Inductor Shielding

RF inductors are crucial components in various circuits, but their performance can be affected by external electromagnetic interference (EMI) and they can introduce unwanted feedback paths via unintended coupling. That's where shielding comes in, offering protection at the cost of some trade-offs. Here's a breakdown of how shielding influences key parameters:

Reduced Inductance:

• Shielding introduces eddy currents within the metallic shield due to the changing magnetic field generated by the inductor. These eddy currents create their own opposing magnetic field, partially cancelling out the inductor's field. This, in turn, reduces the overall inductance compared to an unshielded inductor.

• The reduction in inductance is proportional to the thickness and conductivity of the shield material. Higher thickness or conductivity leads to stronger eddy currents and a greater decrease in inductance.

Increased Distributed Capacitance:

• The shield acts as a plate capacitor with the inductor's windings forming the other plate. This adds to the inductor's inherent distributed capacitance, increasing its overall total capacitance.

• The increase in capacitance is dependent on the area, permittivity, and distance between the shield and the windings.

Increased RF Resistance:

• Due to eddy currents within the shield, energy is lost as heat through Joule heating. This translates to an increase in the inductor's RF resistance.

• Similar to inductance reduction, the increase in resistance is also proportional to the thickness and conductivity of the shield material. Additionally, higher operating frequencies lead to stronger eddy currents and higher resistance.

Trade-offs and Considerations:

• While shielding protects against EMI, it's important to balance the benefits with the drawbacks. Choosing the right shield material, thickness, and even geometry can help minimize performance degradation.

• For critical applications where precise inductance and low-loss operation are crucial, alternative EMI mitigation techniques like proper circuit layout and component selection might be preferred over shielded inductors.