Toward Ultrasmall Mass Detection Using Adaptive Self-Sensing Piezoelectrically Driven Microcantilevers

Over the past decade, microcantilever-based mass sensing has grown to become a significant field of research in the engineering community. The ability of microcantilevers to detect extremely small biochemical particles is being investigated for a number of industrial applications. This paper presents an adaptive self-sensing strategy for ultrasmall tip mass estimation using piezoelectrically actuated microcantilevers. A piezoelectric patch actuator deposited on the cantilever surface actuates the beam through a capacitance bridge mechanism. The same patch is used to measure shifts in the beam natural frequency associated with increase in the mass, which is due to the addition of biochemical particles. The ability to measure frequency shifts due to tip masses as small as 1 fg (10
^-15
g) is demonstrated through extensive numerical simulations. Uncertainty in the measurement of system parameters makes implementation of the self-sensing bridge network difficult at the microscale. The piezoelectric capacitance is also known to vary with temperature. To overcome these difficulties, a novel adaptive mechanism is presented to dynamically balance the capacitance bridge network. Lyapunov-based stability analysis demonstrates the global stability of the adaptation laws. Simulation results demonstrate the feasibility of this mechanism to perform self-sensing at the microscale. Experimental validation of the adaptation mechanism at the microscale involves a number of technical challenges, and hence, is performed on a macroscale cantilever system. This paper aims to motivate research in the development of a powerful, yet portable frequency shift detection-based microcantilever sensor for use in a variety of biochemical applications, where ultrasmall mass detection is a key requirement.