Thermophones and Quantum Mechanics

Thermophones for over a century have been thought to function as thermo-acoustic devices converting an alternating current to rapid temperature changes in thin platinum films. Subsequent pressure changes in the surrounding air allow the sound to propagate. Recently, thermophones from nanoscale sheets of carbon nanotubes (CNTs) are claimed to have far lower specific heat than platinum, and therefore more efficient in producing sound because the temperature changes are produced with less power. However, the CNT power would have to be increased to produce the same temperature change as for platinum. Since the sound from the CNT film at low power is louder than for platinum, temperature changes in the thin film cannot be the source of sound. Understanding how thermophones produce sound independent of temperature requires quantum mechanics (QM) as embodied in the theory of QED induced EM radiation. QED stands for quantum electrodynamics and EM for electromagnetic. Atoms in thin films are under EM confinement at levels beyond the visible (VIS) and ultraviolet (UV) that by QM are restricted to vanishing specific heat, and therefore Joule heat cannot be conserved by an increase in temperature – this is a QM size effect regardless of whether the film is platinum or CNTs. Prompt UV-VIS emission is produced by the QED upconversion of low frequency Joule heat to the EM confinement frequency of the film without any increase in film temperature. Instead, the UV-VIS is absorbed in the air to cause the necessary temperature and attendant pressure changes to produce sound. Recommendations are made that classical heat transfer at the nanoscale be modified for vanishing specific heat as required by QM.