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Diffuse microwave/far infrared heating as a replacement for space heaters?

  1. Sep 29, 2010 #1
    I know there are some obstacles to overcome, but I'm wondering how good the idea would be in theory. First though, a few sub-questions before the main one:

    1: The radiation in a microwave food cooker is like a laser (hence the 'hotspots' in food). Is it possible for microwaves to more diffusely spread their radiation through say, an array of mini-emitters, or by the use of a lens or even by simply using multiple reflections before the laser hits the food? This would then prevent hotspots and a spinny plate thing. If so, then why don't microwave ovens use this technique?

    2: Is it also possible to make the aforementioned microwave laser silent, or is there something inherent to the technology that forces it to sound like a jet engine?

    Main question now: Ignoring the loss of radiation (which metal walls can solve using reflection), how sensible is it to use *perfectly diffuse* microwave radiation as a replacement to space heaters for use in the living room?

    Wikipedia speaks of the relatively limited health effects of general microwave radiation (more 'heating/burn' territory being non-ionizing, but there have been reports of 'clicking/buzzing in the ear' and even cataracts (stronger/focused radiation in that case?) ); however "microwave" covers a broad range of frequencies from 300 Mhz to 300 Ghz, and not just the frequency used for microwave cooking (2.45 Ghz, or down to 915 Mhz used for large industrial microwaves). If there were any concerns, one could increase the Ghz to something approaching infrared to reduce penetration maybe.

    I just think it would be neat to have a 'holistic' warming rather than the relatively surface-style warming of near infrared/convection that ordinary heaters provide. Apparently, suanas use far infrared radiation (3000-15000 GHz) which presumably penetrates further into the body than near infrared radiation (15000-430,000 GHz), though I'm not sure if it penetrates through the body completely.
    Last edited: Sep 30, 2010
  2. jcsd
  3. Sep 30, 2010 #2


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    1: The radiation in a microwave is not like a laser (and it'd be a maser in that case). It does, however, form standing waves which is why the heat is not evenly distributed in the microwave. Microwaves do use waveguides, and the radiation does reflect off the walls.

    2: You need to keep the magnetron cool, or it'll break. So there's a big fan in there.
    In my opinion, entirely nonsensical. To begin with, you wouldn't be able to have any electronics or metal objects in the room. Second - what is the problem you're trying to solve? Electrical heaters have essentially 100% efficiency, microwave ovens are pretty far from that. The benefits of microwave heating for food (thorough cooking at speed) aren't relevant to that application.
  4. Sep 30, 2010 #3
    Thanks, that's all interesting.

    Are you sure about that? For a given space, the energy will be much lower than the space inside the microwave oven, so I'm not sure that electrics/metals will be affected much. We don't want to cook us, only heat us up.

    The surplus heat generated will be similar to a standard convection heater in that case, so it isn't 'wasted', but otherwise, interesting point.

    As I said in my first post, I think the heat generated will penetrate right through the body, rather than heating (on or near) the skin, which then has to heat the body indirectly. Basically, it's quicker and generally an interesting concept I think.

    Finally, is there any solid-state way to avoid the standing wave phenomenon? When I spoke about rebounding off the walls, I realise it did that, but I was thinking of say 100x plus more reflections than what is currently used before it hits the food. I'm not sure if that would help though.

    I take it that it's tricky or much more expensive to create a fanless magnetron, because I bet they'd be popular.
    Last edited: Sep 30, 2010
  5. Sep 30, 2010 #4
    The room/house heater does not heat your body. They heat up the environment so that the heat loss from your body becomes comfortably small.
    If your body temperature, (and especially the internal temperature), changes you are either sick or dead.
    When you feel cold is because you loose a lot of heat and not because your internal temperature decreases significantly. At the most, the superficial (skin) temperature may decrease.
    So the whole idea of heating the inside of the body does not make too much sense.
  6. Oct 9, 2010 #5
    Sometimes I feel cold inside, even though I'm hot on the outside, but point taken. From what I recall, there's only a couple degrees of tolerance before we would die. I may be mistaken there though, or at least off by a bit.

    To add to the thread, this was interesting. It recalls the experience of people who have had a close encounter with a 500 watt radio transmitter:
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