A novel capacitive mass sensor using an open-loop controlled microcantilever

This article presents a method for quantitative estimation of the mass of an entity attached to the surface of an electrostatically actuated clamped-free microbeam implemented as a mass sensor. For this investigation, the microbeam is modeled as a Euler-Bernoulli beam taking into account the effects of electrostatic nonlinearity, viscous energy dissipation together with the effect of the fringing field capacitance. A modal superposition technique is used to simulate the dynamic response of the microcantilever. The dynamic pull-in voltage of microcantilever is evaluated using a developed modal. The present dynamic pull-in voltage results are compared with the existing results and on the basis of comparison, the accuracy of the developed model is ascertained. For mass quantification, firstly, an input shaping technique is employed to stabilize the microbeam at the specified position and then voltage perturbation is induced to make the system sensitive to inertial change. A parasitic mass expressed as a fraction of the total mass of the beam is then added resulting in an increase in the amplitude of vibration and hence an alteration in the capacitance. An empirical relation between the added mass and the change in capacitance is proposed.