New theory shows one-way transmission materials should be possible for sound and light waves

May 03, 2011 by Bob Yirka report

(PhysOrg.com) -- Physicist Stefano Lepri of the Italian National Research Council and his partner Giulio Casati of the University of Insubria, have published a paper in Physical Review Letters, where they demonstrate through mathematical theory that it should be possible to create asymmetric materials that allow most light or sound waves to pass through in one direction, while mostly preventing them from doing so when going the opposite way.

Scientists have for years been trying to figure out if it was possible to get around the reciprocity theorem, which states that identical waves passing through the same medium should behave the same way regardless of direction. If such a feat were possible, true one-way mirrors could be created, or soundproof rooms, or taking it further, quantum computers that use light to perform calculations.

Lepri and Casati, in their paper, propose the idea of constructing a material composed of several layers of ordinary linear material, such as glass or plastic, but that also has two nonlinear layers of material in the center. They then showed that because waves travel best through material when their frequency has a certain with the material it passes through, it should be possible to create a nonlinear material that is fine tuned to allow the maximum amount of waves to pass through for a certain frequency, going a certain direction; but which would not generally be the case for waves traveling in the opposite direction. The result would be a material that lets through most of the waves traveling in one direction, but not the other.

If such materials could be created, scientists envision not just custom building materials that could control how much heat or light comes through, while still allowing people to see out, or true one-way mirrors, or houses made with rooms that are nearly perfectly sound proof, but perhaps wave that could be used in the same way as electronic diodes that allow current to run just one way through a system; paving the way for computers that operate at speeds we can only dream of today.

Neither Lepri and Casati, nor anyone else has yet come up with a nonlinear material that can be fine tuned to provide the custom resonance required to create such a material, however, so for now, this new science is still just theory; the authors believe it’s just a matter of time though.

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More information: Asymmetric Wave Propagation in Nonlinear Systems, Phys. Rev. Lett. 106, 164101 (2011) DOI:10.1103/PhysRevLett.106.164101

Abstract
A mechanism for asymmetric (nonreciprocal) wave transmission is presented. As a reference system, we consider a layered nonlinear, nonmirror-symmetric model described by the one-dimensional discrete nonlinear Schrödinger equation with spatially varying coefficients embedded in an otherwise linear lattice. We construct a class of exact extended solutions such that waves with the same frequency and incident amplitude impinging from left and right directions have very different transmission coefficients. This effect arises already for the simplest case of two nonlinear layers and is associated with the shift of nonlinear resonances. Increasing the number of layers considerably increases the complexity of the family of solutions. Finally, numerical simulations of asymmetric wave packet transmission are presented which beautifully display the rectifying effect.

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User comments : 16

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CSharpner
5 / 5 (1) May 03, 2011
This would be great to use in solar cells. Put a true one-way mirror over a solar cell so light can come in, but bounces around inside until it's absorbed rather than reflecting back out and lost.
kaasinees
1 / 5 (2) May 03, 2011
Imagine how efficient we could become if we design computers that work entirely oh photons, change our grid to carry photons instead of electrons. There will be problems converting this to heat or kinetic energy though, but not impossible. Or possibly we will use 3 lines internet and photons, electrons, nothing else is needed.
axemaster
not rated yet May 03, 2011
Yeah, this won't be theory for long. Expect a mad scramble to build a working experimental system over the next little while.
Chilinuttz
1 / 5 (4) May 03, 2011
This obviously won't work, Imagine a sphere that can't release the incoming light, sooner or later it has collected all the light in the universe...Smash the sphere and behold the lightexplosion.
Modernmystic
1 / 5 (1) May 03, 2011
Imagine how efficient we could become if we design computers that work entirely oh photons, change our grid to carry photons instead of electrons. There will be problems converting this to heat or kinetic energy though, but not impossible. Or possibly we will use 3 lines internet and photons, electrons, nothing else is needed.


Uh, you DO know how an electric motor works...right?
Na_Reth
1 / 5 (2) May 03, 2011
Uh, you DO know how an electric motor works...right?

