Biomedical Engineering Reference
In-Depth Information
To reduce random noise, the average of data from ten impacts was used to compute each
FRF. The
coherence
is a function in the frequency domain that indicates the quality of the
FRF. A perfect coherence is 1.0. A coherence less than that at a given frequency means that
the vibration sensed by the accelerometer at that particular frequency is not a linear
response to the excitation from the impact hammer. A low coherence in general indicates
excessive noise, nonlinearity, or other causes of bad measurement.
Fig. 21. Frequency response function obtained by hitting the melon rind directly
