# The plugin screen.

Calculate influence of shield on the inductance value.

Shielded coil inductances most often used at high frequencies to guard the inductor against external electromagnetic fields. But the shield reduces self-inductance of the coil and its Q-factor and also increases the parasitic self-capacitance, and it's, of course, an undesirable effect. To reduce the derating of the coil under the influence of shield on high frequencies - the shield diameter should exceed the diameter of the coil is not less than 1.6 - 2.5 times, and for stable high-quality coils - 2.5 - 3 times. To estimate the degree of reduction of the inductance under the influence of shield Coil32 have a plugin that called "screen".

The calculation of the decrease of inductance due to the influence of the shield based on the following empirical formula:

where:

- Ls - inductance of the shielded coil
- L0 - inductance of the coil without shield
- Ds - diameter of shield
- H - height of shield
- D - diameter of winding
- L - length of winding

The formula is valid for a cylindrical shield. In the case of a square shield in the input field enter the size of the side and then we can calculate the equivalent diameter, which is used in the above formula. The equivalent diameter is equal to an average diameter of inscribed and circumscribed circles.