Linear alternator
A linear alternator is an electromechanical type of alternator that is essentially a linear motor used as an electrical generator.
An alternator generates alternating current electricity. It converts mechanical energy into electrical energy, unlike a motor, which converts electrical energy into mechanical energy. Although similar to other electric generators, an alternator typically uses rotary motion, while a linear alternator uses motion in a straight line, operating via electromagnetic induction. Moving-magnet linear alternators power thermoacoustic converters.
History
In 2016 NASA introduced a double-fed induction linear alternator, which operates at 950°C for extreme environments such as aircraft systems and downhole drilling, achieving 25% greater efficiency than conventional models. The California Energy Commission funded a high-efficiency, ultra-low-emissions linear generator demonstration project in 2024 to support renewables with fuel-flexible dispatchable power. In 2025, researchers developed and validated a tubular permanent magnet linear alternator for free-piston engine applications. As of 2025, Hyliion's KARNO system integrates a sealed, 3D-printed linear heat engine with an alternator for modular prime power in data centers, defense, and microgrids.Theory
A linear alternator converts back-and-forth motion directly into electricity, eliminating the need for a crank or linkage to transform reciprocating motion into rotary motion for a generator.Applications
A shake flashlight uses a simple linear alternator. Shaking the device moves a permanent magnet through a coil, inducing an electric current via electromagnetic induction. This current charges a capacitor, storing energy to power a light-emitting diode until discharged. Further shaking recharges the capacitor. Other devices employing linear alternators include the free-piston linear generator, an internal combustion engine, and the free-piston Stirling engine, an external combustion engine. NASA’s Glenn Research Center developed a lightweight, double-fed induction linear alternator.A linear heat engine integrated with an alternator can provide modular prime power in data centers, defense, and microgrids.
Other devices that use linear alternators to generate electricity include the free-piston linear generator, an internal combustion engine, and the free-piston Stirling engine, an external combustion engine.