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.