APTNC

Active Pulse Tube Noise Cancellation

Automatic system to reduce vibrations generated by cooling systems for temperatures close to absolute zero without liquid helium. The suppression of vibrations allows the field of use of these systems to be extended even for applications that are particularly sensitive to noise, such as tunnelling microscopy or magnetic resonance imaging (NMR, MRI) equipment.

Pulse tube (PT) chillers operate through the expansions of a gas, typically helium, pulsed at a typical frequency of 1.4 Hz and controlled through the opening of a rotary valve; the advantage of these systems is that they do not require liquefied gas but, nevertheless, the expansion and compression cycle of the gas generates noise and vibrations that can prevent the use of these systems in certain applications.

The idea is to control, in a system consisting of two or more PTs, the opening and closing phases of the valves so that the vibrations cancel each other out, minimising noise.

The system acquires, through special microphones, the noise spectrum of the PTs, which is then processed by a special minimisation algorithm and used to control the opening of the valves, creating destructive interference that actively cancels the noise.

This project has spawned a collaboration with Leiden Cryogenics, which is licensing the noise suppression technology.