Sound-of-Tapping user interface technology with medium identification

Touch screen technologies have become the mainstream of input interfaces for mobile devices. However, due to the small size screens, it is difficult to offer more than two inputs at the same time. In order to achieve input richness, this paper proposes a new sound-of-tapping (S-TAP) technology that is a novel user interface utilizing only microphones embedded in most mobile devices. S-TAP technology extracts the positions of tapping sounds generated at the outside of a smartphone by means of frequency domain features and support vector machine (SVM). The error ratio of an S-TAP algorithm implemented in a smartphone is measured as 8.6%. Additionally, this technology enables the smartphone to identify mediums that the user is tapping on. In the end, we demonstrate two smartphone applications to scroll web pages only by S-TAP and to zoom and rotate a map image by S-TAP as well as touch screen.