Graphene and sound emitting devices

 Single-layer graphene (SLG) is  demonstrated to emit sound. The sound emission from SLG had a significant flat frequency response in the wide ultrasound range from 20 kHz to 50 kHz. SLG can produce a sound pressure level (SPL) as high as 95 dB at a distance of 5 cm with a sound frequency of 20 kHz. The SPL value is among the highest reported to date for sound-emitting devices (SEDs) based on the thermoacoustic effect. A theoretical model was established to analyze the sound emission from SLG. The theoretical results are in good agreement with the experimental results. Conventional acoustic devices with a large size can be reduced to the nano-scale by using this novel SLG-SED material. It has the potential to be widely used in speakers, buzzers, earphones, ultrasonic transducer, etc.

Thermoacoustic (TA) effect has been discovered for more than 130 years. However, limited by the material characteristics, the performance of a TA sound source could not be compared with magnetoelectric and piezoelectric loudspeakers. Recently, graphene, a two-dimensional material with the lowest heat capacity per unit area, was discovered to have a good TA performance. Compared with a traditional sound source, graphene TA sound sources (GTASSs) have many advantages, such as small volume, no diaphragm vibration, wide frequency range, high transparency, good flexibility, and high sound pressure level (SPL). Therefore, graphene has a great potential as a next-generation sound source.

Researchers created a device using electrodes deposited onto two ends of a sheet of SLG, which itself is placed on an anodic aluminium oxide substrate. When an electric sound-frequency signal is applied to the graphene, sound is produced through the thermoacoustic effect. In short, when electricity passes through the graphene, the heat produced is transferred to the air around the device surface. The fluctuations in this heat as the current itself fluctuates causes the air to vibrate, producing sound.

Although a previous piece of work has already used graphene in a thin and transparent sound-emitting device, it was merely used as electrodes. Significantly, this is the first time that the material has been demonstrated to actually be able to produce sound itself.


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