rectangular search coil for metal detector

[nafri]

hi, ı want to make 5*20 cm rectangular search coil. fistly ı search on google but almostly all coil is circular and calculations make according to circuilar. ı do not know how to make calculate inductance of rectangular search coil. how can ı calculate ınductance for example for circuilar we make these calculation::


L=((N^2)*(R^2))/((9*R)+(10*H))

where:
L = inductance in micro-Henries,
N= number of turns of wire,
R= radius of coil in inches,
H= height of coil in inches. [1]

 

[cowboybob]

Just out of curiosity, why do you want to make the search coil rectangular?

The general use of the word "coil" is a big clue...

Anyway, try this calculator.

<EDIT> On second thought, this might be better

 

[shortbus=]

One of the members here, "Chemelec" has a web site with a lot of metal detector circuits and information that might help you. About half way down the page - http://chemelec.com/Projects/Projects.htm

 

[alec_t]

A coil 5*20cm has the same area as a circular one of ~5.6cm radius. I would expect them to have similar inductances. Why do you need to know the value?

 

[nafri]

ı want to use this search coil as a oscillator so ı want to work around 200 KHz. ı use this ınductunce value for generating frequency by using rectangular coil

 

[chemelec]

ı want to use this search coil as a oscillator so ı want to work around 200 KHz. ı use this ınductunce value for generating frequency by using rectangular coil

It is more difficult to calculate the inductance of Rectangular Coils.
I have never found an Accurate calculator for these.

But your Oscillator is probably an "LC" Circuit, so you can correct the frequency with the Capacitor value.

 

[jjw]

Try this: https://www.technick.net/public/code/cp_dpage.php?aiocp_dp=util_inductance_rectangle

 

[chemelec]

Try this: https://www.technick.net/public/code/cp_dpage.php?aiocp_dp=util_inductance_rectangle

Seems to work out Fairly Close to a Tested Coil.
Assuning I did this correctly.
But a Pain to convert all Smaller Measurement values to METERS

TEST COIL:

20 turns of 26AWG
14.5Cm wide = .145M
6.5Cm High =.065
.45mm dia = .00022 Meters of Radus
Ur for Air Core = 1
Calculated Inductance = 0.00017638670844290097
Or 176 uH.

Actual Measured Inductance is 171.5uH

 

[jjw]

You can input values in mm and get inductance in mH.

 

[BobW]

Just out of curiosity, why do you want to make the search coil rectangular?

The general use of the word "coil" is a big clue...

Anyway, try this calculator.

<EDIT> On second thought, this might be better

The first link is a calculator on my website, and I've tested it and will stand behind it. However, it is intended for rectangular 'helical' coils as opposed to rectangular 'spiral' coils. If you don't know the difference between a helix and a spiral, then google "helix vs spiral" and all will be made clear.

A coil 5*20cm has the same area as a circular one of ~5.6cm radius. I would expect them to have similar inductances. Why do you need to know the value?

For the most part, this is generally a good way to handle odd shapes where you can't find a specific formula. However, in the case of rectangles, weird things start happening when the length is significantly greater than the width. Still, this method should get you in the ballpark.

If you find any calculator that claims to use Wheeler's formula, then be very skeptical, because it's often his 1928 long coil formula that isn't remotely accurate for short wide coils.