A novel observer based sensing scheme for the displacement of electrostatically actuated microcantilevers

We present the design and implementation of a novel sensing scheme to reconstruct the displacement of electrostatically actuated microcantilevers that are used in atomic force microscopy. Our approach proposes to estimate rather than measure directly the displacement, by means of an observer that uses the current through the capacitive cantilever as an input. In particular, we formulate the observer problem as an H_∞ optimal filtering problem for periodic systems. We show here our first experimental results regarding the implementation of this sensing scheme, which includes a custom made off-chip circuit to measure very small currents (few pA) at high frequencies (≈ 100 kHz).