ballistic rectifier

John Creighton · 2004-05-07 12:21:07

I recently attended the conference CCECE (Canadian Conference of Electrical and Computer Engineers) and one of the topics presented was a ballistic rectifier. Basically light pass through a wave guide which causes a current around the waveguide. Rectifiers can be made at extremely small scales if they work on the principle of ballistics. The electrons that pass through the two terminals in the direction of the current are deflected in a perpendicular direction. The change is stored based on the capacitance of the wave guide. These things can be created on the scale of nanometers and simulations have shown the efficiency to reach 90% that of a carnot cycle at sufficiently small dimensions.

Ian Flint · 2004-05-07 13:42:03

That's uhh...wow...

Good luck with that... ???

What in the world are you talking about!!??

We laypeople like to at least understand something of what we read here. I suppose it's a switch (binary) of somekind?

John Creighton · 2004-05-07 22:11:10

A rectifier converts an ac current to a dc current. A wave guide is a geometric object designed to guide waves. One example of a wave guide is fiber optics. Microwaves are often guided with metallic wave guides. Electromagnetic waves propagate by the energy switching between an electric field and a magnetic field. The electric field creates the current. In a metallic wave guide with square cross sections the electric field of the wave will be parallel to one of the walls in the wave guide. Electric fields in metals cause currents to flow. It is these alternating currents that are converted to a dc current. This is done by a ballistic rectifier. The current is the motion of the electrons. These electrons can be deflected perpendicular to the direction of the changing electric field and stored in a metal plate (A.K.A a capacitor).The stored charge on one side of a capacitor produces a voltage across it that could be used for power. A carnot cycle is the theoretical maximum efficiency of converting a difference in heat to electricity. It is essentially the second law of thermodynamics. That is on average heat flows from hot to cold.

P.S. I did not present the paper on the ballistic rectifier. It was someone else at the conference.

SBird · 2004-05-08 02:35:50

Wow, do these require monochromatic light or do they work on full spectrum? I'm just wondering if these would be effective at converting sunlight?

John Creighton · 2004-05-08 03:43:21

The paper suggested using it for black body radiation which is basically heat. The sun emits a black body spectrum. The bandwidth of the wave guide depends on its geometry. Probably with a suitable geometry it could have a fairly narrow bandwidth. However, unless it was used as a light sensor, I am not sure there is any advantage of this. An interesting advantage of these devices is that they can be designed to work at a verity of spectrums. Including spectrums above and bellow what solar panels work at. Obviously there must be some limitations or I think there would be a fair amount of news about them.

Shaun Barrett · 2004-05-08 08:19:51

I'm not sure I understand the possible ramifications of this device. Is it likely to be useful only for powering nanomachines or might it be useful for macro power generation? Am I correct in inferring that efficiency falls off quickly in larger versions of the set-up, and is that a possible reason for the lack of excitement about the device at present?
???

John Creighton · 2004-05-08 09:19:18

You are right that efficiency falls off quickly at large scales for this device. However, several layers of this device could be used to try to extract all the power possible from a temperature gradient. I think there is a lack of excitement because the higher efficiency claims are only extrapolations from simulations. Moreover, manufacturing things at the nanometer scale is difficult and expensive. Finial I am not sure if all the details have been worked out on how these devices will be integrated into a larger circuit. I think over time it should be useful for macro power generation. However, I think at the current stage of technology it will just be used to help turn some of the heat microprocessors produce back into power. In the short term this may mean more quite computers, and laptops that can go longer without the need to recharge their batteries.

John Creighton · 2004-05-08 09:30:57

Bellow is the Abstract. I don't think I should post too much of the paper for copyright reasons.

