According to an aspect of some embodiments of the present invention there is provided a method for converting energy. The method comprises receiving energy from an external source, using the received energy for inducing a mass exchange process to release thermodynamic energy, and converting the thermodynamic energy directly into electrical energy at sufficient amount for performing work therewith. In some embodiments of the present invention, a portion of the released energy is converted to a pressure wave, and the mechanical energy constituted by the pressure wave is converted to non-mechanical energy.

System and method for converting energy; the system comprising: an acoustic resonator; a phase-exchange device configured for forming across a section of said resonator a concentration gradient of a first substance in a gaseous medium contained by said resonator, to thereby generate a pressure wave within said resonator; and a conversion device for converting mechanical energy constituted by said pressure wave to non-mechanical energy.

A thermoacoustic engine that consists essentially of: a heat exchanger; and a resonator that is in communication with the heat exchanger. The resonator includes a media configured to absorb one or more electromagnetic signals. The thermoacoustic engine is configured to receive the one or more electromagnetic signals and generate acoustic power.

Disclosed is a resonant expander usable in a cryogenic cooling system. The resonant expander may comprise an expansion chamber with a reciprocating piston. The piston divides the expansion chamber into a warm and a cold displacement volume. Passive acoustic valves allow high-pressure fluid into the cold displacement volume and allow low-pressure fluid out of the cold displacement volume. The low-pressure fluid may cool at exiting the resonant expander. The piston free from solid contact with an external mechanism, thereby not requiring sliding seals. Piston and displacement volumes form a mechanically resonant system at the operating frequency of the resonant expander, ensuring correct acoustic valve actuation. Electromagnetic system having a permanent magnet assembly fixed to the piston and a coil at the expansion chamber with a control system, is disclosed. Disclosed is a cryogenic cooling system having the resonant expander, a compressor and recuperative heat exchanger providing low temperature fluid.