[SI-LIST] Re: TEM wave propagation and standing waves
- From: Ihsan Erdin <erdinih@xxxxxxxxx>
- To: Ankit wangoo <ankit.wangoo@xxxxxxxxx>
- Date: Mon, 4 Mar 2013 00:41:26 -0500
You're right. In normal (unperturbed) propagation mode they will be in
phase but spatially perpendicular to each other. However, standing waves
are the result of boundary conditions (terminal conditions in the case of
transmission lines.) The different behavior of electric and magnetic fields
when they interact with matter (that is, the tangential component of
E-field and normal component of H-field being continuous across a boundary)
is the cause of phase difference on the standing waves.
Regards.
Ihsan Erdin
On Sun, Mar 3, 2013 at 10:04 PM, Ankit wangoo <ankit.wangoo@xxxxxxxxx>wrote:
> Hi Erdin
>
> However that j will cancel out when you will take del cross of E . Suppose
> E=a*e^j(wt-kz) ,taking curl of E will through up j on other side as well.
>
>
> regards
> Ankit
>
>
> On Mon, Mar 4, 2013 at 1:02 AM, Ihsan Erdin <erdinih@xxxxxxxxx> wrote:
>
>> Ankit,
>>
>> Regarding -jw*mu**H*=delcross *E* multiplication of the magnetic field
>> with the imaginary number j indeed shows the electric and magnetic fields
>> are 90 degrees out of phase at any point in space.
>>
>> Regards.
>>
>> Ihsan Erdin
>>
>>
>> On Sun, Mar 3, 2013 at 2:16 PM, Ankit wangoo <ankit.wangoo@xxxxxxxxx>wrote:
>>
>>> Hi
>>> We all know in transmission line structures such as co-axial
>>> cables, strip-line and micro strip-lines(partially ,if we assume field
>>> lines remains inside the dielectric) , electromagnetic energy flows in
>>> TEM
>>> mode, that is electric and magnetic field are always perpendicular to
>>> each
>>> other.
>>> We also know that characteristics of TEM waves guided by transmission
>>> lines
>>> are same as those for uniform plan wave propagating in an unbound
>>> dielectric medium.
>>> When we solve Helmholtz equation we find that Electric field can have one
>>> of solution as E=a*e^j(wt-kz) + b*e^j(wt+kz). where first term is a
>>> forward
>>> travelling wave and send is backward travelling wave.
>>> From Ampere circuital law in point form , we can find that H,
>>> jw*mu**H*=del
>>> cross *E* . Then H some out to be in phase with E field .That means that
>>> at
>>>
>>> a particular position and at particular time when electric field
>>> is maximum , magnetic field will also be maximum.
>>>
>>> however , when we study standing wave in transmission line which
>>> is terminated by short.We find that current (magnetic field ) and Voltage
>>> (electric field) are actually completely out of phase. when current is
>>> max, voltage is zero and vice-versa
>>>
>>> What can explain this difference in analysis ?
>>>
>>>
>>> I was thinking more about this,,, standing waves are formed by two waves
>>> and each of them electric field and magnetic field are in phase.however
>>> in
>>> standing wave , because of reflection one of them get polarized in
>>> different direction such that some points electric field gets cancelled
>>> and
>>> some point magnetic field get cancelled.
>>>
>>> however ,i am not completely convinced.Can somebody shed some light on
>>> this
>>> or refer me to some appropriate reading material?
>>>
>>> Thanks for your help
>>> Ankit wangoo
>>>
>>>
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>>
>
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