Influence of stiffness change due to mass loading on resonant microcantilever mass sensor's performance

Capability of piezoelectric microcantilever mass sensors to detect very small amount of mass, such as detection of a single virus has attracted many researchers' interests. In many cases, detection of mass is performed by adsorbing of materials in porous matrixes on the sensor surface, in which the adsorbed material does not form a solid layer on the cantilever surface. On the other hand, there are materials such as gold and mercury that constitute a solid layer on cantilever surface. The thickness and the young modulus of this layer, increase the cantilever's stiffness. Consequently, both the mass and the stiffness changes, alter the cantilever's natural frequency, which should be considered in modeling. Two lumped parameter modeling approach for resonant microcantilevers mass sensors has been investigated. Model I neglects the stiffness change of the cantilever sensor after mass loading. In model II the added mass constitutes a solid layer on the cantilever bottom surface. This additional solid layer affects the mass and also the stiffness of microcantilever. The results shown that model II represents a better modeling comparing to model I with respect to experimental data. For cantilevers of the same thickness in this study, the stiffness variation percentage due to added mass layer remains constant. Furthermore, the deviation between model I and model II is the same regardless the cantilevers dimensions.