Using Nearfield Acoustic Holography Method For Surface Velocity Measurements of Carbon Nanotube Speakers

Carbon Nanotube (CNT) thin-film speakers make sound without any moving parts, via thermoacoustics. Understanding the physical acoustic properties, like effective particle velocity, can help to validate an accurate electrical-thermal-acoustical model of these speakers which is an important challenge for future design improvements. Because the CNT thin-film is very fragile and does not move, measuring the particle velocity of the air at the film surface is difficult. This paper focuses on the surface particle velocity measurements using near-field acoustic holography (NAH). Probe microphones were used in NAH due to the high temperature on the CNT film. The results show that the velocity distribution is not uniform on the surface and this non-uniformity increases with increasing frequency. Finally, the particle velocity has been used to calculate the sound intensity and directivity patterns of the CNT speaker at different frequencies.