Discussion Forum

Scattering boundary conditions and impedance boundary conditions are not intended to be interchangeable or to model the same thing, so it is not surprising that if you casually replace one by the other that your model will give different results. (Similarly, if you replaced apples with cucumbers when baking a pie, you should not expect the same results.) Are you attempting to model a wave-absorbing surface, an imperfectly conducting material, or perhaps something else?? I suggest you post your model to the forum and explain as clearly as you can what physical situation you are attempting to model, so that others here can help you choose appropriate boundary conditions.

Hi Mr. Robert,

Thank you for the reply. I am just trying to understand why there is a difference between them. I am attaching a model from a simple air domain. in which I am producing a modulated Gaussian pulse, and we see clearly that if you run it with the impedance BC as excitation with an input amplitude of 1, you get 0.5 E-field. However, if you model it with the scattering BC with an input amplitude of 1, you get the true 1V/m in the propagation. I am just trying to understand where is that difference coming from.

Jose Santos.

The impedance boundary condition is not the right boundary condition for launching a wave. It represents a material. In your case, it was air. It is as if you wanted to launch your wave both upward and downward at the same time.

The scattering boundary condition can be used to launch a wave, and (if I recall correctly) was the method of choice roughly 15-18 years ago. But it is usually not the best way to launch waves nowadays. Consider using the "scattered-field formulation." The attached is from the help system: