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Following some discussions on waves in water, I feel
behoven
to wonder whether a piezo device could create ripples with
wavelengths approximating that of light (or a few
multiples
thereof).
If so, the water surface would be tuneably iridescent,
which
would be pretty.
McTartan_27s_20Chav_20Attracting_20Lake
you might like.... version of something similar, but with a purpose! [xenzag, Apr 22 2012]
AHA, maybe it is possible...
http://phys.org/news110191847.html
not from the surface, but from microstructures slightly underneath [4whom, Apr 23 2012]
Surface acoustic wave
http://en.wikipedia...rface_acoustic_wave
[xaviergisz, Apr 23 2012]
Acoustic iridescence
http://usir.salford...ASMAN12931165_1.pdf
[xaviergisz, Apr 23 2012]
Capillary waves
http://en.m.wikiped...wiki/Capillary_wave
Based on surface tension and gravity. [Ling, Apr 23 2012]
Iridescent water.
http://www.bluefing.../cloud-iridescence/
sorry, couldn't hep m'sef [2 fries shy of a happy meal, Apr 24 2012]
Soap bubble screen is 'the world's thinnest display'
http://www.bbc.co.u...technology-18671061
"Viewers may soon be able to watch films on soap bubbles - after researchers developed [...] a display that uses ultrasonic sound waves to alter film's properties and create either a flat or a 3D image." [Wrongfellow, Jul 03 2012]
Ultrasonic Flat Panel Display
[xaviergisz, Nov 10 2012]
[link]
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Well, there are a limited number of categories to select from, so sometimes you have to fudge a little.. |
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For example, there was not a single "weapons: bioweapons:cute" category I could use... |
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I think the killer will be viscosity - as wavelength gets smaller, the ratio of kinetic energy to viscosity gets smaller. Once critical damping is reached, there will be no wave propagation at all. |
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You might be able to get shorter wavelengths on mercury than in water, though, due to its greater surface tension. Short enough? Don't know. |
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Maybe I'm misreading, but ripples in water won't make it
glow. To get visible light you have to knock off some
photons, i.e. Cherenkov radiation. |
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Iridescence isn't about generation of light; it's the modulation (amplification/attenuation) of different wavelengths of light, with the result that the color of the reflected light is dependent on the angle of the reflection. |
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Yes, I too had doubts about getting enough
energy into the water to create really short
[water] wavelengths. There's a lot of new surface
to
create and maintain, so it'll take a bunch of
energy, as well as the aforementioned viscosity. |
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It's easy enough to make ripples with wavelengths
of a few hundred microns, though. We're in need
of maybe 10µm ripples or smaller (ie, no more
than 20 wavelengths of visible light). So, unless
the energy requirements go as the cube (or
higher) of the frequency, it ought to be
energetically doable. |
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If you deliver me a few pints of good British dark ale I will send you a few drops of iridescent oil to add to the top of your water. |
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//deliver me a few pints of good British dark ale//
New or used? |
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If your "used" ale is still dark, I recommend you consult your physician. |
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Hmm, perhaps he has King George's disease. That'd
certainly explain a lot. |
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Vlad the Impaler is suspected to have had porphyria as well. Although I suspect [MB] would prefer a link to British royalty rather than to some foreigner. |
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// British royalty rather than to some foreigner//
You're joking, right? George *was* a foreigner. |
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Vlad III was a total nutter, but he had no fear of sunshine,
being fond of taking noontime tea in courtyards
surrounded by his impaled victims,
and he rode horses everywhere (acute porphyria causes
intense lower abdominal pain). He was also reputedly a
formidable warrior, said to have personally slain hundreds
in battle; the tachycardia and neuropathy associated with
porphyria would have made it nigh impossible to fight for
protracted periods. In addition, he planned and executed
complex extended military campaigns, suggesting an
ordered and logical mindset, all cruelty and sociopathic
behavior aside. I don't care what Wikipedia says, I don't
think Vlad had porphyria. |
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(In one of those weird HB coincidences, I happen to be
reading a book about him right now.) |
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//the required frequency range is that of
infrared.// |
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I don't think that can be correct. We are aiming
to create ripples (say) 10µm apart or so. |
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The frequency of infrared is on the order of a
terahertz (10^12 Hz). |
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Hence, your calculation implies that the ripples
are propagating at 10^7m/s. |
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I think you're confounding things that should
remain unconfounded. |
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I'm saying that we need to make ripples on water,
those ripples having a spacing on the order of 10
microns. |
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The *wavelength* of these ripples (on the water
