Scavenging ambient electromagnetic energy


At this very moment, unseen radio waves are bouncing off almost everything that surrounds you. Emitted by everything from radio and TV stations to cell phone networks and satellites, these waves are full of unharnessed energy. That is, until now. Researchers at the Georgia Tech School of Electrical and Computer Engineering have been working diligently to harness this unused energy, and recently unveiled their new antenna technology at the IEEE Antennas and Propagation Symposium.

The team, led by professor [Manos Tentzeris] has been working to develop ultra-wideband antennas to tap into the energy all around us. Using printers filled with a specially-formulated ink compound, they have been able to print these antennas on paper and polymer substrates. The antennas can harness energy stored in radio frequencies ranging from 100 MHz all the way up to 60 GHz, depending on the printing medium.

The team can currently power temperature sensors using television signals, and is preparing a demo in which they will power a microcontroller simply by holding it up in the air. The technology is still in its infancy, but the list of applications is almost endless. We doubt you’ll be powering your TV with this technology any time soon, but it definitely holds promise for things such as wireless sensor mesh networks and the like.

[Thanks, morganism]

65 thoughts on “Scavenging ambient electromagnetic energy

  1. These waves aren’t unused or unharnessed energy resources! By the law of conservation of energy, these guys are powering devices by attenuating your TV signal.

    The process is quite cool though. I was reading a paper about using photo-lithography to print antennas tuned to the resonant frequency of light to gather energy that way instead of using a photovoltaic cell.

  2. This has been a hot topic in the US DoD SBIR program for a few years now, neat to see some of the technology coming out of that funding (and I’d be surprised if this research wasn’t partially DoD funded, despite the conspicuous absence of any DoD agencies in the list of sponsors).

    It’s not new, just new in the conference circuit, so the “until now” is a bit off…

  3. also @ pedro,

    thats true only if they happen to be in the path between your tv and the transmitter, for a majority of this energy, it will never be received by the intended receiver so yeah, its wasted energy. Wifi routers transmit omnidirectionally, that doesn’t mean you use the energy that’s being beamed into your attic…

  4. The amount of the radio signal that will actually pass by this antenna is very small, so the attenuation of the signal is minimal. Take into consideration HOW MUCH of that signal goes to waste without devices like this.

    If you think of radio waves emitting as an expanding sphere, how much of that sphere does your device’s antenna take up? How much of that energy is actually anywhere near your device?

    If this can generate the ~1.75v needed to run a uController on super-low-voltage mode, it should be fun to see what comes next. Wireless T-Shirt LEDs anyone?

  5. Putting an object in between the signal and the receiver attenuates the signal anyways. The mass of your body for instance. So instead of just being absorbed by your body or the objects in your pockets, why not take that and turn it into something useable.

    Though I have my doubts that this can power a wireless mesh network. Mesh networks transmit at a pretty high power. I imagine it would need to absorb amounts of energy higher than what it transmits. Which would probably make it pretty useless unless it is directly next to a microwave that is always running. Maybe power lines?

  6. Pretty cool stuff. Makes me wish I remembered more of my microwaves network class. While the amount of power you can receive is very tiny (thankfully, as high power radio waves have a tendency to do nasty things to the human body, as studies of people who live near radio towers have shown), this would be good for ultra mobile devices. Fun projects that could use this tech would be things like signal repeaters (transmit one signal based off of other signals in the area? Awesome), GPS tracking device (the perfect spy tool, a GPS tracker that never dies!), or maybe some kind of e-ink display (build up enough charge over time until you have enough power built up to change the image).

  7. you dont need special ink to do this. a LOT of people have been doing it for decades with regular old wire and coils.

    Problem is the amount of electricity these collect is in the levels of femtowatts. incredibly small incredibly low. you need an array to collect more of it and a way to store it up so that your sensor can use a slug of it every 5 minutes and let the other 4.99876 minutes soak up enough energy to fire it again.

