It is the low density and high mechanical strength of the new semiconductor material which makes it attractive for wide-frequency-response electrostatic audio speaker design.
“Low mass ensures good high frequency response, while high strength allows for relatively large free-standing diaphragms necessary for effective low frequency response,” said the paper by University of California Berkeley researchers Qin Zhou and A. Zettl, who have built a miniature graphene-based electrostatic audio transducer.
The speaker/earphone had excellent audio response across the entire audio frequency range (20Hz– 20kHz), and according to the researchers “matched or surpassed commercially available audio earphones”.
The aim seems to be to mimic the lightweight and lightly-damped sharp frequency response of resonators in nature to create a wide-band audio speaker, which typically requires significant damping to broaden the response.
By reducing both the mass and spring constant of the diaphragm using 30nm thick graphene inherent air damping dominates and flattens the response peaks.
The researchers said that graphene was an ideal material for the audio transduction diaphragm which needs to have small mass and a soft spring constant, and be non-perforated to efficiently displace the surrounding air.
“Graphene is electrically conducting, has extremely small mass density, and can be configured to have very small effective spring constant,” said the researchers.
The exceptional mechanical strength of graphene makes it possible to construct large and thin suspended diaphragms, with a lower spring constant.
The researchers created an electrostatically driven, high-efficiency, mechanically vibrating graphene-diaphragm based audio speaker.
“Even without optimisation, the speaker is able to produce excellent frequency response across the whole audible region (20Hz-20kHz), comparable or superior to performance of conventional-design commercial counterparts,” said the researchers.