The operation of the ActivResonance Controller is based around controlling the effective Q of the cantilever system. By using active control, the effect of the natural damping of the cantilever by the surrounding liquid can be removed. The ActivResonance Controller has a frequency range up to 400 kHz.

By using a positive feedback system, as shown schematically below, values of Q of approximately 1000 can be reached.

In other situations, it is desirable to decrease the Q. Whilst sensitivity and lower imaging forces are sacrificed by this mode of operation, increased scan speeds are possible to enable, for example, dynamic processes to be followed.

Tuning the cantilever is a crucial part of dynamic mode operation, especially when working in liquids.

Magnetic driving of the cantilever
Direct driving of a magnetised cantilever using an oscillating magnetic field offers the best way to operate in dynamic mode in liquids. Acoustic operation is often simpler to implement, but leads to the "forest of peaks" where numerous resonances are excited by oscillating the fluid indirectly.
The frequency spectrum below shows a typical peak (at 16.05 kHz) of a magnetically driven cantilever. The Q is approximately 3.

After turning on the ActivResonance Controller, a much sharper peak is obtained with a Q factor of ~300.

Acoustic driving of the cantilever
A typical frequency spectrum for a triangular silicon nitride cantilever being oscillated acoustically with a commercial liquid cell is shown below (frequency range 25 kHz).

Using the ActivResonance Controller on the peak that has been identified as the true resonance of the cantilever, the spectrum below was obtained:

In both these cases, the blue arrow marks 16.05 kHz and the frequency range of the graph is identical.

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