Rock On With Carbon Nanotubes

A new type of headphone that produces sound by heating up carbon nanotubes could prove to be more durable than conventional speakers that rely on moving parts, according to a report in Nano Letters (2013, DOI: 10.1021/nl402408j). On a microchip in the headphones, alternating current passes through carbon-nanotube yarns, heating the material and the surrounding air. As the air warms, it expands, and as it cools, it contracts. This expansion and contraction creates sound waves. The phenomenon is called the thermoacoustic effect. Researchers at Tsinghua University, in China, fabricated the chip by patterning silica with 200-µm-deep grooves. The researchers next coated the chip with a film of carbon nanotubes that were aligned in the same direction. They then cut the carbon film into strips with a laser and treated the strips with ethanol, causing them to shrink into about 1-µm-thick yarnlike strands. The team integrated the chip into commercial earbud-type headphones and played music through them. After a year of playing music, the headphones don’t show significant signs of wear, team member Yang Wei says.