Question 6A94

Shielding an RF inductance with a metallic enclosure introduces several effects detrimental to the coil's performance. Firstly, the changing magnetic field of the coil induces **eddy currents** in the shield. These eddy currents dissipate energy as heat within the shield material, directly **increasing the losses** of the inductance (A). Secondly, the magnetic field produced by these eddy currents opposes the coil's primary magnetic field. This effectively **reduces the net magnetic flux** linking the coil, thereby **lowering its inductance value** (B). The increased losses and reduced inductance collectively cause a significant **reduction in the coil's Q factor** (B), which is a measure of its efficiency. Finally, the coil windings act as one plate of a capacitor, and the metallic shield acts as the other. This creates **parasitic capacitance** between the coil and the shield, effectively **increasing the coil's capacity to the shield** (C). This added capacitance can alter the coil's resonant frequency and high-frequency characteristics. Because all these effects occur, shielding an RF inductance impacts it in all the ways described.