15
Figure 9 An example of a IOOHz pulse as
captured by a Tektronix TDS 2002
oscilloscope (www.tek.com).
"Tap" generation
Atap on the skin can be generated by having the bending actuator flex just once
against the skin. However if the bending actuator were to only flex away from the
subject's skin, very little sensation would be created. By using a bipolar waveform the
bending actuator will flex once each way, guaranteeing stimulation regardless of the
orientation of the bending actuator. A Gaussian monopulse was selected since this
waveform is continuous and provides a very strong flex in the bending actuator without
creating clicks or damaging it. The center frequency of the monopulse can be varied
based on the time constraints of the needed stimulus, although in most cases a 200Hz
monopulse provides a sufficiently instantaneous stimulus (~6ms) that is also robust and
does not produce a noticeable amount of sound.