Inductance of a shielded coil

Models are developed for the inductance of a helical coil and a helical coil inside a conducting shield. Values of inductance are found from analysis. The dependence of inductance on the presence of the shield is assessed quantitatively and explained on the basis of physical principles, and the significance of skin and proximity effects in the wire coil is outlined. The inductance of an isolated, one-turn loop and a one-turn loop inside a conducting tube are measured and are found to be in excellent agreement with computed data. When the conducting shield and coil are very close, the inductance of the coil is found to be greatly diminished suggesting that one must account for the presence of shields when characterizing inductors, which might be used for loading and tuning of antennas. A nearby conducting shield must be accounted for in inductance calculations if reasonable accuracy is expected.