Transmitting power and data through thick metal enclosures

So let’s say you have a submarine, or a nuclear containment chamber which has walls made of thick metal. Now let’s say you want to transmit power or data through this wall. Obviously you’re not going to want to drill a hole since this wall is either keeping seawater out, or potential contamination in, but wireless signals aren’t going to travel well through dense metal. [Tristan Lawry’s] entry in the Lamelson-MIT Rensselaer Student Prize seeks to address this issue by using ultrasound waves to transmit data and power.

In the video after the break [Tristan] speaks briefly about his project, then demonstrates the transmission of power and digital audio simultaneously through a two-inch thick steel plate. This is accomplished with a set of piezo transducers attached to both the inside and outside of the plate. Communications originate by feeding electricity to one transducer, which sends ultrasonic vibrations through the material to be received by its counterpart on the other side. It’s easy for us to understand data transmission conducted in this manner, after all that’s how the knock block receives information. What we don’t understand is how it can “transfer large amounts of electrical power”. If you can explain it in layman’s terms please do so in the comments.

[Thanks Larry via The Register]

49 thoughts on “Transmitting power and data through thick metal enclosures

  1. Piezo transducers tend to have at least 90% efficiency (IIRC) for electrical to mechanical conversion. If you have matched transducers, and have proper acoustic impedance matching through the bridge material, you should be able to get a very good coupling. If this is tied to a highly efficient driving circuit, loss would be pretty minimal up until the receiving element. I don’t recall the efficiencies at this stage.

    This page gives some good information on electrical to mechanical conversion efficiencies:

    Here is a nice overview of acoustic impedance matching for piezo:

    Here is an interesting abstract on thermoacoustic power conversion using piezo transducers:

  2. It looks like it’s converting energy from electricity to physical vibration, to get through the metal barrier, and then the piezo on the other side converts vibration energy back to electricity. The vibration would also be in the form of digital data, so that it transmits not only power but data as well.

    I think the stiffness of the metal is what gives it such good efficiency. You’d probably get some noise in the signal if you used, say, a plastic barrier.

    I’d be concerned about the security of the data, though…would these vibrations be able to be picked up by listeners?

  3. I too am treading carefully on both side of 0104 and genuine article.

    data:yes, power: maybe not, if you look in the video he’s lighting a filament bulb…..110VAC at least.

    Noise is also a big issue but some filtering should sort that.

    I like the idea but it hasn’t done it any favors being published on April fools day. Or do we look fools for our lack of understanding?

  4. This is legitimate. Another group at my company has demonstrated a similar technique on a submarine. They were able to stream video and power a light bulb. Noise is not really that big of a deal becuase high frequencies (MHz) don’t travel very far in water. It acts as a low pass filter. The bigger problems are dealing with the curved hull rather than the flat piece of metal he is using and aligning the transducers on either side of the metal.

  5. There are piezoelectric transformers. They do exist and are fairly efficient. From what I remember they were typically very small scale, where a magnetic based transformer would be too bulky. Also they use very high frequencies. :)

  6. I don’t think (if not a fake) that the “submarine” application would be used in tactical situations… I’m thinking pier side power. However, the continuous application of ultasonics into the skin of a sub would have to proven not to affect the strength of the shell at depth. Sub sailors depend on the shell quite a little bit.

  7. 25W bulb… low bitrate MP3… if he’d investigated the characteristics of his channel (steel block) thoroughly and tuned his encoding scheme to match, I think it could be done. Nevertheless, after watching the video, Youtube suggested I watch “Model bitten by snake on her breast during photo session.” I found that to be very revolutionary, and likely not fake.

  8. What are the chances of a system like this creating constructive interference within the material and causing a catastrophic failure? Either due to normal operation or when in concert with turbines, other transmission stations,etc.

  9. @Leithoa
    Thats exactly what I was wondering. Wouldn’t all that vibration have some sort of adverse affect? The more power you pump into it the greater the amplitude and at some point I would expect the structure to begin tearing apart.

  10. @Steve and @Leithoa: Yeah, kind of like how all those cars trundling across bridges just makes them up and tear themselves apart, right?

