Electropermanent magnet facts for kids
An electropermanent magnet (EPM) is a special kind of permanent magnet that you can turn on and off! Imagine a regular magnet that always sticks, but an EPM can be told to stop sticking or start sticking with a quick zap of electricity. It's like having a remote control for a magnet.
These magnets are made from two different magnetic parts. One part is a "hard" magnet, which means its magnetism is very strong and hard to change. The other part is a "soft" magnet, which means its magnetism can be easily flipped. When these two parts are lined up in a certain way, the EPM acts like a strong magnet. But when one part's magnetism is flipped, they cancel each other out, and the EPM turns "off."
Before EPMs were invented, if you needed a magnet that could be turned on and off, you had to use an electromagnet. Electromagnets need a constant supply of electricity to stay on, which uses a lot of power. EPMs are much better because they only need a tiny pulse of electricity to switch between on and off. Once they are set, they don't need any more power to stay in that state!
Powerful EPMs, often made with rare-earth magnets, are used in factories to lift heavy metal objects. When the object needs to be released, the EPM is simply switched off. Scientists are also exploring EPMs to create amazing self-building robots and structures.
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How Electropermanent Magnets Work
An electropermanent magnet (EPM) uses a clever setup of magnetic materials to control its external magnetic field. Think of it like a magnetic "latch."
A basic EPM often has two permanent magnets placed between pieces of "soft" magnetic material, usually made of iron. These iron pieces help guide and concentrate the magnetic field.
When the magnetic fields of the two permanent magnets are aligned in the same direction, their combined strength creates a strong magnetic field outside the EPM. This is the "on" state. The iron pieces help direct this field outwards.
However, if the magnetic field of one of the permanent magnets is flipped to point in the opposite direction, it cancels out the field of the other magnet. In this "off" state, almost all the magnetic field is contained inside the EPM's structure, and there's very little magnetic force outside.
The cool thing is that the EPM's magnetic field comes from the permanent magnets themselves, not from a continuous electric current. The electricity is only used for a brief moment to "flip" one of the magnets, changing the EPM from on to off, or off to on. After that quick pulse, no more electricity is needed to maintain its state.
The Secret to Switching Magnets
Let's imagine how an EPM switches its magnetic field. Look at the picture below. It shows two permanent magnets with U-shaped iron bars.
If both magnets have their "north" poles pointing up, the iron bar on top becomes a strong north pole, and the bottom bar becomes a south pole. This creates a strong magnetic field flowing outside, making the big magnet "ON."
Now, what if we could magically rotate one of the magnets so its north pole points down? The top iron bar would then see a north pole from one magnet and a south pole from the other. This causes almost all the magnetic field to stay trapped inside the iron bars, creating a closed loop. With the field trapped inside, there's almost no magnetic field outside. This is the "OFF" state.
But we don't actually rotate the magnets physically! Instead, we use a special trick with electricity. Look at this next picture:
A wire coil is wrapped around one of the magnets. When a short burst (a "pulse") of electric current flows through this coil, it creates a temporary magnetic field. If this temporary field is strong enough, it can actually reverse the direction of magnetism in the magnet it's wrapped around.
This is possible because one of the permanent magnets is made of a material that's easier to "flip" its magnetic direction than the other. For example, one magnet might be made of a material like AlNiCo, which is easier to change, while the other is made of NdFeB, which is much harder to change. This way, we can flip just one magnet without affecting the other.
So, with just a quick pulse of current, we can electronically "rotate" one of the magnets, turning the EPM's external field ON or OFF. No power is needed to keep it in either state!
Cool Uses for Electropermanent Magnets
Electropermanent magnets are being used in many exciting ways, from phones to robots!
Modular Phones: Project Ara
Years ago, Google had an idea called Project Ara. They wanted to create a phone where you could easily swap out parts, like the camera or battery, just like building with LEGOs! EPMs were planned to be used to hold these different phone modules together. This meant you could change parts while the phone was still on. However, Project Ara was put on hold in September 2016.
Drone Delivery Systems
Imagine drones delivering packages right to your door! EPMs are perfect for this because they can securely grip a package and then release it without using much power. Companies like Zubax Robotics have developed special EPM systems, such as the FluxGrip EPM, for drone package delivery.
Robots That Build Themselves
Scientists are exploring how EPMs can be used to create "reconfigurable matter." Think of small robot blocks, like dice, with EPMs on each side. These "Pebbles robots" could attach to each other in different ways, allowing them to form various shapes and even build structures on their own!
Logitech MX Master 3 Mouse Scroll Wheel
Even your computer mouse might use EPMs! The Logitech MX Master 3 mouse has a special scroll wheel that can switch between a smooth, free-spinning mode and a precise, clicky mode. This "MagSpeed" technology uses an EPM inside the wheel. A quick electric pulse switches the EPM, making the wheel feel clicky or smooth. Since it's an EPM, it only uses power when switching modes, saving battery life and reducing wear and tear.
Images for kids
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Design ideas for the coil that helps switch the EPM.
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A graph showing the magnetic force of an EPM when it's ON versus when it's OFF.
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Computer simulations showing the magnetic field of an EPM in its ON and OFF states.
See also
- Magnet
- Electromagnet
- Magnetic base
- Variable Halbach array
