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Hi,
Any explanation for negative phase I have observed in regular tapping mode? I am looking at Polypropylene/rubber compounds with a cantilever with k~1N/m (autotune looks fine - phase is centered at 90 degrees, I am imaging at 5% offset from peak), and see negative phase on the rubber domains. That doesn't seem to be physically meaningful so not sure what that means.
Thanks,
Dalia
In the Bruker and Agilent software that I work with, the +-10V DAQ input is mapped into +-90 degrees instead of 0-180 degrees (or 0 to -180). So 90 degrees is reported as zero. (Thus the "zeroing the phase" operation, when in fact one is "ninety-ing the phase".) So negative phase corresponds to one side of 90, rather than a (nonphysical) >90 degrees to one side of 90.
Hi Dalia,I agree with RW’s post and to provide a little more detail. In our autotune routine we do set the Phase to zero at resonance, rather than leave it at the perhaps expected 90deg. I should note that you do have the option to not do this (by not hitting the “zero phase” button, or by doing a manual tune.) In your original post, you mention that the phase was at 90deg after autotune. Because of our autotune algorithm, and the negative number you report, I expect that it actually was set to zero – please double check.Physically, and assuming the phase was zeroed at resonance, if it went negative it means the resonance shifted lower, or an attractive gradient was experienced.Best,Steve