BackTrack: 2D Back-of-device Interaction Through Front Touchscreen

BackTrack: 2D Back-of-device Interaction Through Front Touchscreen Chang Xiao, Karl Bayer, Changxi Zheng, Shree K Nayar CHI ’21: The 2021 ACM CHI Conference on Human Factors in Computing Systems Session: Vision and Sensing Abstract We present BackTrack, a trackpad placed on the back of a smartphone to track fine-grained finger motions. Our system has a small form factor, with all the circuits encapsulated in a thin layer attached to a phone case. It can be used with any off-the-shelf smartphone, requiring no power supply or modification of the operating systems. BackTrack simply extends the finger tracking area of the front screen, without interrupting the use of the front screen. It also provides a switch to prevent unintentional touch on the trackpad. All these features are enabled by a battery-free capacitive circuit, part of which is a transparent, thin-film conductor coated on a thin glass and attached to the front screen. To ensure accurate and robust tracking, the capacitive circuits are carefully de