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Inductive coupling and EM Power Chargers

  1. Feb 13, 2013 #1
    Recently saw the invention on PhysOrg for a device the recharges a AA battery using "waste" EM radiation from the ambient environment. In the photos, the author was placing an array of them near a power sub-station.

    This brings up two questions:

    1) Does this create an inductive load on the source? Why, or why not?

    2) Would this phenomena affect sources over long distances if there are millions of recharging units? (The article suggests using these in homes and offices to tap into waste EM radiation.)

    Thanks in advance for any answers.
  2. jcsd
  3. Feb 13, 2013 #2


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    If the system takes a commercially significant amount of power then it's sure to be a legal issue wherever you live. However, Detecting and Using are two different things. Cell phone charging is somewhere in the middle of the two.
    As with all of the 'harvesting' ideas one reads about, it is necessary to consider the power levels involved and the situations where such systems could work. Not many people live next to an electricity substation, for instance. There are many stories of farmers who have heated their greenhouses using power from nearby transmission lines or railway overhead lines and been taken to court for it (mostly folk tales, I'd bet).
    You have to consider the cost of the energy that a cell phone will use over its life and the cost of one of these installations. You can bet they would be as expensive as manufacturers can dare to charge. So would it be worth bothering with?
    As to the question of actual 'drain' from the power source, if you are 'matching' a system to extract as much power as possible then it will take more power than any old random arrangement of steel framed buildings and cables. I doubt whether the few tens of mW (max) is relevant to the supply company but if every building near every substation was 'harvesting' even a couple of Watts then perhaps the price of electricity might go up to compensate - at the expense of the rest of us.
    I would say that improved efficiency for all devices is the way forward, rather than these 'fun' ideas. You may like to search these threads for stuff on Harvesting Acoustic Noise; pretty misguided in most instances.
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