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Using EM waves to heat copper

  1. May 24, 2012 #1
    Is it possible (and practical) to use electromagnetic waves to heat copper (or other metals such as iron, steel or an aluminium alloy) over long distances (such as 1km)?
     
  2. jcsd
  3. May 24, 2012 #2

    davenn

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    possible maybe with a million Megawatt or so transmitter
    practical no.

    how hot did you want to heat it ?
    The transmitted energy in a radio signal falls off with the inverse sqr law
    so even for a 100W transmitter the power level at a few 100 metres is microWatts

    cheers
    Dave
     
  4. May 24, 2012 #3
    It wern't half hot when I got in my car this afternoon:cool:
     
  5. May 24, 2012 #4

    berkeman

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    Sure, it's easy.

    Just use your cell phone.... :smile:
     
  6. May 25, 2012 #5

    QuantumPion

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    The air force developed a 747 with a laser that would have been used to shoot down launching ballistic missiles by heating them until they failed. It had a range of something like 200 miles.The program was cancelled recently though due to the high cost and limited practicality.
     
  7. May 25, 2012 #6

    sophiecentaur

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    At a distance of 1km, I should have thought a good quality mirror with a big enough area (a bit over 1msq for every kW you want) could focus a reasonable amount of solar radiation to 'warm up', if not 'heat up' a copper target. the optics wouldn't be too demanding but you'd need good tracking.
    What would be the actual scenario?

    btw, the airborne laser was a chemical laser. Much more efficient than an electrical one and weight is very relevant.
     
  8. May 25, 2012 #7

    ZapperZ

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    The question is very vague and puzzling. I mean, leave a piece of metal out in the sun and voila! It gets hot! All thanks to electromagnetic waves. So what is the mystery here?

    Zz.
     
  9. May 25, 2012 #8
    Inductance heaters can take a block of metal and get it red hot within seconds. Build a giant inductor and maybe it will work!
     
  10. May 26, 2012 #9
    I am wondering if there is a certain frequency I can use that would heat up copper efficiently (similar to how water molecules react to microwaves with dielectric heating).
     
  11. May 26, 2012 #10

    Bobbywhy

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    ANarwhal, will you please reaffirm if your question includes the requirement of the heating be done over at distance of one km, as in your opening post?

    What experiment/process are you asking about? The more specific you are, the more accurately members may form a useful response. The more vague your description is, and the more speculation over your intentions, the less meaningful responses can be made.
    Thank you,
    Bobbywhy
     
  12. May 26, 2012 #11
    I can affirm that my question does include the initial requirement. I'd also like to add that I am open to using directional antennas in this hypothetical.
     
  13. May 26, 2012 #12

    Bobbywhy

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    Your proposed experiment is to heat some metal such as copper at one kilometer’s distance using microwaves.

    Radar is used to detect distant targets by transmitting microwave energy outwards, the target reflecting some of that energy back towards the radar set. Then it is received and detected. Materials such as metal are strongly radar reflective and tend to produce strong return signals. Even though the peak pulse power transmitted may be very high, the intensity falls off with the square of the distance. So you may expect microwatts (really tiny quantities of power) striking the target, and even smaller quantities being reflected back, and maybe, if you’re lucky, enough power to be detected in the receiver.

    Reflecting energy means incident energy is not absorbed. In order to absorb energy one needs to coat the metal with radar absorbent material. The SR-71 Blackbird and other planes were painted with a special "iron ball paint". This consisted of small metallic-coated balls. Radar energy is converted to heat rather than being reflected.

    With radar absorbent material (RAM), it can be used in the original construction, or as an addition to highly reflective surfaces. There are at least three types of RAM: resonant, non-resonant magnetic and non-resonant large volume. Because the non-resonant RAM dissipates incident radar energy over a larger surface area, it usually results in a trivial increase in surface temperature, thus reducing Radar Cross Section without an increase in infrared signature.

    Short answer, NO, you cannot expect to heat up chunks of copper metal at one kilometer’s distance using microwaves. No way.

    http://en.wikipedia.org/wiki/Radar_cross-section
     
  14. May 26, 2012 #13

    ZapperZ

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    This still doesn't explain much, and you have not addressed the simple, basic, and obvious example that I had given. What is the problem with that example?

    Many materials, including copper, have such a broadband absorption, unlike molecules which can have narrower absorption. So I am not sure what you are trying to get at here.

    Zz.
     
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