Fundamental efficiency of thermophones

Visa Vesterinen, Antti Niskanen, Juha Hassel, Panu Helistö

Research output: Contribution to conferenceConference articleScientific


We have designed and fabricated air-bridge arrays comprising hundreds of thousands of aluminum wires. Thermally decoupled from the underlying silicon substrate, the nanometer-thick wires act as thermoacoustic sound sources (thermophones). Periodic heating of wire surfaces is induced by a.c. current. In the surrounding air domain, rapidly attenuating thermal waves excite pressure waves that we understand as sound or ultrasound. Recent experiments with our array loudspeakers and other nanoscale thermophones have revealed properties which are poorly understood theoretically. We have developed analytical Green's function methods that quantitatively explain some features. For example, the effect of a heat-absorbing substrate in the proximity of a suspended source can be studied. We have verified our field-theoretical efforts with finite difference method simulations, and the results are in good agreement with acoustic measurements. We have also found a generic- ultimate limit for the efficiency of thermophones. It is valid in the linear regime of thermoacoustics. The measured efficiency of our array loudspeakers is 1 order of magnitude below the upper bound. At low frequencies this is caused by the presence of the substrate, while at ultrasound frequencies wire heat capacity limits the performance
Original languageEnglish
Publication statusPublished - 2011
MoE publication typeNot Eligible
Event6th Forum Acusticum, FA 2011 - Aalborg, Denmark
Duration: 27 Jun 20111 Jul 2011


Conference6th Forum Acusticum, FA 2011
Abbreviated titleFA 2011


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