Creating a "Moving" EM Field Between Two Coils

it's unclear what you are trying to do. What are the requirements of the volume outside this "zone" ?

--
This email has not been checked by half-arsed antivirus software

Your are talking about exciting a side-by side pair of air coils at 100Hz, with a controlled phase difference.

If the two coils are excited in the same phase the will add, and there will be a maximum 100Hz field half way between them. If they are excited 180 de grees out of phase, the field half way between them will be zero.

There are multi-output direct digital synthesis chips that will generate si ne waves with programmable phase differences

l

The AD9958 has two outputs, and might do the job. It's much faster than you need, but it's all there in one package.

Synchronous motors depend on a moving magnetic field in the way that you se em to be talking about. You might look at motor driver chips - they must ex ist to drive two and three phase synchronous motors, not that I've had occa sion to look a them in recent years.

Stepper motors are synchronous motors.

"Microstepping" involves changing the magnetic field in small steps to drag the rotor around smoothly.

--
Bill Sloman, Sydney

Of course you cannot have phase changes when both coils are driven at the same frequency! You will need to drive one at 100Hz and the other at 101Hz to achieve this.

Not enough coils for the field to move. In fact, if what you want is some spot in space that has a field surrounded by a space with little or no field, you're either SOL or you need a whole bunch of coils -- I'm pretty sure you're SOL.

You can have an area in space that has a field that reverses itself. If you put the coils at right angles then you can have a field that both rotates and that moves it's maximum around, but the maximum position and the angle will be tied together. You could have one maximum that moves, but it'd be a broad one.

--
www.wescottdesign.com

To clarify, I would like to have the position of the maximum additive field move at a regular rate back and forth between the faces of the two coils arranged axially and spaced apart.

Ths requires not simply a difference in phase between the signal to each coil, but that this changes from 0 to 180 degrees at a predetermined uniform rate.

Kevin Foster

This is interesting. What would happen between four coils arranged in a square? How would the field in the center rotate in relation to the current flow.

Could I enhance this effect by suspending permanent disk magnets above and below the center of the coils?

Kevin Foster

in

h d d

Hz, with a controlled phase difference.

will be a maximum 100Hz field half way between them. If they are excited 18

0 degrees out of phase, the field half way between them will be zero.

e sine waves with programmable phase differences

.html

you need, but it's all there in one package.

u seem to be talking about. You might look at motor driver chips - they mus t exist to drive two and three phase synchronous motors, not that I've had occasion to look a them in recent years.

drag the rotor around smoothly.

Sorta DC fields? Or RF? For a single coil the field is maximum in the center. With a whole series of coils you could move the field maximum back and forth by switching them on and off.

George H.

Search on how an inductive motor works -- you should get pictures of coils and rotating magnetic fields.

Maybe you should rig something up and experiment?

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com 

I'm looking for work -- see my website!

I think this fellow is asking for the impossible. He wants to add two 100 Hz EM fields and time delay one of them to have the position of the peak slide back and forth between the two coils. One wavelength at 100 Hz is

3000 km, so unless he wants to space his coils at least a few hundred km apart, it's just not gonna work. If his coils are say 3m apart, then the phase difference between the fields of the two coils changes by 720 x 10^-6 degrees at as you move from one coil to the next. Ain't gonna work.

180 degrees, 100 Hz, speed of light, 1500 kilometers

Is your lab hig enough?

--
This email has not been checked by half-arsed antivirus software

Although it may not have been clear in my OP, I am just looking for a way to achieve a concentrated magnetic field the position of which moves gradually back and forth a few times per second in the empty space between the ends of two solenoids.

The position of the concentrated (additive) field at any given moment would depend upon the relative field intensities of the two coils.

This is what I am seeking to control, not by switching but in a way that provides a gradual and uniform transition.

Phasing was a solution that came to mind. Another possibility might be two digital posts fed with inverted signals. The coils would then be energised with DC.

Kevin Foster

At DC or low frequency, can't be done. The addition-subtraction fills spac e, and isn't localized in the way you want. You could do it using an iron rod (where the maximum attraction moves from one coil to another.) Stick a steel ball to the rod, and force it to roll back and forth between the co ils. But it doesn't work in empty space.

For DC or low freq, the maximum fields are located at the coils. If you w ant to create a "hotspot" in space, then you'll need to use RF up in the UH F or GHz.

What's the spacing between your coils? If it's 6in, then you'll need freq uencies higher than roughly 6GHz microwave. The short wavelengths can add and subtract to produce small maxima and minima.

On the other hand, it's not impossible to do this with loudspeakers and sou nd pressure. 10KHz sound can create inch-wide patterns. The speed of sou nd is roughly a million times slower than the speed of light, so 10KHz soun d waves give similar results to 10GHz radio waves.

I agree. A difference of 1 Hz between the two frequencies will create a standing wave of 1 Hz. Thus a phase reversal once per second.

Oh, also, if we could create such a field-maximum hanging in space, away from the coils ...that means we could levitate iron objects, or even clouds of iron powder. No feedback circuit required.

We could make a tiny screw float between the coils, much like styrofoam beads can float between two 30KHz loud-speakers as seen below.

Smarter every day

Kickstarter, hobbyist uSound lev

Yet another trick: if the coils are opposing, so their alike- poles are facing each other, then we've created a small "magnetic null" which hangs half-way between the coils. This zero-field spot can be seen by using a sheet of that green magnet-pole viewing film. Or, use my iron-filings bottle of mineral oil, edu. demo.

(((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))) William J. Beaty

beaty, chem washington edu Research Engineer billb, amasci com UW Chem Dept, Bagley Hall RM74 x3-6195 Box 351700, Seattle, WA 98195-1700

how big. how far apart.

how large can the aparatus be?

field intensity tends to peak at the surface of the solenoid

getting it to be stronger elsewhere seems very tricky.

--
This email has not been checked by half-arsed antivirus software

How about splitting the DC drive to a Helmholtz coil pair so that they have independent current supplies and then adding your few-Hz sine wave of lesser current to the DC for each coil, but of opposite polarity for each?

Getting what you want with cavity resonators is easy, but 100 Hz, much less a few Hz is out of the question for feasible cavity dimensions.

You could try mechanically moving your coils around while your test sample/instruments remain fixed. Attach the coil base to another board with some drawer sliders and

Mark L. Fergerson

Thank is a great idea. Thanks.

Keven Foster

Thank is a great idea. Thanks. ============================================================

Go to

and download it. It can do a lot but they have some examples that should let you get started with coils pretty quickly. Play with some solenoidal geometries and you will get a feel for field strengths and shapes, and overlap of fields from adjacent solenoids. If you need side access leave a gap between the coils, if axial access is enough butt them together for higher fields. If you need a gap, wind them on iron cores to get more field.

----- Regards, Carl Ijames

Oops. Should continue:

run a link from a variable speed geared down e. g. sewing machine motor attached to the board- the coil mount moves back and forth sinusoidally like a starter motor cranking a piston engine.

Mark L. Fergerson