A typical acceleration waveform and its Fourier transform (FFT)
are shown in Fig. 11 for one participant while walking at 3 mph
(4.8 km/h). On the acceleration waveform, the footsteps are seen as
sharp peaks in the waveform at a frequency of 1.88 Hz. On the plot,
‘L’ indicates a left foot strike and ‘R’ indicates a right foot strike.
Every other peak on the waveform has slightly lower amplitude,
indicating that for one foot(assumed to be the leftfootin the graph)
the acceleration observed by the accelerometer is lower than for
the other foot. The lower acceleration observed when the left foot
strikes is because the accelerometer and energy harvester are offset
slightly toward the right side of the person’s chest, so higher acceleration
is observed for the right foot impacts. This is a non-ideal
effect seen in the acceleration spectrum at 1 Hz.