Effects of amplitude modulation on vibrotactile flow displays on piezo-actuated thin touch screen

This paper investigates effects of different amplitude modulation methods of frequencyswept excitation patterns for creating vibrotactile flow displays on a spatiotemporally actuated thin touch screen. Four piezoelectric actuators (bimorph type) located at the midpoints of each side of a screen can be used to make eight directional (horizontal, vertical, diagonal) vibrotactile flows by spatiotemporally actuating two or more piezo-actuators. To determine which amplitude modulation method is the most effective in generating directional vibrotactile flows, an excitation pattern having sweeping frequencies in the range of 50 Hz to 250 Hz with four different time-varying amplitudes are investigated: 1) constant amplitude modulation, 2) linear amplitude modulation (linearly increasing and decreasing amplitude), 3) exponential amplitude modulation (exponentially increasing and decreasing amplitude), and 4) logarithmic amplitude modulation (logarithmically increasing and decreasing amplitude). A user study shows that the exponentially increasing and decreasing the amplitude pattern is the worst in terms of human perception (accuracy, validity, and refinement), while other amplitude modulation methods give similar results. Another user study shows that the eight directional vibrotactile flows can easily be distinguished on the users' palms. As such, it is expected that these vibrotactile flows can be applied to the user interface design of a mobile device, for example, for identifying callers or giving directions to the elderly and the blind.