Terahertz wave modulation structure and results. (a), (e), (i) Sample stages rotating around the X, Y, and Z axes. (b), (f), (j) Initial positions and rotation directions of the double-layer structures with a 90° included angle. (c), (g), (k) Frequency domain diagrams corresponding to the respective double-layer structures with a 90° included angle. (d), (h), (l) Frequency domain diagrams corresponding to the respective double-layer structures with a 45° included angle.