Developments in underwater thermophones

Thermophones are acoustic projectors powered by resistive heating elements. The thermophone was invented shortly after Alexander Graham Bell’s invention of the telephone, and since then, thermophone development has primarily focused around its use in air. Thermophones have historically been used as a precision source of sound for calibrating microphones and have been unable to break out of this limiting role largely due to device inefficiencies. The recent implementation of nanomaterials, which greatly improve the overall electric to acoustic conversion efficiencies, has brought about a resurgence of interest surrounding these devices; however, practical applications remain elusive. One of the most likely fits for this unique technology is as an underwater projector. Recent calibrated acoustic testing on various designs of encapsulated underwater thermophones reinforces our notional assumptions of the electro-thermo-acoustic transduction process as well as the general effect of various device parameters on acoustic performance. While efficiency is still a major concern, thermophones possess many other desirable features such as their low cost, wide bandwidth, and ability to produce low frequencies in a compact package.