Liquid filled encapsulation for thermoacoustic sonar projectors

Abstract

Thermoacoustic projectors produce sound by rapidly heating and cooling a material with low heat capacity. These “thermophones” were originally demonstrated in 1917 using thin platinum filaments [Arnold, H., I.B Crandall, (1917) Phys. Rev. 10(1):22-38], but were very limited in their efficiencies and bandwidth until the much more recent discovery of new nanomaterials. The first underwater thermophones were made by Aliev et al. in 2010 [Aliev, A. E et al, (2010) Nano letters 10 (7), 2374-80] which utilized a carbon nanotube (CNT) sheet submerged in deionized water. These devices worked well for demonstrational purposes, but the CNT sheet would become damaged when retracted from the water, which made characterization difficult. More recently, new methods for enhancing the robustness of freestanding sheets have been developed which allow few layer CNT sheets to be repeatedly dipped and withdrawn from a water bath without damage. Such methods have enabled revisiting the study of submerged thermoacoustic projectors. Our studies of CNT thermophones in various liquid baths give evidence to the mechanism for acoustic wave generation in these systems. The potential to improve the impedance matching between the thermoacoustic source and surrounding fluid media suggest enhanced designs for compact sonar transducers.