TAC &TAR generator (engine) & MEMS-TAR Solar collector process

The TAR uses heat energy to amplify acoustic pressure waves that flow through a high density gaseous medium, inside a resonant waveguide. The heat energy increases the magnitude of these acoustic waves, or pressure pulses; in pressure, temperature and velocity. The density of the working fluid determines Specific Power. This renders Specific Power of the TAR as almost solely a materials issue. With lightweight alloys, the TAR can achieve Specific Power densities greater than five kilowatts per kilogram (5 kW/kg).

What sets the Nexgen Thermo acoustic engine apart from other technologies is the ability to heat and cool a traveling wave acoustic impulse in microseconds. It is the thunderclap-like expansion of the internal working gas; repeating hundreds, and even thousands of times per second, that converts the heat energy into mechanical power. The acoustic wave is not only amplified thermally, it is accelerated in velocity, multiplying its kinetic energy. The resultant is a repeating train of large, dynamic pressure fluctuations.

The pressure fluctuations in the internal working gas drive a spring-mounted diaphragm piston, causing it to oscillate in step with the waves.  In one respect, this is the same principle as the common internal combustion engine, where the pressure of expanding gases drives a piston. 

The difference is that in an internal-combustion engine, the fuel-air mixture is burned directly inside the piston cylinder to produce those expanding gases, while in an external-combustion engine, like the TAR, the heat required to expand the gas inside the cylinder is conducted into the engine through the walls of a heat exchanger that is heated by an external source.  Just as in the automobile engine, the rapidly repeating pressure impulses push on a piston and cause it to reciprocate.

In the case of the TAR engine, the piston is attached to the armature of a linear generator.  Most generators have a rotating armature that converts that rotary motion into electrical energy.  The armature shaft turns in lubricated bearings, and the armature rotates within a magnetic field.  The armature rotation is produced by connecting the generator, by means of mechanical linkages, to an internal-combustion engine.

In the TAR, the armature has no linkages, and it reciprocates instead of rotating. The piston-armature is freely mounted on spring diaphragms, and it vibrates back-and-forth at high frequency, in sync with the acoustic pressure waves.  Length of stroke averages about 5mm. 
NexGen White Paper on TAC and TAR