Magnetic current
Magnetic current is, nominally, a current composed of moving magnetic monopoles.
The usual symbol for magnetic current is
Magnetic currents produce an electric field analogously to the production of a magnetic field by electric currents.
Magnetic current density, which has the unit V/m2 (volt per square meter), is usually represented by the symbols
[a] The superscripts indicate total and impressed magnetic current density.
[1] The impressed currents are the energy sources.
In many useful cases, a distribution of electric charge can be mathematically replaced by an equivalent distribution of magnetic current.
This artifice can be used to simplify some electromagnetic field problems.
[b][c] It is possible to use both electric current densities and magnetic current densities in the same analysis.
[4]: 138 The direction of the electric field produced by magnetic currents is determined by the left-hand rule (opposite direction as determined by the right-hand rule) as evidenced by the negative sign in the equation[1]
Magnetic displacement current or more properly the magnetic displacement current density is the familiar term ∂B/∂t[d][e][f] It is one component of
where The electric vector potential, F, is computed from the magnetic current density,
, in the same way that the magnetic vector potential, A, is computed from the electric current density.
[1]: 100 [4]: 138 [3]: 468 Examples of use include finite diameter wire antennas and transformers.
[5] magnetic vector potential:
electric vector potential:
is calculated from magnetic currents at distant position
is a source point within volume Ω that contains the magnetic current distribution.
, is a volume element around position
is called the retarded time, and calculated as
Retarded time accounts for the accounts for the time required for electromagnetic effects to propagate from point
When all the functions of time are sinusoids of the same frequency, the time domain equation can be replaced with a frequency domain equation.
Retarded time is replaced with a phase term.
A distribution of magnetic current, commonly called a magnetic frill generator, may be used to replace the driving source and feed line in the analysis of a finite diameter dipole antenna.
[4]: 447–450 The voltage source and feed line impedance are subsumed into the magnetic current density.
In this case, the magnetic current density is concentrated in a two dimensional surface so the units of
The outer radius is chosen so that
However, a coaxial cable feed line is not assumed and not required.
The amplitude of the magnetic current density phasor is given by:
where Surface equivalence principle
