Nanoantennas: Solar arrays that absorb energy even in the dark!!

By | February 11th, 2008 85 Comments

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A collaboration of physicists, scientists and businesses have teamed up to create cheap and highly effective solar cells on a nanoscopic scale. Spearheaded by the Idaho National Laboratory, this team is onto a fresh way of producing solar panels that can continue to absorb energy even after the sun has set. The technology, not only efficient at nearly 80%, will also be cheap to manufacture, at estimated pennies a yard.
A specialized manufacturing process will stamp tiny square spirals of a conducting metal onto a think sheet of plastic that have been coined “nanoantennas.” At the slight width on the order of 1/25 the diameter of a human hair, these nanoantennas can absorb energy produced through the infrared spectrum. Infrared energy is produced in massive quantities by the sun, a portion of which is absorbed by the earth only to be released as radiation after the sun has set. These nanoantennas can absorb energy from both the rays of the daylight sun and the heat radiated from the earth at a higher efficiency than modern solar cells.


Steven Novak, a physicist at the Idaho National Laboratory spoke on this technology he is working on at the National Nano Engineering Conference in Boston. He said, “I think these antennas really have the potential to replace traditional solar panels.”
The technology simply mimics that of your cell phone or television antenna, absorbing energy by resonance. The theory that has born the research to produce these nanoantennas was based upon this platform; just make an antenna small enough to absorb the miniscule wavelengths produced by electromagnetic radiation.
The technology behind these atomic sized power modules is nothing new, but it has taken many years to discover an efficient way to print these miniscule spiraled antennas. It wasn’t until the inception of booming advancements in nanotechnology that this fine concept was taken from the theory to the tooling with production of these nanoantennas. The team at the INL forecast seeing the antennas produced akin to that of foil or plastic wrap in rolls of highly efficient solar cells. The team has been able to demonstrate an imprinting process with six-inch circular stamps, with each stamp containing more than 10 million antennas.
Instead of pairing this technology up with conventional solar cells to give them a boost in efficiency, the developers decided instead to make the nanoantennas independent energy harvesters. The team has estimated that individual nanoantennas are capable of absorbing nearly 80 percent of the available energy bombarded onto us daily by the sun. That is a staggering number compared to the conventional panels producing at around 20 percent.
Nanoantennas are not limited to silicon mediums, the circuits can actually be made from a variety of conducting metals and the antennas can be printed onto very thin and flexible materials such as polyethylene. The team has also estimated that the nanoantenna arrays can be available for as much as an inexpensive roll of carpet.
Although the physics of one resonating nanoantenna is certainly achievable, the trick to making this work lies in the matrix of complex vast arrays. The trouble will be in predicting the properties and perfecting the design before tackling the manufacturing obstacles that lie ahead. Multiple antennas create complex and sometimes unpredictable interactions. To jump this hurdle the researchers are developing a computer model of the resonance in these invisible structures, seeking out ways to fine-tune the efficiency of an entire array through tinkering with the materials and shapes of the antennas for example. “The ability to model these antennas is what’s going to make is successful, because we can’t see these things,” says Novack. “They are hard to manipulate, and small tweaks are going to make big differences.”

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  • Bob

    RF: You make a great salesperson. For a few minutes you almost had be convinced that the antennas might work.

    Bob: I thought hard trying to make you see there are reasonable mechanisms to address your concerns about entropy. I have found yet more academic papers suggesting IR as a source of energy for antennas to be used with. To prove that the concept of thermal energy scavenging of environmental IR is not a pipe dream, the following abstract shows a microscopic silicon based MEMS heat engine that works on as little as 1.5C thermal gradiants which is far less than hot roof/cold air.

    “Resonant operation and cycle work from a MEMS-based micro-heat engine”
    L. W. Weiss1
    (1) Louisiana Tech University, Institute for Micromanufacturing, 911 Hergot Ave, Ruston, LA 71272, USA
    Received: 14 June 2008 Accepted: 3 October 2008 Published online: 31 October 2008

    Abstract The documentation of a new engine thermodynamic cycle on the micro-scale is presented. This new cycle is the result of resonant operation and cycle work production from a MEMS-based micro-heat engine. The engine is constructed of two thin membranes surrounding a cavity filled with working fluid. This new thermodynamic cycle is shown to include nearly constant volume pressure increase, expansion, heat rejection, and compression components. A thermal switch is integrated with the micro-engine to control heat rejection. The micro-engine is shown to produce up to 6.7 μW of cyclic mechanical power when operated on this cycle. Micro-engine natural frequency is shown to vary from 90 to 140 Hz. The Micro-engine is shown to operate across a low temperature gradient of 1.5°C. “

    So basically, we have a virtually solid object that sits in a plane surface absorbing IR and making power. In this case its mechanical power but that could be converted, as others do, to electrical power. The only difference between the antenna and this is that this uses a physical working fluid in a very small cavity vs. an electron gas in the metal. Reduce this engine down to its theoretically most simple construction and you will invent the antenna.