Nanotechnology Based Energy Generation From Thermal Radiation
Quentin Diduck and Martin Margala
Department of Electrical and Computer Engineering,
University of Rochester, Rochester, NY, USA
diduck/margala@ece.rochester.edu

Abstract
This paper presents a novel thermal to electrical energy
conversion technique that utilizes black body radiation.
We have mathematically modeled this conversion
technique in order to determine a design methodology as
well as provide a means to evaluate the performance of
specific designs. The main principle of operation of the
conversion technique is in utilizing microscopic waveguides
in combination with specialized rectifying
structures, called ballistic diodes. These structures, when
properly combined, enable DC power generation using
switching supply techniques. This is achieved by treating
the infrared radiation as a high frequency AC source.
This conversion methodology is now possible due to the
fact that ballistic rectifiers are much smaller (~200nm)
than a wavelength of thermal energy radiation (~18µm).
We have shown that it is possible to obtain voltages on
the order of 0.02 volts from one wave-guide, while using
rectifiers that are only 14% efficient. Furthermore, we
have shown that it is possible to extract 90% of the
available energy within 10µm of depth of the wave-guide
structure (assuming a wave-guide opening of 3µm x
9.4µm). We have observed that power densities on the
order of tens of watts per cubic centimeter are
theoretically possible using this technique. In addition,
we address the limitations of this methodology with
respect to current technology and future manufacturing
techniques..1
Keywords: Power, Energy Generation, THz Electronics,
Ballistic Diodes

Palomar · 2004-05-08 09:32:44

http://www.space.com/businesstechnology … 7.html]New material grabs more solar energy

*I'm probably way off base here, and I generally don't chime in on discussions where I feel I'm really out of my league. But I saw the above article at space.com today.

Does this tie in with what you all are discussing, in any way?

I don't intend to take the thread off-topic, btw, and sorry if this is a totally different thing. But I thought I'd take a chance and post it.

Now back to more familiar territory.

--Cindy

John Creighton · 2004-05-08 09:37:40

It’s as good a place as any to post it since I don’t know how much discussion will take place on the ballistic rectifier since know one else has the paper.

dicktice · 2004-05-08 12:04:25

You've got a keen eye, Cindy. The object overall is to improve performance and efficiencies in power conversion, and your reference (re. solar cells) is of greater interest, in the short term, than ballistic rectifiers (sorry John). I'd like more, practical discussion regarding thermoelectricity in space, emphasizing e.g., convex mirrors to concentrate sunlight on the hot bimetallic junctions on the front side, and shield the cold ditto junctions on the dark, back side. What with solidstate chopper circuits, transformers and high voltage rectification either solidstate or thermionic. I would welcome more space electronics discussions involving very largescale "electron tubes" without envelopes, erected in orbit from prefabricated metallic components e.g., electron guns with solar-heated cathodes, and control grid voltages derived from (the above-mentioned) thermocouples--for space industrial manufacturing purposes. . . .

Shaun Barrett · 2004-05-08 17:29:38

This is all very exciting stuff!
I had a note scribbled out relating to your link here, Cindy, and was going to post the same link when I got the chance, but you beat me to it. ... Great minds .. ! :laugh:

I have to say I agree with Dicktice that the three-band-gap solar panel looks to be more practicable for the near future. And, with any luck, it may prove possible to mass produce it quickly and relatively cheaply.
Electrically self-sufficient homes with solar panel covered roofs ... here we come!

Having said that, I don't mean to detract from the intriguing and perhaps very promising energy-conversion device John has brought to our attention. It may be the start of something big! Thanks, John.

Euler · 2004-05-08 17:57:22

Wait, the ballistic rectefier is a heat engine that could convert heat energy to electricity with 90% efficientcy, right? Wouldn't that make nearly every source of power that we use vastly more efficient? So it's long term potential should be far greater than the new solar cells.

John Creighton · 2004-05-08 20:59:43

Wait, the ballistic rectefier is a heat engine that could convert heat energy to electricity with 90% efficientcy, right? Wouldn't that make nearly every source of power that we use vastly more efficient? So it's long term potential should be far greater than the new solar cells.

I think that is about right. Be careful though with what the efficiency numbers mean. I asked the speaker what kind of efficiency he meant. I asked if that was the percentage of the heat that flowed that was converted to electricity or if that was the relative efficiency as compared to the http://www.taftan.com/thermodynamics/CARNOT.HTM]Carnot cycle. The speaker said that was relative to the Carnot cycle. The efficiency of the http://www.taftan.com/thermodynamics/CARNOT.HTM]Carnot cycle is given by:
(Q_H-Q_L)/Q_H=1-T_H/T_L
Q_H is the thermal energy flowing into the heat engine
Q_L is the thermal energy ejected from the heat engine
T_H is the temperature on the hot side of the heat engine
T_L is the temperature on the cold side of the heat engine

Some other efficiency numbers were given and someone asked the speaker what he meant by efficiency. The person asked is that the percentage of electrons that are deflected. The speaker said yes. This makes me wonder, if the percentage of electrons that are deflected the same thing as the carnot efficiency. It could be. Let me give it some more thought.

