Thermoacoustic Headphones Make Sound With Hot Nanotubes

Inside these earbuds, something big is happening on a very small scale. Set on a tiny lattice of silicon, electrified nanotubes of carbon are rapidly warmed up and cooled down, producing sound waves as their temperature fluctuates. The technique is known as "thermoacoustics," and it means these speakers lack the moving parts of conventional, mechanical models, and as a result are likely to last much longer.

If thermoacoustic speakers are so great, why haven't they been used before? Material limitations, really. The principle of thermoacoustics—heating a material to produce sound—was explained at least as early as 1878, but it's only in recent times that nanotubes have made it really feasible, thanks to their durability and excellent conductive properties. In 2008, researchers made a carbon nanotube loudspeaker. In 2009, Finnish researchers made a thermoacoustic speaker from thin aluminum wires. This latest design, by researchers at Tsinghua University in China, sets the carbon nanotubes on a silicon lattice so that the heat, needed to make sound, doesn't also damage the speaker.