# How to make oblique planewave in FDTD?

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#### ys0521

##### Newbie level 1
plane wave fdtd

In order to generate normal incident planewave, we can easily implant it using TF/SF boundary condition or periodic boundary condition.

However, if I want to excite oblique incident planewave, it is not easy for me.
Is there any good reference or example for this?

how to make oblique

u can implement an oblique incident wave by multiplying the field you would use for a normal incident wave with a phase term.
the phase term is a function of position.
for example, lets assume you excite an incident wave in a 2D simulation by forcing the E field at y=y0: Ez(x,y0)=Ez(t).
this is a plane wave traveling in the y directions.
if you add a phase term such as Ez(x,y0)=Ez(t)*exp(j*β*x) you can now simulate an oblique incident wave which incident angle is a function of β.

john schneider+fdtd

In order to generate normal incident planewave, we can easily implant it using TF/SF boundary condition or periodic boundary condition.

However, if I want to excite oblique incident planewave, it is not easy for me.
Is there any good reference or example for this?

For the basics Taflove or even Kunz&Lubbers should be ok.

For more accurate methods check the relevant papers by J. Schneider (google for john Schneider FDTD) and the papers referenced there

u can implement an oblique incident wave by multiplying the field you would use for a normal incident wave with a phase term.
the phase term is a function of position.

This is the simplest method. If the results are accurate enough for you then I would use it.
The problem is that the analytical formula does not match the wave speed at different angles.
As a result you get lots of spurious reflections. How to reduce these is the topic of some of
the papers I mentioned above.

Another problem, also addressed in these papers is the case when you have material
interfaces crossing the TF/SF boundaries.

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