Calculate influence of shield on the inductance value.
Shielded coil inductance is most commonly used at high frequencies to protect the inductor from external electromagnetic fields. But the screen reduces the self-inductance of the coil and its Q-factor, and also increases the parasitic self-capacitance, and this, of course, is an undesirable effect. To reduce the deterioration of the characteristics of the coil under the influence of the screen at high frequencies, the diameter of the screen must exceed the diameter of the coil by at least 1.6 - 2.5 times, and for stable high-quality coils - by 2.5 - 3 times.
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.
