Home / Math and Physics Files / Physics / Transmission Lines / Notes By Chapter and Appendix / Appendix D EB round
App D the Helm phi equation REVIEWED
DOCX · 34.0 KB
Open DOCX file
Reviewed notes for Appendix D of Phil's transmission line work, now folded into section D.3. He substitutes his Er and Eφ solutions (Bessel functions Jm and Jm+1) into the Eφ Helmholtz equation in m space and confirms it holds, one part by Bessel's equation and one with Maple. He then considers the m=0 case and asks whether the φ equation follows from the other equations and div E = 0, starting in Cartesians.
AI-written summary; may contain errors.
Extracted text (machine-read; may contain errors)
What about the Helmholtz Eφ equation?
This stuff is now incorporated as Appendix section D.3.
Here are the Er and Eφ equations in m space:
[2E]r + β2 Er = 0 :
[r2∂r2 + r∂r - (m2+1) + r2(β2-βd2)] Er(r,m) - 2jm Eφ(r,m) = 0 (D.1.17)
[2E]φ + β2 Eφ = 0 :
[r2∂r2 + r∂r - (m2+1) + r2(β2-βd2)] Eφ(r,m) + 2jmEr(r,m) = 0 (D.1.18)
How do I know that my solutions Eφ and Er satisfy this last equation? Maybe they don't! Why should they?
Rewrite the above in this manner
[x2∂x2 + x∂x - (m2+1) +x2] Er(r,m) - 2m jEφ(r,m) = 0 (D.1.17)
[x2∂x2 + x∂x - (m2+1) + x2] jEφ(r,m) - 2mEr(r,m) = 0 (D.1.18)
I solved the first equation for Eφ in my work, and I solved the Hz equation for Er. So what happens when I insert these two solutions into the last equation above? Rewrite the last as
[x2∂x2 + x∂x - (m2+1) + x2] jEφ(r,m) = 2m Er(r,m).
It would certainly be nice if this were true. I have
Er(r,m) = am x-1 Jm(x) + Jm+1(x) . (D.2.11)
jEφ(r,m) = - am x-1 Jm(x) + ( + ) Jm+1(x) x = β'r . (D.2.15)
Then we get
LHS = [x2∂x2 + x∂x - (m2+1) + x2] {- am x-1 Jm(x) + ( + ) Jm+1(x) }
RHS = 2m{ am x-1 Jm(x) + Jm+1(x)}
You would think this has to balance separately as if Km and am were independent constants. So then
LHSK = [x2∂x2 + x∂x - (m2+1) + x2] ( Jm+1(x) )
RHSK = 2m Jm+1(x)
Then I would have to show that
[x2∂x2 + x∂x - (m2+1) + x2] Jm+1(x) = 2m Jm+1(x)
or
[x2∂x2 + x∂x - (m2+1) + x2 - 2m] Jm+1(x) = 0
or
[x2∂x2 + x∂x - (m2+1+2m) + x2] Jm+1(x) = 0
or
[x2∂x2 + x∂x - (m+1)2 + x2] Jm+1(x) = 0
or
[x2∂x2 + x∂x + x2- (m+1)2] Jm+1(x) = 0
Bessel's equation does say that
[x2∂x2 + x∂x + x2 - (m+1)2 ] Jm+1(x) = 0
so it works!!!!! I am totally amazed. At least the Km terms balance.
Now let's try the am balance.
LHS = [x2∂x2 + x∂x - (m2+1) + x2] {- am x-1 Jm(x) + Jm+1(x) }
RHS = 2m{ am x-1 Jm(x) }
LHS = [x2∂x2 + x∂x - (m2+1) + x2] {- x-1 Jm(x) + m-1 Jm+1(x) }
RHS = 2m{ x-1 Jm(x) }
This is a much messier situation. I could try Maple. Here is Maple evaluating the LHS:
But this is exactly the RHS !! I am again astounded to see this working right.
Now I can consider the notion of trying to find the m = 0 solution for Eφ using the φ equation,
[r2∂r2 + r∂r - (m2+1) + r2β'2] Eφ(r,m) + 2jmEr(r,m) = 0
which for m = 0 becomes
[r2∂r2 + r∂r -1 + r2β'2] Eφ(r,m=0) = 0
or
[x2∂x2 + x∂x -1 + x2] Eφ(r,m=0) = 0
This seems to say that
Eφ(r,0) = Cφ0 J1(x)
where Cφ0 is some constant.
How does this then figure into my boundary conditions stuff? If I want this to be zero on the surface using my equipotential idea, then for m =0 I must conclude that Cφ0 = 0. But that is not required, and I suppose you could allow an m = 0 rotating current on the surface?
Question: Can the φ Helm be derived from the others and div E = 0?
[2E]z + β2 Ez = 0 :
[r2∂r2 + r ∂r - m2 + r2 β'2] Ez(r,m) = 0 ok (D.1.16)
[2E]r + β2 Er = 0 :
[r2∂r2 + r∂r - (m2+1) + r2 β'2] Er(r,m) - 2jm Eφ(r,m) = 0 (D.1.17)
[2E]φ + β2 Eφ = 0 :
[r2∂r2 + r∂r - (m2+1) + r2β'2] Eφ(r,m) + 2jmEr(r,m) = 0 (D.1.18)
div E = 0 :
∂r [r Er(r,m)] + jmEφ(r,m) -jβd r Ez(r,m) = 0 (D.1.19)
Maybe ponder in Cartesians first.
(∂j2 + β2) Ei= 0
∂jEj = 0
(∂12+∂22+ ∂32 + β2) E1= 0
(∂12+∂22+ ∂32 + β2) E2= 0
(∂12+∂22+ ∂32 + β2) E3= ????
Start with
∂1E1 + ∂2E2+ ∂3E3 = 0
then
(∂12+∂22+ ∂32 + β2)∂1E1 + (∂12+∂22+ ∂32 + β2)∂2E2+ (∂12+∂22+ ∂32 + β2)∂3E3 = 0
or
∂1 (∂12+∂22+ ∂32 + β2) E1 + ∂2 (∂12+∂22+ ∂32 + β2) E2+ ∂3 (∂12+∂22+ ∂32 + β2) E3 = 0
or
∂1 0 + ∂2 0+ ∂3 (∂12+∂22+ ∂32 + β2) E3 = 0
or
∂3 [(∂12+∂22+ ∂32 + β2) E3] = 0
Well it certainly works but not a hard proof. Go back to
(2+ β2)E = 0 => grad(div E) – curl (curl E) + β2 E = 0
When div E = 0 this says
– curl (curl E) + β2 E = 0