Self-powered ‘smart skin’ eases design of touch-capable robots, bionic limbs

Self-powered ‘smart skin’ eases design of touch-capable robots, bionic limbs

Technology News |
By Rich Pell

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).

Schematic stack of an analogue smart skin.
SEM image of the micro-structured
optically transparent PDMS film

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.

Working principle of analogue smart skins. (a) Charge distributions and currents in different working stages. (b) Electrostatic theory analysis of analogue smart skins. (c) Relationship between the electrode voltage and horizontal position. The inset shows the voltage ratio between the left electrode and the right electrode. (d) Relationship between the electrode voltage and horizontal position. (e) Equivalent circuit model of analogue smart skins. (f) Real-time voltage outputs of the right and left electrodes using the circuit diagram in (e) and SPICE. (g) Frequency domain analysis of analogue smart skins reveals that, at low frequency, the ratio of the electrode voltage is determined by ratio of C1 and C2. At high frequency, the ratio tends to be 1. The inset of the phase frequency characteristic curve shows the phase shift at different frequencies. (h) Voltage distribution with different charge locations. The unit of voltage is volt. (i) Voltage ratio of electrode a and electrode c with the location of charges changing. (j) Voltage ratio of electrode b and electrode d with the location of charges changing.

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