Bodily interface Handy too

Finding the keypad on your cellphone or music player a bit cramped? Maybe your forearm could be more accommodating. It could become part of a skin-based interface that effectively turns your body into a touchscreen.

Called Skinput, the system is a marriage of two technologies: the ability to detect the ultralow-frequency sound produced by tapping the skin with a finger, and the microchip-sized “pico” projectors now found in some cellphones.

The system beams a keyboard or menu onto the user’s forearm and hand from a projector housed in an armband. An acoustic detector, also in the armband, then calculates which part of the display you want to activate.


But how does the system know which icon, button or finger you tapped? Chris Harrison at Carnegie Mellon University in Pittsburgh, Pennsylvania, working with Dan Morris and Desney Tan at Microsoft’s research lab in Redmond, Washington, exploit the way our skin, musculature and skeleton combine to make distinctive sounds when we tap on different parts of the arm, palm, fingers and thumb (see video).

Bone machine

They have identified various locations on the forearm and hand that produce characteristic acoustic patterns when tapped. The acoustic detector in the armband contains five piezoelectric cantilevers, each weighted to respond to certain bands of sound frequencies. Different combinations of the sensors are activated to differing degrees depending on where the arm is tapped.

Twenty volunteers tested the system and most found it easy to navigate through icons on the forearm and tap fingers to actuate commands.

“Skinput works very well for a series of gestures, even when the body is in motion,” the researchers say, with subjects able to deftly scroll through menus whether they moved up and down or flicked across their arm.

The system could use wireless technology like Bluetooth to transmit commands to many types of device – including phones, iPods and even PCs. The researchers will present their work in April at the ACM Computer-Human Interaction meeting in Atlanta, Georgia.

Body control

Pranav Mistry of the Media Lab at the Massachusetts Institute of Technology warns that users will have to position the armband very precisely so the projection always appears in the right place.

Nevertheless, Skinput looks a promising idea, says Michael Liebschner, director of the Bio-Innovations Lab at Baylor College of Medicine in Houston, Texas, who has worked on bone acoustic conduction technology for gadget-to-gadget transmission.

“This sounds a very feasible approach to using the body itself as an input device,” he says. “When you are immersed in a virtual game using a head-mounted 3D display, you cannot just take it off to fiddle around with control buttons. This will make things much easier.”