  8. Oh god. The “free energy” weirdos and people selling magic stickers and copper shavings in resin will use this to “prove” their crackpot theories and sell…junk…excuse me, I have to go make some copper shavings and resin.

  9. This is a neat idea at first glance. ANCIENT in concept as I knew many folks with Crystal Radios harvesting enough energy to drive large speakers. Some apparently first installed in the late 60’s as diodes got both affordable and “Good Enough” to work in such applications.

    BUT! If we deploy too many such devices, we *WILL* begin sucking down signals that otherwise would allow useful communications.

    Being Blunt= this has potential to Bugger many comms paths up beyond comprehension.. As it can suck up Handset>Cloud signals too. Of course, if degrading paths is by intent? New Term of- RFDdOS?

  10. @Pedro I thought the same thing when I read “unused”. Also cool about the visible light harvesting (radio waves are light too)I didn’t know people were doing that yet but as an amateur horticulturalist I wondered how long before someone would. Plants work by harvesting specific frequencies for different stages of photosynthesis.
    I highly recommend, to anyone interested, the book “Eating the sun: How Plants Power the Planet” Plants are green in order to use the different energy levels caught up in blue and red light.
    Leaves vs. Eyeballs (pdf warning):

  11. In my city, there is a powerful AM radio station operating at around 700KHz. A couple hundred meters away, there used to be an area of allotment gardens. Since there was no (offical) supply of electricity to the gardens, the tenants would use antennas and resonators to draw power from the RF generated by the radio station to provide some lighting to their garden sheds. I have never den such an indtallation, but I guess hat you can draw quite a lot of power id the RF fiel is strong enough, given that you can make a fluorescent lamp light up with a cellphone…

  12. Remembers doing this with shortwave bandwidth in school with ‘copper film’..

    Let me guess..specialized patented manufacturing specs owned by GT investor(s)? I’ll stick to the old cheaper/more-efficient ways..good luck getting richer off the ‘green market’ though..

  13. Imagine an IC tunable to a frequency that gives the most power.Imagine an IC with square meters of nano layers as antennas.Imagine that IC connected to a small sMD LED. Voila….free energy. BTW this was originally Tesla’s Idea. Wonder why big semiconducter companies like ST or TI not look into this. Using VLSI tools for IC design like Virtuoso or mentor graphics tools you can create a chip that runs on RF. Wish someone can pay for such designing such an IC.. any takers …? cause I have bunch of guys who have the skills.Wish somebody pays for the fab.

  14. @Pedro

    Yes, making antennas small enough to resonate at these frequencies is possible. I doubt this is possible with (light)lithography though since the structures in the antennas would obviously be smaller than the wavelength.
    It is be possible with (electron)lithography though.

    The main problem why “nantennas” aren’t feasible is that we cannot transmit these frequencies over any reasonable distance before it radiates off again and there is no known semiconductor which could operate at these frequencies to rectify them efficiently.

  15. Ah, this takes me back. I built a device like that using some wire, diodes and a capacitor. It worked but as some posters have commented this sort of system doesn’t get/recieve a whole lot of power.

    I wonder if anyones ever tried to use this sort of device in place of (or inside of) a RF shield, for those electronic circuits that generate alot of RF interference. Might be a good way to scavenge power for certain battery powered devices.

  16. @ notsureonthis
    Totally missing this shiny printed circuits…
    The article hints at silver nanoparticals. Google shows “silver nanoparticle ink preparation” is popular and might get to DIY status. Perhaps this can bring down the $100 per 5 ml pricetag? The good news is the 5ml vial is 20% silver by weight and could be thined to 1 to 5% for actual printing. The printer companies have already programmed us to pay $36 for ~10ml of ink in a cartridge so we are almost there. Note: I hate my Dell (Lexmark) 948 printer that constantly tells me I am out of ink, will not let me refill, and then shuts down a cartridge even when it is printing fine and disassembly shows there is still ink inside the cartridge. Welcome to Dell hell. Any solutions to this?

