ENTC 3331 RF Fundamentals. Dr. Hugh Blanton ENTC 3331. Magnetostatics . Magnetism Chinese—100 BC Arabs—1200 AD Magnetite—Fe 3 O 4 Found near Magnesia (now Turkey) Permanent magnet Not fundamental to magnetostatics. A permanent magnet is equivalent to a polar material in electrostatics.
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ENTC 3331
RF Fundamentals
Dr. Hugh Blanton
ENTC 3331
Magnetostatics
Magnetism
Chinese—100 BC
Arabs—1200 AD
Magnetite—Fe3O4
Found near Magnesia (now Turkey)
Permanent magnet
Not fundamental to magnetostatics.
A permanent magnet is equivalent to a polar material in electrostatics.
Equivalent to electrostatics
The theoretical structure of magnetostatics is very similar to electrostatics.
But there is one important empirical fact that accounts for all the differences between the theory of magnetostatics and electrostatics.
There is no magnetic monopole!
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N
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N
A magnetic monopole does not exist—A magnetostatic field has no sources or sinks!
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I
I
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D s
u
rv
D l
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volume
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projection of
projection of onto the surface normal
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Electrical Currents
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constant of proportionality (mobility)
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Ohm’s law
conductivity
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cylindrical shape.
A2
A1
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The reciprocal of conductivity Resistivity (ohms/meter).
Do not confuse charge distribution!
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JeanBaptiste Biot & Felix Savart developed the quantitative description for the magnetic field.
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field comes out of plane due to the cross product
point of interest
differential section of conductor
contributes to field at
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magnetic field strength
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useful relationship
BiotSavart Law
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righthanded rule
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righthanded rule
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closed loop = 0
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z
BiotSavart Law
x
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z
x
at P(x,z), points into the plane
Note that for a small dq, R is approximately unchanged when separated by dq which implies:
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z
x
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X
z
x
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z
x
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z
y
field by I1 at location of I2
x
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z
y
x
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Charge is the source of the electrostatic field
No equivalent in magnetostatics
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X
line differential
field vector of the magnetostatic field
surface
current flowing through the surface
contour
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zaxis
z
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z
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y
0.25m
0.25m
x
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0.25m
0.25m
x
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