  We review the current technology underlying surface haptics that converts
passive touch surfaces to active ones (machine haptics), our perception of
tactile stimuli displayed through active touch surfaces (human haptics), their
potential applications (human-machine interaction), and finally the challenges
ahead of us in making them available through commercial systems. This review
primarily covers the tactile interactions of human fingers or hands with
surface-haptics displays by focusing on the three most popular actuation
methods: vibrotactile, electrostatic, and ultrasonic.
