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Video of a phenomenon: Standing waves that won't stand still
And yet they move: An international team of scientists involving physicists from the Center for Nanointegration (CENIDE) at the University of Duisburg-Essen (UDE) has observed a new phenomenon: They have generated standing waves – which travel. The results of their research have been published in the scientific journal "Physical Review B", including videos.
A wave consists of antinodes and nodes. If you imagine this on a rope, the antinodes are the areas which swing up and down, whereas nodes are the points in between. With a standing wave, nodes and antinodes always remain at the same position and do not move along the rope.
In travelling waves on the other hand, nodes and antinodes do not remain in place: If you start shaking a rope from one end, you will excite a wave that travels down the rope until it reaches the other end.
Benjamin Zingsem from the research group of UDE's Professor Michael Farle has now observed the apparent paradox for the first time: For this purpose, he worked with, what physicists call a chiral magnet:
A magnetic material in which the so called Dzyaloshinskii-Moriya interaction occurs. In such magnets, all dipoles – the tiny magnets that make up the solid – are slightly tilted towards each other with a certain direction, like screw windings.
If the system is resonantly excited, a standing wave with travelling properties is formed. This wave has stationary nodes and antinodes, but at the same time a continuous phase shift creates the impression of a travelling wave. "I had to look at it for a long time before I could put it into words. I only really understood it by watching a video of the phenomenon," says Zingsem.
The effect reveals previously unknown transport properties in such systems. Which may, for example, be harnessed in future technology, as, information can be stored, transmitted and processed via magnetic oscillations without generating heat, which is the main bottleneck in conventional electronics.
(Score: 2) by Rupert Pupnick on Tuesday August 13 2019, @11:41PM (4 children)
I think there is a lot of semantic confusion in the article that leaves room for a lot of hype.
That second composite wave has no nodes that I can see, neither traveling or stationary. It just adheres in parts to the white template from left to right as it travels. To have a traveling node, there should be a point where the wave amplitude is zero, but moves uniformly at some speed. I’m not seeing that, and white template doesn’t help in revealing that to me. But consider, all simple propagating sinusoids have traveling nodes, i.e. the places where the wave has zero amplitude which moves along with the rest of the wave. Nothing special about that.
(Score: 2) by AthanasiusKircher on Wednesday August 14 2019, @12:44AM (3 children)
Huh?
There are clear nodes in the video graphic I'm looking at, at the places where the nodes are in the white standing wave template. That's the whole reason that template is there -- to show you that. The nodes don't travel either -- they are fixed and don't move horizontally.
(Score: 2) by AthanasiusKircher on Wednesday August 14 2019, @12:49AM (2 children)
(And yet again if my point still isn't clear: the fixed nodes make it primarily a standing wave, not a travelling one. Hence the classification in TFA.)
(Score: 2) by Rupert Pupnick on Wednesday August 14 2019, @01:37AM (1 child)
Yes, you’re clear. Let’s say the waveform has properties of both standing and traveling waves. The nodes of the first simple waveform are also (stationary) nodes of the second complex one. The second waveform also has zero crossings at other places that appear to move from left to right. Not sure if these should be called nodes or not. TFS isn’t clear and consistent with this terminology either.
Still, I don’t see what the big deal is mathematically. You can construct any waveform you like with weighted sinusoids, right? After all, the illustrator had to plug in an equation for some periodic function (almost certainly the sum of two sinusoids in this case) into some Matlab like tool to make that animated plot.
(Score: 2) by AthanasiusKircher on Wednesday August 14 2019, @10:48AM
Yep. And I'd say that's a somewhat rare property of a waveform. Not unique, and perhaps not mathematically groundbreaking, but an unusual property.
I have no idea whether that means those kinds of characteristics mean these waves can do the stuff TFA claims (as I can't read the original study), but the vast majority of waves don't have the characteristics you described, which was my point.