surface) is roughly similar to the *wavelength* of
infrared light. |
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However, assuming that ripples on water move at
less than the speed of light, their *frequency* is of
course very much less than the *frequency* of
infrared light. |
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Once again, we're unnecessarily arguing in a vacuum. The few peer-reviewed papers I've been able to find on the subject suggest that the limit is about 70µm, and that much beyond that viscosity does indeed prevent the production of water-air surface waves. Wavelengths of that order are produced with two laser beams detuned by the corresponding frequency. The water is thus subjected to pulses of heat at the beat frequency of the two laser beams, which in the case of 70µm surface waves is about 35kHz. |
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I've changed the figure to 35 kHz, because I misunderstood the context - on rereading, that paper used up to 100 kHz, but did not get good surface waves at that frequency. A different paper more clearly suggests that 70 µm corresponds with 35 kHz. |
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I lifted that figure from a couple of research papers. It's the frequency and speed of the surface waves, not of the light. |
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Well, others used "a piece of a razor blade (1x1cm) soldered down to the 3cm long wire
which is pasted to the membrane of the speaker", but were only working with a few hundred Hz. |
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OK, I can't find any clear statement of the speed
of ripples on water (and I presume it depends on
their wavelength and on other factors. But, let's
guess a propagation speed of 1m/s. |
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We need a wavelength of (say) 10µm, which
equates to an excitation frequency of 100kHz. |
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Hmm - that is quite high. But you might get some
iridescence even at a wavelength of 100µm (they'll
just be higher-order reflections - or do I mean
lower order), or 10kHz, which sounds reasonable. |
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Actually, this could fail at being purposeless. |
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If you could contrive many little ripple-tanks side by
side, each independently driven, you could bounce
white light off them and have a display. |
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Exactly! But without the GM, bio- and luminescence
parts. |
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//surface wave speed and its 'much slower'// |
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Suggested experiment: take a plastic sandwich
box full of water, and tap one side. The ripples
definitely take an observable time (>0.1s?) to
reach the other side, giving a speed o.t.o.o. 1m/s. |
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These ripples have a long wavelength (maybe a
millimetre or a few), and I'm guessing that shorter
capillary waves travel faster, and it's all a bit
guessy. |
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//but with oscillations below the surface you
really would need 150MHz// I'm not quite sure
what you're saying. (Actually not at all sure.) If
you're talking about compression waves ("sound")
in the body of the water then, yes, the speed will
be high and hence so will the necessary
frequency. But compression waves in the body of
the water wouldn't do much to light anyway. |
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But your point does trigger another idea... |
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La Chance ne favorise pas les esprits mal prepares.
[bigsleep] discovered amphibian butterflies, and
concluded "nothing happened." |
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"Said the mouse of cream yellow birds"? |
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Bien sûr, vous faire. Comment naïve de moi. |
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Ah, putain! Mon mauvais. L'argot est difficile. |
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Vous n'avez pas à l'avaler, vous le faites? |
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I'l ont deux coups d'argent, monsieur hôtelier. |
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Oh, fantastique! Olympia? Oh, vous avez dit Monet?
Olympia était la prostituée, non? |
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L'enlèvement est obligatoire. |
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Bon, bon, jusqu'à demain, mon ami! |
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It's almost 4pm Tuesday. Not exactly sure where you
are. |
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I'm sorry, this must be the FrogBakery. I was looking for the
HalfBakery. My mistake. |
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[Wrongfellow] - cool link!! |
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La DemiBoulangerie, c'est là-bas. |
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you need a liquid with extremely low surface
tension, but would water with surfactants do the
trick? |
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No, you need a liquid with an extremely *high* surface tension (but a low viscosity). |
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If it's not possible to create short enough ripples for
light, it should at least be possible to do this with
far infrared or UHF radio (wavelengths about 0.1mm-
10cm). |
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In fact, what would happen if I made a huge
parabolic reflector out of jelly, and then used a
piezo to drive ripples in the surface of the jelly?
Would I be able to make a tuneable parabolic
receiver? |
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