The researchers designed a triboelectric micro-texture on a silicon wafer (patterned with 10μm square windows through a lithographic process) before using it to imprint a spin-coated polydimethylsiloxane (PDMS) film. The resulting film stacked onto a set of four electrodes (using transparent silver nanowires patterned on a PET substrate) uses the spontaneous triboelectric charge that builds up at a contact points to power its sensing ability, eliminating the need for batteries.
In what they describe as a “self-powered analogue smart skin”, the researchers explain how only four electrodes suffice (two pairs of opposite electrodes placed orthogonally) around a two-dimensional analogue smart skin to detect location as well as contact velocity, based on a single-electrode contact electrification effect and planar electrostatic induction (by analysing the ratio of opposite electrode voltages).
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 researchers’ experiments showed that, when wrapped around a robotic hand, the analogue smart skin can determine the location of an applied force with an average resolution of 1.9 mm. They were able to detect very small forces (equivalent to a few decigrams). This potentially very cost-effective and self-powered touch-sensing film could be used to design touch-capable robots or bionic limbs.
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