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E dot B equals 0 REVIEWED
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Short working note by Phil dated 1.27.14, revisiting his proof around equation (3.7.1) that E dot B equals 0, which fails below some frequency. He expands curl B in cylindrical coordinates, keeps only the Bθ and Bz terms, and uses H/E ≈ 1/Z0 for a round wire to bound cosθ. The resulting estimate is a very low frequency, around 1 Hz to tens of Hz, and the arithmetic is left tentative with question marks.
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The E dot B equals 0 problem PhL 1.27.14
See red comment in the v1 doc.
I have to say something about my little proof around (3.7.1). It is not valid below a certain ω and I would like to make an estimate.
I get to this point
C E B = C E B cosθ = ( ∂xBy - ∂yBx)Bz + ( ∂yBz - ∂zBy)Bx + ( ∂zBx - ∂xBz)By
C E B = curl B B = [ r-1∂θBz - ∂zBθ] + [∂zBr - ∂rBz] + [ r-1∂r(rBθ) - r-1∂θBr ]
[ Br + Bθ + Bz ]
= Br[ r-1∂θBz - ∂zBθ] + Bθ[∂zBr - ∂rBz] + Bz [ r-1∂r(rBθ) - r-1∂θBr ]
Let's just assume Br = 0 for simplicity. Then
C E B = curl B B = + Bθ[∂rBz] + Bz[ r-1∂r(rBθ) ]
= Bθ[∂rBz] + Bz[ r-1Bθ + ∂rBθ ]
where
C = j(β2/ω) = j [ωμ( jωε + σ) /j] /ω = μ( jωε + σ)
where μ and σ are for the dielectric. So then
C E B = C E B cosθ = μ( jωε + σ) E B cosθ = ( jωε + σ) E H cosθ
So then,
C E B cosθ = Bθ[∂rBz] + Bz[ r-1Bθ + ∂rBθ ]
But B ≈ Bθ so then roughly
C E cosθ = [∂rBz] + Bz[ r-1 + (∂rBθ )/Bθ]
μ( jωε + σ) E cosθ = [∂rBz] + Bz[ r-1 + (∂rBθ )/Bθ]
( jωε + σ) E cosθ = [∂rHz] + Hz[ r-1 + (∂rHθ )/Hθ]
I need estimates for E and B.
E D = V(z) 2πa H = i(z) at surface
D = transverse dimension H = field outside round wire
H = i(z)/2πa 1/E = D/V(z)
H/E = i(z)/V(z) * D/2πa = (D/2πa) 1/Z0
so then roughly we have
H/E = 1/Z0 amps/m // volts/m = mhos
so that
1/E = 1/(Z0Hθ)
Then above becomes
( jωε + σ) E cosθ = [∂rHz] + Hz[ r-1 + (∂rHθ )/Hθ]
( jωε + σ) cosθ = { [∂rHz] + Hz[ r-1 + (∂rHθ )/Hθ] }/ (Z0Hθ)
Now yes, if you set Hz≡ 0, you get cosθ = 0 so θ = 90o . But let's keep only a few terms so that
( jωε + σ) cosθ = { Hz[ D-1] }/ (Z0Hθ) = (1/DZ0) (Hz/Hθ)
Dimensions? σ = mho/m DZ0 = m ohm 1/DZ0 = mho/m checks
Let's now assume that σ = 0 for dielectric, then we have
jωε cosθ = (1/DZ0) (Hz/Hθ)
cosθ ≈ (1/DZ0) (Hz/Hθ)(1/ωε0)
A condition for E B = 0 is then
(1/DZ0) (Hz/Hθ)(1/ωε0) << 1
ω >> (1/DZ0ε0) (Hz/Hθ)
Now assume ω > 60 Hz so at least we have
Z0 = K 30Ω
ω >> (1/DK30ε0) (Hz/Hθ)
ω2 >> (1/DK30ε0)2 (Hz/Hθ)2
Then from below
ω2 >> (1/DK30ε0)2 = (1/DK30)2 (1/ε0)
ω >> (1/DK30)2 (1/σε0)
Now (1/σε0) ≈ 1/[ 108 10-11] = 103
So ω >> (1/DK)2
This is a very low frequency! Suppose D = 1 cm = 10-2 m and suppose K = 2. then
ω >> [ 2 10-2 ]-1 = 100/2 = 50 Hz.
Then
D Z0 ε0 = D K 30Ω 10-11 dim = m ohm farad/m = ohm-farad = sec OK
Then
ω >> 1011 / (30DK) * (Hz/Hθ)
Now for my round wire I think I had
Bz(r,0) = (β'/ω) J0(x)
Bφ(r,0) = (β'/ω) ( + ) J1(x)
Then
Hz/Hθ= (βd/β) J0(x)/J1(x) ≈ (βd/β) = ( .)-1/2 from below (D.2.2)
call this
Hz/Hθ ≈ ( )-1/2
Then I get
ω >> 1011 / (30DK) * (Hz/Hθ)
ω2 >> 1022/ (30DK)2
ω >> 1022/ (30DK)2 = 1022 / (30DK)2 * 10-11 / 108
ω >> 1011 / (30DK)2 / 108
ω >> 103 / (30DK)2
2πf >> 103 / (30DK)2
f >> (1/6)(1000 Hz) / (30* .01m * 5)2
(1/6)(105 Hz) / (30* 1 * 5)2 = 105 / 135000 = 100000/ 135000 = 1 Hz ???
curl B = [ r-1∂θBz - ∂zBθ] + [∂zBr - ∂rBz] + [ r-1∂r(rBθ) - r-1∂θBr ]
Now keep only Bθ