Anyway, I believe it is possible to make heat engines with efficiencies close to that of a http://www.taftan.com/thermodynamics/CARNOT.HTM]Carnot cycle. I recall a problem though. I think as the efficiency goes up the power goes down. This is because the power is related to the flow of heat coming into the heat engine. The rate heat flows depends on how much the temperature changes with distance. The greater the change the faster the heat flows. But the more the temperature drops without being turned into heat the less efficient the heat engine. I wonder if the ballistic rectifier could help improve this trade off. As far as solar panels go maybe if the band gap energies are reduced enough they could reach similar efficiencies. I don’t know enough about solar panels to make this claim.

Shaun Barrett · 2004-05-09 04:32:14

I'm not at all sure how efficient this novel 'heat engine' might ultimately become but, if it were ever to reach macro-scale 90% efficiency ratings, it would be an incredible breakthrough indeed!
One can imagine a time, far in the future, when the universe is expanding ever faster under the influence of the dark energy in the space-time continuum, when everything is declining into a long slow 'heat-death', that heat engines of this kind could help to maintain life among the sentient beings who populate the cosmos in that dismal era.
Sorry, the 'Cecil B. De Mille' in me suddenly came to the surface there for a moment!

In the meantime, a macro device of that kind could revolutionise our present civilisation by providing almost unlimited usable energy.
But I still favour the three-band-gap solar panel to do us more good in the near future, if it can be mass produced and if it can deliver on the 50%+ figure.

SBird · 2004-05-10 00:13:34

Actually, higher efficiency solar cells really don't help that much for making solar energy practical. These triple junction cells will be terribly expensive, the manufacturing process is horribly difficult. It will have an impact on space missions where much more energy will become available for space probes.

On the ground, cost is far more important. Current cheap solar cells are at about 15% efficiency. Even if triple junction cells come down to that price, you've only gotten a 3-fold increase in the cost of power/$. On the other hand, if you can reduce the cost of colar cells, even poor ones, you suddenly open up the power market for people to start implementing the things at a local level. There's several companies currently working on low cost polymer/nanoparticle cells that could bring a 10-fold drop in solar cell cost.

When the cost to put solar cells drops from $10,000 to $1000, I'll be happy to slap some onto the roof of my house.

Shaun Barrett · 2004-05-10 02:31:05

I see your point, SBird.
Well then, how about a 50%+ efficiency rate and a 10-fold drop in solar panel costs?!!

Ever the optimist, I'll stick my neck out and predict it'll happen in the not-so-distant future.

dicktice · 2004-05-10 07:34:33

Shaun: I don't have your ultimate universe prediction ambition (indeed, the "Dark Force"--I mean "Matter"--may turn out to be just another "Aether Fix"), but regarding the manufacturing of solar cell elements and arrays, my ambition would be to provide totally automated production in orbit, using astroid-mined materials, to be shipped anywhere needed on or off Earth. The only cost would be transportation e.g., tether de-orbited re-entry packets (you fill in the details), or self-assembled self-propelled habitat sized arrays (my ultimate) for interplanetary space. On the other hand, I still think Solar thermocouple generated power would be ideal for compact, rugged, easily maintained trans-orbital space vehicles, however propelled.

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Re: ballistic rectifier

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Re: ballistic rectifier

#5 2004-05-08 03:43:21

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#7 2004-05-08 09:19:18

Re: ballistic rectifier

#8 2004-05-08 09:30:57

Re: ballistic rectifier

#9 2004-05-08 09:32:44

Re: ballistic rectifier

#10 2004-05-08 09:37:40

Re: ballistic rectifier

#11 2004-05-08 12:04:25

Re: ballistic rectifier

#12 2004-05-08 17:29:38

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#13 2004-05-08 17:57:22

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#14 2004-05-08 20:59:43

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#15 2004-05-09 04:32:14

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