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.
At the same time, the paper’s matrix of cellulose fibres have piezoelectric properties and change shape when a voltage is applied. This increases the bending. The research team have even improved the paper’s piezoelectric properties even further by adding carbon nanotubes to the paper mix.
The team has made strips of paper 40 millimetres long and 0.3 mm thick that bend by 10 mm, producing a force of more than 10 micronewtons. That is enough to lift about 1 gram.
“This new discovery of cellulose paper as a smart material gives us a lot of possibilities that we can play around with,” Jaehwan Kim, who researches smart materials at Inha University.
Kim’s team is interested in using the material as a kind of artificial muscle for mobile robots. He hopes to power the robots remotely by fitting them with a simple electronic device called a “rectenna”. This converts the energy of a microwave beam into a small voltage. –ns
This is from 2006 but still interesting. I wonder how the progress is going.