Robots get touchy with smart skin

Toward this goal, scientists have come up with various smart skins to layer onto devices. But boosting their sensitivity has involved increasing the numbers of electrodes, depending on the size of the skin. This leads to a rise in costs. Other systems require external batteries and wires to operate, which adds to their bulk.

Now scientists are reporting a self-powered, transparent smart skin that is simpler and less costly than previous versions. Haixia Zhang and colleagues have fabricated a smart skin that is self-powered by its frictional contact with the objects that it touches. Triboelectric charges occur anywhere two objects touch each other, although these charges are so small that they often go overlooked. When a honeybee crawls across the smart skin, the skin not only senses the insect, it also uses the spontaneous triboelectric charge that builds up between the honeybee and the smart skin to power its sensing ability, eliminating the need for batteries. The smart skin could have applications for robots, artificial intelligence systems, and bionic limbs for amputees.

This self-powering method is possible because the smart skin consumes very little energy in the first place. Most other previously developed smart skins are digital, meaning their resolution sensitivity is determined by a grid of pixels. Increasing the resolution usually requires increasing the number of pixels and electrodes.

In contrast, the new smart skin uses an analogue method that requires only four electrodes. The electrodes are positioned at four opposite ends of the smart skin. When an object, such as a finger, applies a pressure to the smart skin, it generates a current through the skin that induces a voltage on each electrode. Since the distance between the applied force and each electrode is different, the voltage at each electrode will also be different, and the relative voltages can be used to pinpoint the location of the applied force. The smart skin is made from ultra-thin plastic films and demonstrates electrical stability, maintaining the same level of output over 30,000 cycles.

"Compared with digital smart skins which have been studied extensively, analogue smart skins still need more in-depth study," says Zhang said. "Analogue smart skins have obvious advantages at resolution and energy consumption."