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Using atomic force microscopy (AFM) for studying soft, biological material has become increasingly popular in recent years. New approaches allow the use of recursive least squares estimation to identify the viscoelastic properties of a sample in AFM. As long as the regressor vector is persistently exciting (PE), exponential convergence of the parameters to be identified can be guaranteed. However,...
A major difficulty in multifrequency atomic force microscopy (MF-AFM) is the accurate estimation of amplitude and phase at multiple frequencies for both z-axis feedback and material contrast imaging. A lock-in amplifier is typically chosen for its narrowband response and ease of implementation. However, its bandwidth is limited due to post mixing low-pass filters and multiple are required in parallel...
A fundamental but often overlooked component in the z-axis feedback loop of the atomic force microscope (AFM) operated in dynamic mode is the demodulator. Its purpose is to obtain a preferably fast and low-noise estimate of amplitude and phase of the cantilever deflection signal in the presence of sensor noise and additional distinct frequency components. In this paper, we implement both traditional...
Identification of mechanical properties of cells is known to be an effective tool for medical diagnosis, and holds potential for future developments in treatment of various diseases. In this paper a novel method for identification of viscoelastic properties of a soft sample using atomic force microscopy in dynamic mode is presented. The estimation scheme is based on parameter identification of a lumped...
Amplitude estimation or demodulation plays a vital part in the control loop of dynamic mode high-speed atomic force microscopy (AFM). The closed-loop bandwidth will be limited by the convergence speed of the estimator. Recent developments have introduced new ways of demodulating the measured deflection signal. This article reviews and compares present methods for AFM amplitude demodulation and introduces...
A novel imaging method for atomic force microscopy based on estimation of state and parameters is presented. The cantilever dynamics is modeled as a linear system augmented by the tip-sample interaction force. The states of this augmented system are observed. The tip-sample force function is based on the Lennard-Jones potential with a nonlinearly parameterized unknown topography parameter. By estimating...
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