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Designing Air Core Inductor
An air core coil is an inductor formed by winding several
turns of enameled wire on a none ferromagnetic cylinder that the
cylinder can be removed after construction the coil.
The advantages of an air core coil are as follows:
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The inductance of coil is independent of the
current, because there is no
ferromagnetic core to saturate by the current increasing.
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There is no iron losses which affect
ferromagnetic cores, then you can get better Q Factor and
lower distortion as frequency is increased
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They can be used to operate truly at frequencies
as high as 1 Ghz.
To calculate a single layer air core
coil, see the above picture and use the following formula:
Where,
- L = Inductance in uH
- a = Average diameter of the coil in Inches
- b = Length of the coil in Inches
- c = Radial depth of the winding in Inches
- n = Total turns of wire
It is important to note that
the formula will be true if value of b is greater than
0.4a .
A practical example:
Let's calculate the inductance of coil in above picture.
The mechanical specifications are as follows:
- a = 0.2480 Inches
- b = 0.3149 Inches
- c = 0.0866 Inches
- n = 7
Now we let them in the formula, then:
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