Anomalous thermoacoustic effect in topological insulator for sound applications

Abstract

Topological insulators possess unique surface states, which can be very useful for low power electronics. Most research on topological insulators focuses on their fundamental physical properties, and until now, there has been little work on their practical applications. Here, we extend the application of topological insulators to the field of acoustics. We show that topological insulators can be used for sound source applications using a large area of Bi2Se3. The sound pressure level (SPL) can reach up to 30 dB with an 85 mW input at a measured 1 cm distance at room temperature. More interestingly, an anomalous valley with a sound pressure level (SPL) drop of ∼9 dB occurs at 21.5 kHz in a Bi2Se3 topological insulator, which is not observed in monolayer graphene. This anomalous phenomenon is related to the unique surface and bulk states of Bi2Se3. A theoretical equivalent circuit model is built for a topological insulator and compared with that of graphene. Based on the equivalent circuit model combined with thermoacoustic sound-generation theory, such an anomalous thermoacoustic effect with an SPL valley at around 21.5 kHz can be simulated. Our work shows that topological insulators have potential as powerful sound sources, such as earphones and loudspeakers, and that the unique surface states are highly conducive to frequency-selected sound emission.