In this study we identify and measure the parameters that can perceptually drive a smooth and continuous vibrotactile sensation exerted by a focused ultrasound array at the palm of the dominant hand. We conducted a psychophysical experiment that measures (1) the minimum stimulation duration that is perceived by the participants as continuous, (2) the minimum stimulus onset asynchrony (SOA) duration that is perceived as continuous, and finally, (3) the minimum stimulation intensity that is perceived by the participants expressed in terms of the driving signal modulation frequency. The effect of the first two parameters was also examined spatially by repeating the experiment with an increased number of stimulation points. Results showed that a perceivable stimulation can occur for a stimulation duration between 5ms and 60 ms and an SOA of less than 50 ms. The study also showed that these parameters can be relaxed if the density of stimulation is increased (higher number of stimulation points for the same stimulation pattern). Finally, the study showed that the minimum perceivable modulation frequency is about 470Hz. In the conclusion, we summarize the study findings and provide perspectives for future work.