    RF: So your saying the antennas would automatically absorb IR, release microwaves or radio waves, and produce electrical energy?

    Bob: Only with a thermal gradiant or radiative net flux and only with the sum of all the types of energy produced being higher in entropy that the source.

    RF: That means that one could set up a bank of antennas in a house powered by IR radiating from the walls and use the electricity to cook with or whatever.

    Bob: I have shown you that an antenna functions like a heat engine and that silicon based micro heat engines exist scavaging temperature differences as small as 1.5C (basically stray blackbody IR). So my response to your continued tests is to ask yourself for any concievable scenario, “how will a panel of planar micro heat engines that take stray heat and make electrical power work in this situation?”. However they act, the antennas will do the same but likely more efficiently because they couple hot source to working fluid more efficently. It's really that straightforward.

    • Ramsey Frist

      Where in these nanoantennas is the intelligent demon that tells the difference between an IR photon coming from a cool wall or one from the sun? Why would nanoantennas only work if they are cooler than their surroundings?

  • Bob

    RF:Where in these nanoantennas is the intelligent demon that tells the difference between an IR photon coming from a cool wall or one from the sun? Why would nanoantennas only work if they are cooler than their surroundings?

    Bob: Where in the gas or fluid of a Sterling engine or any heat engine is the demon that tells an atom that a photon /phonon it is going to absorb is from the hot source or from the cold source?

    RF: Why would nanoantennas only work if they are cooler than their surroundings?

    Bob: They “work” all the time. If the net flux at the antenna in ingoing the antenna produces net power. If it is outgoing the antenna radiates heat to a cooler environment. If it is in equilibruim the rates going in and out are the same and no net power is produced or radiation released.

    • Ramsey Frist

      I see no problem with micro heat engines working with a small temperature gradient.

      Your electron fluid and “cooler” matrix is a very good description of how antennas in general work. Coherent radiation from a distant source is absorbed, energy trapped, and some heat and less coherent radiation is given off to the cooler environment. I accept your heat engine analogy.

      On the other hand, if the nanoantennas work with black body IR when they are in cool surroundings with flux from the sun its not clear why they would not work to extract heat from an insulated house or if they were put in an oven. We both agree the latter cannot happen but why not?

  • Bob

    RF:Your electron fluid and “cooler” matrix is a very good description of how antennas in general work. Coherent radiation from a distant source is absorbed, energy trapped, and some heat and less coherent radiation is given off to the cooler environment. I accept your heat engine analogy.

    Bob; Thanks. I really appreciated the lively debate.

    RF: On the other hand, if the nanoantennas work with black body IR when they are in cool surroundings with flux from the sun its not clear why they would not work to extract heat from an insulated house or if they were put in an oven. We both agree the latter cannot happen but why not?

    Bob: We agree when the antenna is at the temperature of the inside of the house or oven no net power will be produced. If the antenna is at the house or oven temperature to start with no net power is produced because they are already in equilibruim with the only source available. They are “working” but with zero percent efficiency.

    But here is how I think they would be used;

    Take a room in the house at 70F. Nothing happens and all is in equilibrium. Take a strong heat lamp and aim it at the walls where the antennas are arrayed. They see a “distant” source much hotter than the air/walls they are in and start to work. Of course, they don't work 100% and some IR has to go into the walls, air, lattice atoms of the antennas ect. The temperature rises above 70F. They ONLY thing they can do is to keep the room from rising as fast as if they were not there. They can NEVER lower the temperature of the room below 70F. They cannot even keep it there (thus obeying the Second Law).

    From a purley practical point of view then what good are they and how can they be claimed as “cooling” devices? If the temprature rises at a rate of 10F/hour instead of 30F per hour then in a practical sense (but NOT in a thermodynamic sense) they have kept the room “cool”. “Cooling” was probably a poor word to use and they should instead claim it helps “regulate” the heat.

    In the oven, let the oven start at room temperature and rise to a hot temperature. At first there is no equilibrium as the antennas see a hot source but the air is not that hot yet so they work for a while. Some of the IR that would have gone into heating the antenna lattice is converted to power but not enought to keep the lattice from rising to the hot air temperature. Eventually the antenna gets so hot it sees not much difference if any from the source and stops working.

    The bottom line is that they work to the extent there is no equilibrium and they stop working when there is equilibrium meaning the lattice is in equilibruim with the source as I see it.

    • Ramsey Frist

      I don't think the proposed nanoantennas will be that smart but if you can find an example of a rectenna that works when one shines a heat lamp on it I will be a believer.

