OPTIMIZATION OF THE POWER TARGETED TO THE FREQUENCY REGION OF MAXIMUMTACTILE SENSITIVITY

Tactile stimulation is a means of transferring information to visually handicapped individuals. A study of the power delivered by the drivin g waveform to a transducer used for tactile stimulation as a function of the parameters of the waveform is presented. The power delivered wi thin the region of maximum tactile skin sensitivity, Q(fw), is compare d to the total power delivered by the waveform in one cycle, P-T, as a function of the waveform parameters with the objective of finding the parameters that would maximize the ratio Q(fw)/P-T In this study, the driving waveform is composed of an excitatory period followed by a re covery time. The excitatory period is formed by a burst of rectangular pulses modulated in amplitude by different waveforms. After a Fourier decomposition of the excitatory waveform, the contribution of each ha rmonic was added to compute the power delivered within the frequency r egion of interest. Additionally, to take in account the contribution o f each harmonic in the overall tactile sensation, the power delivered within the region of maximum tactile skin sensitivity was weighed by t he skin tactile sensitivity function and then linearly summed. The res ults show that the ratio Q(fw)/P-T has a maximum for pulse widths betw een 0.8 and 1.2 ms for all pulse frequencies in the range 50-700 Hz wh en the tactile sensitivity function was not considered. The optimum pu lse width, when the tactile sensitivity weighing function is considere d in the computations, was in the range between 0.7 and 1.7 ms for pul se frequencies between 50-700 Hz. The ratio Q(fw)/P-T is invariant to changes in the number of pulses per burst and the length of the recove ry time. Once the tactile system frequency response is identified, all the waveform parameters can be specified for maximum power targeted t o the region of maximum tactile sensitivity.