How to design a Air Core Coil (Inductor)

[Shane]

An air core coil is an inductor formed by winding several turns of enamelled wire on a none ferromagnetic cylinder that the cylinder can be removed after construction the coil.

coil.PNG (8.7 KiB) Viewed 3134 times

The advantages of an air core coil are as follows:

1. The inductance of coil is independent of the current, because there is no ferromagnetic core to saturate by the current increasing.
2. There is no iron losses which affect ferromagnetic cores, then you can get better Q Factor and lower distortion as frequency is increased
3. 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:

1.png (625 Bytes) Viewed 3134 times

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 0.4 A

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:

2.png (2.61 KiB) Viewed 3134 times