-- Actually, he hasn't, since he only presented half of the solution. What would be required, in addition to the coil, would be a capacitor with a reactance equal and opposite to the reactance of the coil at 60Hz in order to make the system resonant and generate the EM field via the radiation resistance of the circuit.
The best way is to stick your fingers in an outlet socket. Your body makes a great aerial at 60Hz. We do it all the time in the UK, but it's not as efficient as we are on 50Hz...
True, but supposedly it's easier to let go when you need to mind the chickens or somesuch at 50Hz than 60Hz...
In Kaiser's "Electromagnetic Compatibility Handbook," he does include the human body in an (otherwise?) completely serious table of antennas and their various properties!
(You guys might not have access to this book, as being upwards of 4" thick and heavy enough to double as a hammer it's probably classified as a weapon over there... :-) )
A coil doesn't have to be resonated to radiate EM waves. Resonating it just reduces the load on the AC power supply.
But "high intensity" is another matter. Hard to do with a reasonable-sized coil, at 60 Hz.
John
-- Not true. For a given power output, if the circuit is parallel resonant, then the power supply has to supply the voltage and current required to drive the tank's resistance. If it's series resonant, the power supply still has to supply the voltage and current required to drive the tank's resistance.
gh
If all the circuit parameters are known, what equation is used to calculate the RF power emitted? TIA.
I believe that is true, John. The field is radiated by passing current through the *radiation resistance*. It doesn't care how the current comes to be, whether it is due to circulating current or from a source which can supply the current without resonance.
Yes, the tank's resistance plus radiation resistance.
Yes, the tank's resistance plus radiation resistance.
Well, check the radiation resistance vs the system's resistance. In the case of a 60 Hz loop of "reasonable dimensions", you will probably find the radiation resistance to be in the micro-ohms or less. This will give nano-percent efficiency.
By the way, I am assuming we are discussing transverse electromagnetic radiation.
Who said anything about "reasonable?" ;-)
Cheers! Rich
John Larkin schrieb:
Hello,
a coil would radiate a (strong) magnetic field with 60 Hz, but a very weak electric field. For an efective radiation of EM waves, you would need the electric and magnetic fields together, with balanced strength. Otherwise the EM waves could not work over larger distances.
Bye
thought experiment..
take a small coil with a large current that radiates as you say a strong magnetic field but a weak electric field.
right next to it, put a small probe with a high voltage that radiates a strong electric field but a weak magnetic field.
Phased correctly these two should be an efficient EM radiator....
But they are not...
Mark
On a side note...
A single pulse into a coil inside an armor case will shrink coins just fine!
The coil evaporates, but the coin shrinks from the magnetic force.
http://205.243.100.155/frames/shrinkergallery.html
Loop antennas work fine. They just get a tad large at 60 Hz.
Joh
Excellent is there any prize money involved?
George H.
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Oh I could spray plenty of 60 Hz around without a capacitor. But sure add cap. Series resonance? Do you want a share of my prize money?
George H.
gh
The 60 Hz AC magnetic fields have gotten so bad at the place I work, that I now have to schlep the optical pumping apparatus back to my home to test it. (~0.5 milli Gauss line widths at ~10 Gauss fields.) The AC fields are ~1-2 mG in strength. I thought about trying dectect and cancel them over a small area.. but gave it up.
George H.
How about a BIG COIL plugged in to the transmission line from Hoover Dam :-)
Bill K7NOM
Go look at the quarter shrinking site.
My office opens onto a weld shop. When the weldor[1] guy strikes a
300 amp arc, my monitor screen distorts.Cheers! Rich [1] weldor: a guy who uses a welder. welder: the machine the weldor uses.
Take a 220 volt pigtail, and hook it up to a 60 Hz resonant antenna. If necessary, use a matching network. That should do it.
- Stan :-)
A permanent magnet is analogous to a superconducting coil. But how to build a 60Hz AC permanent magnet? Simple.
Two permanent magnet rods held side by side, with alike poles adjacent, will create an extensive magnetic field in the surrounding volume. But the same two PM rods, if held side by side with unlike poles adjacent, will create no extensive magnetic field, since the adjacent opposite poles cancel out (and the field strength at a distance is ~0)
So, in order to create a "60Hz permanent magnet," spin two PM magnets so they flip end over end. Let them spin in opposite directions. Use maglev to suspend them. Spin them in a vacuum chamber. Friction will be very low, so you can keep them going at 3600RPM by using a small 'kicker' coil. Better use ceramic magnets to avoid inductive braking. Perhaps use magnetized ferrite spheres rather than rods.
Next, create a quarter-wave radiator. Build more of the levitated- bar-magnet devices. And more. Build a vast array which covers thousands of square miles of landscape. If the phases of the flipping ceramic magnets are adjusted, you can have strong N/S poles appearing and vanishing at 60Hz along the border of the array. Or let those poles rotate around the array if you prefer (and radiate circ polarized 60Hz RF.) The output will rival that of a gigantic superconducting loop antenna.
And once the array grows large enough, radiation resistance will start slowing the magnets. You'll have to add more microwatts to each kicker coil.
With even a small version of this device, probably we could use it as the stator of an induction motor, with a large number of spinning squirrel-cage rotors nearby, each running a bit below 3600RPM.
Such a rotor would benefit from having long "antennas" to couple the rotor to the ambient 60Hz b-field, "antennas" in the form of long rods composed of laminated iron sheets, or perhaps clusters of iron cable.
Antennas for picking up Mag-tricity waves!
((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty, chem washington edu UW Chem Dept, Bagley Hall RM74 billb, eskimocom Box 351700, Seattle, WA 98195-1700 ph 206-543-6195
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