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How high frequency nanopositioning works
High frequency nanopositioning employs piezoelectric actuators with direct action. This means, that the actuator is directly pushing the platform without any conversion or amplification mechanism, which would drag the first resonance down. The piezo actuator provides a few microns positioning range but with picometer resolution. Positioners usually include a sensor to achieve closed-loop control. Depending on the displacement range, resonance frequency can be of several kHz.
Positioning of an Atomic Force Microscope (AFM) probe
An example of high frequency nanopositioning is for the vertical positioning of an AFM probe. Here, the probe has to follow the surface of a sample, either in contact or at a short distance (few nanometers). This requires very fine positioning with sub-nanometer resolution and very low noise. Furthermore, the high resonance frequency provides improved stability of the control loop, enabling faster imaging. While conventional AFM will take minutes for a scan, fast positioning can allow imaging down to fractions of a second.
Custom designed multilayer actuators
Multilayer actuators are preferred for their high strain and low operating voltage. Depending on the required travel range, positioners can include single actuators or actuator stacks. Usually a soft-doped ceramic NCE51 provides good results.
For example, a plate actuator stack such as NAC2012-H06 can be used. It provides 6µm of free displacement and an unloaded resonance of 200kHz (free-free). Taking into account the different boundary conditions and the mass of the platform, the first resonance in the application will be lower, in the order of tens of kHz, enabling imaging in a few seconds.
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