Further discussion of “multiple frequency bands of square split resonant rings and metal wires metamaterial”

In view of the peer reviewer's suggestion, we sincerely make a further discussion of the paper published in Appl. Opt. (52 (2013) 6309–6315) titled “Multiple frequency bands of square split resonant rings and metal wires metamaterial”. We choose square split resonant rings (different in size) stacking in the X and Y axes, the same arrangement as the previous paper coupling in the Z axis, to form a two-layer or a three-layer metamaterial unit. All of the two-layer and three-layer units exhibit multiple negative pasbands. A comparison on the resonant frequencies with coupling cells in different directions is accomplished.