Optimization of the power targeted to the frequency region of maximum tactile sensitivity.

Abstract

Tactile stimulation is a means of transferring information to visually handicapped individuals. A study of the power delivered by the driving waveform to a transducer used for tactile stimulation as a function of the parameters of the waveform is presented. The power delivered within the region of maximum tactile skin sensitivity, Qfw, is compared to the total power delivered by the waveform in one cycle, PT, as a function of the waveform parameters with the objective of finding the parameters that would maximize the ratio Qfw/PT. In this study, the driving waveform is composed of an excitatory period followed by a recovery 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 harmonic was added to compute the power delivered within the frequency region of interest. Additionally, to take in account the contribution of each harmonic in the overall tactile sensation, the power delivered within the region of maximum tactile skin sensitivity was weighed by the skin tactile sensitivity function and then linearly summed. The results show that the ratio Qfw/PT has a maximum for pulse widths between 0.8 and 1.2 ms for all pulse frequencies in the range 50-700 Hz when the tactile sensitivity function was not considered. The optimum pulse width, when the tactile sensitivity weighing function is considered in the computations, was in the range between 0.7 and 1.7 ms for pulse frequencies between 50-700 Hz. The ratio Qfw/PT is invariant to changes in the number of pulses per burst and the length of the recovery time. Once the tactile system frequency response is identified, all the waveform parameters can be specified for maximum power targeted to the region of maximum tactile sensitivity.