Submitted via IRC for Bytram
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: 0) by Anonymous Coward on Tuesday August 13 2019, @09:01PM (2 children)
"information can be stored, transmitted and processed via magnetic oscillations without generating heat"
Because the Patent Office stopped accepting perpetual motion patents 100+ years ago.
(Score: 0) by Anonymous Coward on Tuesday August 13 2019, @09:06PM
That doesn't mean it won't experience energy loss through some other method (EM radiation comes to mind, perhaps photons (light)).
(Score: 0) by Anonymous Coward on Tuesday August 13 2019, @10:32PM
ARGGGGH!
Why must you science illiterates always chime in?? Ever heard of a superconductor? Maybe wait for claims of free energy or perpetual motion before you pop off?
(Score: 4, Informative) by Rupert Pupnick on Tuesday August 13 2019, @09:48PM (12 children)
A standing wave is really a steady state condition in which you excite the line or rope at an integer multiple of a half wavelength of its overall length. It’s a superposition of the incident waves coming from the shaken end with the reflected waves coming from the far end. Before you establish those standing waves, though, the initial wave has to propagate down and back.
“...stationary nodes and antinodes, but at the same time continuous phase shift...”
Phase shift of what with respect to what? Without the full animated video, I can’t figure out what they are talking about.
(Score: 5, Informative) by inertnet on Tuesday August 13 2019, @09:58PM (2 children)
Apparently this [uni-due.de] is the video.
More information here [idw-online.de].
(Score: 0) by Anonymous Coward on Tuesday August 13 2019, @11:28PM
It's an animation, not a real video... by that standard, I could use Blender to "prove" that dark matter exists.
(Score: 3, Informative) by Runaway1956 on Wednesday August 14 2019, @12:20AM
Yes, that was helpful. The video linked to won't play anywhere for me. I picked the least locked down browser, and told it to allow all scripts and everything - still wouldn't play for me. Your link works!
Now this is where I brag on Honda, and it's standing wave exhaust system? The GL500 and CX500 twins have twin exhaust, with a connector between them. Even if you remove the mufflers, the engine is quieter than you expect, because the sound pressure waves tend to cancel each other out in a standing wave. That is late 1970's technology.
Yeah, I know, car analogies are more acceptable than motorcycle analogies, but you gotta work with what you got!!
(Score: 4, Informative) by AthanasiusKircher on Tuesday August 13 2019, @10:06PM
There is a video link at the bottom of TFA to here [udue.de].
Basically, the wave looks like a kind of superposition of two different waves with different wavelengths -- a long-wavelength component with stationary nodes and antinodes, and a shorter wavelength component that is "travelling," i.e., phase shifting. In other words, you have a travelling wave (of some period) which is also wobbling up and down with a longer period. But the longer wavelength results in fixed points for nodes and minima/maxima (antinodes), so overall it appears to have something similar to "standing wave" characteristics on one level.
I didn't look more into the details of how this all is generated and works, but I think that's what they are claiming.
(Score: 3, Informative) by Rupert Pupnick on Tuesday August 13 2019, @10:26PM (7 children)
OK, thanks for those links.
To my eye, it looks like two waves superimposed— a high frequency and low frequency component— both moving from left to right at different speeds. There’s some relationship between the two speeds and frequencies that keeps parts of the overall waveform in contact with the white standing wave template, but I’m not seeing any standing wave components.
Maybe it’s an unexpected result in the medium in which this is occurring, but trust me, from a purely mathematical point of view there’s nothing unusual that wave action.
(Score: 2) by AthanasiusKircher on Tuesday August 13 2019, @11:05PM (5 children)
I wasn't aware that standard travelling waves have fixed nodes. I assume at least that element is rather rare.
The rest of the motion -- I agree -- looks like basic superposition of different components.
(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.
(Score: 2) by AthanasiusKircher on Tuesday August 13 2019, @11:36PM
The full article is paywalled, but if I'm not mistaken, the second image (available free) at the article page [aps.org] shows a FFT with the periodic components of this type of wave.
(Score: 0) by Anonymous Coward on Tuesday August 13 2019, @11:30PM
If you look at it one way you see a standing wave with traveling properties. But look again and you see a chipmunk chasing a squirrel. Remarkable!
(Score: 0) by Anonymous Coward on Wednesday August 14 2019, @07:14AM
This is my interpretation: https://media.giphy.com/media/Zy8RoJzzJyjug7n8MS/giphy.gif [giphy.com]
Hope that helps :-)