  • Bob

    I

    RF: I don't think the proposed nanoantennas will be that smart but if you can find an example of a rectenna that works when one shines a heat lamp on it I will be a believer.

    Bob: Well, I think its not the antennas that are so smart but nature knows how to keep things in balance.
    The paper abstract below is one example of how the antennas are characterized in the lab. They heat the device on a hotplate and measure its emissions which by Kirchoff's laws are equal to its absorption characteristics so this is like using a heat lamp but is an equivalent but more convenient lab setup. The Novack paper does the same (it seems the Boreman group did some of the measurments for the INL).

    What you (and I) really want to see is the final product that produces power from IR. Glimpses of that future ability are in the literature in the form of small functioning test rectennas designed for broadband IR. I have seen at least one paper which in addition to the typical laser source used for testing did also use a monochomatic but otherwise conventional (i.e. non coherent, non laser) source and the antenna/diode rectenna still worked- produced a current.

    Infrared Frequency Selective Surface Based on
    Circuit-Analog Square Loop Design
    Brian Monacelli, Student Member, IEEE, Jonothan B. Pryor, Member, IEEE, Ben A. Munk, Life Fellow, IEEE,
    Dale Kotter, and Glenn D. Boreman, Member, IEEE
    Abstract—A frequency selective surface (FSS) was designed to
    have a resonant spectral signature in the infrared. The lithographically
    composed, layered structure of this infrared FSS yields a resonant
    response in absorption to infrared radiation at a wavelength
    determined by its FSS element structure and the structure of its
    substrate layers. The infrared spectral characteristics of this surface
    are studied via Fourier transform infrared spectroscopy and
    spectral radiometry in the 3 to 15 m region of the spectrum. The
    design is based on circuit-analog resonant behavior of square loop
    conducting elements.

  • Bob

    RF: I don't think the proposed nanoantennas will be that smart but if you can find an example of a rectenna that works when one shines a heat lamp on it I will be a believer.

    Bob: This is the paper that uses a quartz lamp. It's in the optical range but proves the point.

    “Investigation of resonance light absorption and rectification by subnanostructures”

    Guang H. Lin, Reyimjan Abdu, and John OM. Bockris
    Chemistry Department, Texas A&M University, College Station, Texas 77843

    http://jap.aip.org/japiau/v80/i1/p565_s1

    • Ramsey Frist

      If there antennas worked in 1996 one would think there would have been more progress would have been made by now. If the diodes work at such low voltages why bother with the antennas? Just paint them black.

      • Bob

        I think the diodes would not respond to the heat converted to random thermal motion of the atoms as well as they would the alternating current from the antenna's. Thermocouples that make voltage from a temperature difference are used in special cases but are very inefficient and costly.

        As far as progress goes sometimes the simple direct ideas are the hardest to make work. Fusion energy was thought to be easy when thet first started to work on it in the 1950's. The only point of this work was to show they solved the “cheap printing of a massive amount of antenna's” problem but not the complete problem with rectification.

  • Bob

    I think the diodes would not respond to the heat converted to random thermal motion of the atoms as well as they would the alternating current from the antenna's. Thermocouples that make voltage from a temperature difference are used in special cases but are very inefficient and costly.

    As far as progress goes sometimes the simple direct ideas are the hardest to make work. Fusion energy was thought to be easy when thet first started to work on it in the 1950's. The only point of this work was to show they solved the “cheap printing of a massive amount of antenna's” problem but not the complete problem with rectification.

  • Reggie

    Ramsey, the antennas, nanoscale or otherwise, do not reduce any entropy or destroy any energy. Antennas simply transform and move energy, causing an increase in the entropy of the electrical load placed on the system. The electrical load subsequently either stores or immediately re-radiates the energy as heat, light, RF, sound or whatever else back out into the universe.

    For an energy transfer to occur there does not need to be a downward gradient in total energy from the source to the sink. There only needs to be a downward gradient of the specific form of energy being transferred, which in this case would be infrared light at specific wavelengths.

    After sunset, there may still be objects in the vicinity of the solar collector which had absorbed heat during the day and which would continue to radiate for some time. Perhaps the very building the collector was mounted on would even radiate some IR light into the collector from behind.

    During the day, the collector is cooler than the sun, so no problem with a gradient. At night, the collector array would tend to cool off sooner than the building it is mounted on, so there would still be a gradient of heat into the collector.

    “People who say it cannot be done should not interrupt those who are doing it.”

  • Missoula

    This project is ridiculous based on the infrared solar panels. promise not working because the radiant head around is extremely low flow but huge amount. Try use it for small devices. unless you need to bombard the semiconductor with photons. For those who think is possible or why is not better do not ask to much because you will disappointed. remember:”the answer sometimes is so simple but peoples mind blowing thinking the wrong way”.

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