In general terms, Skinput is an attempt to appropriate human body as an input interface. Skinput is a novel bio-acoustic sensing system developed by Chris Harrison from Carnegie Mellon University and Desney Tan and Dan Morris, employees at Microsoft Research. From the practical viewpoint, Skinput represents a bio-acoustic sensing array coupled with a small-size pico-projector, which turns user's skin into a touch-screen. The system of acoustic sensors identifies signals produced with our fingers onto skin surface, utilising the skin as an input surface. Chris Harrison's invention of Skinput rests on the idea that human skin constitutes an ideal input device: humans have roughly 22 square feet of skin area, which is accessible by hands and proprioception (understanding of how individual's body is configured in three-dimensional space) enables users to accurately interact with their bodies in an eyes-free manner (Harrison et al, 2010).
Unlike previous examples of always-available input systems, Skinput idea is largely based on the principles of bio-sensing and acoustic transmission. Bio-sensing technology has been widely utilised in diagnostic medicine with electroencephalography (EEG) and functional near-infrared spectroscopy (fNIR) being notable examples (Harrison et al, 2010). Simultaneously, the principles of acoustic transmission have been applied to support the idea of the skin being used as a finger input surface. From the practical standpoint, when a finger taps the skin, the impact creates a magnitude of useful acoustic signals. In order to capture these signals, Chris Harrison's team developed a special bio-acoustic sensing array. During the series of experiments, Chris Harrison and his colleagues opted in for a sensing array built into an armband. This bio-acoustic sensing array aimed to detect vibrations transmitted through the body is comprised of two sensor packages each containing five cantilevered piezo films responsive to a particular frequency range. Because variations in bone density, muscle size and filtering effect produced by soft tissues and joints make different locations being acoustically distinct, Skinput software analyzes impacts and classifies them (Harrison et al, 2010). In addition, Skinput's armband works with a special purpose pico-projector, which allows various interactive elements to be displayed on the skin (see Figure 1 for complete illustration of Skinput device).
Figure 1. Skinput technology.
HOW SKINPUT WILL BE USED
During the series of their study, Chris Harrison et al. illustrated the range of Skinput's applications, most of which were concerned with tap-based interfaces. In the first example, the researchers projected a series of buttons onto the forearm, on which a user can finger tap to navigate a hierarchical menu (Harrison et al, 2010). The second example reveals how individual uses a scrolling menu tapping top or bottom of his forearm. The third example illustrates a projection of numeric keypad, which can be tapped to dial a phone number. From the practical perspective, thanks to embedded program algorithms, Skinput's interface can accurately identify user's gestures in motion, for instance, during walk.