Analysis and application of modulated-demodulated control

We review the modulated-demodulated control technique, emphasize its linear time invariant nature and develop state space controller models. We have previously outlined the implementation of a modulated-demodulated positive position feedback controller and extend upon this result with the implementation of a resonant controller. Negative imaginary systems theory has important implications in the control of many practical systems and use of the derived state space model simplifies the design of negative imaginary controllers. To conclude, we demonstrate the closed loop control of the quality factor of a Bruker DMASP microcantilever and highlight improvements in atomic force microscopy (AFM). The modulated-demodulated control technique is well suited to the control of systems with high-frequency resonant dynamics.