Wireless Power Question

Discussion in 'General Electronics Chat' started by cl10Greg, Jan 8, 2015.

  1. cl10Greg

    Thread Starter Active Member

    Jan 28, 2010
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    Hello Everyone,

    I know there has been a lot of talk recently about wireless power capability and there are numerous examples out there that work. My question is health related and design related. I was purposing a idea to my company for a wireless power design and my boss brought a potential issue. He recalled during his college days that a teacher emphasized the fact of how dangerous high power electric fields are. I know the premise of all the wireless power technology is based on the resonance of the magnetic portion of the EMF. Does his claim hold weight? How do you transfer the magnetic resonance while blocking the electric? How does the strength of the magnetic field relate to distance of the power able to transferred?

    Just a few questions I was pondering.
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    high power electric fields are dangerous, and there is also a danger with high power rf fields. the "Wireless" energy transmission of today has nothing to do with resonance or rf, its just a coil in a pad you set your cell phone on to induce some charging current. not high power at all. and no danger unless you set in it.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    From cell phones to cars, the wireless power systems I'm seeing today are basically air-core transformers. Without a ferromagnetic core to couple flux between the windings, air-core transformers are very inefficient compared to the iron and ferrite critters we are used to. Running such a transformer at its resonant frequency improves overall efficiency in much the same way as IF transformers in a radio, but the principle is the same. And just like the radio transformers, air-core power transformers can be shielded.

    Back in the 60's there was an item on the evening news about beamed power. The demonstration was an RF-powered "helicopter." Microwave dish on the ground pointed up. Above it was a small box with microwave dish pointed down and a rotor blade on a shaft coming out the top of the box. The box was held in alignment above the ground dish by two vertical guy wires. As the beam power went up and down, the box rode up and down on the guy wires. It all worked, but way inefficient.

    ak
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Way back in the 70s, I did some work in coupled energy transport through the skin for implanted artificial organs. For an implanted artificial heart, it takes ~25W continuously to move the blood through the circulatory system. We did lots of experiments with coupled RF coils with tissue (sheep and calves) between the coils (one implanted, the other on the skin). The most serious side effect was due to heat from the I^2R losses in the coils, not from the RF...
     
    Last edited: Jan 8, 2015
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there was also a demonstration of power "beamed " from solar satelite, a 100 ft dish with a 50 kw microwave transmitter pointed at an other antenna 1.5 km away. they got 1.5 kw and claimed 74 % efficency. kinda fudged the numbers a bit. more like .3 & with path loss included.and I dont know of any satelites only 1.5 km away.
     
  6. #12

    Expert

    Nov 30, 2010
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    Make one and attach it to the cage of a mouse. If the mouse drops dead, you have a problem. :rolleyes:
     
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  7. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I'd probably use a cockroach instead... I have a soft spot for mice... (not rats, though)...
     
  8. ramancini8

    Member

    Jul 18, 2012
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    I worked on RADAR, and I have seen the energy from a high power pulse RADAR (APS20) light gas soaked rags at about 60 feet. Also, I see what a microwave does to meat and I stay away from RF energy.
     
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  9. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Not all RF is bad.... check this thread that I posted earlier
     
  10. ramancini8

    Member

    Jul 18, 2012
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    I know that all RF is not bad, but since I don't know the good guys from the bad guys, and I don't have a driving incentive to use RF I just stay away. P.S. I don't use a cell much because I don't know how dangerous the RF in a cell phone is, and the published literature is primarily cell phone manufacturer supported. Even if it costs me a pico bit of brain power I can't afford to squander it.
     
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  11. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I think there's some truth in what you say about cell phones... though I also think that people that worry about high voltage power lines close to their homes are a bit paranoid... truth being told, I wouldn't buy a house near them, not because I consider them dangerous, but because they're simply too ugly.
     
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