# Can a solenoid have its magnetic field "focused"?

Imagine a solenoid generating a magnetic field. Can this field be focused so that it exists only in a certain section of that solenoid at a given time. If a typical solenoid looked like:

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... and then had current applied and generated a field around it:

~~~~~~~~~~~~~~
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I would like to adjust, say, a dial all the way to left to generate a field like:

~~
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... and then dial it to the right:

            ~~
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... or anywhere in between:

     ~~
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Is this possible with a single solenoid, or would I have to use a number of different solenoids each given current independently?

• You could place taps along the coil and then choose where to put the current in and out. Of course the field won't look like you've drawn, for a thin coil it will look more like the field from a dipole. Aug 1 '14 at 18:22

In short NO.

A solenoid would produce a field similar to what you show in the second "picture". The only difference you could make would be to increase or decrease the amplitude of that field (or make it negative). Although this field is for the most part inside the solenoid (not the outside).

The simplest way to do something similar to what you're after would be to split the coil into two. Then alter their amplitudes so that you get maximums or null fields where ever you want with relation to the center of both of those coils by simply changing the magnitude and direction of either coil. Using 2 PWMs with simple filters and 2 solenoids you could accomplish pretty much what you're after.

It would look something more like this:

////////////   ////////////////
<       ~~~       >
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Where the field can be "moved" anywhere between the two greater/less than signs.

• Magnetic field phased array _b Aug 2 '14 at 1:30