    Here, let me introduce you two to a little friend of mine called “resonant frequency”…

  11. I honestly can’t see nhe point since there hasn’t been made any full closure usfull container yet , and there for it’s completely use less.
    @MoogolyGuy Do you know that if you crash in to an object hard enough the resonance frequency of any part of your body doesn’t mater any thing at all?
    @WorkingEngineer yes that’s true but since were not talking about a round object we will introduce frequencies, where the frequency on an object aligns with a pulse of an other resulting in a magnified pulse and if both frequencies are static a static frequency.

  12. I’d be concerned about the security of the data, though…would these vibrations be able to be picked up by listeners?

    Posted at 6:41 am on Apr 1st, 2011 by Josh

    Sorta like the shine-the-laser-on-the-window effect?

  13. FAKE, FAKE, FAKE, I can see the potential for data transmission using the ultrasound but no way is he getting 50 watts of power out of that. Not to mention it would be almost impossible to use that kind of power transmitting device in a hazardous location with the ludicrous restrictions UL/ETL/ATEX put on devices that operate in a hazardous location. Not to mention if he can get 50 watts out of the device how much is he putting in?

  14. This was in the news a couple weeks ago because MI6 has already been using this technique, probably for spying, and they asked the student not to show his findings, which he went ahead and did anyway.

  15. @ MooglyGuy Yes, I’ve heard of resonant frequency. I meant it as a serious question. What ARE the chances of it happening. I understand that it wouldn’t happen every time to every submarine/nuclear reactor/airplane, but all it takes is once to ruin someones day. And as I said above the Tx/Rx pair aren’t the only things vibrating on your sub, so would you have to redesign the turbines and props so that when the vibrations are combine they don’t create constructive interference?
    Tremendous amounts of money and time have been spent over the years on vibration damping technologies, so how much of these systems needs to be redone so that you can transmit signals through the material? Is it worth the initial investment to redesign everything or just double the strength and drill on through as usual.

    I’m not a structual/mechanical engineer and don’t pretend/claim to be so perhaps you could leave the sarcasm out next time.

  16. The ultrasonic waves should propagate as a halfsphere from the point of the emitter. So there should be an energy loss if the receiving device does not cover a lot of area compared to the thickness of the metall. Related to WiFi-Antennas only with sound. I therfore think that “large amount of power” should be compared to other wireless power transmission channels. If its efficency is near direct inductive coupling i would be very impressed but not supprised.

  17. @Leithoa
    The resonant frequencies of large objects are very low – a few Hertz. You just can not resonate a tonne of steel with kHz and the low harmonics decay exponentially and will not reach the low Hertz regime even if a standig wave (resonance) is exists. There should not be any problems at all from my point of view. Only the transducers could be damaged by a standing wave.

  18. The potential that I see for this would be in transmitting critical sensor data through reactor compartment bulkheads. Bulkhead penetrations are capable of handling a significant pressure but eliminating as many as possible would definitely be an improvement.

    Power — pierside or otherwise, I don’t see this as a real boon. A single shore line is allowed 400A and subs get 4-8 of these at typical facilities. Underway…well the reactor is already up why take more efficiency hits on transmission that you already are?

  19. I don’t know about the 50W power claim (disclaimer: I work at a piezo energy harvesting company; in this industry claims of more than 10s of mW from such a device raise eyebrows), but the data transmission part is definitely plausible. We actually designed something similar 8 or so years ago to get environmental logger data out of the sealed Tomahawk (missile) AUR casing. The acoustic modem prototypes “worked”, but transmitting consumed a lot of power (we did not see significant energy transfer through the structure in terms of powering the transmitter acoustically) and working around the acoustic resonances of structures themselves was a challenge. The structural modes can vary with temperature and even minor changes to the structural “environment” (boundary conditions), like stacking something on top of it or moving it from a concrete floor to grass, etc. For the missile environment monitor specifically, the POC for the project later informed us there was a 30-some conductor umbilicus exiting the canister with unused pins we were welcome to wire to, so that’s as far as the acoustic modem foray went ;-)

  20. It’s really interesting that you talked about how information can be sent by ultrasonic vibrations. I have been interested in learning more about data transmitting. I have heard of a few different ways, but I hadn’t thought about vibration. I can see how it would be helpful to have various means of transmission, in case one form works faster than others.

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