Science & Environment

Scientists manipulate magnetically levitated objects

Chamber black light Image copyright George M. Whitesides group
Image caption The objects are embedded in a magnetic liquid and manipulated with two external magnets

Researchers from Harvard University have discovered how to orientate small objects in any direction using magnetic levitation.

Methods to manipulate small objects are crucial to manufacture complex structures such as electronic components in assembly lines.

But few methods exist that deal with fragile and arbitrarily shaped objects.

The researchers rotated delicate objects of varied shapes and sizes without "touching" them.

The results of their experiments are published in PNAS journal.

Lead author, Dr Anand Bala Subramaniam, from Harvard's Department of Chemistry and Chemical Biology told, BBC News: "Magnetic levitation in liquids has been used before to separate materials based on their density, but never to manipulate objects."

Magnetic levitation is commonly referred to as MagLev.

Dr Andrew Steele, who was not part of the study, specialised in magnetism at the University of Oxford during his PhD.

He said: "The classic way of doing magnetic levitation is using magnets. Take two magnets, or a magnet and a piece of superconductor, which will then have opposing magnetic fields."

The repelling force lifts the magnetic object against gravity. The method used in the new study is slightly different.

"What they are doing is suspending a non-magnetic object that is embedded in a liquid that is itself magnetic. It's an advanced form of floating."

The device consisted of a chamber filled with a paramagnetic fluid - a fluid that is attracted to a magnetic field - with magnets at the top and bottom.

Image copyright George M. Whitesides group
Image caption The two magnets were located at the top and bottom of the container

The magnets "pulled" the liquid upwards and downwards, creating a density gradient: the liquid was more compressed in the regions close to the top and bottom lids, and less in the middle of the chamber.

"If you place an object in that chamber, gravity is pulling it down and buoyancy is pushing it up. The object finds a position where it wants to float based on its density compared to that of the liquid around it," explained Dr Steele.

The key aspect is that this method does not require the object to be magnetic at all.

Image copyright George M. Whitesides group
Image caption Applying an external magnet also caused the screw to rotate inside the chamber

"You can levitate almost whatever you want as long as it's lighter than the liquid you are levitating it in."

The device has potential applications in the automated manufacture of soft objects that try to mimic biological systems.

Dr Subramaniam said: "If you have a hard gripper coming in and trying to grab a soft object it may deform it and even damage it.

"There really is a need for methods that can manipulate and orient objects without contact, which is what the MagLev does."

The researchers found that rotating or adding another external magnet to the chamber caused the object to rotate in different directions.

"We tried two different methods to show that MagLev is very versatile to orient objects.

"Sometimes bringing an external magnet is more useful than rotating the whole chamber."

At the moment, Dr Subramaniam's team has experimented with jelly-like materials, silicon grippers that are commonly used in robot assemblies, and gas bubbles of different shapes and sizes.

But the trials were limited to a single object at a time.

"The next step that we need to take is to put more than one object [in the chamber] and try to assemble them in the liquid. For this, you need a more complex configuration of magnets and control algorithms to bring in an object, orient it, then bring in another object, orient it and attach it to the first.

"The results are a starting point. They will require a little more work for practical applications."

Dr Subramaniam will be joining the School of Engineering at the University of California, Merced, this Autumn.

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