hisham
Joined: 25 Sep 2003
Posts: 12
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 29 Jan 2005 10:07 Re: Differences of Hard Source and Soft Source in FDTD |
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A hard source is one that superimposes some wave excitation in the FDTD grid. so you cannot study the reflections or calculate S11 at that point. A soft source is one that caters both the wave excitaion by the mathematical function and the reflection.
In terms of implementation you can set some point in the FDTD grid like:
Ez(i,j)= Eosin(2*pi*f*n*dt);
this would be a hard source. But to implement it in terms of a soft source, you can simply add the reflected component calculated by the FDTD algo.
i.e
Ez(i,j)=Ez(i,j)+Eosin(2*pi*f*n*dt)
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Winn
Joined: 21 Aug 2008
Posts: 8
Helped: 2
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| 03 Sep 2008 10:18 Re: Differences of Hard Source and Soft Source in FDTD |
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| hisham wrote: |
Ez(i,j)= Eosin(2*pi*f*n*dt);
this would be a hard source. But to implement it in terms of a soft source, you can simply add the reflected component calculated by the FDTD algo.
i.e
Ez(i,j)=Ez(i,j)+Eosin(2*pi*f*n*dt) |
This is actually not totally accurate, based on three reasons:
1) The electric field Ez(i,j) is impressed as a current density at the timestep of the magnetic field.
2) The missing operator in front of the sin-function
3) Since the excitation is impressed as a current density, which is coming from the left equations system, we need a minus in front of the amplitude.
this yields for a soft excitation to
Ez(i,j,) = Ez(i,j) - Ehat*sin(2*pi*f*(n+0.5)*dt)
Ehat = (Amplitude*dt)/eps0
Nevertheless, i have some difficulties with the soft excitation, since the impressed excitation function gets differentiated through the curl equations and following time loop, which means, if i superpose a gaussian pulse, i get an differentiated gaussian pulse at the port (see pseudo code). How do i get a "real" gaussian pulse as a soft excitation ?
time loop
[
(1) hx(i,j) = hx(i,j) - (dt/mue0)*[ ez(i,j+1) - ez(i,j) ]
(2) hy(i,j) = hy(i,j) + (dt/mue0)*[ ez(i+1,j) - ez(i,j) ]
(3) ez(i,j) = ez(i,j) + (dt/eps0)*[ hy(i,j) - hy(i-1,j) - hx(i,j) + hx(i,j-1) ]
(4) ez(i,j) = ez(i,j) - (dt/eps0)*exp(-(((n+0.5)*dt-t0)/tw)^2 )
]
After setting the exc-function (line 4), in the next time step the calculation of the magnetic component uses the "new" electric (line 1 and 2) and split the energy to hx(i,j), hx(i,j+1), hy(i,j), hy(i+1,j), the following ez calculation uses this and split it again, the result -> differentiated gaussian impulse 
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