Sort Of Electromagnet Attracts Copper, Aluminum

It is a common grade school experiment to wind some wire around a screw, power it up, and watch it pick up paper clips or other ferrous materials. It is also grade school science to show that neither an electromagnet nor a permanent magnet will pick up nonferrous items like copper or aluminum. While technically not an electromagnet, it is possible to build a similar device that will weakly pull on copper and aluminum, and [Cylo] shows us how it works in a recent video you can see below.

The device sure looks like an electromagnet made with magnet wire and a steel core. But when he shows the ends of the core, you’ll see that the side that attracts aluminum has a copper ring embedded in it. The coil is fed with AC.

The magnetic field from the coil induces an opposite field in the copper ring that is out of phase with the exciting field. The two fields combine to produce a force on the metal it interacts with. This is often referred to as a shaded pole, and the same technique can help AC motors self-start as well as hold in relays driven by AC. If you want to see much more about aluminum floating on a magnetic field, check out the 1975 video from [Professor Laithwaite] in the second video below.

You probably have a shaded pole AC motor in your microwave oven. Or, maybe,your old 8-track player.

Continue reading “Sort Of Electromagnet Attracts Copper, Aluminum”

3D Printing Improves Passive Pixel Water Gauge

Here at Hackaday, we feature all kinds of projects, and we love them all the same. But some projects are a little easier to love than others, especially those that get the job done in as simple a way as possible, with nothing extra to get in the way. This completely electronics-free water gauge is a great example of doing exactly as much as needs to get done, and not a bit more.

If this project looks a bit familiar, it’s because we featured [Johan]’s previous version of “Pixel Pole” a few years back. Then as now, the goal of the build is to provide a highly visible level gauge for a large water tank that’s part of an irrigation system. The basic idea was to provide a way of switching a pump on when the tank needed filling, and off when full. [Johan] accomplished this with a magnetic float inside the tank and reed switches at the proper levels outside the tank, and then placed a series of magnetic flip dots along the path of the float to provide a visual gauge of the water level. The whole thing was pretty clever and worked well enough.

But the old metal flip dots were getting corroded, so improvements were in order. The new flip dots are 3D printed, high-visibility green on one side and black on the other. The only metal parts are the neodymium magnet pressed into a slot in the disc and a sewing pin for the axle. The housing for each flip dot is also printed, with each module snapping to the next so you can create displays of arbitrary height. The video below shows printing, assembly, and the display in action.

[Johan]’s improvements are pretty significant, especially in assembly; spot-welding was a pretty cool method to use in the first version, but printing and snapping parts together scales a lot better. And this version seems like it’ll be much happier out in the elements too. Continue reading “3D Printing Improves Passive Pixel Water Gauge”

Halbach Array Makes Magnets Strong, Weak

If you want a strong magnet, the obvious answer is to buy one. However, for a variety of reasons, you might want to combine several smaller magnets. There are a few ways to do this, but the Halbach array, as [wannabemadsci] explains, allows you to make an array of magnets where one side is very strong, and the other side is very weak.

The example uses a 3D-printed housing and five cube magnets. To form a Halbach array, the poles of the magnets are in a specific orientation that effectively rotates ninety degrees for each — in this case — cube.

Continue reading “Halbach Array Makes Magnets Strong, Weak”

Hoverboard Rides On Eddy Currents

The famous hoverboards of Back to the Future haven’t quite gotten here yet, but that hasn’t stopped anyone with a unique personal vehicle from using the name any time they need some quick marketing. The self-balancing scooter trend of the mid-2010s was the best example of this in recent memory, but there are also water-propelled platforms that use the popular name as well as a myriad of other more skateboard-like devices that never got off the ground at all. This project from [Damien Dolata], on the other hand, might be the most authentic prototype we’ve seen compared against the fictional version presented in the movie.

The hoverboard uses a set of rotating magnets, referred to in this build as magneto-rotational repulsors, which spin up to an extremely high rotational speed underneath the board. When above a metal surface, the spinning magnets generate eddy currents in the metal beneath them which create the strong magnetic field needed to levitate the board. Unlike the Lexus hoverboard system which used supercooling magnets, this is a much more affordable way of producing magnetic fields but is a little bit more complicated due to the extra moving parts.

As this is still in the prototyping stages, it has only been able to lift around 30 kg and hasn’t been tested in motion yet, but there are two small turbines built into the hoverboard to generate thrust whenever [Damien] gets to that point. It would require a larger metal surface to move across as well, which might be the main reason why it hasn’t been tested this way yet. For any native French speakers taking a look at this project, be sure to fill in any of our gaps in the comments below, and for other ways that eddy currents have been used in transportation take a look at this bicycle that uses them in its drivetrain.

Continue reading “Hoverboard Rides On Eddy Currents”

A Bicycle Powered By A Different Kind Of Eddy

When you think of a bicycle and an Eddy, you’d be forgiven for thinking first of Eddy Merckx, one of the most successful competitive cyclists to ever live. But this bicycle, modified by [Tom Stanton] as shown in the video below the break, has been modified by ditching its direct drive gearing in favor of using the friction-like eddy currents between magnets and copper to transfer power to the wheel.

