Modulated-Demodulated Q Control of an Atomic Force Microscope Microcantilever

We outline the application of the modulated-demodulated control technique to the quality (Q) factor control of an atomic force microscope microcantilever. The modulated-demodulated controller developed can be modeled as a linear time invariant controller, which resembles a positive position feedback (PPF) controller. We utilize negative imaginary theory to concisely summarize the requirements for robust stability of the closed loop system. The Q controller is verified experimentally on a microcantilever. Modulated-demodulated control appears to be well suited to the control of high frequency dynamics, simplifying the bandwidth requirements of the baseband controller. Due to the controller parameterization, the tuning process is extremely simple. We believe modulated-demodulated control could find applications in high speed atomic force microscopy (AFM) and microelectromechanical systems (MEMS).