Obviously you are the one here who does not know how an electrical motor works.
Modernmystic
1 / 5 (1) May 03, 2011
Uh, you DO know how an electric motor works...right?

Obviously you are the one here who does not know how an electrical motor works.


So how do you make an electric motor work without electrons?

Nice sock puppet BTW Kass...
PinkElephant
not rated yet May 03, 2011
I tend to agree with Chilinuttz (great handle, by the way); there's something missing in the above description. If one could construct a flawless one-way sound diode, then one could convert random vibrations (a.k.a. heat) into directional energy flow, which could then drive a motor within an otherwise closed system at thermal equilibrium. Basically, this leads to violation of the second law of thermodynamics.

If their proposed construction is at all realizable, then probably what it will amount to in reality is a kind of bandpass filter that strongly affects a certain narrow range of wavelengths but preferentially "leaks" the rest of the spectrum in the opposite direction, thus not allowing construction of any sort of an efficient Maxwell's Demon.
malapropism
5 / 5 (1) May 03, 2011
Imagine a sphere that can't release the incoming light

That would be quite useful though, wouldn't it? Not only would it be a very good physical model for a black hole, without the attendant gravitational problems for the observer, but it would make for a really good energy storage mechanism (assuming that it would be possible in some way to tap the energy back out at a later time).
mrwolfe
not rated yet May 04, 2011
@chilinuttz

What's missing from the description is that this effect only works over a limited range of wavelengths. RADAR radomes and dielectric reflectors (think about those rainbow coloured reflectors on halogen downlights) already use the multilayer principle, problem is it works in both diections. i.e if a dielectric material is transparent from the front, it's also transparent from the back.

The limitaition with dielectric reflectors is that you can make them broadband at the cost of reflectivity. The idea presented here has the same limitation, so visible light would go in but energy would leak back out in the form of heat and infrared radiation.
georgert
not rated yet May 04, 2011
Didn't Maxwell Smart and Chief use this stuff for their 'cone of silence?'
bluehigh
1 / 5 (1) May 04, 2011
No one way mirror. One side would be black (light input) and the other side? Would it seem to be transparent or combine the reflected ambient light in a messy mix? To be effective the viewer would still need to be in a darkened room and the downside side would be instead of a mirror you have a black panel.

bluehigh
1 / 5 (1) May 04, 2011
.. and no sound proof room either using this material. Inside the room all sound would be echoed highly efficiently. I doubt a conversation would be possible.
CSharpner
not rated yet May 04, 2011
No one way mirror. One side would be black (light input) and the other side? Would it seem to be transparent or combine the reflected ambient light in a messy mix? To be effective the viewer would still need to be in a darkened room and the downside side would be instead of a mirror you have a black panel.


One side black, yes, the other would be transparent and reflective. (both incoming and reflecting images added together). This would be more effective in an police interrogation room. Inside the room the panel would appear black and the suspect would see it as just part of the wall. On the other side, they could watch what was going on in the room. They'd, of course, have to turn their own lights down to reduce reflectivity of themselves so they could see through it more easily.
CSharpner
not rated yet May 04, 2011
This obviously won't work, Imagine a sphere that can't release the incoming light, sooner or later it has collected all the light in the universe...Smash the sphere and behold the lightexplosion.

Well, they did say that a small amount does escape, but I like the idea of a sphere of this. I wonder what would happen if there were a small hole. I imagine you could make a bright beam. I don't know how focused it'd be, but you'd be collecting most of the incoming light from all directions and sending it out of one hole. I wonder also if there'd be a delay if you started in a dark room and turned on a light... if the light would spend some time bouncing around before coming out... probably some would come out immediately, then it would get brighter until it reached maximum brightness... Don't know... Cool thought though.
StandingBear
not rated yet May 04, 2011
Somebody just created the energy storage system of the 'Destiny', the starship in the latest Stargate series. Now we just carry some black boxes close to the biggest light source in the sky and collect away. Now before we built a 'solar' ship bear in mind that we do not have the shielding that the 'Destiny' possesses, so we cannot dive into the star and go back out again as anything other than vapor. However, it should be a dandy way to recharge from, say, the orbit of Mercury.