A device for generating an acoustic signal in a fluid includes an engine operable to repeat a thermodynamic process to vibrate a membrane of the engine to generate an acoustic signal having more than one period. The thermodynamic process includes heating mass inside a chamber of an engine to generate pressure inside the chamber; in response to generating the pressure, moving in a first direction a portion of a membrane of the engine; removing mass from inside the chamber to decrease the pressure inside the chamber; and in response to decreasing the pressure inside the chamber, moving the membrane portion in a second direction. Because the engine repeats the thermodynamic process, the engine can generate and sustain an acoustic signal for a significant amount of time. In addition, because the heat in the engine's chamber is generated by a chemical reaction, the engine may quickly generate a significant amount of pressure inside the chamber to quickly accelerate the membrane, and thus generate a powerful acoustic signal. Furthermore, various properties of the membrane and/or the thermodynamic process may be modified to tune the acoustic signal to a desired frequency and/or amplitude. Thus, the engine may be effectively used to generate acoustic signals for a number of different purposes, such detecting and ranging objects in a region, and in a number of different marine environments, such as a littoral environment that contains a large amount of noise, or a deep sea environment at high water pressure.