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Driving Helmholtz Coils - Best Practice

The following questions are with regard to driving two coils arranged in a Helmholtz configuration.

By convention, is a bipolar or unipolar signal applied? It would appear the former would have the effect of doubling the emitted frequency due to AC field reversal.

Are the signals most commonly applied in phase of out of phase? In terms of field topology, what are the desirable effects of each method?

What is the difference in effect between having the coils magnetically aligned (N facing S), and having them oppose (N facing N)?

Thanks for any insights along these lines.

Robert Miller

Reply to
Robert Miller
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Whichever you like, depending on whether you want to change the field direction or not. No it doesn't double the frequency- the field changes direction. If you only measure amplitude you will get double the frequency in the same way that looking at CFL flicker will get you double the mains frequency. The magnetic field is a 3D vector field.

Out of phase with *what*?

They are oriented so that the fields are in the same direction (use the right-hand rule). Direcion of winding and current direction determine the field direction.

The purpose is to get a fairly uniform field in a volume between the two coils.

BTW, ISTR that Helmholtz didn't quite get the optimum for many applications you might find that a slightly different proportion is better.

--sp

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Best regards,  
Spehro Pefhany
Reply to
Spehro Pefhany

The signal to each coil anti-phase toi the other.

Robert Miller

Reply to
Robert Miller

The signal to each coil anti-phase with the other.

If bipolar, cancellation. If unipolar, a motional field.

Robert Miller

Reply to
Robert Miller

With current in "the same direction" you get a fairly uniform B-field between the coils. With currents driven in "opposite directions" you get a fairly uniform field gradient (dB/dz) between the coils.

A field gradient puts a force on a magnetic dipole. a uniform field puts a torque on a dipole.

George H.

Reply to
George Herold

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