STAR Motors & Alternators

STAR™ linear motors -alternators are the driving force behind all Qdrive pressure wave generators and cryocoolers. These are linear reciprocating devices that combine the unique Commuter™ flexing axial suspension with plunger-mounted high-energy magnets and robust coil-over-iron stators. Each model is designed to operate for well over 10 maintenance-free years with a calculated mean time between failures per MIL-STD 217F (military standard method) of 129,760 hours. This is supported by 100’s of installations worldwide. STARTM motors - alternators offer efficiencies in the 80%-90% range, much higher than similar linear reciprocating devices. The superior performance and unique features make them the natural driving force for Qdrive’s cryocooler and pressure wave generator products.

For detailed parameters on each motor/alternator click the product at the bottom of this page.

How It Works

Motor Mode:

  • Alternating voltage is applied to the linear motor. Current flows through the motor windings, causing a magnetic field in the iron they surround.
  • The applied field, oscillating due to the reversing electrical input, pushes and pulls on permanent magnets mounted on the moving assembly, (called the piston-plunger).
  • When the applied voltage frequency is close to the resonant frequency of the motor and load combined, the piston oscillates and power is delivered to the acoustic load by phase separation of the current and piston displacement.
  • Typically, when connected to an acoustic load like a cryogenic coldhead, helium gas is cyclically compressed and expanded relative to the mean (charge) pressure by the piston of the driver to power a thermodynamic cycle for refrigeration.


Alternator Mode:

  • Alternating pressure is applied to the piston. The force of the pressure (and associated gas flow) causes the piston to oscillate. The frequency of oscillation is a system variable – applied pressure frequency must be close to the system resonance for optimal performance.
  • The oscillatory movement causes changing flux links between the magnets moving with the piston and the iron stator.
  • The reversing flux changes in the iron induce voltage in the windings.
  • If connected to a load resistance, the voltage causes current to flow and power to be delivered from the alternator.
  • Power factor (phase of voltage and current) can be corrected by use of an appropriate capacitor in series with the alternator and load


STAR Motor Diagram

Contact Info

contact us form