Imagine a loudspeaker that is bendy, transparent and stretches to twice its length without breaking or changing the intensity of the sound it amplifies. This is what Kaili Jiang and Shoushan Fan of Tsinghua University in Beijing, China, and their colleagues have made. By attaching one of their prototype films to the screen of an iPod they have used it to play sound from the device.
The invention exploits the thermoacoustic effect, which was first realized in the nineteenth century with the platinum thermophone. The effect describes what happens when a material is heated and cooled, thus expanding and contracting the air around it, which creates sound waves. The film on the researchers' iPod generates sound 260 times more efficiently than this historical gadget because the sheets of parallel carbon nanotubes that it is made of warm up and transfer heat to air faster.