Carbon nanotubes (CNT) can generate smooth-spectra sound emission over a wide frequency range (1–105 Hz) by means of thermoacoustics (TA). However, at low frequencies f, where the need for large-area sound projectors is high, the sound generation efficiency of open CNT sheets is disappointingly low. In addition, the nanoscale thickness of CNT sheets, their high sensitivity to the environment and the high surface temperatures useful for TA sound generation can also present technical hurdles.

Reporting their results in the journal Nanotechnology, Ali Aliev and his co-workers explore the effects of different thermodynamic regimes on the fundamental efficiency of TA sound generation. In the study, the team shows that TA sound generation efficiency can be enhanced by i) encapsulating the free-standing multi-walled carbon nanotube sheets in high molecular weight inert gases, ii) using vibrating membranes or rigid plates having high resonant quality factors, iii) reducing the volume of the enclosure, and iv) by modulation of the applied high frequency carrier current with a low frequency resonant envelope.

Despite the low density of acoustic power of CNT-based TA projectors achieved so far (~0.01 W/cm2), the wide band and high gravimetric acoustic power density (~50 W/kg) and capability to fabricate thin (<1 mm), large size (>1 m2) and lightweight sound projectors makes the approach a promising one.

More information can be found in the journal Nanotechnology.