Before even beginning to construct a mechanism for powering the bicycle, [Tom] had to figure out the basics: what kind of materials could be used for a metal disk? The answer, after much testing, turned out to be copper. What kind of magnets work best, and in what formation? Expensive high grade, aligned North to South pole for added eddy-dragging goodness. Would the mechanism work with any efficiency?

The end result is interesting to watch, and it’s not exactly as you’d have expected. Yes, eddy currents drive the copper hub, but at a 100 RPM difference. Where does all of that energy go? Hint: not to the wheel, and certainly not into propelling the bicycle. All in all it’s a fantastic experiment with unpredictable results.

If bicycle based bumbling about bakes your biscuits, you might appreciate this tennis-ball-enhanced ride too.

Continue reading “A Bicycle Powered By A Different Kind Of Eddy”

A Crash Course On How MRI Machines Work

Of all the high-tech medical gadgets we read about often, the Magnetic Resonance Imaging (MRI) machine is possibly the most mysterious of all. The ability to peer inside a living body, in a minimally invasive manner whilst differentiating tissue types, in near real-time was the stuff of science fiction not too many years ago. Now it’s commonplace. But how does the machine actually work? Real Engineering on YouTube presents the Insane Engineering of MRI Machines to help us along this learning curve, at least in a little way.

Both types of gradient coil are stacked around the subject inside the main field coil

The basic principle of operation is to align the spin ‘axis’ of all the subject’s hydrogen nuclei using an enormous magnetic field produced by a liquid-helium-cooled superconducting electromagnet. The spins are then perturbed with a carefully tuned radio frequency pulse delivered via a large drive coil.

After a short time, the spins revert back to align with the magnetic field, remitting a radio pulse at the same frequency. Every single hydrogen nucleus (just a proton!) responds at roughly the same time, with the combined signal being detected by the receive coil (often the same physical coil as the driver.)

Time taken for the perturbed spin to return to magnetic alignment

There are two main issues to solve. Obviously, the whole body section is ‘transmitting’ this radio signal all in one big pulse, so how do you identify the different areas of 3D space (i.e. the different body structures) and how do you differentiate (referred to as contrast) different tissue types, such as determine if something is bone or fat?

By looking at the decay envelope of the return pulse, two separate measures with different periods can be determined; T1, the spin relaxation period, and T2, the total spin relaxation period. The first one is a measure of how long it takes the spin to realign, and the second measures the total period needed for all the individual interactions between different atoms in the subject to settle down. The values of T1 and T2 are programmed into the machine to adjust the pulse rate and observation time to favor the detection of one or the other effect, effectively selecting the type of tissue to be resolved.

Time taken for the relative phasing inside a tissue locality to settle down to the same average spin alignment

The second issue is more complex. Spatial resolution is achieved by first selecting a plane to virtually slice the body into a 2D image. Because the frequency of the RF pulse needed to knock the proton spin out of alignment is dependent upon the magnetic field strength, overlaying a second magnetic field via a gradient coil allows the local magnetic field to be tuned along the axis of the machine and with a corresponding tweak to the RF frequency an entire body slice can be selected.

All RF emissions from the subject emanate from just the selected slice reducing the 3D resolution problem to a 2D problem. Finally, a similar trick is applied orthogonally, with another set of gradient coils that adjust the relative phase of the spins of stripes of atoms through the slice. This enables the use of a 2D inverse Fourier transform of multiple phase and frequency combinations to image the slice from every angle, and a 2D image of the subject can then be reconstructed and sent to the display computer for the operator to observe.

See? It’s easy.

We cover MRI technology from time to time, here’s a little update on state-of-the-art resolution for those wishing the dig a little deeper.

Continue reading “A Crash Course On How MRI Machines Work”

MRI Resolution Progresses From Millimeters To Microns

Neuroscientists have been mapping and recreating the nervous systems and brains of various animals since the microscope was invented, and have even been able to map out entire brain structures thanks to other imaging techniques with perhaps the most famous example being the 302-neuron brain of a roundworm. Studies like these advanced neuroscience considerably but even better imaging technology is needed to study more advanced neural structures like those found in a mouse or human, and this advanced MRI machine may be just the thing to help gain better understandings of these structures.

A research team led by Duke University developed this new MRI technology using an incredibly powerful 9.4 Tesla magnet and specialized gradient coils, leading to an image resolution an impressive six orders of magnitude higher than a typical MRI. The voxels in the image measure at only 5 microns compared to the millimeter-level resolution available on modern MRI machines, which can reveal microscopic details within brain tissues that were previously unattainable. This breakthrough in MRI resolution has the potential to significantly advance understanding of the neural networks found in humans by first studying neural structures in mice at this unprecedented detail.

The researchers are hopeful that this higher-powered MRI microscope will lead to new insights and translate directly into advancements healthcare, and presuming that it can be replicated, used on humans safely, and becomes affordable, we would expect it to find its way into medical centers as soon as possible. Not only that, but research into neuroscience has plenty of applications outside of healthcare too, like the aforementioned 302-neuron brain of the Caenorhabditis elegans roundworm which has been put to work in various robotics platforms to great effect.

Continue reading “MRI Resolution Progresses From Millimeters To Microns”