Question on equation for instantaneous E field along the transmission medium.by yungman Tags: equation, field, instantaneous, transmission 

#1
Jan1109, 05:38 PM

P: 3,843

I am studying Poynting vectors. I run into question that I don't see any good explaination in all the books I have. All the books claimed
E[tex]_{(z,t)}[/tex] =E[tex]_{(z=0)}[/tex] Re[e[tex]_{j(wt\beta z)}[/tex] + [tex]\Gamma[/tex] e[tex]_{j(wt+\beta z)}[/tex]] But sinse E0 is complex so this is what I have and is not equal to what the book gives. In fact the Electromagnetic by Ulaby actually say ignor the phase angle of E0!! Below is what I have: Obviously the answer does not agree. This is particularly obvious when working on Poynting vectors. Please tell me what do I miss in this whole thing. Thanks 



#2
Jan1109, 07:58 PM

P: 47

Once you go into phasor domain, all information is just relative time. Therefore you can assume your Incident Phase Angle is zero. As well as that I believe that your book is assuming that maximum amplitude occurs at z=0(From your Latex Code). These two assumptions seem to be apparent in line 1, but not in line 3 of your derivations.




#3
Jan1109, 09:12 PM

P: 3,843

A phasor strip the time domain [tex]\omega[/tex]t out, but the phase angle of incident E field is absolute a spacial domain and cannot be ignor. The solution from the two cannot be made equal to justify that. I spent 2 days deriving the formulas and just can not make the two agree. I don't see how they can ignor the phase angle unless the incident E field at z=0 is always at maximum which is cosine(0)=1 like you suggested!!! But what is the justification that the forward travelling E field is ALWAYS maximum at z=0? I have modify my original equation drawing above, please take a look again. 



#4
Jan1209, 12:38 PM

P: 47

Question on equation for instantaneous E field along the transmission medium.
If you were given an oscilloscope, could you distinguish between the incident wave having a phase shift of 0 degrees, 10 degrees, 20 degrees, 30 degrees...?




#5
Jan1209, 02:41 PM

P: 3,843





#6
Jan1209, 05:09 PM

P: 3,843

I have been looking up quite a few books today on both Plane Wave phasor and transmission line travelling wave phasor. All the books specified that the amplitude at z=0 is REAL. There is not phase angle. If the amplitude is real, then I agree with the book!!
Can anyone give me a conclusive theory why the amplitude at z=0 is always real? The only book that claimed the value can be complex, that is Ulaby book. 


Register to reply 
Related Discussions  
Calculate Electric Field in Medium  Classical Physics  2  
electric field of an infinite carged wire in a conductive medium  General Physics  2  
The action integral for the EM field in a dielectric medium  Advanced Physics Homework  5  
Lagrangian density for the EM field in a dielectric medium  Classical Physics  5  
When is field interaction instantaneous?  Classical Physics  9 