What is "% fs" Meaning in AFM Oscillation?

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SUMMARY

The term "% fs" in the context of AFM oscillation refers to "percent full scale," which indicates the magnitude of the cantilever's displacement relative to its full-scale output. This measurement is displayed by the "ACQUIRE" software from "Signal Recovery" during frequency sweeps of the AFM-style cantilever. The resonant frequency, denoted as "Fs," is crucial for interpreting these measurements, although its exact calculation method within the software remains unclear. The discussion highlights the need for clarity on how the software determines resonant frequency amidst noisy spectral data.

PREREQUISITES
  • Understanding of AFM (Atomic Force Microscopy) principles
  • Familiarity with lock-in amplifiers and their applications
  • Knowledge of QPD (Quadrant Photodiode) measurement techniques
  • Basic grasp of frequency response analysis
NEXT STEPS
  • Research the calculation methods for resonant frequency in AFM systems
  • Explore the functionality and settings of "ACQUIRE" software by "Signal Recovery"
  • Investigate techniques for reducing noise in frequency response data
  • Learn about the implications of "% fs" in signal processing and measurement
USEFUL FOR

This discussion is beneficial for researchers and engineers working with AFM technology, particularly those involved in signal processing, measurement analysis, and environmental condition studies affecting resonant frequencies.

stephenx_86
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Meaning of "% fs"

Hi,

We're using a lock-in amplifier to oscillate an AFM-style cantilever (across a frequency sweep) and measure the response using a QPD. The aim of this is to see how the resonant frequency changes with changing environmental conditions.

The software we use ("ACQUIRE" by "Signal Recovery") is displaying this frequency response in terms of "Mag. (% fs)", which I assume is some sort of magnitude - maybe the magnitude of cantilever displacement? What we're least sure of is what exactly "% fs" means in this context. From looking round the internet it seems Fs is resonant frequency, but I don't know if this is the same Fs as the fs output by our machine! In the manual this is written as "MAG% (10V fs)", which might shed some more light on the situation.

If this actually is a percentage of the resonant frequency, does anyone know how resonant frequency is being calculated by the software? The spectra we get out (Mag (% fs) as a function of driving frequency (Hz)) is pretty noisy with no single, clear peak and goes up to ~300 (% fs).

If anyone could shed some light on what "% fs" is, we'd be really grateful.

Thanks
Stephen
 
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