In my project, I am using CST Particle Studio to simulate Smith-Purcell Radiation. Now I am facing some problems to find a material which will absorb microwave at THz range without reflection. I tried Ecossorb, but these are not in the THz range and I got reflection if I use these. I know there should be another way to define a new material with will completely absorb microwave in THz with zero reflection. Would you please share the way I can select such material!