Q coil calculator formula

[simonbaker]

Hi Qiaozhi:

Do you still have the formula used in your coil calculator?

If so, can you provide it?

Regards,

-SB

[Qiaozhi]

Hi Qiaozhi:

Do you still have the formula used in your coil calculator?

If so, can you provide it?

Regards,

-SB

Here's the information you're looking for ->
http://info.ee.surrey.ac.uk/Workshop...air_coils.html
Search for "Brooks" in the text.

[simonbaker]

Here's the information you're looking for ->
http://info.ee.surrey.ac.uk/Workshop...air_coils.html
Search for "Brooks" in the text.

Great, thanks!

[mikebg]

Brooks ratio is not suitable for design of efficient search head. The ratio is used to achieve maximal self-inductance at given length of wire (See[1] and [2]). However for metal detecting we need the opposite - minimal self-inductance at given length of wire.
The formula for self-inductance in [1] and [2] can be represented for analyzis as:
L=AL * N^2
where N is turns number and AL is a design parameter. It follows that parameter
AL=L/(N^2) has dimension Henries for square of turn number.
NOTE: The producers of ferrite cores give AL value as nanoHenries for turns number.
The efficiency of TX and RX windings is proportional to N (in first power only) because TX field is proportional to ampere-turns and EMV induced in RX winding is proportional to turn number.
At EMI sensor, the self-inductance L of TX and RX winding appears as limiting parameter because it decreases resonance frequency of tank circuit.

CONCLUSION: For efficient search head we need winding having low AL parameter, for example increasing distance between turns (using cotton or plastic thread). Minimal AL parameter has the flat spiral coil with thread for distance between turns.
Unfortunately, in practice we can not reduce significant the AL parameter.

REFERENCES [1] and [2]:
http://en.wikipedia.org/wiki/Inductor
http://www.circuits.dk/calculator_mu...er_aircore.htm

[Qiaozhi]

Brooks ratio is not suitable for design of efficient search head.

The Brooks equation is much more accurate for our purposes than the equivalent Wheeler formula. If you read the text (and wind a few coils for real world testing) you will find (as stated in the text) that the Brooks formula works well, even when outside the boundaries of maximal self inductance for a given length of wire. Many members here have already proved that for themselves.

Sometimes things actually work as expected, and are neither "not suitable" or "incompetent" ... as you are very fond of saying.