Researchers at the University of California, Berkeley have created the first ever graphene audio speaker: an earphone. In its raw state, without any kind of optimization, the researchers show that graphene’s superior physical and electrical properties allow for an earphone with frequency response comparable to or better than a pair of commercial Sennheiser earphones.
A loudspeaker (or earphone or headphone) works by vibrating a (usually) paper diaphragm (aka a cone), creating pressure waves in the air around you. Depending on the frequency of these waves, different sounds are created. Human ears, depending on their age, can usually hear frequencies between 20Hz (very low pitch) and 20KHz (very high). Generally, the quality of a speaker is defined by how flat its frequency response is — in other words, whether it produces sounds equally well, no matter where they fall on the 20Hz to 20KHz scale. A poor speaker, or, say, a bassy set of headphones, might be very strong in the lower ranges, but weaker at the top. (See: In search of the perfect headphones.)
In Berkeley’s graphene earphone, the diaphragm is made from a 30nm-thick, 7mm-wide sheet of graphene. This diaphragm is then sandwiched between two silicon electrodes, which are coated with silicon dioxide to prevent any shorting if the diaphragm is driven too hard. By applying power to the electrodes, an electrostatic force is created, which causes the graphene diaphragm to vibrate, creating sound. By oscillating the electricity, different sounds are created.
Given graphene’s status as a wonder material we shouldn’t really be surprised, but it turns out that this graphene speaker — the first of its kind — has intrinsically excellent performance. As you can see in the graph above, the graphene earphone’s frequency response is superb. The reason for this is down to the graphene diaphragm’s simplicity: Whereas most diaphragms/cones must be damped (padded, restricted) to prevent undesirable frequency responses, the graphene diaphragm requires no damping. This is because graphene is so strong that the diaphragm can be incredibly thin — and thus very light. Instead of being artificially damped, the graphene diaphragm is damped by air itself. As a corollary, the lack of damping means that the graphene diaphragm is also very energy efficient — which could be important for reducing the power usage of smartphone and tablet speakers.
Remember, we are talking about a completely untuned, unoptimized earphone, and yet its frequency response is superior to a magnetic coil speaker that has been the target of decades of research and development. If that wasn’t exciting enough, the researchers say that their method of growing graphene with chemical vapor deposition can easily be scaled to produce larger diaphragms and thus larger speakers. In all likelihood, following some more research, graphene will go on to become the material of choice for studio speakers — and hopefully, cost permitting, consumer speakers and earphones as well.
Research paper: arXiv:1303.2391 – “Electrostatic Graphene Loudspeaker”