Acoustic performance of a condenser microphone is derived mainly from the size of the membrane (the part that converts sound into an electrical current), surface mass and achievable static tension. The widely-studied and available nickel, as well as plastic, have been the dominant membrane materials for professional microphones for several decades.
And now, enter graphene – researchers at the University of Belgrade, Serbia, have developed a proof-of-concept microphone with a vibrating membrane made from the so-called “wonder material”, and were able to show up to 15 dB higher sensitivity compared to a high-end commercial microphone, at frequencies up to 11 kHz.
This translates to nearly 32 times the sensitivity of a standard nickel-based construction – yet another victory for graphene that’s been rather slow to translate into practical, real-world applications since its arrival on the scene in 2004.
The results were published on November 27, 2015, in the science journal 2D Materials.
“Given its light weight, high mechanical strength and flexibility, graphene just begs to be used as an acoustic membrane material,” said one of the study authors Marko Spasenović.
The team started by growing the graphene membrane, approximately 60 layers thick, on a nickel foil substrate using a chemical vapour deposition process to ensure quality across all samples. Then they etched the foil away and fixed the resulting graphene membrane on a housing used in standard nickel-based microphones for direct comparison.
Virtual modelling also showed that stretching a 300 layers thick membrane near its breaking threshold could potentially enable performance far into the ultrasonic part of the spectrum (up to 1 MHz) when under maximum tension.
While having such light-weight, ultrasonic microphones could be very useful for the industry, the team is “not quite there yet experimentally”, said Spasenović.
“At this stage there are several obstacles to making cheap graphene, so our microphone should be considered more a proof of concept,” he concludes. “The industry is working hard to improve graphene production – eventually this should mean we have better microphones at lower cost.”