Static magnetic fields

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radiation
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power out power in
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E must be in the surface of the sphere.
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R
E
Stationary charges do not radiate. E not in
sphere. E ? R-2
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Charges in motion with a constant velocity do not
radiate. E not in sphere. E ? R-2
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A?B accelerate
B?C constant velocity
no kink
kink joins two Coulomb fields
kink
Radius of sphere ct
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from triangle
r ct
v aDt
acceleration
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E decays as 1/R
accelerated charges radiate em waves
time-varying currents radiate in a preferred
direction
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vector potential A
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vector potential A
Current element DI I DL uz
transform into spherical coordinates
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far field
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far field
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z
?
r
y
j
x
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small loop half wave dipole
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far field
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current loop
In far field, E will be in the uj direction and
H will be in the uq direction
I DL uj
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Could a realistic antenna be described in terms
of the sum of many small antennas?
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far field
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educated guess list
I(z) confined to length of antenna
h
Imax at z 0
Integrable function
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AM radio
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AM radio
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