(786d) Effects of Minor Asymmetries in Boundary Conditions of Cantilever Resonators On Sensing Properties

Engineering new cantilever sensors has pioneered various new sensing applications, including atomic-level microscopy and versatile bio-chemical sensing applications.  In particular, dynamic-mode (resonating) cantilevers have become increasingly used since sensing principle involves direct transduction of added-mass by resonant frequency shifts.  The canonical driving force for improving cantilever sensitivity suggests exploring designs that increase cantilever resonant frequency and reduce mass.   Thus, various techniques have been examined, such as miniaturization, use of high-order resonant modes, and non-rectangular geometries.  All such methods focus on the continuum of the structure (i.e. its size, motion, and geometry), but ignore the boundaries which present an equally rich potential for optimization.  We demonstrate an alternative method to continuum engineering of such devices based on introducing minor perturbations in constrained cantilever boundaries (anchored regions)  using finite element analysis and experimental measurements.  The technique enhances cantilever resonant frequency, and thus, the realizable sensitivity of resonating cantilever sensors.  The inclusion of asymmetric constrained boundaries also has a significant impact on the mode shapes and deflection magnitudes relative to those found in conventional cantilever sensors which contain ideal symmetric boundary conditions.  Besides the potential for this phenomena as an applied technique for enhancing cantilever sensing properties, it is also important for describing experimental measurements in extremely small cantilevers fabricated near the precisions limits of micro-fabrication techniques where inherent asymmetry in the boundaries may arise.  Therefore, understanding the effects of minor perturbations in constrained boundaries may become a central theme of future cantilever sensor engineering and design.