other tech: Smart paper may put lighter, smaller UAVs in the sky

Paper aeroplanes could fly by flapping their wings thanks to smart paper that bends when bathed in an electric field. The material raises the prospect of swarms of tiny lightweight aircraft carrying sensors that act as the eyes and ears of a surveillance network.

Electroactive paper (EAPap) is ordinary cotton-based paper, similar to the material used to make US bank notes, coated on each side with a thin layer of gold. The smart paper has been made by researchers from Inha University, South Korea, and Texas A & M University, US

Unlike ordinary paper, EAPap bends as a result of two effects working together. When a voltage is applied, the gold coating on one side of the paper becomes a positively charged while the other side becomes negatively charged. Sodium ions in the paper move towards the negative electrode, taking water molecules with them. This makes that side of the paper expand, causing it to bend.