Closed-loop tracking of amplitude and frequency in a mode-localized resonant MEMS sensor

In this paper, the amplitude and frequency stability of a mode-localized sensor are characterized in a closed loop setup. The system describes an absolute amplitude ratio sensitivity of 5250 to stiffness perturbations in linear operation. A stability of 432ppm at 500s integration time is observed for amplitude ratio measurements. A resolution of 85ppb corresponding to normalised stiffness perturbations in amplitude ratio measurements is thus demonstrated at 500s integration time. Comparisons to frequency shift sensing within the same device shows that amplitude ratio sensing provides higher accuracies for long term measurements due to intrinsic common mode rejection properties in a mode-localized system.