A team of researchers in China have used graphene to create headphones that extend well beyond the frequency range of traditional commercial headphones. These new graphene headphones extend into frequencies well beyond those detectable by humans making them the first ever headphones that you can share with your pets. Why you would ever feel the need to do that is a question unaddressed in the paper.
Published last month in ACS Nano, the work focuses on a technique for generating sound that differs from that of standard headphones. Generally, sound in speakers is made by mechanically pushing and pulling a speaker cone, but a new type of sound generation, called electro-thermoacoustics (ETA), uses heat instead. In these systems, nothing moves. Instead, the ETA surface heats up and cools down the surrounding air molecules, which in turn transfer energy to other nearby molecules in a cascading process that yields sound waves.
The ETA material needs to be a thin, conductive substance with good thermal properties, so it was only a matter of time before graphene was considered. Interestingly, the authors were able to employ laser-scribed graphene. Laser-scribing graphene (you may have heard of this as the graphene that gets made in a CD drive) is a really quick and easy method of making graphene, but it yields a sort of foam-like structure which is not ideal for many electronics applications. Hoever, the many air gaps are actually beneficial for acoustic applications.
The resultant graphene headphones have a frequency range of 100 Hz to 50 KHz and theoretical calculations suggest this could be extended as far as 1 MHz. For some context, commercial headphones cover about 20 Hz to 20 kHz which is roughly the range of human hearing; however, these miss the higher frequency ranges at which many animals (dogs, bats, dolphins) operate.
In conclusion, what would dolphin headphones look like anyway?
Image reprinted with permission from ACS Nano, Article ASAP, DOI: 10.1021/nn5009353. Copyright 2014 American Chemical Society.