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Advancements in Thermophones
Overall, low efficiency, the mechanical fragility of highly po- rous thermophone heaters, and an effective lack of receiv- ing capability has limited thermophones from making their way into any practical commercial devices. Still, a few niche use cases exist in which thermophones could outshine their traditional counterpart projectors due to their broadband response and low manufacturing cost. Use as an underwater sound projector place thermophones in an ideal environ- ment where they can be run in their most efficient regimen at high power with ample cooling capability.
Moreover, most thermophone technologies are easily upscaled with various active heating elements being produced using VLSI processes. New materials are being explored as more me- chanically robust thermophone elements, although freestand- ing CNT sheets currently remain the most efficient transduc- tion material. Thermophone encapsulation provides a means of protecting the relatively fragile active material from harsh environments but also results in a resonant device. This reso- nance can be tuned independently of the active material that is usually suspended from a substrate. Thermophone elements are usually arrays of wires or planar films that are suitable for making large area projectors that are very thin and lightweight.
The future of thermophone projectors is still largely un- known. The ability to generate sound without any mechani- cally moving parts makes thermophones a fascinating tech- nology to study for potential applications. However, modern thermophones are still a relatively new technology and are certainly not an end-all replacement for conventional de- vices. Indeed, an inspection of recent thermophone publica- tions shows that most studies on the topic have been con- ducted from a physics or materials science perspective and not for direct applications. Thus, additional evaluation and critique by trained acousticians and engineers is sought to more rigorously quantify thermophone performance and help progress this exciting technology. Along with develop- ing the theoretical foundation of thermophones, input from biologists, sonar technicians, medical doctors, and many others is needed to highlight the various niche areas in which the advantages of these projectors can be utilized. Only time will tell as to what other practical devices this technology can produce. In the meantime, it continues to provide a very curious tabletop demonstration for students.
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