  17. A couple of people said this will only attenuate signals if it’s in the direct path between transmitter and receiver, as if it were casting a a shadow.

    Well, that’s not exactly true.

    The voltage produced by an antenna like this will typically be milli- or micro-volts. Which is too low to be usable, or even to efficiently rectify.

    So to boost that voltage, you’d use a resonant circuit, just like in a crystal radio. For more effective energy scavenging, you might even use more than one, tuned to different frequencies.

    And that’s where the problem starts. Those circuits will be resonating out-of-phase with the original, received signal. Some of that energy will be coupled back to the antenna and re-transmitted. Every receiver with a tuned circuit is inadvertently also a transmitter.

    Now what happens when you phase-shift a received radio signal and re-transmit it? Destructive interference. Yep, every one of these devices is a little radio jammer, that attenuates radio signals for a greater area than you might expect; not just in the direct line-of-sight between transmitter and receiver.

    The more energy one of these is able to gather, the more interference it produces.

    This also means that you can’t connect ten of these together in close proxy to gather ten times the power. Even if they’re arranged so they don’t “shadow” each other from line-of-sight of the transmitter, each is still well within the others’ radius of interference. Each additional scavenger close to another produces diminishing results. And so does the performance of any receiver for which the RF signal was intended!

    RF energy scavenging is very old tech. It’s improved relatively little over time, and I question whether these researchers have advanced it at all. You could make the same antennas out of laser-cut foil or etched PCBs; and although manufacturing them this way instead of from conductive ink might cost a little more, the end product would perform the same.

    The real advances are in circuits that require less power to run, making them able to be powered by a scheme like this.

    However, I would not want a large number of these devices around my home! It’s already enough of a challenge to get adequate reception of my WiFi, FM, ZigBee, X10 RF, and Bluetooth signals everywhere I need them.

  18. Here’s how I see it.. Integrate the antennas into roofing shingles. Not only would you get “some” power from it, it could also help reduce heat transferring into your attic.

  19. Anyone seen a PDF of the paper they presented? I’m pretty sure it is titled “A Battery-less, Wireless Mote for Scavenging Wireless Power at UHF (470-570 MHz) Frequencies”, but can’t find a copy…

  20. There have been legal rumblings about this sort of thing for years in the UK. Although every crystal radio does it the broadcasters have apparently threatened people living near enough to the transmitter to get some benefit from it against harvesting their signal.

    Of more concern disruption wise are things like model train sets and motor scooters which can kill my TV signal when they go past. Over the air TV in the UK is really patchy – I live in a major city and still get crap reception.

  21. I once assembled a large coil and a low ESR capacitor resonant at 60Hz, with germanium diode rectification. I got max 100mv out of it if it was left near the lab soldering irons. I hoped to get enough out of it to flash an LED once a minute or so, but no luck.

    I’ve had success printing etch-resist directly to flexible copper-clad kapton to make antennas for other purposes. Perhaps a useful method for others wanting to make small, lightweight antennas like these.

  22. @ everyone that says energy is being wasted by transmitters. Energy is not being wasted by TV and radio transmitters when they broadcast. That energy is being used to transmit information to an area not a single point.

    Any device that draws on this signal to power itself will reduce the area covered by that signal. Granted a single device won’t have much of an effect, however if these devices became common place it would.

    If TV and radio stations wanted to, they could sue. There are already a couple of legal cases that would back them

  23. Just remember, there is NO free lunch.

    This is fine if just a couple people are doing it, but really, if you have lots of people doing this, they’re taking power from somewhere.

    Just think “loosely coupled transformer.”

  24. I have heard that they are developing a stealth coating for high rises. The shadow they can’t do anything about but the reflection is a nusince. So they would rather have it absorbed.

