First,the open circuit ringdown waveform was captured for each
device in every mounting configuration. The ringdown test was performed
by pulling the magnet to the top of the box and releasing it
to ring down within the box. The model and measurement results
of the ringdown waveform are shown in Fig. 6. It was found that
the measured device frequency was about 0.3 Hz higher than the
model’s prediction, due to the shaker’s internal magnet and deviation
in the device dimensions and material properties. The damping
force was found by fitting the model ringdown with the measured
ringdown waveform.