Exploring the static acoustic force sensitivity using AFM micro-cantilever under single- and bimodal-frequency excitation

We present here a numerical calculation for sensitivity comparison of single- and bimodal-excitation of micro-cantilever (owing rectangular shape) on the measurement of static acoustic force. We model the micro-cantilever as a point mass in our simulations similar to forced harmonic oscillator with damping. In bimodal operation, the micro-cantilever is excited at its first two flexural modes. Results of amplitude and phase shift obtained through bimodal-frequency excitation are compared with the ones obtained using single-frequency excitation scheme. Oscillation observables are calculated in both excitation schemes with respect to magnitudes of excitation forces at fundamental and second eigenmode. Influence of driving force for micro-cantilever actuation on amplitude and phase shift is explored so that optimum excitation parameters can be provided for highest observable sensitivity. Moreover, we relate our findings with virial and energy dissipation to understand the physics behind observed dynamics. Our results clearly indicates that phase sensitivity at the fundamental eigenmode to static acoustic force could be enhanced using multi-frequency excitation scheme. In addition, results of virial and dissipated power at second eigenmode point out the existence of interaction of flexural modes in the presence of static acoustic force in bimodal-frequency excitation scheme. Therefore, our approach can be used to increase sensitivity of dynamically excited micro-cantilever for measuring ultra-low (pN) acoustic forces.