The applied signals are equal and opposite (assuming the turns are close together relative to the distance the field is measured at), so the sum is zero.
I think a DC offset would provide a fixed field the alternating field would be superimposed on.
In this case the magnetic fields will only add. This can not give a new frequency. You may be thinking of multiplying the fields. For example, if you had an alternator where the rotor was turning at frequency X and you varied the field coil at frequency Y you would end up with frequency X+Y in your output.
You have it backwards, I think. He's driving the OUTSIDE of one coil with the + signal, and the INSIDE of the other coil with the - signal, so the currents in the two coils will be (more or less) the same.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I believe that Tim is mistaken. Well, in this case I _know_ that _some_ Tim is mistaken, because I believe that Tim Williams is mistaken. In fact, I can be certain that some Tim _W._ is mistaken. See my other post, but I believe the effects will add, not subtract.
In that case then you want to drive both the inside and the outside with the same signal.
Your language is confused. If we forget, for the moment, the wacky coil arrangement and just consider a single flat coil (i.e., twist the wires together in the center, and drive your zip wire with your +signal and your
-signal), then the polarity of the field will, indeed, reverse at 200Hz -- this is just a really confusing and indirect consequence of feeding 100Hz AC to the coil.
The much more direct and easy to understand consequence is that you'll have a magnetic field that follows a 100Hz sine wave (assuming you're shoving a sine wave into the thing).
That's hard to tell...
If one or both of your signals are DC offset, then the magnetic field will have a DC component to it.
Clearly you're trying to do _something_. Perhaps if you pull back a bit from the bark and tell us about the tree you're pursuing, if not the whole forest.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Excuse me if I posted this before. I was having trouble with my news server. It did not appear in my news reader or Google groups, so I am trying again.
Behavior of Spiral Coils
I would like to wind a flat spiral coil out of thin zip wire. This will give me two separate windings side-by-side.
One signal, any audio frequency, will be fed into one winding at its outer end. The other signal will be fed from the center of the second winding. The remaining ends are grounded via a common load resistor.
The signals are the identical, except that one is 180 degrees phase shifted (anti-phase). According to my understanding, this will produce a magnetic field that reverses polarity at twice the frequency of the applied signal.
I am then wondering what change would happen between the windings if one of the two signals was given a DC offset.
Can anyone please comment on this, or otherwise advise on the arrangement described above?
in air, magnetic fields are linear, which means superposition applies. Which means you can solve the problem for one source, then solve the problem for another source, then ADD the two together. Your description discombobulated my brain [doesn't take much] but remember you will NOT get any new frequency fromanything you do like you described. And fields are a vector addition.
If you want a 'circularly' polarized field, take two equal coils and mount them concentrically in quadrature, Envision a world globe with a Greenwich meridian coil and an equator coil. Now drive each coil not in 180 phase but 0 phase and 90 phase THEN you will get a circularly polarized magnetic field extending out from your coil systeem. It will act EXACTLY like hanging a permanent magnet and spinning it at the frequency of choice.
Given the bifilar winding, my thinking was that while the current in the CW winding is increasing, the current in the CCW winding (driven by the antiphase signal) would decrease. That would mean one polarity would dominate.
When the situation is reversed, the other polarity would dominate.
Both signals swing positive relative to ground BTW.
This seems logical to me. Maybe I didn't explain it well enough.
I am not sure what you mean by + and - signal. Both have the same swing, one is just inverted.
In the configuration I described above, it would seem that the added DC offset would result in current opposition that would inhibit the emitted field.
This is really just an experiment to help me understand spiral coils. You can do those sort of strange things once you retire.
Having read some of the other responses I am left wondering if you were looking at a Magnetic Amplifier or even a Magnetic Modulator . It would be clearer if you were to identify your aims.
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You need to learn more about physics and electromagnetics.
1) a flat spiral coil out of thin zip wire is going to be troublesome to implement if the wire pair plane is flat on the winding plane: -- oo --- oo ----- (looking into the wiring plane and seeing 2 turns). The reason is that the inner-most wire of the pair is gong to be compressed, and the outermost wire is going to be stretched. Simple physics.
2) Your understanding concerning the magnetic field is totally incorrect. Visualize the magnetic field of just one winding all by itself. Then do so for just the other winding. Use the simple physics and electromagnetic principle of superposition OR just add them at every place. Note they more-or-less cancel. AC, DC, one on the other, whatever. Same principle. Go back to the textbooks.
Why don't you simulate this in any program such as LTspice? I think you have some fundamental misconceptions.
and add them. See what the sum produces.
I'll point out the simple statement that addition of sine waves of the same frequency always produce another simple sine wave of the same frequency with the amplitude possibly being zero. Look up linearity. There should be nothing non-linear about your coils.
The situation you describe here is phase quadrature. sin(wt) & cos(wt). They don't cancel and you get a field of sqrt(2)sin(wt+pi/4)
*Antiphase* means exactly that the voltages are Vsin(wt) and -Vsin(wt)
The fields would then almost exactly cancel out or double depending on how the two coils were wired together.
You can work out the resulting linear super position of two (or more) magnetic fields of the same frequency (or different frequencies for that matter) from the mathematical identity:
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