlying each impedance element is also given. This analysis unambiguously verifies the existence of a previously hypothesized key electrical system parameter: the sliding interfacial impedance (or air gap impedance). This parameter represents the large increase (100-1000 percent) in overall electrical impedance observed when a finger is sliding versus when it is stationary. It is concluded that this impedance increase cannot be explained by other measured electrical impedance elements in the system and that it vanishes again when the finger comes to rest.