How Do You Design a Coil with a Specific Inductance?

[Hussman]

Hi all, I'm studying computer aided design at university but i have to complete an electronics module. My knowledge is extremely basic and my lecturer 'does not have the time to go through basic physics' so i need a little help.

I have been asked to...

'Design a coil which has a given inductance value of 1 mH. The coil is to be
wound on a non-magnetic former of 5mm diameter, 20 mm long. The diameter
of the winding should not exceed 7 mm.

Specify the number of turns, wire diameter, number of layers needed and
calculate the resistance of the winding.'


I haven’t attempted this question yet as i have no idea where to start. Any help would be massively appreciated

Many thanks

 

[gomboc]

There is a simple equation that describes the inductance of a solenoid - basically any coil with many turns of wire on it. This is it:

$$L = \frac{\mu_0 n^2 A}{l}$$

where $$\mu_0$$ is the magnetic permeability of free space, n is the number of turns of the wire, A is the area of one of the wire loops, and l is the length of the coil, measured from the first turn to the last.

Just make sure everything is entered in SI units (meters, amps, etc.) and you should be fine. Take note that the wire diameter is not part of this equation. The only reason it will matter for you is you know that given the inner and maximum outer dimensions of the coil, the wire will need to be a certain thickness to get the needed number of turns to fit into the space you have.