Acoustic signal recovery by thermal demodulation

One operating mode of recently developed thermoacoustic transducers is as an audio speaker that uses an input superimposed on a direct current; as a result, the audio signal occurs at the same frequency as the input signal. To extend the potential applications of these kinds of sources, the authors propose an alternative driving mode in which a simple thermoacoustic device, consisting of a metal film over a substrate and a heat sink, is excited with a high frequency sinusoid that is amplitude modulated by a lower frequency signal. They show that the modulating signal is recovered in the radiated waves due to a mechanism that is inherent to this type of thermoacoustic process. If the frequency of the carrier is higher than 30 kHz and any modulating signal (the one of interest) is in the audio frequency range, only this signal will be heard. Thus, the thermoacoustic device operates as an audio-band, self-demodulating speaker. (c) 2006 American Institute of Physics.