This work is of a survey nature based on the results of studies of the processes of sound emission in gases and liquids by thermo-acoustic film sources - thermophones. The purpose of the article is to show the features of the calculation, operation and determination of the main acoustic characteristics of thermophones, ways to increase the efficiency of their radiation and directions of possible practical application.The basic relations and formulas are presented, the calculation of which is confirmed by the experimental results carried out, analyzed ways to excite and improve the effectiveness of thermophones.Film thermophones of various shapes without a thermally insulating substrate have uniform, reproducible acoustic characteristics, which can be predicted by calculation, knowing the thermal-physical constants of the materials used for the construction of thermophones. As the active elements of guns are used for a thin film formed by the vacuum deposition of metals on surfaces of bearing plates made of polymer materials. When passing through the active element of an alternating electric current with a frequency f, an acoustic wave is emitted at a doubled frequency of 2f. Film thermophone are the only sources of sound emitting surface which meets the definition of a piston radiator. Thermopane work in the frequency range from 1.0 to 150 kHz.A promising direction of research is the use of thermophones as sources of radiation of sound in a liquid medium. The results of a study of the radiation of a film thermophone in two liquids (distilled water and kerosene) are presented. Compared to radiation to air, radiation to kerosene, for example, is about 20 dB higher.
