Nanothermal trumpet: thermoacoustic sound source made with a suspended metal nanowire

From the paper “Suspended metal wire array as a thermoacoustic sound source,” Appl. Phys. Lett. 95, 163102 (2009); by AO Niskanen, J. Hassel, M. Tikander, P. Maijala, L. Grönberg, P. Helistö, from VTT Technical Research Centre of Finland, PO BOX 1000, 02044 VTT, Finland. dx.doi.org A suspended metal wire array is used to produce high-pressure sound waves over a wide spectrum using the thermoacoustic effect. It is fabricated with an air-bridge arrays containing up to 2×105 wires covering an area of a few square centimeters. The supporting silicon wafer was isotropically plasma etched to release the wires thereby avoiding heat contact with the substrate. Sound pressure levels reaching 110 db at a distance of 8 cm were demonstrated near 40 khz in free field. The devices are also able to reproduce music and speech. They have potential for applications especially in the ultrasound range.