  25. Seriously if this gets big it will be annoying and self-limiting. Imagine your signal constantly flickering in and out because people walk past your house with an energy-sapping device. I already waste 100% reliable money on 90% reliable content provision services; where does it end?

  26. So this is the ancient concept of coupling a wideband antenna to a rectifier to get “free” energy. The main novel concepts of this group appear to be (1) using printed antennas, and (2) fairly large bandwidth compared to previous systems.

    I am fairly dubious of the benefits of (1) since the economies of scale usually go towards large scale production of conventionally printed circuit boards with photolithography, which includes flexible circuits on substrates like polyimides. Printing is great for fast, precise, on-off prototyping but it’s not great for production since the nanoparticle ink is so expensive, not to mention it doesn’t have the same performance of the same materials plated on a board, and are they doing a post-plating process to ensure it won’t corrode after the paper is published? The article hints at them printing “carbon nanotubes” as well, but if that was a useful part of this work they would not just hint at it.

    Innovation (2) is good, as semiconductor technology marches forward the rectifiers can perform at higher and higher frequencies. It takes some effort to get a wideband match between the antenna and rectifier. Course I don’t know how much people are transmitting these days above 5GHz wifi, but there may be some power being transmitted between 5-15GHz that is worth harvesting.

  27. I’ve been wanting to do this sort of thing since like 1986. maybe not 1986 because i was born in 1986 but like 1988.. except i was thinking i’d have to transmit my power on a specific frequency and receive it.. or just find the frequency that the universe is already oscillating at or whatever, thinking there is already a frequency that the sun transmits its energy on, besides visible light. or gravity or something. of course, i’ve got far more important shit to think about nowadays, like finding a job in this shitty whateveryoucallit.. and getting an HDtv so i can have a non-CRT computer monitor and actually pick up what little channels my shitty location has to offer.

  28. @Matt

    In regards to (1), the ink is printed on paper for the specific reason of having an extremely cheap, flexible substrate. Earlier papers from the same group were in reference to RFID implementations which could use the cost reduction of the substrate to make cheap tracking tags for logistics. This is an extension of that research. Currently, the circuits are printed because they are exactly what they say — prototypes. It takes about a day to produce a usable prototype with this process, but this could be significantly reduced for mass quantities by screen printing the ink. Paper also has the advantage of already available processes for sealing the printed antenna. This is similar to a printed photo. There’s the question of how this coating would interact with the antenna, but this shouldn’t affect the antennas as currently made.

    The ink is currently a mix a silver nanoparticles as was previously stated. While it is expensive, there are a quite limited number of suppliers/buyers of the ink currently. Like many prototyping-friendly products, all it needs is a push in the cost-effective direction with a viable end-market.

    The carbon nanotubes is another possible extension of the research that hasn’t been explored as much.

    This technology is best suited for burst communications (as was previously mentioned in the comments) but can power a uController given the right conditions.

  29. @MattQ
    What “nasty things” do radio waves do to the human body? I’d like to see these studies about people living near radio stations that you mention, because it all sounds like the same old woo-woo bullshit from people that don’t understand basic science (e.g. the WiFi scare in the UK)

  30. @jeditalian
    if you do some research on Tesla you would find that he did a lot of work in this field. he actually lost a lot of funding and he could of been a vary rich man if he was not so obsessed with wireless power. he also worked with resonant energy. i think i remember some thing about him finding the frequency of a building and destroyed part of it. the Sun actually gives off a vast amount of radiation over a wide range offrequencies.

  31. This could be used to constantly trickle charge cellphones to give greater usage times by constantly topping them up with charge. so you would not have to plug in to a charger so often. One day most of the battery charge could be done this way and only plug into charger once a month.

  32. Does anybody have any listings of the typical outputs of common devices, in Wattage or Db? Averages would work. Though a hacked Linksys can have its transmission power upped and I have seen some that needed a cooling fan added, so that would certainly be outside of averages.

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