Transmission and negative refractive index （NRI） of metal-dielectric-metal （MDM） metamaterials perfo- rated with different thickness of dielectric layer are studied. It call be found that transmission peaks of rectangular hole are sensitive to the thickness of the dielectric layer. NRI and the bandwidth of NRI are increased with the increasing of the thickness of dielectric layer. NRI of rectangular hole with the thickness of dielectric layer almost follows a linear law when the thickness of dielectric layer in 2-5 μm. A high NRI of metamateriral can be obtained by adjusting the thickness of the dielectric layer of the rectangular hole on MDM metamateriral arrays.
Transmission and negative refractive index （NRI） of metal-dielectric-metal （MDM） sandwiched metamaterial perfo- rated with four kinds of shapes of holes are numerically studied. Results indicate that positions of all transmission peaks of these kinds of holes are sensitive to the shape of the hole. Under the same conditions, the circular hole can obtain the maximum NRI and the rectangular hole can obtain the maximum frequency bandwidth of NRI. Moreover, the figure of merit （FOM） of the circular hole is the maximum too. As a result, we can obtain a higher NRI and FOM metamaterial by drilling circular hole arrays on MDM metamaterial.
