# printed inductors

Discussion in 'Electronic Basics' started by Tom Del Rosso, May 14, 2013.

1. ### Tom Del RossoGuest

When an inductor is printed on a PCB in the shape of a 'square wave' or
square zigzag, each time it zags the trace doubles back on itself. Doesn't
this cancel the magnetic field to an extent? How much does the coil
structure matter to a coiled inductor, or would the straight wire have the
same inductance?

2. ### brentGuest

perhaps it is a high frequency inductor which is more like a
distributed transmission line inductor?

3. ### Phil AllisonGuest

"Tim Wescott"

** Tim has no idea just how stupid he is.

..... Phil

4. ### George HeroldGuest

We make spiral coils on PCB to 'shim' magnetic fields.
I'm not sure what you mean by zig-zagging back... maybe a picture?

Re: a coil versus a length of wire. You get more inductance from the
coil. I think if you have a fixed length of wire and wanted to make
the largest inductance then you'd wind it as one big single turn
coil. (hopefully someone will correct me if that is wrong.)

George H.

5. ### BaronGuest

George Herold Inscribed thus:
I suspect the OP is refering to the meander lines on a pcb used to match
signal timing over varying trace lengths.

6. ### Tom Del RossoGuest

I should have said that this definitely is an inductor. It's a choke
connected to the power trace on a 4GHz board.

7. ### George HeroldGuest

Yeah just DC coils.
OK thanks... (of course I have to go and check it now... grumble)

George H.

8. ### George HeroldGuest

Hard to tune... I bet. This has just 4 coils, one each for the X, Y
and Z gradient and then a Z^2 gradient. (Z is the diectron of the
static field.)
OK I'll have to check... gotta run

George H

9. ### Spehro PefhanyGuest

Optimal coil length is a bit less than the coil radius.

A Brooks coil is pretty close to optimal.

11. ### Tom Del RossoGuest

You mean for a given length of wire? Doesn't seem useful, since you can use
a different length.

12. ### petrus bitbyterGuest

Sure. But if you need to produce some 100,000 coils, wirelength may become
an important parameter.

petrus bitbyter

13. ### George HeroldGuest

What about a toroid? (I always want to put to r's in torroid)
Or do you get more B field by spraying it everywhere?

George H.
(I love SED, say something stupid and learn something new, thanks)

14. ### Tim WilliamsGuest

You get more B by focusing it into a smaller space, but that doesn't
usually give you more inductance -- it takes a lot of work to make B,
because B is energy density (in fact, e ~ B^2).

Dunno about the length required for an air-core toroid. Should be easy to
find from the thin, infinite-turns toroid formulas though.

Tim

15. ### George HeroldGuest

Yeah, I get to integrate the B field over all space so letting it
spread out is a win. (In other ways toroids seem like a nice inductor
shape.)

George H.

16. ### Phil AllisonGuest

"Spehro Pefhany"
** You have just linked a page from a Kiwi radio ham ??

WTF ??

The wanker does NOT even mention that his question is restricted to single
layer coils.

With any number of layers permitted, the solution is more like a sphere with
a hollow centre.

Coils made for loudspeaker crossovers were sometimes wound like a ball of
wool in a "beehive" shape for maximum utilisation of the wire used.

..... Phil

17. ### Robert BaerGuest

The only geometries i saw were spiral in nature on one side (shaped
either circular or square); inner end of spiral to via withstraight exit
to outside of area.

18. ### josephkkGuest

That is not an inductor, that is a delay line (transmission line type).

?-)

19. ### josephkkGuest

At 4GHz it is not so clear. If you really want to know the tools are
expensive (in part to really encourage you to buy platform enough). Like
serious 3D EM solvers. Ask Dr. Hobbs.

?-)

20. ### josephkkGuest

Not always. The relationship between A (area enclosed) l (length of coil
transverse to its axis) and n (number of turns) is not that clean. Crank
the formulas and see for your self where the first and second order terms
are.