US Patent 7944776 Engine and technique for generating an acoustic signal

An embodiment of 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 may generate and sustain an acoustic signal for a significant amount of time.