Thermophones for sonar applications

Abstract

Thermophones are electrically driven thermoacoustic sound projectors which have historically been used as a primary source of sound. Thermophones have a sound spectra that are largely determined by their housing and support and efficiencies that are determined by the device’s ability to maintain a dynamic temperature gradient across a gaseous layer surrounding the thin heating element. A number of factors make thermophones an attractive technology for underwater use including the relative ease and low cost of production, the large thermal reservoir provided by the surrounding aquatic environment, and the ability to tune the spectra over a broad range of frequencies. We present calibrated acoustic underwater tests performed on thermophones which demonstrate the potential for a new class of sonar transducers. Small, 6.35 cm diameter, inert gas filled laminate pouch thermophones were fabricated which provide a low frequency resonance. Additionally, a liquid filled thermophone demonstrates a smooth response over a wide frequency band.