|
|
|
|
|
The self-resonance and self-capacitance of solenoid coils.
David W Knight.
|
Download the full article: Self-res.pdf (version 0.01). + Open Document spreadsheets: Medhurst.ods , CL_theor_test.ods , CL_dynamic.ods . + Scattering experiment photograph . |
|
Abstract: Medhurst's semi-empirical formula for the self-capacitance of a single-layer solenoid inductor is derived from low and high-frequency limiting behaviour except for an approximately frequency-independent shape factor. The expression is further improved by the inclusion of a 1/Cos²ψ factor (where ψ is the pitch angle), which accounts for a neglected second-order relationship between self-capacitance and the number of turns. The 1/Cos²ψ dependence is consistent with experimental data, whereas formulae based on the inter-turn capacitance are radically in error. Medhurst gathered data for coils wound on solid polystyrene rods and analysed it on the basis that the coil former dielectric makes no difference to the self-capacitance. We presume that he did so because data for long thin coils converges to an asymptotic formula which depends only on external permittivity. By consideration of boundary conditions relating to an electromagnetic wave propagating along the helix, an expression which reconciles Medhurst's data with supplementary data for air-cored coils is obtained. >>> Full article: Self-res.pdf . |
© D W Knight 2008, 2010.
|
|
|
|
|
|