New vibration-dampening magnet enables peak output from precision devices

Anyone who has attempted to keep a camera steady for a long exposure in low light conditions knows what usually happens: the camera shakes, resulting in a blurry image.

The same issue can occur with telescope images or other long-distance imaging equipment. Even minor ground vibrations can disrupt the results for highly sensitive optical systems.

To address the issue, scientists at the Vienna University of Technology (VUT) have developed a new type of vibration-damping technology using electro-permanent magnets.

Like ordinary permanent magnets, these magnets maintain their magnetism permanently without needing a power supply. They are also fitted with a coil, so an electrical pulse can change their magnetization extremely fast.

This makes it possible to suppress vibrations in mirrors of large telescopes actively and thus dramatically increase their performance.

The tech involved

The vibration-damping system of VUT consists of a permanently mounted base and a free-floating platform above it.

The platform is suspended in the air and kept in place by strong magnetic forces.

Several electromagnetic actuators can then fine-tune the platform’s position with high precision in fractions of a second—even when a load of several kilograms is mounted on it.

“In sensitive applications, such as the positioning of mirror segments, the position of this platform must be kept stable to within a few tens of nanometers,” Prof. Ernst Csencsics from the Institute of Automation and Control Technology at VUT said.

“This is only possible if you can compensate for even tiny ground vibrations, such as those that occur when someone walks past outside the laboratory, or those caused by normal building vibrations.”

Therefore, the platform’s position must be measured extremely accurately, and any movement must be counteracted immediately.

This makes it possible to suppress vibrations very efficiently, especially low-frequency vibrations, which are usually problematic in such applications.

External power supply not needed

“Electromagnets are usually used for such active vibration damping,” Prof. Georg Schitter, VUT director, explained.

“A current flows through coils in a magnetic field, and depending on how strong this current is, different forces can be generated. This works very quickly and precisely.”

However, one major disadvantage of this technology is that the current must flow continuously; otherwise, the magnetic forces will disappear instantly.

On the other hand, a permanent magnet can maintain its magnetic properties for any time without any external energy supply – once a very strong magnetic field has magnetized it.

Everyday permanent magnets, such as the ones used in magnetic boards or fridge magnets, are also created this way.

They need a suitable, magnetizable material and are once exposed to a strong magnetic field.

This creates a magnetic order in the material, causing it to remain magnetic permanently.

Working with magnets

Scientists have now combined the advantages of electromagnets and permanent magnets in vibration damping using a so-called electro-permanent magnet.

“This is a permanent magnet that is also fitted with a coil,” Csencsics said.

As long as the strength of the permanent magnet is in the correct range, it does not require any power, and the hovering platform is held in place. Only small corrective measures by the actuators are necessary to compensate for vibrations.

However, suppose the strength of the permanent magnet is no longer appropriate, for example, because the weight resting on the hovering platform has changed or needs to be tilted. In that case, then more drastic methods are used.

This involves sending a short, strong current pulse through the coil, which temporarily creates a very strong magnetic field and thus also changes the magnetization of the permanent magnet.

By selecting the right magnetic pulse strength, the permanent magnet can be set to a new operating point, at which it remains constant again without needing an energy supply.

“With our prototype, we have shown that extremely precise and energy-saving vibration suppression is possible,” Schitter said.