In 2015, scientists from Germany's Saarland University presented us with their iSkin stickers, which could be placed on the body to touch-control mobile devices. Now, led by Prof. Jürgen Steimle, they've built upon that technology to develop what's known as Multi-Touch Skin.

Inkjet-printed onto a thin substrate of PET (polyethylene terephthalate) plastic in less than a minute, and then adhered to the skin anywhere on the body, Multi-Touch Skin can be made in any two-dimensional shape. It incorporates two stacked layers of electrodes arranged in rows and columns, forming a grid. In its current form, each piece of the Skin is hard-wired to a touch-controller microchip, which is in turn connected to a tiny battery-powered Raspberry Pi Zero microcomputer.

That chip constantly measures the electrical capacitance at every intersection within the grid of electrodes. When the user touches the Skin at a given location, their fingertips conduct electricity, allowing the charge to drain away at that intersection (the insulating bottom layer of the Multi-Touch Skin keeps the user's underlying skin from having an effect). The chip detects that change in capacitance, and registers it as a touch in that location – it can do so for multiple touches simultaneously.

The resulting signals are wirelessly transmitted to separate electronic devices, causing them to do different things depending on the type of touch detected.

This Multi-Touch Skin patch allows the user to accept or reject calls Saarland University

So far, the researchers have used the technology to create four different touch-control interfaces. These include a bracelet on which a two-finger rotation allows users to change the color of an LED lamp, with a two-finger sweep controlling its brightness; a behind-the-ear sticker that lets users control the volume of a music player by swiping up or down, advance through tracks by swiping left or right, and pause playback by pressing; a forearm sticker that, when squeezed, causes a smartphone to send a text message; and, a palm-mounted sticker that lets users accept or reject calls from a smartphone, with a touch.

The research was recently presented at the CHI Human Factors in Computing Systems conference, in Montreal.

Source: Saarland University